Remarkable changes to carbon emission budgets in the IPCC Special Report on Global Warming of 1.5C

by Nic Lewis

A close reading of Chapters 1 and 2 of the IPCC Special Report on Global Warming of 1.5°C (SR15) reveals some interesting changes from the IPCC 5th Assessment Report (AR5), and other science-relevant statements. This article highlights statements in SR15 relating to carbon emission budgets for meeting the 1.5°C and 2°C targets.

It seems fairly extraordinary to me that the AR5 post-2010 carbon budget for 1.5°C, which was only published four years ago, has in effect been now been increased by ~700 GtCO2 – equal to 21st century emissions to date – despite SR15’s projections of future warming being based very largely on the transient climate response to cumulative emissions (TCRE) range exhibited by the models used in AR5.

Key points

  • The SR15 estimates of the carbon budgets that will allow us to remain within the 1.5°C and 2°C targets are far larger than those given in AR5 – over five times as high from end 2017 for a 66% probability of not exceeding 1.5°C warming.
  • SR15 switches the measure of past (up to 2010) warming for the 1.5°C and 2°C targets from near-surface air temperatures (SAT) everywhere (as in AR5) to a blend of near-surface air temperatures over land and sea-surface water temperatures (SST).
  • SR15 bases its estimates of the relationship of future warming to future CO2 emissions very largely on the behaviour of the current generation of Earth system models (ESMs)[i], as used for AR5. However, unlike AR5 it does not do so directly. Instead, it assumes a fixed probabilistic relationship between post-2010 cumulative CO2 emissions and the warming they cause, and derives (using simplified climate models) an allowance for warming from other causes.
  • SR15 ignores ESM simulation estimates of warming to date, instead estimating it using observational data.
  • The resulting SR15 estimate of the post-1875 cumulative CO2 emissions that would give a 50% probability of meeting the 1.5°C target is approximately 720 GtCO2 larger than per AR5, partially offset by a 210 GtCO2 increase in estimated 1876–2010 emissions, giving a net increase of 510 GtCO2 for the post-2010 carbon budget.
  • Approximately 180 GtCO2 of the ~720 GtCO2 increase in the post-1875 budget is due to lower projected post-2010 warming relative to post-2010 cumulative CO2 The lower projected warming appears to be because of two factors:
    • The TCRE value used in SR15 matches the average of the full set of ESMs in AR5; however the budgets calculated for AR5 were based on a subset of ESMs that had a higher average TCRE value.
    • Lower non-CO2 warming is projected in SR15 than in AR5

and possibly also to other, unidentified, factors.

  • The remaining 540 GtCO2 of the increase relates to changing the measure of warming up to 2010 from a model-simulation basis to an observational basis and may be allocated approximately as follows:
    • half (270 GtCO2) to the models used for the AR5 budgets warming more by 2010 than do the full set of AR5 CMIP5 models, and
    • half (270 GtCO2) to changing the measure of past warming from the globally-complete near-surface air temperature to a blend of SAT over land and SST over ocean, as measured (on a globally-incomplete basis) by the average of four observational temperature records.

SR15’s definition of warming for carbon budget purposes

In order to understand the changes in the SR15 carbon budgets from those given in AR5, it is necessary to examine the way that SR15 defines warming. The key part of SR15 here is Section 1.2.1: ‘Working definitions of 1.5°C and 2°C warming relative to pre-industrial levels’.

The SR15 report ‘adopts a working definition of “1.5°C relative to pre-industrial levels” that corresponds to global average combined land surface air and sea surface temperatures either 1.5°C warmer than the average of the 51-year period 1850–1900, 0.87°C warmer than the 20-year period 1986–2005, or 0.63°C warmer than the decade 2006–2015’. It states that these offsets are based on all available published global datasets, combined and updated.

SR15’s working definition of warming over the historical period is based on an average of the four available global datasets that are supported by peer-reviewed publications: the three datasets used in AR5 – HadCRUT4, NOAA, GISTEMP, as updated – together with the Cowtan and Way infilled version of HadCRUT4.[ii] Berkeley Earth (BEST) and JMA are not used because ‘no peer-reviewed publication is available for these global combined land–sea datasets’.

SR15 explains that ‘The IPCC has traditionally defined changes in observed global mean surface temperature (GMST) as a weighted average of near-surface air temperature (SAT) changes over land and sea surface temperature (SST) changes over the oceans’. Consistent with that, the SR15 1.5°C remaining carbon budgets are based on anthropogenic warming up to 2006–2015 of 0.87°C, which is based on surface temperature datasets that mostly combine near-surface air temperature over land and sea surface temperature over the (open) ocean.

Average global warming simulated over the historical period (1850 to date) by the ESMs used in AR5 exceeds that shown by the observational temperature records used in SR15.[iii] It is likely that part of that difference in warming is due to the ESMs using SAT as the measure of temperature over the ocean as well as land, and to incomplete global coverage of observations. The importance of this issue is reflected by SR15’s statement that ‘the use of blended SAT/SST data and incomplete coverage together can give approximately 0.2°C less warming from the 19th century to the present relative to the use of complete global-average SAT.’

However, it is doubtful that SR15’s warming measure is that far below the old one, or even by as far as the calculated 13% warming shortfall in CMIP5 models reported in SR15.[iv] Although two of the four temperature datasets used in SR15 use SST measurements for the oceans, the other two use a hybrid of SST and SAT, so the average of the four would not be expected to differ from a pure SAT dataset by as much as SR15 calculates.[v] Moreover, warming estimates for recent decades in two versions of the globally-complete ERA-interim reanalysis – one based on SAT everywhere, and one based on SAT over land but SST over ocean – differ only very marginally.[vi] In addition, one of the four datasets fully infills areas with missing data, while two others infill substantially. SR15 shows (Table 1.1) that over the long term, lack of complete infilling makes little difference: the fully infilled Cowtan and Way dataset was only 0.02°C higher over the length of the record than per the SR15 average.[vii] Moreover, over recent decades warming in the Cowtan and Way dataset matched or exceeded that in the two globally-complete reanalysis datasets featured in SR15, despite the latter using SAT everywhere while Cowtan and Way use SST over the oceans.[viii]

Although the reasons for deciding to measure warming for the purposes of the 1.5°C and 2°C targets by combining SAT over land with SST over ocean (rather than SAT everywhere, as in AR5) are not entirely clear, it is in my view a sensible decision scientifically. Surface air temperature over the ocean has been (and still is) less well measured than SST, and also has much less direct relevance to humans and the biosphere than does SST. The change has the effect of making the remaining carbon budgets larger. However, SR15 is inconsistent in applying its decision to use a weighted average of SAT and SST: it only does so in respect of past warming; future warming is in effect still projected using a fully SAT-based measure.

It is arguable that when determining warming some allowance should be made for the cooling effect of heavy volcanism during the last two decades of the 1850-1900 primary reference period. However, such cooling is likely to have been partially offset by early anthropogenic warming; the net cooling is probably small and of the same order as the excess since 1850-1900 of the GMST increase per the fastest warming observational dataset (Cowtan and Way) over the average of four datasets used in SR15.

The remaining 1.5°C carbon budget

Section 2.2.2, ‘The remaining 1.5°C carbon budget’ is particularly revealing. The key measure that affects carbon budgets is the transient climate response to cumulative emissions (TCRE), being the transient GMST change per unit cumulative CO2 emissions.[ix] Unless otherwise stated, the unit of emissions is 1000 GtC, not 1000 GtCO2 (1000 GtCO2 = 1 TtCO2 = 273 GtC).

My interest was piqued by the statement that, although:

considerably uncertainties remain, there is high agreement across various lines of evidence assessed in this report that the remaining carbon budget for 1.5°C or 2°C would be larger than the estimates at the time of the AR5.[x]

How much larger? Well, later in the section, SR15 says this:

This assessment finds a larger remaining budget from the 2006-2015 base period than the 1.5°C and 2°C remaining budgets inferred from AR5 from the start of 2011, [which were] approximately 1000 GtCO2 for the 2°C (66% of model simulations) and approximately 400 GtCO2 for the 1.5°C budget (66% of model simulations).[xi] In contrast, this assessment finds approximately 1600 GtCO2 for the 2°C (66th TCRE percentile) and approximately 860 GtCO2 for the 1.5°C budget (66th TCRE percentile) from 2011.

So, the remaining carbon budget from 1 January 2011 for a 66% probability of keeping below 1.5°C has been increased by 460 GtCO2, from 400 to 860 GtCO2 – more than doubled. Deducting the estimated 290 GtCO2 emissions during the 2011 to 2017 period,[xii] the change from 1 January 2018 is from 110 GtCO2 to 570 GtCO2 – over five times as high.

While SR15 says that the AR5 and SR15 carbon budgets are ‘not directly equivalent’, both use the same 1.5°C warming target, both measure from the 1850–1900 mean, both require the same 66% chance of meeting it (albeit derived in slightly different ways) and both allow for forcing from non-CO2 emissions.[xiii]

The SR15 carbon budgets are based on TCRE values rather than directly on climate model projections. In principle that is sensible, since the current generation of ESMs clearly have major deficiencies. However, SR15 sticks with the 0.8–2.5°C (0.22–0.68°C/TtCO2) TCRE range from AR5, which represents ‘expert judgement based on the available evidence’. This range agrees to, and appears to be largely based on, the TCRE range from CMIP5 ESMs and EMICs, and has a similar mean and median.[xiv] As a result, the best-estimate temperature response to CO2 emissions using the SR15 method should in theory be very similar to that per the AR5 ESM projections. However, in SR15, warming due to non-CO2 emissions (which is as projected by simplified ESMs) is lower than that projected by the AR5 ESMs.

As an aside, the most sophisticated TCRE study cited in AR5 was Gillett et al. (2013)[xv] – one of the two key observational-constrained, scaling-based ‘detection and attribution’ studies underlying the main AR5 human-caused warming finding.[xvi] Gillett et al. scaled CMIP5 ESM patterns of temperature responses to greenhouse gas warming so that they were consistent with the observed warming and found a TCRE range of 0.7–2.0°C, with a mean of 1.35°C. The range adopted in SR15 has a 22% higher central value and a 25% higher upper bound than this observationally-constrained range.

If one assumes a normal distribution, as SR15 does, the AR5 ‘likely’ range (taken as covering 66% probability) implies 50% (median) and 66% probability points for TCRE of 0.45°C/TtCO2 and 0.55°C/TtCO2 respectively. SR15 points out that observation-based TCRE estimates have reported log-normal distributions for TCRE, which, for a given symmetrical probability range, have a longer upper tail but a lower median than for a normal distribution. SR15 estimates that, based on its adopted 0.22–0.68°C/TtCO2 TCRE range, if it had treated the range as coming from a log-normal rather than a normal distribution – which would have implied a median TCRE of 0.38°C/TtCO2, in line with the best estimates SR15 cites from studies using observational constraints[xvii] – then the median remaining carbon budget could have been 200 GtCO2 larger.[xviii]

The median TCRE of 0.45°C/TtCO2 used in SR15 is, unsurprisingly, close to the 0.47°C/TtCO2 median TCRE of the reduced-complexity MAGICC model used in AR5 to emulate the behaviour of the set of more complex CMIP5 ESMs. SR15 introduces a new simplified ESM, the ‘Finite Amplitude Impulse Response’ (FAIR) model. The new model embodies more up to date forcing assumptions than MAGICC, which (although used in AR5) has, for instance, aerosol forcing close to the AR4 best estimate rather than to the substantially lower AR5 best estimate. FAIR is thought to produce more realistic near-term temperature trends than MAGICC. FAIR has a median TCRE of 0.38°C/TtCO2, very close to the Gillett et al. (2013) central value of 0.37°C/TtCO2. However, when calculating its carbon budgets, SR15 only uses MAGICC and FAIR (averaging their results) to project post-2010 temperature changes in response to non-CO2 emissions.

It is simple to derive the SR15 1.5°C post-2017 CO2 budgets. Subtracting the assessed anthropogenic warming up to 2006-2015 of 0.87°C from the 1.5°C target leaves allowable post-2017 warming of 0.63°C. SR15 states that ‘The mitigation pathways assessed in this report indicate that emissions of non-CO2 forcers contribute an average additional warming of around 0.15°C relative to 2006–2015 at the time of net zero CO2 emissions.’ After deducting this non-CO2 warming (more accurately, 0.155°C), the 1.5°C target allows only 0.475°C further CO2 warming. Based on the assessed 50% and 66% probability TCREs, the corresponding implied post-2017 CO2 budgets are respectively 1055 and 864 GtCO2. After deducting the 290 GtCO2 emitted during 2011–2017, and rounding to the nearest 10 GtCO2, these agree to the corresponding SR15 1.5°C post-2017 CO2 budgets at 50% and 66% probability, of 770 and 570 GtCO2 respectively.

Why is there a huge discrepancy between the AR5 and the SR15 carbon budgets, when the TCRE range used in SR15 is almost the same as the TCRE range of the ESMs used to derive the AR5 carbon budgets?

SR15 claims that Figure 2.3 (a version of which is reproduced below as Figure 1) illustrates that ‘the change since AR5 is, in very large part, due to the application of a more recent observed baseline to the historic temperature change and cumulative emissions’.

In my view this statement in SR15 lends itself to misinterpretation. A naïve interpretation of this statement is that both observed warming and observed emissions were lower than projected (by ESMs, under the RCP8.5 scenario) in AR5 over the period since then, with both of these factors contributing to an increase in the remaining carbon budgets consistent with 1.5°C or 2°C warming.

In fact, observed emissions between 2005 (the observational baseline date for emissions per the RCP scenarios) and the end of 2017 were almost identical to those per RCP8.5. And, if the ‘blended-masked’ CMIP5 models’ temperature (thin black line in Figure 1) is a fair comparison with the global temperature observations used in SR15 (thin blue line in Figure 1), then there is little difference between models and observations over that period.


Figure 1: Temperature changes from 1850-1900 versus cumulative CO2 emissions from 1876 on.
Solid lines with dots reproduce the temperature response to cumulative CO2 emissions plus non-CO2 forcers as assessed in Figure SPM10 of WGI AR5, except that points marked with years relate to a particular year. The AR5 data was derived from available ESMs for the historic observations (black) and RCP 8.5 scenario (red) and the red shaded plume shows the uncertainty range across the models as presented in AR5. The purple shaded plume and the line are indicative of the temperature response to cumulative CO2 emissions and non-CO2 warming adopted in SR15. The non-CO2 warming contribution is averaged from the MAGICC and FAIR models and the purple shaded range assumes the AR5 WGI TCRE distribution. The 2010 observations of temperature anomaly (0.87°C based on 2006-2015 mean compared to 1850-1900) and cumulative carbon dioxide emissions from 1876 to the end of 2010 of 1,930 GtCO2 is shown as a filled purple diamond. 2017 values based on the latest cumulative carbon emissions up to the end of 2017 of 2,220 GtCO2 and a temperature anomaly of 1.04°C based on an assumed temperature increase of 0.2°C per decade is shown as a hollow purple diamond. The thin blue line shows annual observations, with CO2 emissions from Le Quéré et al. (2018)[xix] and temperatures from the average of the HadCRUT4, NOAA, GISTEMP and Cowtan-Way datasets. The thin black line shows the CMIP5 models blended-masked estimates with CO2 emissions from Le Quéré et al. (2018). Dotted black lines illustrate the SR15 remaining carbon budget estimates for 1.5°C. Reproduced from SR15 Figure 2.A.3, which is a version of Figure 2.3 that additionally shows warming projections (not used in SR15) direct from the MAGICC and FAIR models.

One potential source of misunderstanding is what the change in observed baseline date involved is. It is not from 2005 to 2017, or between any other recent periods. Rather, it is from the 1850–1900 mean to the 2006–2015 mean (from 1875 to 2010 for CO2 emissions). This change in baseline date has two effects.

First, it increases cumulative CO2 emissions in both 2010 and at end 2017 by approximately 210 GtCO2, largely due to an upwards revision of pre-2000 emissions from land use change. In itself, this change reduces the remaining carbon budget by some 210 GtCO2.[xx]

As an aside, when the 2011–2017 observed emissions of 290 GtCO2 are also added, the updating of the pre-2011 emission estimate brings the post-2010 increase in the cumulative emissions estimate to 500 GtCO2. This figure exceeds the AR5 budget for a 66% probability of keeping warming below 1.5°C, of 400 GtCO2. Moreover, since 2018 emissions are expected to exceed 40 GtCO2, the 50% probability AR5 post-2010 budget of 550 GtCO2 will be breached before mid-2019. The corresponding SR15 50% probability 1.5°C budget of 1060 GtCO2 is 510 GtCO2 higher and not likely to be breached before the 2030s.

Since the effect of baseline changes on emissions estimates is to reduce the carbon budget by 210 GtCO2, it follows that the second effect of those baseline changes – the impact on historical temperature change estimates – must in large part both compensate for that reduction and give the doubling of the remaining carbon budget over AR5 estimates. The total increase in the carbon budget involved is:

  • at 66% probability, 670 GtCO2 (that is, 460 + 210 GtCO2)
  • at 50% probability, 720 GtCO2 (that is, 510 + 210 GtCO2).

A clue to the explanation lies in two observations made in SR15:

  • that ‘the use of blended SAT/SST data and incomplete coverage together can give approximately 0.2°C less warming from the 19th century to the present relative to the use of complete global-average SAT’
  • that blended-masked CMIP5 warming[xxi] from 1850–1900 to 2006–2015 is essentially identical to SR15’s measure of observed warming.[xxii]

The ‘approximately 0.2°C less warming’ referred to appears compatible with the gap of 0.24°C between:

  • CMIP5 ESMs/EMICs warming (i.e. on a fully SAT basis) of 1.11°C; and
  • CMIP5 models blended-masked warming (i.e. a blend of globally-incomplete SAT and SST) of 0.87°C.[xxiii]

for 2010 (see Figure 1).

It appears to follow that in very large part the increase in the SR15 remaining carbon budgets over those in AR5 plus an additional 210 GtCO2 – approximately 700 GtCO2 in total – is due simply to changing from using globally-complete near-surface air temperature, to incomplete temperature data – a blend of SAT and SST – as a measure of past warming. This seems remarkable, particularly as in SR15 projected future warming remains, in effect, based on AR5’s globally-complete SAT measure.[xxiv]

However, there is something odd in Figure 1 as regards warming from 1850–1900 to 2006–2015. The values for the observations and (on a blended/masked basis) for the full set of ESMs used in AR5 are essentially the same, in agreement with SR15 Table 1.1. However, the AR5 warming to 2006–2015 (red line: globally complete, SAT basis)[xxv], at 1.11°C, is 12% higher than the comparable CMIP5 figure for the same period given in SR15 Table 1.1 (0.99°C, also globally complete, SAT basis).[xxvi] This 0.12°C difference presumably arises from a different set of models being involved. It accounts for half (0.12°C / 0.24°C) of the total effect of the baseline changes on the carbon budgets.

SR15 states that the increase in carbon budgets is due ‘in very large part’ to the baseline change, indicating that it does not account for the whole of the increase. The cause of the remainder of the increase must logically be that SR15 projects lower warming relative to CO2 emissions post 2010 than does AR5. The difference between the post-2000 GtCO2 slopes of the purple and red lines in Figure 1 shows how much the median (50% probability) SR15 carbon budgets are affected by its projected warming in relation to future CO2 emissions (purple line) being lower than per the AR5 CMIP5 ESMs/EMICs (red line). The emissions producing median warming of 1°C are approximately 290 GtCO2 higher on the SR15 projections than on the AR5 projections. This difference will account for some 180 GtCO2 of the 720 GtCO2 excess of the SR15 50% probability 1.5°C budget over that in AR5 (since there is 0.63°C allowable post-2010 warming to reach 1.5°C).

Why does SR15 project lower median future warming relative to cumulative CO2 emissions post 2010 than AR5, if the TCRE range used for projections in SR15 is almost identical to that of the models used in AR5, and the AR5 CMIP5 ESMs have a similar mean and median TCRE to that used in SR15?

I believe one key reason is that the subset of ESMs actually used for the simulation runs from which the AR5 carbon budgets were derived was biased towards ESMs with a significantly higher TCRE than average. Neither SR15 nor AR5 appears to discuss this possibility, and there is only limited published information as to the TCRE values of the AR5 ESMs. However, my best estimate is that the subset of CMIP5 ESMs and EMICs used to generate the AR5 carbon budgets had a median TCRE approximately 10% higher than the 1.65°C median TCRE used for the SR15 budgets,[xxvii] which TCRE appears representative of AR5 ESMs as a whole.

Another reason for the faster future warming relative to cumulative CO2 emissions in AR5 than in SR15 appears to be that warming from changes in non-CO2 emissions is greater in AR5. This can be seen from Figure 1. The green line, which shows total warming in the MAGICC model, has a similar slope to red AR5 projections line. This is as expected, since MAGICC is set up to emulate AR5 ESMs, both as to warming from cumulative CO2 emissions and warming from non-CO2 emissions. MAGICC’s TCRE is only slightly higher than the median value used for the SR15 projections. Therefore, the excess of MAGICC over SR15 projected warming (the difference between the green and purple lines in Figure 1) should to a substantial extent be due to warming from non-CO2 emissions being greater in MAGICC (and therefore in AR5 projections) than in SR15. For SR15’s projections, the MAGICC non-CO2 warming is averaged with that in the FAIR model, which is lower (particularly in the decades following 2010).

One final point. As SR15 says, calculating carbon budgets from TCRE estimates requires the assumption that the instantaneous (actually multidecadal) warming in response to cumulative CO2 emissions equals the long-term warming or, equivalently, that the residual warming after CO2 emissions cease is negligible. That is broadly the case in CMIP5 ESMs, with the slow continuing absorption of emitted CO2 by the ocean and land biosphere as they equilibrate with higher atmospheric CO2 concentration being balanced by continuing surface warming as the sub-surface ocean gradually warms and absorbs less heat, thereby offsetting a smaller proportion of greenhouse gas etc. radiative forcing. However, if there is less difference between transient and equilibrium sensitivity in the real climate system than in current ESMs, or if CO2 uptake increases more with atmospheric concentration and/or declines less with increasing temperature in the real carbon-cycle system than in current ESMs, then GMST will fall after emissions cease. In that case – which observational evidence seems to support – TCRE will overestimate the long-term warming caused by CO2 emissions.


SR15 uses essentially the same range for TCRE – the warming per unit CO2 emissions – to project future warming, and hence derive carbon budgets, as those exhibited by the models used to derive the AR5 carbon budgets. And although SR15 says that it defines “1.5°C relative to pre-industrial levels” as corresponding to global average combined land surface air and sea surface temperature warming, as opposed to surface air temperature warming everywhere (as for the AR5 carbon budgets), it only applies that definition to past warming, not to projected (post-2010) warming.

Despite these close links between the SR15 and AR5 bases for deriving carbon emission budgets, the SR15 remaining carbon budgets are far higher than those in AR5. The budget for a 50% probability of meeting the 1.5°C target is 510 GtCO2 larger. SR15 says that this increase is very largely due to the updating to 2005–2016 of the early historical period observational baseline for temperature and cumulative carbon emissions. While the explanation SR15 gives for the increase in the carbon budgets since AR5 may be literally correct, it obscures the true influence of the various factors involved. The re-baselining of cumulative carbon emissions actually results in a 210 GtCO2 reduction in the remaining carbon budget, due to an upwards re-estimation of pre-2010 CO2 emissions. Therefore, changes relating to temperature account for a 720 GtCO2 increase in the SR15 50% probability 1.5°C budget over the corresponding AR5 budget. Noting SR15’s finding that the observed warming matches warming simulated by the full set of AR5 CMIP5 models when calculated on the same basis, I deduce that this 720 GtCO2 increase can be divided into:

  • approximately 180 GtCO2 due to lower projected post-2010 warming relative to post-2010 cumulative CO2 The lower projected warming appears to be due partly to AR5 having used a subset of ESMs with atypically high TCREs to derive its budgets and partly to SR15 estimating lower non-CO2 warming (and possibly also to other, unidentified, factors);
  • a balance of 540 GtCO2 relating to changing the measure of warming up to 2010 from a model-simulation basis to an observational basis, which may be allocated approximately
    • half (270 GtCO2) to the models used for the AR5 budgets warming more by 2010 than do the full set of AR5 CMIP5 models, and
    • half (270 GtCO2) to changing the measure of past warming from globally-complete near-surface air temperature to a blend of SAT over land and SST over ocean, as measured, on a globally-incomplete basis, by the average of four observational temperature records.

What’s the betting that the new SR15 carbon budgets will also turn out to be unrealistically low?

Nicholas Lewis                                                                                 18 Oct18

[i]  Earth system models represent both the climate system and the carbon cycle, and usually some other biogeochemical cycles as well. Most current ESMs, as used in AR5 and SR15, are versions of CMIP5 3D general circulation models, but some are models of intermediate complexity (EMICs).

[ii]  To estimate changes in the NOAA and GISTEMP datasets, which start in 1880, relative to the 1850–1900 reference period, warming is computed relative to 1850–1900 using the HadCRUT4.6 dataset and scaled by the ratio of the linear trend 1880–2015 in the NOAA or GISTEMP dataset with the corresponding linear trend computed from HadCRUT4.

[iii]  Warming to date in ESMs used to derive the AR5 carbon budgets does not directly affect those derived budgets (since they are based on warming at later dates in the continuing ESM simulations), but it helps diagnose the reasons for differences in carbon budgets between AR5 and SR15.

[iv]  SR15 Table 1.1: 1850–1900 to 2006–2015 column.

[v]  NOAA and GISTEMP use ERSST ocean temperature data. Over decadal and longer periods, ERSST warming is, except in the recent part of the record, primarily tied to measurements of (night-time) SAT.

[vi]  Lewis, N. and J. Curry, 2018: The impact of recent forcing and ocean heat uptake data on estimates of climate sensitivity. Journal of Climate, 31, 6051-6071.

[vii]  Taking the change between the average over 1850–1900 and the average over 1998–2017; SR15 Table 1.1.

[viii]  SR15 Table 1.1. The reanalysis datasets involved are ERA-interim and JRA-55.

[ix] TCRE is usually measured in models as the response at the point of CO2 concentration doubling when increased by 1% per annum, taking 70 years, but it is not sensitive to the exact period or profile of CO2 increase. As the SR15 Glossary says, TCRE combines information both on the airborne fraction of cumulative CO2 emissions (the fraction of the total CO2 emitted that remains in the atmosphere, which is determined by carbon cycle processes) and on the transient climate response (TCR).

[x]  The erroneous use of “considerably” rather than “considerable” here is the IPCC’s error.

[xi] The AR5 carbon budget figures in SR15 appear to come from Table 2.2 of the IPCC AR5 Climate Change 2014 Synthesis Report, first published in 2015.

[xii] SR15 Table 2.2 note (2).

[xiii] SR15 also points out that there are some additional uncertainties that its stated probabilities don’t allow for. However, the SR15 1.5°C likely range for the remaining carbon budget is wider than that for the AR5 budget that SR15 presents for comparison, so it appears probable that the AR5 budget is also subject to these or comparable additional uncertainties. (In IPCC parlance, ‘likely’ means at least 66% probability, and a ‘likely’ range is usually interpreted as a 17%–83% probability interval.)

[xiv] AR5 WG1 section reported a TCRE range of 0.8–2.4°C for 15 CMIP5 (full-complexity) ESMs and of 1.4–2.5°C for the EMICs used. The mean and median TCRE found for CMIP5 ESMs by Gillett et al. (2013) was close to the 1.65 K value for the TCRE distribution used in SR15 to derive its carbon budgets; the mean TCRE of the EMICs used in deriving the AR5 carbon budgets also appears to be close to 1.65°C.

[xv] Gillett, N. P., et al., 2013: Constraining the ratio of global warming to cumulative CO2 emissions using CMIP5 simulations. Journal of Climate 26.18, 6844-6858.

[xvi] Detection and attribution methods allocate observed overall changes, usually in temperature, between several factors (typically changes in greenhouse gas concentrations, in other anthropogenic climate drivers, and in natural solar and volcanic activity) by scaling the differing spatiotemporal patterns of change that each factor produces in climate models so as to obtain the best match to observed overall changes. Scaling is necessary because models vary in the magnitude of their simulated responses to the various factors; models may be too sensitive or insufficiently sensitive to individual factors and/or may over- or under-represent the magnitude of those factors.

[xvii] SR15 states that “studies using observational constraints find best estimates of 0.35–0.41°C/TtCO2, and (Table 2.A.1) that using a log-normal distribution for its TCRE range would give a median TCRE of 0.38°C/TtCO2.

[xviii] The increase would have been less (Table 2.2 indicates 100 GtCO2) at the 66% probability point.

[xix] Le Quéré, C. et al., 2018: Global Carbon Budget 2017. Earth System Science Data, 10(1), 405-448.

[xx] Comparing the RCP8.5 and latest observational estimates of cumulative emissions to 2010 and their rate of increase since then, as shown in Figure 1.

[xxi] Blended-masked CMIP5 warming is based on a weighted average of SAT over land and SST over ocean in CMIP5 models, including only grid-cells for which there were adequate observational temperature data over the historical period.

[xxii] SR15 Table 1.1; or compare thin blue and black lines in Figure 1.

[xxiii] Figure 2.A.3 of SR15, which Figure 1 reproduces, shows blended-masked CMIP5 warming in 2010 as being identical to the 0.87°C observed 2010 warming. SR15 Table 1.1 gives temperature changes to the 2006–2015 mean for these two measures of respectively 0.86°C and 0.87°C.

[xxiv] Since SR15 warming projections are based on a TCRE range that primarily reflects simulated SAT warming in climate models.

[xxv] Warming accelerates slightly between 2000 and 2020 along the red line in Figure 1, so the temperature rise averaged over 2006–2015 will if anything be very marginally higher than the 1.11°C 2010 value,

[xxvi] For the CMIP5 RCP8.5 multimodel-mean, warming to 2010 is almost identical to warming to the 2006-2015 mean.

[xxvii] The AR5 carbon budgets were computed using RCP scenario simulations by 15 CMIP5 ESMs and 4 EMICs. The average TCRE of the five of those CMIP5 ESMs that were analysed in Gillett et al (2013) was 2.1°C. Extending the estimates over the remaining CMIP5 ESMs by treating similar models to ones for which TCREs were diagnosed as having the same TCRE, and by using data from Friedlingstein et al. (2014; DOI: 10.1175/JCLI-D-12-00579.1) Table 3, brings the mean (and median) TCRE estimate for all 15 CMIP5 ESMs down to ~1.85°C. Assuming that the 5 EMICs have a mean and median TCRE in line with the 1.65 K used in SR15, the overall mean and median TCRE of the models used for the AR5 carbon budgets would be ~1.8°C.


121 responses to “Remarkable changes to carbon emission budgets in the IPCC Special Report on Global Warming of 1.5C

  1. Curious George

    Nic, you must have actually read the document. You should not do that to the IPCC. The document is meant to be quoted to alert us to many dangers, but certainly not to be read, or, God forbid, analyzed.

  2. Doesn’t the differences show that their temperature to C02 sensitivities are screwed?

    Do they have 2 or more of these graphs?

    1. Actual temperatures
    2. Additional man made temperatures
    3. Natural temperatures without anthropogenic effects

    Any two will do.

    I suspect that they don’t publish them because they would have to explain why graph 3 above has flat lined.

  3. “the most sophisticated TCRE study cited in AR5 [..] scaled CMIP5 ESM patterns of temperature responses to greenhouse gas warming so that they were consistent with the observed warming”.

    And that’s the source of so many of the problems: They have assumed that GGs caused the observed warming. It is just an assumption, because no-one has demonstrated that the observed warming was caused by GGs. If some other factor was responsible for all or some of the observed warming, then all of their calculations and all of their conclusions are worthless.

    • “If some other factor was responsible for all or some of the observed warming, then all of their calculations and all of their conclusions are worthless.”

      Yes. If.

      What would that other factor be? And CO2 as a greenhouse gas is certainly not an assumption.

      • Scott Koontz
        “ would that other factor be? And CO2 as a greenhouse gas is certainly not an assumption.”

        Water vapor as a greenhouse gas is also not an assumption. That nature plays little to no part in climate change is a humongous (readers can replace humongous with an adjective of their choice) assumption.

      • Water vapor is a feedback. No way you’re going to magically get more water vapor without warming.

        Common knowledge. You would need to back it up and tell us why the earth is warming first, which simply bring us back to my question. What is causing the warming if not additional CO2?

      • Donn Armstrong

        Air Pollution, Not Greenhouse Gases: The Principal Cause of Global Warming. J. Geography Environ. Earth Sci. Int. 17(2) 1-8; Article no.JGEESI.44290

      • Steve K
        What could possibly be warming the earth apart from CO2 ?, you ask.
        Same thing/s behind the MWP ?

        And do you maintain that CO2 variation is the one and only factor in the earth’s temperature variations ?

      • “And do you maintain that CO2 variation is the one and only factor in the earth’s temperature variations ?”

        No. Did I stutter? Did I write “CO2 is the only forcing?” Nope. Why do you pretend that I wrote something like that? Not even close.

        “Same thing/s behind the MWP ?”

        There are many papers on the MWP you can read. The Medieval Warm Period was caused by an increase in solar radiation and a decrease in volcanic activity. Not CO2. I can send you a link if you’re interested.

        These Gish Gallops are easy to knock down. Google is a good place to start for many of you.

      • “Air Pollution, Not Greenhouse Gases: The Principal Cause of Global Warming”

        That’s a strange “science” article to put it nicely. Even someone looking for decades to counter climate scientists, like Watts, doesn’t believe in that stuff.

        Filed under: crackpot.

      • Albert Hopfer

        That other something could be the only other heat source other than the Sun. The Earth’s core.

  4. What about water vapor? Astronomer Tompkins’ article in The Atlantic argued this was an important GHG from the same premises that make CO2 important, yet here it is again… conspicuous in its absence from discussion.

  5. The IPCC SR15 1.5C Carbon budget is fiction because it is based on a spurious correlation. Please see

  6. Nic Lewis, thank you for this essay.

  7. This post misses an interesting aspect of this issue, presumably because the IPCC released its latest report without releasing the draft versions that led to it to allow people to see how the report evolved. If the previous drafts had already been published by the IPCC, I suspect Nic Lewis would have noticed this part of a previous version of the report’s SPM:

    The threshold peak budget compatible with a 50% likelihood of limiting warming to 1.5°C without overshoot is estimated to be 580 (490-640) GtCO2 (Table SPM1). This budget would be exhausted in 12-16 years if emissions were to continue at 2015 levels, and thus it would be impossible, at that point, to limit global warming to 1.5o C without overshoot. {2.2.2}

    More details were provided, and a table in this version listed the budget for a 66% chance of keeping warming to only 1.5C was 390GtCO2. This position was later changed to:

    The remaining carbon budget for a one-in-two chance of limiting global warming to 1.5°C is about 750 GtCO2, and about 550 GtCO2 for a two-in-three chance (medium confidence). These remaining budgets are larger than those estimated in AR5 [6]. Estimates of remaining budgets for 1.5°C vary by more than 50% due to assessed uncertainties in the climate response to emissions, and by ±250 GtCO2 due to assessed uncertainties in global warming until the decade 2006-2015.

    Which was later changed to:

    The associated remaining budget is being depleted by current emissions of 42 ± 3 GtCO2 per year (high confidence). The choice of the measure of global temperature affects the estimated remaining carbon budget. Using global mean surface air temperature, as in AR5, gives an estimate of the remaining carbon budget of 580 GtCO2 for a 50% probability of limiting warming to 1.5°C, and 420 GtCO2 for a 66% probability (medium confidence).14 Alternatively, using GMST gives estimates of 770 and 570 GtCO2, for 50% and 66% probabilities,15 respectively (medium confidence).

    It should be interesting when the IPCC finally releases the draft versions of its reports and people can examine what literature was used as support in each of these SPM drafts.

    • Brandon S, thanks you for drawing attention to the evolution of SR15. I have no doubt that there was significant political as well as scientific input into this process. But if it was that helped drive the authors of SR15 away from the clearly unrealistic AR5 ESM projections of warming relative to cumulative carbon emissions towards a simpler and better way of representing that relationship, maybe political pressure has on this occasion had some positive effect.
      It seems that the 1.5 C carbon budgets were increased by almost 270 GtCO2 between the draft you refer to and the final version. It is not clear to me how exactly the budgets in the draft version were derived (I suspect that they used the FAIR model to derive them), but that question is now only of academic interest.

      • For what it’s worth, I do not think this is merely “of academic interest.” I have some “insider” information in that i was given a full copy of a previous draft of the report (along with some other information) which I promised not to disclose so it’s tricky for me to say too much, but the jockeying which goes into aspects like this of IPCC reports can have significant effects. There is some appearance (at least to me) these budgets were changed by people with the intent of influencing policy decisions.

        That said, I do see your point in that the IPCC report is what it is. The question of how reliable/trustworthy the process used to make the report is relevant to some people/purposes but not to others. Personally, I look forward to having the full draft versions published as I think the final report has some truly troubling things in it which cannot be adequately understood without additional documentation.

    • Brandon S thank you for the expose on the settled science. It is amazing that over such a short period the figures used can change so much.

  8. It’s easy to talk about amounts of carbon gained or lost due to natural or human activities but it’s no longer easy to know if these budgets and targets are moral guides or objective standards.

  9. Geoff Sherrington

    I cannot follow the logic.
    On one hand, “Berkeley Earth (BEST) and JMA are not used because ‘no peer-reviewed publication is available for these global combined land–sea datasets’.”
    OTOH, we have “However, SR15 sticks with the 0.8–2.5°C (0.22–0.68°C/TtCO2) TCRE range from AR5, which represents ‘expert judgement based on the available evidence’.”
    How do you conduct peer review on an expert judgement?
    Is this no more than a case of the writers saying what they want to have heard, with convenient excuses to exclude/include what suits them?

    Nick, thank you again for yet another detailed analysis. I have not yet read/digested the IPCC report SR15, so perhaps you could help here. These changes from the AR5 findings are large, as you describe. In SR15, are these changes clearly and prominently flagged, or are they hidden in fine print?
    Also, is there an attempt at proper estimation of error in SR15?

    • Geoff
      The idea is that the “expert judgement” in AR5 was based on peer reviewed literature, which constitutes the “available evidence” (or the bulk of it). Unfortunately, much of the peer reviewed literature is of poor quality, and much of it consists of reports and analyses of the behaviour of ESMs rather than of the real world.
      IMO, the overall AR5 uncertainty ranges (which are generally very wide) probably in many cases encompass the real world value of the key parameter that they estimate, but that value may be nowhere near the best estimate (or, if none is given, the centre of the AR5 uncertainty range). However, in the case of remaining carbon budgets, both in AR5 and SR15, I think that the IPCC ranges, and not just the best estiamtes, are probably quite a way off.

      SR15 does state that the carbon budgets have been increased since AR5 and quantify the changes. But I wouldn’t say that the changes are prominently flagged, or properly explained. IMO there should have been a quantitative analysis given, along the lines of mine, that reconciled the SR15 budgets to the AR5 ones. That is standard practice, for instance, when a publicly quoted company presents its financial results each year: a “bridge” breaking down the change in profit into multiple contributing, quantified, causes is typically shown.

      There is a fair bit of error estimation in SR15, but no real attempt to go beyond the AR5 assessed 0.8-2.5 C TCRE range other than investigating the effect of assuming it represents a log-normal rather than a normal distribution. I would have liked to see a table in the Technical Annex showing carbon budgets at TCRE levels at the top and bottom of the AR5 TCRE range, and at quarter-up and quarter-down points in that range, with reference to them made in Ch.2.

      If you are interested in the scientific issues, IMO it is worth reading sections 1.2.1 of Ch.1 and 2.2.2 of Ch.2 of SR15, but little else.

      • That is standard practice, for instance, when a publicly quoted company presents its financial results each year: a “bridge” breaking down the change in profit into multiple contributing, quantified, causes is typically shown.

        Yes, this would be great — the world badly needs GAAP for IPCC.

  10. Hi Nick,

    You might find my recent Carbon Brief post on the carbon budget revisions of interest. I plotted the temperature increase since preindustrial in the ESMs vs. the full CMIP5 ensemble and found about ~0.1C more warming, as you suggest. The 33% of ESMs with the smallest cumulative emissions when 1.5C is reached (and which were used in part for the AR5 66% avoidance budget) show a significantly larger mismatch.

    Another issue is that ESMs notably underestimate cumulative emissions compared to observations:

    • Curious what the spread of “observed” emissions estimates looks like in the literature over the past 20 years. There seem to be a number of efforts.

    • Geoff Sherrington

      What is the accepted process for calculating error bounds around interpolated data such as much of the SST set? As opposed to actual data?

    • Hi Zeke,
      Thanks for your comment. As it happens, my attention was drawn to your article, after I had drafted mine, and I did read it. I thought that you made a number of interesting and valid points. However, I have a few questions and comments on it:
      • You say SR15 raises the budget for a 66% of avoiding 1.5C to 420GtCO2 and the budget for a 50/50 chance of exceeding 1.5C to 580GtCO2. How does this reconcile to the post-2017 budgets SR15 gives (Table 2.2), of 570 GtCO2 at 67%, and 770 GtCO2 at 50%, probability of avoiding >1.5°C ?
      • You point out that ESMs underestimated historical emissions by around 280 GtCO2 and that because the carbon budget is based on the relationship between temperature and cumulative emissions, underestimating cumulative emissions will lead to a carbon budget that is too small. I agree. But this also implies that the ESMs’ TCRE values are unrealistically high. Since SR15 derives its carbon budgets from TCRE estimates that correspond closely to those of these same ESMs, that in turn implies that the SR15 carbon budgets are unrealistically low. Do you agree?
      • You point out that much of the difference between ESM and GCP cumulative emissions arises from the period around 1940, where ESMs suggest a large drop in emissions that is not present in the GCP dataset. Clearly, the ESM emissions (which are diagnosed from simulations in which evolving CO2 concentrations are prescribed) are wrong. CO2 emissions cannot possibly have fallen by 60% between the late 1930s and the late 1940s, a period over which gross world product grew by 30%. The culprit must surely be the very slow increase in the RCP specified CO2 atmospheric concentration between the late 1930s and the early 1950s, probably linked to the estimated CO2 levels being too high prior to the late 1930s.
      Would you not agree that however (within reason) one alters the estimated path of CO2 evolution between 1860 and 2017 (without changing the end concentrations), the ESMs will always underestimate cumulative emissions over the full period?

      • niclewis: Hi Zeke,
        Thanks for your comment.

        thank you both to Zeke Hausfather for his comment, and to nic lewis for his reply.

      • On the 1940s… you can see the “budget imbalance” here

        The land sink & atmospheric uptake are really weak, even though emissions continue. Since the ESMs were run in compatible mode (concentration to emissions) then emissions probably track the concentrations quite well unless they have a really smart land model. The land use transitions will be inputs, so garbage in equals garbage out…

        Better land modelling of Russia (& other war affected areas) might help explain, but there are likely other factors too. Here are some articles:

        Import area to resolve, as apart from this, the budget imbalance would be close to zero mean over the long term.

      • Hi Nick,

        The 420GtCO2 / 580GtCO2 numbers are from the SPM, and refer to a global TAS definition. The 570/770 numbers in Table 2.2 refer to a blended TAS/SST definition of surface temperatures. The global TAS budget is present in the SPM but not chapter 2, which is interesting, and I suspect the result of some last-minute discussion on the implications of changing how the global surface temperature is defined between the AR5 and SR15.

        Regarding if the past cumulative carbon mismatch means that TCRE is too high, as Glen points out below (and you can see from the blue whiskers in my figure) the uncertainty in the observation-based carbon budget is large enough that its hard to claim with certainty that the mean estimate from ESMs is getting cumulative carbon emissions wrong, though it at least suggests that they are. The AR5 TCRE estimate is not based solely on the ESMs, but the fact that the ESMs to run hotter than the CMIP5 MMM does at least suggest that they would give a high-biased TCRE (though the effect of this bias on the remaining carbon budget would be smaller than in the AR5 approach of relying on ESMs for warming and emissions since pre-industrial).


      • Hi Zeke,
        Thanks for clarifying re the carbon budget difference. I hadn’t studied the SR15 SPM, as in theory it should not contain anything which isn’t in the main report. I can’t find anything in the main report that supports the global TAS carbon budgets in the SPM that you cited.

        I like you had wondered whether the change from the global TAS based warming basis for carbon budgets in AR5 to a blended TAS/SST basis in SR15 might have been a late change. But it evidently wasn’t. The First order draft of the SPM referred to global mean surface temperature change being relative to the climatology of pre-industrial levels “as combined land surface air temperature and sea surface temperature”.

        You say that the AR5 TCRE estimate is not based solely on the ESMs. Agreed, but as I wrote the 0.8–2.5 K/TtC range agrees to, and appears to be largely based on, the TCRE range from CMIP5 ESMs and EMICs, which had a similar mean (and median) to that used in SR15 (1.65 K/TtC). The only post-2009 observationally-based estimate of TCRE cited in AR5 was rather lower: 0.7–2.0 K/TtC range, with a mean of ~1.35 K/TtC.

        You say “the fact that the ESMs to run hotter than the CMIP5 MMM does at least suggest that they would give a high-biased TCRE”. Yes indeed, quite apart from the fact that the CMIP5 multimodel mean has warmed much faster than observations in recent decades, during which models’ forcing growth has ceased to be depressed by high aerosol forcing. The CMIP5-mean historical/RCP4.5 TAS warming trend over 1979–2016 of 0.242 K/decade is 1.37x the 0.177 K/decade trend of the homogenized ERA-interim surface air temperature record (Simmons et al. 2017; DOI:10.1002/qj.2949).

        Moreover, it seems fairly clear that current ESMs poorly simulate the land carbon cycle. Their climate-carbon feedback is too high, and their carbon-carbon [carbon fertilisation] feedback probably too low. That is unsurprising, since the estimates of total CO2 emissions that they were trained on have since been revised upwards substantially.
        Friedlingstein (2015, states “These independent methods point to climate-carbon cycle feedback at the low-end of the Earth System Models range, indicating that these models overestimate the carbon cycle sensitivity to climate change.” Friedlingstein obtains an observationally-based land climate-carbon estimate of −28 GtC/K, near the bottom of the ESM range of −20 to −177 GtC/K. He estimates a land carbon-carbon feedback of 2 GtC/ppm CO2, about 70% towards the top of an ESM range of 0.2 to 2.8 GtC/ppm CO2.

      • Glen Peters,
        Thanks for the links.

        You wrote abou the 1940s: “The land sink & atmospheric uptake are really weak, even though emissions continue.”
        The last Global Carbon Budget 2017 estimates do not support the contention that the land sink was weak in the 1940s. They have a mean of 0.7 GtC/year over 1940-1950, compared with 0.5 GtC/year during the 1930s.

        “Import area to resolve, as apart from this, the budget imbalance would be close to zero mean over the long term.”
        I agree that it is an important area to resolve. But the only likely resolutions involve the CO2 change over the 1940s and/or the 1940s land (and/or, possibly, the ocean) sink being revised strongly upwards. Neither of these would help to bring ESM carbon budgetting into line with estimated reality (unless the estimate of preindustrial CO2 concentration is also revised downwards).

        BTW, CO2 change over the 1940s has been doubled in the CMIP6 GHG concentration series (Meinshausen et al 2017) compared to the CMIP5 series. But it remains a fraction of the CO2 growth over the 1930s.

    • Zeke, Nic, Judith: I followed Zeke’s link to his useful post, particularly the graph showing all of the hindcast and observed warming. After more than a decade of looking at such graphs, it suddenly dawned on me how absurdly all such graphs appear to be constructed. FWIW, I do recognize that the thoughts that follow are fairly unconventional, if not wild or absurd, but they might be worth reading.

      Firstly, we don’t measure global mean surface temperature. If I understand correctly, we measure temperature in about 80% of the HadCRUT grid cells. Some of those grid cells have problematic data. Cells with seasonal sea ice can be measured only part of the year. We use a variety of techniques to deal with grid cells without any data. In the ocean with slowly changing currents and eddies, extrapolating from a changing set of ship tracks seems fairly dubious.

      Secondly, we know the most about current temperature, but align all of our records beginning in 1860 or some other absurdly early starting date. By taking anomalies with respect to some middle period, we have the absurd situation that the confidence intervals are smaller in the middle than at either end.

      Suppose we aligned all records so that the current temperature anomaly were zero. Suppose we wanted to present warming since 1860. Shouldn’t we only be calculating warming for the grid cells for which we have reasonably complete observations since 1860 and showing a map of where those grid cells are located. Characterizing that change as “global” is grossly misleading.

      If we then want to compare observed warming to modeled warming, we should use hindcast temperature only for the grid cells with observations. Validating the warming hindcast by models should only be done in grid cells where we have reliable data. The absurdity of measuring warming from a pre-industrial climate would quickly become apparent if we were more candid about the paucity of data defining that climate. Then maybe we could focus on the key issue: limiting warming from present, how much that costs and how much that saves. That has nothing to do with the political targets of 1.5 and 2.0 degC.

      From a pragmatic perspective, we are not very interested in increasing GLOBAL mean surface temperature. We are interested in temperature where people (and agriculture) exist, which is where the thermometers are (and tide gauges for SLR) located. You might argue that SLR means we are worried about temperature in Greenland and Antarctica, but the melting caused by surface temperature isn’t the real problem. The rate at which these ice caps are flowing towards the sea is the problem. For the GIS, this is determined at the junction with the bedrock, which is completely insulated from air temperature. The temperature of the water flowing there is always 0 degC (though the volume may change). For Antarctica, the problem is melting at the junction between the land and ice, also well below the surface. Most of the steric expansion of the ocean is controlled mostly the rate at which heat penetrates below the mixed layer. As best I can tell, this isn’t a massive problem.

      • Whatever problems there might be with the current data, it just gets worse with the data from 150 years ago. At some point common sense ought to send up a red flag about coverage in the 19th Century. They will be along shortly to tell you not to worry, they’ve got things covered.

        Getting only part of the story is just as bad for Greenland and Antarctica as it is for the historical temperatures. Out of curiosity I spent a couple of hours last night reading IPCC AR5 to see what was said about geothermal activity in both locations. I could not find a single sentence devoted to the activity under the Ice Sheets, even though it’s been the subject of several recent papers. Admittedly, the knowledge about the level of geothermal was sketchy pre AR5, but there had been research going back decades identifying the possibility of those magma plumes affecting basal melting. At a minimum, AR5 should have simply said much more information was needed to address the possible impacts, and no conclusions could be made.

        A legitimate science would have made every attempt to explain the current knowledge of all variables that could be influencing the Ice Sheets, not just the atmosphere and waters. But we’re dealing with climate science, and they had their perpetual blinders on, skewing the discussion toward only one thing. Guess what that was.

      • Frank, this is exactly how I would do it also. In evaluating climate models, we should filter the model grid cells to match the observation sites.

        The complaint of course is that the Arctic gets undersampled, which is where a big part of the warming is. Well the arctic is warm during the past two decades because of warm phase of the AMO; once we shift to the cold phase, we can have a better understanding of the impact of AGW on the Arctic.

        The other concern is sea level rise, which affects huge population on the coast. We have framed this whole problem incorrectly. Agree that ice sheets are the potential concern (not steric rise). I’ll have an ice sheet update soon, some interesting new results; geology and ocean circulations are the driver, AGW not so much.

      • The complaint of course is that the Arctic gets undersampled, which is where a big part of the warming is. Well the arctic is warm during the past two decades because of warm phase of the AMO; once we shift to the cold phase, we can have a better understanding of the impact of AGW on the Arctic.


      • Judith

        I look forward in the coming years to papers that address the following:

        Percent of Antarctica and Greenland contributions to SLR from atmospherics, OHC and geothermal activity respectively.

        Estimates of water temperature increases that have been interfacing with Glaciers/Ice Sheets since 1950. How much less SLR without that increase.

        Contribution to SLR from not only sub glacial / Ice Sheet geothermal activity but also that identified under Greenland fjords and the sea floor under AABW as discussed in this paper.

        I’m having a difficult time understanding how the geology affecting the respective Ice Sheets could have been ignored for so long.

      • Judith: Yes, I realize that recent rapid Arctic warming is undersampled, whether that warming is due to GHG-mediated forcing or the warm phase of the AMO, or is coupled to the lack of warming in the Antarctic. However, my point was that we should be focusing on warming where people and agriculture exist – which is where the thermometers have been located. If this approach were taken seriously, this would focus attention on the land record in non-polar regions, and temperature has been warming FASTER over land than the ocean. So the goal of the proposal isn’t to direct attention away from the one region with the greatest warming, but to direct attention towards the regions where climate change is the most important (and best documented, especially in the distant past). “Human mean surface temperature” in place of GMST.

        The key objection should be that warming ice caps could collapse and produce catastrophic SLR. However, it isn’t obvious to me that the surface temperatures we measure in the Arctic and Antarctic are relevant to the processes at the bedrock that produce collapse. AFAIK, the GIS (and polar bears) survived two millennia of the HCO, so collapse in the next century appears very unlikely. The absence of publicity about warming water at the subsurface grounding line of West Antarctic glaciers suggests little is happening there either.

  11. Pingback: Apocalypse delayed | Climate Scepticism

  12. The SR15 estimates of the carbon budgets that will allow us to remain within the 1.5°C and 2°C targets are far larger than those given in AR5 – over five times as high from end 2017 for a 66% probability of not exceeding 1.5°C warming.

    Just imagine where they’ll be in SR22!

    Every IPPC report should be required to report the trend in forecast changes over all previous IPCC reports. It won’t help anything, but it will be funny.

  13. I have been feeling I should get back to work lately. Funny – I have grown my hair long and wear tie died pants. Not engineering. High level environmental science. Social, economic, cultural, coastal, environmental, scientific… Risk and opportunity. I may refer to JC’s recent Rand analysis.

    Aside of what exactly I am skeptical of in Earth system science – I was pondering a system that has an underlying, evolving state of perpetual and more or less extreme and abrupt change. Powerful and driven by the dynamical system itself. We are changing the planet and small changes matter in a dynamical system.

    But in engineering we were warned early on of faux precision. This post is an impossible precision based on the shakiest of underpinning assumptions. CMIP5 is a sleight of hand. Each of the 102 ‘models’ are themselves only one of many feasible trajectories in a model solution space. Its gets worse with imprecisely known initial conditions, depth and breadth of process coupling and grid size. How a solution emerges must be a quandary faced by modelers every day – but rarely made explicit. The proper use of models may be as initialized decadal ensemble forecasts given much more computing power and better observations over a much longer time.

    The numbers themselves – 1.5 etc. – are derived from simple extrapolations of surface temperature and atmospheric carbon dioxide. Shaky ground here is the assumption that surface temperature warming in the 20th century didn’t have a significant intrinsic component. And that future climate states are not more likely to surprise us than confirm expectations – 1.5 degrees or not.

    From Earth system science – the experiment has been done. The 20th century surface warming from intrinsic causes and AGW was some 0.1 k/decade. Still a relatively short record for a system with decadal to millennial variability. For the future – prosperity and resilience to yet wilder weather extremes – whatever the source – seems a good idea. A good part of that is optimum water and carbon management across land and ocean. The rest is just technology and trade.

  14. dlightfoaeica

    Nick Lewis: great work and it shows you are familiar with AR5.

    There are two facts missing from the IPCC work about CO2 and climate change.CO2 has an upper limit to warming as the radiative forcing (RF) reaches and asymptote at approximately 655 ppmv.

    This is seen in Figure 1. If the figure does not come through, it is Figure 4 from Reference [1]. The quadratic is a better and more realistic approximation than the logarithmic function. There are three reasons for this: (1) the quadratic starts at zero concentration and zero RF, (2) the quadratic exactly covers the logarithmic curve over the range of 275 to378 ppmv, and (3) the quadratic reaches an asymptote [1]. Thus, there can be no more warming by CO2 after approximately 655 ppmv.

    Figure 1. Logarithmic and quadratic approximations of radiative forcing
    versus concentration for carbon dioxide show the actual RF of CO2 at
    current levels is approximately 9 W m-2.

    In AR5, the IPCC notes that between 1750 and 2011, CO2 concentration increased by 116 ppmv, RF by CO2 increased by 1.68 W m-2 and Earth’s temperature increased by 0.8oC. Therefore, they conclude that CO2 causes global warming.

    This is a common mistake and occurs because it does not take into account how CO2 reacts within the atmosphere. In the atmosphere, along with the ideal other gases, CO2 responds to the Gas Laws. Thus, as the air temperature increases from winter to summer the concentration of CO2 falls and it tries to cool the atmosphere as in Figure 2 at Hamburg, Germany. While CO2 is trying to cool, back radiation is warming the atmosphere and counteracting the cooling. [2]. If Figure [2] did not come through; it is Figure [1] in Reference [2].

    Figure 2 The warming effect of back radiation rises by 70Wm–2 from January to July while CO2 causes cooling of 0.45 Wm–2 as its concentration falls.

    For reference: Back radiation is the sum of the radiative forcing of all of the greenhouse gases. Figure 2 is constructed from actual physical measurements of atmospheric temperature, relative humidity and back radiation. Thus, it will be difficult to prove it is wrong.

    [1] Lightfoot HD, Mamer OA. Calculation of atmospheric radiative forcing (warming effect) of carbon dioxide at any concentration. Energy & Environment. 2014;25(8).
    [2] Lightfoot HD, Mamer OA. Carbon dioxide: sometimes it is a cooling gas, sometimes a warming gas. Forest Res Eng Int J. 2018;2(3):170-175. DOI: 10.15406/freij.2018.02.00043

    Hope this helps.

    How does one post a figure. I have tried a couple of different formats, but nothing works. I see that some others are able to post figures.


    H. Douglas Lightfoot

    • Douglas: Your paper claims that: “It is widely recognized that this relationship provides only ∆RF and its validity outside the range 275 to 378 ppmv is not established.” However, you provide not citation for this claim.

      Myhre (1998) calculated radiative forcing using line-by-line methods for CO2 concentrations from 275 to 1000 ppm. There is no plateau at 655 ppm. Your quadratic model – and the deductions you draw from it – are (grossly) incorrect.

  15. Settled science. 400% variations.
    “A carbon budget does not serve much purpose if none of the future emission scenarios stick to it. Negative emissions can make the carbon budget largely meaningless, as emissions that greatly exceed the budget can simply be counterbalanced by assumed future negative emissions.

    The amount of negative emissions ranges widely across the 1.5C scenarios – from 400GtCO2 to 1,600GtCO2 (10-40 years of current emissions). The use of negative emissions effectively increases the size of the remaining 420GtCO2 carbon budget by between 90% and 380%, allowing total positive emissions of between 800 and 1,600GtCO2 by 2100.”

  16. “the idea of a remaining carbon budget simply may not be very useful concept for strict mitigation targets such as 1.5C.”
    Should that be impossible rather strict?
    “Policymakers cannot be expected to take a sudden carbon budget extension as a welcome opportunity to step up mitigation efforts, only because meeting 1.5C now seems a little less unrealistic. Rather, such an extension reinforces their long-held belief that it will always be ‘five minutes to midnight’, although global emissions are still not decreasing”
    If it was the nuclear clock instead we would already be several minutes after zero.

  17. Didn’t Beenstock and Reingewertz establish there was no TCS and ECS? And how reliable are the figures for carbon stock? Agriculture used to be a net source but arguably is a net sink. And what happened to the log effect on CO2 forcing, if one believes in such a thing? The IPCC is a joke, a very expensive joke.

  18. Wolfgang Richter

    It should be looked in the SR 15 report what is written as a “result” of the new CO2 budget and -I think- of the observations what in the real world is going on: the arctic probably extremely seldom could be ice-free in summer, and whether the ice sheets of Greenland and Antarctica would melt further is completely “open”. Please read chapter 3! The alarmism on ice-free arctic and on melting ice-sheets is finished!

    Page 3-8: “There is high confidence that the probability of a sea-ice-free Arctic Ocean during summer is substantially higher at 2°C when compared to 1.5°C. It is very likely that there will be at least one sea-ice-free Arctic summer out of 10 years for warming at 2°C, with the frequency decreasing to one sea-ice-free Arctic summer every 100 years at 1.5°C. There is also high confidence that an intermediate temperature overshoot will have no long-term consequences for Arctic sea-ice coverage and that hysteresis behaviour is not expected.”
    Page 3-140: „The timescale for eventual loss of the ice sheets varies between millennia and tens of millennia and assumes constant surface temperature forcing during this period. Were temperature to cool subsequently, the ice sheets might regrow although the amount of cooling required is likely to be highly dependent on the duration and rate of the previous retreat.”
    “The Antarctic ice sheet can contribute both positively and negatively to future GMSL rise by, respectively, increases in outflow (solid ice lost directly to the ocean) and increases in snowfall (due to the increased moisture-bearing capacity of a warmer atmosphere).”

    They only have forgotten to regard that then the sea-level will not rise faster than during the last 100 years what is seen in the land based measuerments.

  19. Nic I’ve checked the HAD Crut 4 temp trends before, but it seems to have changed a lot since Phil Jones’s Q&A with the BBC in 2010, after the Climategate scandal.

    In 2010 he listed 4 warming trends since 1850 and there wasn’t much difference in the trends. The 4 trends were—-

    1860 to 1880- 0.163c dec

    1910 to 1940- 0.150 dec

    1975 to 1998- 0.166 dec

    1975 to 2009- 0.161 dec.

    Today the York Uni tool has the SAME 4 trends for Had 4 Crut at—–

    1860 to 1880- 0.156c dec lower

    1910 to 1940- 0.137 dec lower

    1975 to 1998- 0.191 dec much higher

    1975 to 2009- 0.193 dec. much higher

    So just 8 years after Jones’s BBC Q&A we see both earlier warming trends have been adjusted down and the two later trends have been adjusted up. And people wonder why we don’t trust these temp data-sets?

    And this is the temp data-set that the IPCC uses to try and convince us to waste endless billions $ for zero gain. Who are they trying to fool? And why hasn’t one of their top scientists noticed this and blown the whistle?

    Here’s Dr Jones’s 2010 BBC Q&A. See question A.

    Here’s the YORK UNI tool using HAD 4 Crut krig global.

    • ngard2016,
      HadCRUT is not perfect, but I would trust its temperature record more that GISTEMP or NOAA GlobalTemp. Some revisions to past values are to be expected, as more historical records are dug out, and homogenisation adjustments to the data reappraised (particularly in relation to ship measurements of SST). The revisions are only a cause for concern if they have not been pursued in an even handed way, but with a bias towards favouring changes that depress early temperatures and boost recent ones.

      • Nic, that was a very polite way of noting the bias :)

      • bitchilly
        I didn’t seek to imply that revisions to HadCRUT were biased. There have been remarkably few significant changes to HadCRUT4. The 1901-2010 trend is the same (0.074 C/decade) in the current HadCRUT4v6 as per the original HadCRUT4 record nearly 7 years ago. On the other hand, since 2011 the 1901-2010 GISTEMP trend has gradually been revised up from 0.075 to 0.085 C/decade.

  20. Salvatore del Prete

    The only reliable data is Dr. Spencer’s satellite data and that is the ONLY data I use. Al the rest is manipulated garbage.

  21. Salvatore del Prete

    A discussion I had recently.

    It is a shame how much energy fake AGW theory has taken away from real discussions about climate change. A waste since CO2 has ZERO to do with the climate.

    Which magnetic fields influence the climate?? The solar/geo magnetic fields. Why? Because they moderate UV light/Near UV light which effects global surface oceanic temperatures, they moderate galactic cosmic rays which moderate global cloud /snow coverage and major volcanic activity, the magnetic fields also moderate EUV light which in turn effects the atmospheric circulation patterns and cloud and snow coverage.

    I assert the solar and geo magnetic fields DO determine the climate. The reason it is not apparent is because most of the time the duration and degree of magnitude change of the fields is to small and many times they do not move in sync. This time however they are both weakening rather dramatically and moving in sync so the chances of more apparent climatic effects is on the rise.

    Bob your assertion that it is just TSI is entirely wrong. TSI varies inversely within itself meaning the whole TSI spectrum does not EVEN move in unison with a weakening or strengthening sun. The sum change being so small that TSI alone can not impact the climate to any significant degree which you keep saying. Yes TSI has maybe a .2c effect upon the climate at most. Any additional climatic changes go well beyond TSI itself.

    As far as supporting data the Dalton and Maunder solar minimums supply some supporting evidence but the geo magnetic field back then was stronger then it is now and the compounding effect was less then what it will be now.

    I say the missing part of the puzzle is the geo magnetic field strength and orientation meaning the location of the magnetic poles which will direct galactic cosmic rays to certain latitudes where by they would be much more effective in cloud creation and lower latitude major volcanic activity.
    I say how fast the geo magnetic field weakens going forward is going to be a big factor in what happens to the climate. How weak does that have to become ? I would say at levels it has achieved in the past that took the field to the point of approaching a geo magnetic excursion. It is probably above the levels that would be associated with magnetic field excursions.

  22. Pingback: Nic Lewis: Remarkable changes to carbon emission budgets in the IPCC Special Report on Global Warming of 1.5C - The Global Warming Policy Forum (GWPF)The Global Warming Policy Forum (GWPF)

  23. Nic/Judith: So many aspects of the IPCC’s analysis make little sense to me:

    Why measure starting from pre-industrial conditions? We can’t change where we are where we are today (which I will call 1990-2010 mean temp and 400 ppm of CO2). According to most economists, past warming has been net beneficial. Some economists apparently estimate we are at the breakeven point where damages begin to outweigh benefits, but others think that point hasn’t been reached yet. So why don’t we use this as the starting point ofr discussing future emissions and future warming?

    One obvious reason is that the 1.5 degC POLITICAL target (which lacks any scientific or economic rational) is only about +0.5 degC in the future. The idea that going 0.5 degC or even 1.0 degC past a break-even point justifies drastic and expensive measures is ridiculous. The whole framework for calculating a carbon budget is absurd.

    Why not present a budget in CO2 equivalents? Right now the assumptions and uncertainties about rising CH4, minor GHGs, aerosols and land use changes are hidden a model. We can certainly influence some of these factors, just like we can influence CO2. We will get far more benefit from reducing CH4 (and HCFC?) emissions later in the century when the transient warming they produce causes much more damage.

    • franktoo
      “Why measure starting from pre-industrial conditions?”
      I think this was, as you say, a political decision. But SR15 does at least accept where we have got to, using observationally-based estimates of mean 2006-15 temperature and projecting warming from then on based only on subsequent emissions, although it’s projected post 2006-15 warming still looks to me much too high in relation to emissions.

      “Why not present a budget in CO2 equivalents?”
      Fair point, but the atmospheric lifetimes of emissions vary hugely, and CO2 is different from most other gases in that it is pretty chemically inert in the atmosphere and not only has a long lifetime but does not asympotically return to the pre-emissions atmospheric concentration even after 1000 years; 10-20% still remains in the atmosphere (versus 40-50% after a century).

      • Nick: Thanks for the reply. The 2010 and 2017 data points on your Figure 1 are far to the right of the AR5 projections (or below, depending on how you look at it.) The difference on the x-axis amounts to about 500 GtC or about 20-25% of cumulative emissions. Re-reading your summary in light of this graph helps me understand it better: a) Pre-industrial temperature (T(t=0)) has been shifted up on the y-axis – by the equivalent of 0.270 TtCO2 on the x-axis. If I use a conversion factor of 0.45? TtCO2 = 1 K, that would be 0.12 K (or 7 years of warming). b) Current temperature is lower than projected – by the equivalent of another 270 GtC (another -0.12 K) c) The slope of future warming (TCRE) has been reduced by averaging the inferior? MAGICC model (0.45 TtCO2/K) with the newer FAIR model (0.38 TtCO2/K). I would like to know your value based on energy balance models.

        If you re-publish this article for other audiences, I suggest that you condense the key information into a table and provide a range of conversion factors:

        1) Converting cumulative emissions to warming: 0.45 K/TtCO2, 0.38 K/TtCO2, convert your preferred TCR to TCRE.
        2) Emissions Rates: currently 0.35? TtCO2/decade, 0.22? TtCO2/decade in 1990. ??? TtCO2/decade under Paris Accords. Average emission rates in RCP6.0 and RCP8.5. (Values per decades easier to comprehend than any other unit of time.)
        3) A reality check for some of these numbers: For the past 3-4 decades, 0.45 K/TtCO2 * 0.3 TtCO2/decade = 0.15 K/decade (slightly low). That is because we need to use CO2 equivalents, which may be as much as 50%? higher. So we need emissions rates in CO2 and CO2 equivalents.
        4) Warming needed to reach +1.5 K and +2.0 K. Decades before reaching these targets at varies warming rates. For the first time, this answer is obvious to me: 2-3 decades, probably 33% longer using your values for TCR.

        I (and presumably most readers) have trouble seeing the forest through the many details in your recent posts, particularly this one. Since you are often kind enough to reply to my comments, writing my deductions down and receiving help works for me. Would it help if I collected some values and sent them to you?

      • franktoo:

        “The slope of future warming (TCRE) has been reduced by averaging the inferior? MAGICC model (0.45 TtCO2/K) with the newer FAIR model (0.38 TtCO2/K).”
        Only in relation to non-CO2 caused warming, which is a relatively minor fraction of total warming. As I wrote: “when calculating its carbon budgets, SR15 only uses MAGICC and FAIR (averaging their results) to project post-2010 temperature changes in response to non-CO2 emissions.” The MAGICC TCRE is 0.47 K/TtCO2. The mean (and median) TCRE used for projecting CO2 warming in SR15 is 0.45 K/TtCO2, being the mid-point of the IPCC AR5 TCRE range..

        “I would like to know your value based on energy balance models.”
        My estimate of TCRE, observationally-based as far as possible, is approximately 0.3 K/TtCO2.

        “If you re-publish this article for other audiences, I suggest that you condense the key information into a table and provide a range of conversion factors”
        Thank you for this suggestion, which I agree has merit.

  24. Nick wrote: “SR15 sticks with the 0.8–2.5°C (0.22–0.68°C/TtCO2) TCRE range from AR5, which represents ‘expert judgement based on the available evidence’.”

    What value would you recommend using for TCRE?

    If TCRE is calculated from TCR for various models, this implies that there is no uncertainty about the fraction of total CO2 emissions that will remain in the atmosphere later in the century. Right now we apparently are emitting enough CO2 to raise levels by 4 ppm/yr and 2 ppm of the current increase above steady state (400 – 280 = 120 ppm) is “disappearing” into sinks. IMO, a lot depends on how this situation evolves. Emissions predicted to produce RCP 8.5 might result in CO2 concentrations for RCP 6.0 if more CO2 disappears into sinks. The opposite could be true if sinks “saturate”.

    • franktoo wrote: “If TCRE is calculated from TCR for various models, this implies that there is no uncertainty about the fraction of total CO2 emissions that will remain in the atmosphere later in the century.”

      Agreed; that is why models’ TCREs are not normally calculated from their TCRs, although TCRE is strongly correlated with TCR in models (and reality). Carbon cycle behaviour varies significantly between different ESMs – hugely so for the land carbon sink.

      • Thanks for the reply. So different ESMs have different “free fractions” for the amount of CO2 remaining in the atmosphere after a certain of anthropogenic CO2 has been released (mostly by burning fossil fuel). Is there a table of projected “effective free fractions” for models available somewhere or is this parameter buried in time-dependent models and inaccessible?

        Does the difference between TCR and TCRE depend on anything else besides “free fraction”?

    • ‘Does the difference between TCR and TCRE depend on anything else besides “free fraction”?’

      Only on the preindustrial atmospheric CO2 content, which is well known to be ~ 0.59 TtC.

      TCRE = TCR * Airborne fraction of CO2 emissions / 0.59

  25. “It seems fairly extraordinary to me that the AR5 post-2010 carbon budget for 1.5°C, which was only published four years ago, has in effect been now been increased by ~700 GtCO2 – equal to 21st century emissions to date…”

    It’s framing, that is it’s political. We can’t do this versus we can do this because it’s not as bad as we said. Saying we can’t do this means an abandonment of mitigation solutions and a move to adaptation policies. Everyone retracts from world solutions to national solutions. They flat out gave us more time so we wouldn’t give up with mitigation.

    If we assume they had in AR5 cranked up the warnings, cranking it back down aligns it more with what is really going on with the climate. I can’t see how they can give us more emissions, roughly all of those since about 2001 as a freebie without saying, things are better than we said before.

    Looking at this one issue here and at about 700 GtCO2 above, this is huge. You can’t just pull that amount emissions out of somewhere and tell us you knew what was going on. The prior accounting was atrocious. They had better keep the broad range of 1.5 to 4.5 C ECS to cover themselves and leave plenty of wiggle room in case they need to do something like this again.

    We know the GMST and CO2 levels and don’t do too bad figuring out emissions. This stuff needs to balance out. Who in the heck loses or finds 17 years of emissions, the driver of it all? These people are not accountants. They should stop pretending they are. They need to qualify it all with something like this: If it was possible to account for the stuff, this is what it might be. But we aren’t sure that’s possible because key things like the TCR and observation data are not well constrained. They should not at this time be referred to as accountants. They have a failed accounting system. We don’t know what’s going on. And this is the whole thing. It’s not someone stealing a little postage. And who let’s politics into their accounting system?

  26. My French is rather limited, but I think I am in agreement with this. We don’t account enough for the natural absorption of CO2. If we reduce our emissions by 50% we can stabilize CO2 levels at today’s values, and we don’t need zero emissions for zero net CO2 growth. This assumes that the natural sink remains as effective as it has been. Official estimates have it becoming less effective with time, but it is hard to find why or the extent of that effect. I have done calculations with continuing effective absorption and I think we can emit 2000 GtCO2 between now and 2100 and stay below 2 C. That is still a large reduction in average rate from today applied over the next 80 years.

  27. Raymont, you should consider that the french of the most readers here could be limited. For myself: it’s very, very limited, I know only a few words in this language, not the right ones for this blog ;-) . However, google translate was improved in the last year or so very remarkably. I copied your text and this is the English machine translation which makes much sense to me:
    Reasoning on cumulative values of masses of CO2 that would be inert does not seem relevant to me.
    “It is the flux expressed in g CO2T / y that must be studied.
    Today 40 gCO2T / y are emitted (industrial and agricultural), 20gCO2T / y are absorbed by land and sea. The airborne fraction, for 20 gCO2T per year, is 50%.
    If emissions were reduced by 25%, to 30 gCO2T / y, growth in CO2 content would be reduced to 10 gCO2T, an airborne fraction of 33%. A limited reduction in emissions would initially result in a decrease in the growth of atmospheric CO2 levels and a reduction in the airborne fraction.
    These emissions should be <absorbed (20 gTCO2 / yr) to finally see decreasing atmospheric levels and with them less effective carbon sinks.
    Reasoning by despising the impact of the carbon cycle appears to be a profound mistake of logic.".
    Only copy'n paste and the language problem is (almost) solved…

  28. Greenhouse Bookkeeping 101

    If you can balance your checkbook you can trash the greenhouse effect.

  29. As a British citizen I’m embarrassed by the fact that it seems to be English speaking countries that are at the forefront of the Luddite movement to use global warming as a pretext to destroy the world’s industrial-technological economy. Australia, UK’s ecofasc1st Guardian and academia, Canada, the US powerful left, etc. They should be careful what they wish for.

    Economies are not just numbers for academics. People live and die by them. Typically if economies run more or less OK people generally are subdued and content but once the economy start going seriously downhill, people get agitated and politics get interesting in a bad way.

    Contemplate the following sentence:
    “Anglo Saxon is the new Cosmopolitan.”

    If you follow European politics you will be aware of rumblings on the German far right about a “rootless global class”. They’re not talking about Jews. They refer to people who “speak fluent English, are equally at home in Berlin or Singapore, and have no connection with where they live”.

    If IPCC 1.5 degree madness takes hold in government policy of major economies, the result is an inevitable disastrous economic crash / depression. When this happens folks will cast about for a class of people to blame. The Anglophone community of CAGW fanatics are doing their utmost best to make sure that when this time comes, they are the ones who will be in the spotlight.

    But this is not the spotlight that even the most ardent narcissist really wants. It’s more like a concentration camp searchlight.

    • “As a British citizen I’m embarrassed by the fact that it seems to be English speaking countries that are at the forefront of the …..”

      As a British citizen I’m proud of the fact that it seems to be English speaking countries are at the forefront of advocacy of a sustainable future for the generations to come after us.

  30. “Scientists can also learn to avoid certain pitfalls. I spoke with Gretchen Goldman, research director of the Union of Concerned Scientists’ Center for Science and Democracy, which offers communication and advocacy workshops.”… …”A better approach, she suggests, is to reframe the issue. Don’t just keep explaining why climate change is real—explain how climate change will hurt public health or the local economy.”

    I don’t think they thought that one through. I doesn’t hurt public health or local economies. The skeptics are waiting for them to bring that up. And those are their strongest arguments. The scientist steps into economics and policy. I fail to see their point other than to suggest, stop arguing the science. We could evaluate SkS’s work on this all, and give them an F. What did they change? They could argue in favor of nuclear power. Something they might have more authority with than economics. And if they lose that one, we are no worse off.

  31. Pingback: Weekly Climate and Energy News Roundup #332 | Watts Up With That?

  32. Pingback: Weekly Climate and Energy News Roundup #332 |

  33. stevefitzpatrick

    “What’s the betting that the new SR15 carbon budgets will also turn out to be unrealistically low?”

    It’s a sure thing. If a budget is projected which says there will be X degrees of warming when we have emitted Y tons of CO2, then it will be awfully hard to explain when that level of warming doesn’t happen at Y tons of CO2. The goal posts must be kept in constant motion to avoid inconvenient questions about validity of the warming projections. “X degrees warming for Y tons emitted” is mostly a political statement, to be used for political purposes. At some point, most people will roll their eyes at the obvious errors in projected warming and the constantly moving goal posts, but we are not quite there yet. Maybe in another decade.

    • “Maybe in another decade.”
      It’s already happening. People aren’t interested in AGW despite the fact that the “warnings” are getting more shrill. It’s not even on the list of things Americans think are interesting in the mid-terms.
      The IPCC is a political organization that feels the need to give a pass to more emissions while the globe is retreats from the warm’s preferred “action.” Never underestimate the ability of a political organization to give politicians what they need.
      The website The Oil Drum is a useful example of how things can play out. They also kept postponing the apocalypse (peak oil in their case) while decrying the ignorant masses who ignored their expert warnings. Until one day they simply shut down and went home.
      Meanwhile we’re entering winter and I’m already hearing the old joke- “for the next four or five months the newspaper will be saying the weather is just weather again ”
      Cheer up, though. Electric cars are inevitable as is the switch to gas and ultimately nuclear power (+ some renewables where it makes sense). The IPCC is on it, they’re writing the science that justifies real world transition.

      • stevefitzpatrick

        I hope you are right, but I doubt global warming alarm will diminish any time soon. The Oil Drum (like all malthusian disaster prophets) never admitted there was anything wrong with the peak oil scare…. even as recoverable reserves globally continued to balloon, and the site closed up shop. Same as the Club of Rome, Paul Erlich, and the other Mathusians of the late 1960s and 1970’s… those who are still around insist they were and are still right (we are all doomed… still DOOMED!), even though every one of their predictions was 100% flat wrong. Those predictions were laughable on their face, just as are most global warming predictions of doom. The ever moving goal posts only delays the decline of global warming to nothing more than another of the many problems humanity has dealt with and will deal with.

      • “It’s not even on the list of things Americans think are interesting in the mid-terms.”

        Despite what many Americans may think. You?
        It’s not the world.

      • Tony, it’s global.
        Germany is the most invested and won’t hit it’s 2020 goals- emissions actually increased there the last two years.
        The EU as a whole isn’t even close.
        Every ton of emissions reduced in the west has been offset by at least two tons in additional emissions in China. We’ve been hearing for 30 years that renewables work just fine and cost less than fossil fuels or nuclear yet we now have 30 years of evidence that developing nations- which have the highest need for cost and effectiveness- don’t choose them. Including in communist nations.
        Australians talk a great game at home and export coal. Canadians laugh at Trump and keep the oil sands going. Brazilians cheer a leftward shift and cut down the rainforest. The Washington Post calls the guy who has been president all of two years “complicit” in the weather and educated people roll their eyes and turn the page. The warm war against the two alternatives to coal that have actually reduced CO2 emissions- natural gas expansion and nuclear – based on the odd assumption that we may have no time left, but we can spend the next 30 years trying for the same policies that they’ve failed to get for the last 30 years.

      • stevefitzpatrick

        “based on the odd assumption that we may have no time left, but we can spend the next 30 years trying for the same policies that they’ve failed to get for the last 30 years.”

        Makes perfect sense once you see that reduced CO2 emissions are secondary to the real policy goals: public control of private economic activity… international control of national policies… ‘economic justice’ (and reduced material wealth!) forced down everyone’s throat. Maxism Lite (or maybe not-so-lite) is what they are after, and they would want that even if there was no problem at all with global warming. Global warming alarm is a mainly a means to an end.

    • One very telling thing about “skeptics” is when they read about adjustments or modifications, then treat the two directions in very different ways.

      Adjust recent temps up, and they cry “see, they are warming the record.” Adjust temps down, and they say “see, this is closer to the truth, so they must have lied earlier.”

      In this case an adjustment of budget serves the same purpose. The earth is still warming, it’s not the sun, and CO2 is definitely the primary culprit. At least that is admitted (mostly) on this site.

      • stevefitzpatrick

        One very telling thing about “alarmist” is that they endlessly offer the same straw-man arguments about the stupidity of “skeptics” and the “certainty” of global warming disaster, while refusing to see that their proposed ‘solutions’ are both set in stone and 100% politically motivated. Yes, more infrared absorbing gases in the atmosphere will cause some warming. No need to argue about that. Yes, in the long run humanity will need to transition away from reduced carbon as it’s principle energy source. No need to argue about that either. No need to rail against people who think climate scientists have (and always have had) their thumbs on the scale, willfully exaggerate, and tell “scary stories” to motivate their desired public policies; true or not, it doesn’t matter at all. Those are all straw men issues. The real issues, and the ones that seem never seriously addressed by the “alarmed” are how much warming (and where) versus the obvious economic and social benefits of using fossil fuels, and what will be the east expensive and most beneficial way to make a long term transition away from fossil fuels. So long as you insist on “solutions” (solar panels, reduced material wealth, wind turbines everywhere, stop eating meat, etc.) people will not accept, nothing much will happen. CO2 emissions are high and will be high for multiple decades, and the longer “alarmists” insist on unworkable public policies, the longer those emissions will remain high.

      • I’ve always wondered what I was skeptical of.

        It seems ‘forcing’ since 1750 is overwhelmingly anthropogenic. And the total feedback for 1 K warming is some -2 W/m2 – neglecting cloud. Cloud feedback – computer parametizations all – has a wide range but is considered to be some 0.25 W/m2/K (Klein et al 2017).

        But it seems that natural wiggles in the CERES record are very large – mostly as outgoing energy as the planet resonantly responds.

      • Geoff Sherrington

        You are poorly equipped to comment about adjustments unless/until you know of studies that include the effect shown in this graph. I know of no such studies, formal or not.
        This work was originated by a “sceptic” because The Establishment seemed to prefer glib approximations and half-truths to make problems seem solved or unworthy of diligence.
        Here in Australia, our informal sceptic group has done man-years of work that satisfies us that national global warming in the century to 2010 was at most 0.5 degrees C, not the official guess of 0.9 degrees C.
        Requests to our BOM to contemplate our work and correct their errors are met with statements like “We cannot consider such work unless it has been peer-reviewed and published.” When we submit for journal publication, we find that the process is controlled by The Establishment including BOM reviewers, who are hardly likely to question their dogma and let pass a paper that shows them wrong. It happens, it is all documented for the inevitable commission of enquiry.
        We particularly resent the low level of science from people who ask for a formal publication of a paper no more advanced than adding up and taking away, and calculating an average. Science does not progress through such childish chores, but it can be slowed by intellectual arrogance.
        There is a lot wrong with Australian understanding of climate change. Sadly, an improvement that can be made quickly and easily with the expensive, ttaxpayer-funded tools that The Establishment have, can languish because the home PC and raw state of data are hardly a match for a supercomputer plus an existing specialist data base.
        There is a lack of will in the establishment to confront poor science. It has been there since before the 2008-9 climategate episode in which scientists like me, having dared to question, were described by BOM staff as stupid.

        There was never a need for this standoff. It was not created by sceptics. It should not be perpetuated by ignorant bloggers like you, Scott Koontz whose skill seems to peak at stirring the pot with the doubtful wisdom of the words of other people on ‘his’ side.

      • Geoff pull of insults. Site monitor loves it, keeps the post. Doesn’t want anyone to call him out.

        This is all too common on sites like this.

      • Yup.

      • Geoff Sherrington

        If you accept these observations and improve the quality and science of your blogging, that will be an OK outcome. Geoff

  34. As with ‘war-weariness,’ there’s ‘boy-who-cried-wolf-weariness,’
    comes a time yr no longer believe it…

  35. Beththeserf

    Did’nt the boy who cried wolf get eaten by the wolf nobody else believed in?

  36. Robert Whitmore

    On the Political forum, it seems we have two heavyweights. Each has taken opposing views.

    I would appreciate the experts here checking the topic out and picking a side so to speak.

  37. Some uncommon common sense on CO2.

    Yes the bomb test C14 data really does show normal fast CO2 clearance from the atmosphere. All this fantastical and exotic recycling maths and “human CO2 is different” is nonsense.

    The supposed century-millennium lifetime of CO2, preposterously unphysical, is the archetypal type example of a politically mandated scientific outcome. It won’t stand.

    • I’m afraid that Ed Berry is wrong in his preprint. See the comments by Ferdinand Engelbeen at and following, and by others. Ferdinand E. is very experienced at debunking reasonable looking but incorrect claims about CO2 lifetime like those by Ed Berry.

      I think that the carbon cycle models in most ESMs reduce atmospheric carbon too slowly, have excessive positive CO2 feedback from warming and leave too much CO2 in the atmosphere on a timescale of centuries to a millenium, relative to what observational data indicate is probable. However, subject to that I think that they do in general correctly represent carbon cycle physics and chemistry.

    • Using a more optimistic estimate of the absorption of CO2 by the earth system still means we need to reduce emission rates by half to stabilize the climate at today’s levels. This would be a good start even if that was an uncertainty.

  38. Nic or Judith could you please explain this Q&A from the Royal Society and NAS report?
    Question 20 and answer states that the world could STOP all emissions today and we wouldn’t see a change in Co2 levels for at least a thousand years or perhaps thousands of years. No change in temps as well.
    I know the ice core data shows this to be the case, but why doesn’t the media disclose this extreme lag?
    IOW could we be waiting until 3018 or 4018 and beyond before co2 levels STARTED to decline?
    BTW the RS and NAS are probably the world’s premier science expert groups.

    • They are saying the temperature and CO2 levels will stay elevated relative to those 200 years ago for a long time, not that they would not drop at all from today’s levels. They both would drop if emissions stopped and their graphs show that.

    • ngard2016
      “Question 20 and answer states that the world could STOP all emissions today and we wouldn’t see a change in Co2 levels for at least a thousand years or perhaps thousands of years.”

      No, it doesn’t say that. Read it again, more carefully. It says:
      “If emissions of CO2 stopped altogether, it would take many thousands of years for atmospheric CO2 to return to ‘pre-industrial’ levels due to its very slow transfer to the deep ocean and ultimate burial in ocean sediments.”

      According to EMIC simulations, if emissions ceased CO2 levels should fall back half of the way to preindustrial levels in between 50 and 300 years, depending on the model used (Archer et al 2009, doi:10.1146/ But thereafter they fall more slowly, so that after 1000 years they have only fallen back 70-80% of the way to the preindustrial level, which it takes tens of thousands of years to get close to.
      The Royal Society’s graph is badly labelled. Unless you click on the “larger version” button, it only shows panel (b), being surface temperature.

      “No change in temps as well.”
      It is surface temperature that most CMIP5 ESMs and EMICs show as changing very little for 1,000 years after emissions cease. I think that they are over-pessimistic about this, although even assuming temperatures do decline they can be expected to remain significantly elevated from preindustrial even after 1000 years.

      • Nic and ngard2016: If we are currently emitting enough CO2 to raise atmospheric level by 4 ppm/yr, but only observe a rise of 2 ppm per year, sinks must be taking up 2 ppm/yr when driven by the current level slightly above 400 ppm. So, if there were no anthropogenic emissions next year, common sense says that CO2 would drop 2 ppm/yr until atmospheric CO2 was well below 400 ppm. If emissions were cut by 50%, atmospheric CO2 would remain constant until sinks began to saturate. (This would make a sensible intermediate-term goal, because there is a great deal of uncertainty about sinks.)

        A lot of carbon is no longer sequestered as fossil fuel in compartments that exchange with the atmosphere only on geological time scales, and is now present in other compartments (ocean, soil, plants) that exchange more quickly. This change does mean that CO2 won’t fully return to 280 ppm until that released carbon is again geologically sequestered (as CaCO3 in new ocean sediment). However, it doesn’t make any practical difference if CO2 remains above 300 or 320 or even 340 ppm (1970, halfway back) for a long time as atmospheric CO2 slowly declines.

        It’s been taken 50 years to rise from 340 to 400+ppm, so the possibility of returning in as little as 50 years suggests release from with these non-geological compartments could be a very minor factor. If it were to take 300 years to return to 340 ppm, then my intuition suggest the “free fraction” accumulating it the the atmosphere today should be well above 50%. So my “common-sense” answer appears reasonable for a long time.

  39. ngard2016 | October 24, 2018 at 9:42 pm | Reply “Question 20 and answer states that the world could STOP all emissions today and we wouldn’t see a change in Co2 levels for at least a thousand years or perhaps thousands of years. No change in temps as well.”

    A little bit of common sense goes a long way.
    A little more precision in your statement would help as well.
    There would be ongoing changes in CO2 levels and temperatures all throughout that 1000 years or more, not no change [your words and incorrect assertion].
    Secondly very slow CO2 transfer to the deep ocean and ultimate burial in ocean not the only mechanism of removing CO2 effectively from the atmosphere. Plant utilization for one could effectively sequester it very quickly for millennia until the slow processes kicked in.
    [Not considered in the inept RS report]

    Look at it this way.
    If all the emissions emitted in the last 150 years could alter the future levels, how could stopping them not change it also?
    Two rules of physics?
    Choose what you want on the way up and down?

  40. Contradictions do not exist. Whenever you think you are facing a contradiction, check your premises. You will find that one of them is wrong. Ayn Rand
    So when a warmist sees the Antarctic ice not melting for 30 years he immediately assumes the measurements are wrong rather than his/her theory.
    Wonderful thought and very apt both for skeptics and AGW

    • So explain to us how this mitigation would work in practical terms?
      China and India emissions will continue to soar until at least 2030 and other non OECD countries seem to be heading in the same direction.
      The ice core data does show examples of temp rising first and a long lag time while co2 remains at higher levels for many thousands of years.
      When the Eemian temps dropped into the last full glaciation about 118,000 years bp co2 levels remained at about 275ppm for many thousands of years. See Petit et al study.
      And today co2 levels are 407 ppm and rising thanks to the non OECD, Compared to levels of 275 ppm this seems to be a problem if you believe in co2 as their main driver of so called CAGW? Just asking?

      • Do you know about Henry’s Law? It’s from chemistry.

      • Geoff Sherrington

        Henry’s Law does not mention temperature.
        It is about solubility of gases in a liquid when gas pressure changes.
        It is from chemistry, my science major.

        Have you heard of the Ideal Gas Law?
        It gets really complicated because it deals with pressure, volume, two constants and temperature, so you have to have a multi-dimensional thought capability to use it optimally.

      • Henry’s Law absolutely mentions temperature. The equilibrium between air and water is temperature dependent. At warmer temperatures the ratio goes more to the air side of the interface. This is why in warming from the Ice Age, the CO2 concentration went from 190 ppm to 280 ppm. It is well understood.

      • Geoff Sherrington

        You are assuming the power to re-write the delinition of Henry’s Law, which conventionally commences “At constant temperature. …. ”
        But then, I suppose that you want to re-write geological ages to include the non-relevant and unqualified “Anthropocene”. This is not progress, this is not laudable pro-active thinking, it is just wrong. Like your Henry’s Law.
        If you get to examine the writings of Nic Lewis, you will see an attention to detail, an earnest thrust to be correct. Not uncommonly, he is correct when the ‘experts’ who were too shallow of thought, were wrong. Nic is the antithesis of what I have been writing for a decade now, that the quality of climate science is generally poor.

      • Henry’s Law has a “constant” that actually varies with temperature in a well defined way from basic chemical equilibrium principles. This is why the CO2 level increased from 190 ppm to 280 ppm after the last Ice Age and no one who knows chemistry is surprised by warmer water holding less carbon in its equilibrium with the atmospheric CO2 level.

      • Jim D: Henry’s Law has a “constant” that actually varies with temperature in a well defined way from basic chemical equilibrium principles.

        This appears to be a loose use of language. The “constant” in Henry’s law depends on the gas and liquid under consideration and on the temperature. These dependencies are not part of the statement of “Henry’s Law”, and are determined empirically through systematic experimentation. Daniels and Alberty, Physical Chemistry, 2nd ed, 1963, Chapter 7.

      • Henry’s Law refers the CO2 equilibrium between the air and water. The temperature dependence is critical to understanding how the Henry’s Law equilibrium changes with climate.

  41. “Alarmism and hyperbole undermine Mr. Gore’s cause. Substantial damage has been done to the science of climate change by the theatric… a cursory examination of the state of the world in 2017 shows that the Four Horsemen have yet to even saddle up.”

  42. Question – I’m trying to find recent data on Australia’s share of world GHG emissions, but can only find old estimates on warmist sites. Any advice? Thanks.

    • Faustino

      angech has given a good answer. You might find more information here as well


      • Thanks, Tony. Stay warm as November approaches, and don’t envy the recent 36C in Brisbane..

      • Faustino

        I can not think of anything worse than 36C unless it was 37C. The summer was too hot.

        Really beautiful sunny crisp weather here the last few days with the maximum daytime temperature around 8C. Simply glorious.

        The warmest summer CET remains at 1976 hotly followed by 1826. 2018, despite all the hype was tied with 3 others on the shorter scale, but that record doesn’t take into account UHI like CET does.


      • Tonyb
        Always nice to see you here.
        San Francisco Indian Summer sunny and warm in middle of day.
        Fog in morning and at night but still pleasant.

        Warmer than June. Expecting El Nino in January but for now, best weather of the year. My daughter getting married at Cliff House overlooking the ocean on Saturday. Keep rain away till that is complete.

        Eleven months since I retired. My daughter and I argue about climate a lot. She is an environmental scientist at a consulting company but is too busy on near term consequences to think much about 100 years in the future at this time. I keep working on her and showing her long term temperature records and sea level rise plus major droughts but she believes in the CAGW for now. Still hoping for sea level rise part 2, Roman era to Middle Ages. We have a big $s sea wall going to construction that we need whatever the level rise will be.

        always thank Dr Curry for this excellent web conversation.

      • scott

        glad you are enjoying your retirement. good luck with the wedding

        My one visit to SF was in the mid 70’s. I was totally surprised by the fog and the cool temperatures. they don’t tell you about that on the films!


      • Tony, I visited SF in ’78, while briefly living in Hollywood. Fog free. We do get into the ’40s in Bris at times, perhaps the worst weather was about 40C and near 100 per cent humidity while I was in a monastery in NE Thailand. My son is living in Iceland, that might suit you better.

  43. China’s shift away from coal will see demand for LNG surpass 300 million tonnes for the first time ever, raising concerns of short supply. 2018
    On the supply side, BNEF forecasts around 30 to 33 million tonnes per annum of new LNG will be added between 2018 and 2020, with capacity to peak at 396 million tonnes per annum in 2021.The greatest level of supply will come out of Australia.
    Thermal coal is believed to have reached a high watermark this year as it hits $22 billion,[world not australia]
    Australia has the 11th-largest natural gas exports (31,610,000,000 cu m) in the world. The top 10 countries by natural gas exports are: Russia, Qatar, Norway, Canada, Netherlands, Turkmenistan, United States, Algeria, Malaysia, Indonesia. Jan 8, 2018 – Australia is expected to become the world’s biggest natural gas exporter by next year as huge projects near completion
    That’s why there are currently 1,142 new coal fired power generators planned or under construction in Asia.*.
    2017 The $56.5 billion is split between 200 million tonnes (Mt) of thermal coal valued at $20.8 billion, and 172Mt of coking coal valued at $35.7 billion.
    Crude Oil Production in Australia increased to 279 BBL/D/1K in June from 272 BBL/D/1K in May of 2018. Crude Oil Production in Australia averaged 471.62 …
    Tricky Australia the country is a net importer of oil but Australia as defined by Australian companies like BHP mine and sell a lot more oil. Is it Australian, we get the money or foreign, mined elsewhere.

    • Thanks, angech. Government policies (State and Federal) over many years made oil refining in Australia unviable, we’ve now made coal-fired power plants non-viable while state restrictions on gas exploration and extraction have made use of gas in industrial processes unviable and gas-fired power extremely expensive. Australia is being rapidly deindustrialised, but don’t worry, we have an ever-increasing proportion of the workforce in the public service and government-funded service programmes. Until reality strikes.

  44. Looking at the recent PBL emissions I conclude that we are inbetween SRES A1B A1T, no need to use RCP8.5 as “business as usual”

  45. And with business as usual growing sink, there will be no physical ceiling in the emission carbon budget. This graph shows the break even emission for a given co2 concentration:
    BAU 16 GtC/y will give you an absolute concentration ceiling of 690 ppm

  46. Robert F Brost

    I am not a climate scientist so this may be a stupid question. NASA has published a series of papers which indicate solar system-wide climate change is occurring. If this is true, it is certainly NOT a result of anthropogenic climate change. One obvious possibility is a variation in solar radiation (amount or frequency). For example, a shift in the sun’s light spectrum toward greater UV-C radiation could cause greater ocean warming. I believe there is evidence of greater UV-C. Another possible contribution of energy to the all the planets could involve the solar system entering an area of the local galactic environment (crossing the galactic plane?) which is more energy dense. Also with the sun at a solar minimum, the heliopause is weakened, the diameter of the sun’s corona is smaller and thus all the planets are exposed to a higher flux of cosmic rays. Cosmic rays penetrating deep into the Earth can deposit their kinetic energy and heat the Earth from within. Why is no one talking about these effects? Do astronomers talk to Earth scientists? Just asking.

  47. Robert F Brost

    My links did not make it in the post above. Here they are: