Sea level rise acceleration (or not): Part II – The geological record

By Judith Curry

Part II of the Climate Etc. series on sea level rise –the geological record provides context for the recent sea level rise.

Part I provided a context for examining observations and causes of global sea level rise. I greatly appreciate the comments on the blog posts, and the resources and comments I received via email.

Part II provides an overview of definitions of sea level and the causes of sea level variations and rise. An overview of the geological record of sea level rise is provided, with a focus on Holocene (the current interglacial). Historical and archaeological evidence (prior to the instrumental period) of sea level variations is also discussed.

Definition of sea ‘level’ and causes of sea level rise

A recent paper by Rovere et al. (2016) provides a helpful overview of the definitions of sea level, why it varies and how it is measured.

An understanding of sea-level change requires maintaining a clear distinction between global (or eustatic) sea-level and local relative sea-level. Sea level changes can be driven by either variations in the masses or volume of the oceans (‘eustatic’), or by changes of the sea surface relative to the land (‘relative’). Several techniques are used to observe changes in sea level, including satellite data, tide gauges and geological or archeological proxies.

Eustatic change (as opposed to local change) results in an alteration to the global sea levels due to changes in either the volume of water in the world’s oceans or net changes in the volume of the ocean basins. Determination and interpretation of sea level rise is complicated by the fact that both mean sea level and the solid earth surface move vertically with respect to each other. This movement in effect changes the shape of the ‘bathtub’. Some land movements occur because of isostatic adjustment of the mantle to the melting of ice sheets at the end of the last ice age. The weight of the ice sheet depresses the underlying land, and when the ice melts away the land slowly rebounds. This is referred to as glacial isostatic adjustment (GIA).

Around the world, significant regional variations occur in the rate and direction of sea-level change. While some regions of the world’s oceans are today rising rapidly, in other regions sea level is falling. This is partly due to variations in the rate of warming and salinity changes and proximity to discharges of meltwater. Primarily, these variations reflect the influence of major ocean circulation systems that redistribute heat and mass through the oceans. Hence, at any location around or within the oceans, the observed sea level trend can differ significantly from the global average.

Melting of sea ice has no impact on sea level – water or ice that is already floating does not change the sea level by melting/freezing. Ice on a continent that melts and runs into the ocean increases sea level due to increasing the mass of ocean water. Antarctic ice shelves are in the ocean but are supported by the continent of Antarctica – melting these ice sheets will increase sea level.

The geological record

The geological record provides some insights and constraints into understanding how much, and how fast, sea level might rise in the coming centuries. It also provides critical context for understanding whether current sea levels and rates of sea level rise are unusual.

How is past sea level revealed in the geologic records? Proxy records of sea level are preserved in a variety of marine and terrestrial settings, such as sediments and organisms in deep ocean cores or once-submerged shorelines, and uplifted fossil reefs. Analysis of oxygen isotopes in tiny ocean organisms, and radiometric techniques are used to interpret and date the records. (JC note: I could use some good overview references here)

The IPCC AR5 summarizes our understanding of the geological record of sea level variation in the Last Interglacial (LIG) period:

There is very high confidence that maximum global mean sea level during the last interglacial period (~129 to 116 ka) was, for several thousand years, at least 5 m higher than present and high confidence that it did not exceed 10 m above present, implying substantial contributions from the Greenland and Antarctic ice sheets. This change in sea level occurred in the context of different orbital forcing and with high latitude surface temperature, averaged over several thousand years, at least 2°C warmer than present.

For the time interval during the LIG in which GMSL was above present, there is high confidence that the maximum 1000- year average rate of GMSL rise associated with the sea level fluctuation exceeded 2 m kyr–1 but that it did not exceed 7 m kyr–1. Faster rates lasting less than a millennium cannot be ruled out by these data. Therefore, there is high confidence that there were intervals when rates of GMSL rise during the LIG exceeded the 20th century rate of 1.7 [1.5 to 1.9] mm yr–1.

During the past 20,000 years (the Holocene), since the end of the last glaciation, sea level has risen a total of about 120 m above modern shorelines, initially at a rate many times faster than observed anywhere today. The figure below shows sea level for the last 24,000 years. These data were compiled from a number of different regions and proxies. Sea level was lowest between 22,000 and 18,000 years ago, rising sharply between 15,000 and 8,000 years ago.

This figure was prepared by Robert A. Rohde from published data, and is incorporated into the Global Warming Art project.

During deglaciation between 19,000 and 8,000 years ago, sea level rose at extremely high rates (Cronin, 2012). At the onset of the deglaciation, a ~ 500-year long, glacio-eustatic event may have contributed as much as 10 m to sea level with an average rate of about 20 mm/yr. During the rest of the early Holocene, the rate of sea level rise varied from a low of about 6.0–9.9  mm/yr to as high as 30–60 mm/yr during brief periods of accelerated sea level rise. For reference, these values are compared to modern values of sea level rise ranging from 1 to 3 mm/yr.

A zoom in on the past 8000 years is shown in the figure below. On average, sea level has been relatively stable and slow to rise over the past 6,000 years. However, some of the data (i.e. Malacca) indicate that sea levels approached or exceeded modern values ~ 6,000 – 4,000 years ago.

This figure was prepared by Robert A. Rohde from published data, and is incorporated into the Global Warming Art project.

From the IPCC AR5:

Since the AR4, there has been significant progress in resolving the sea level history of the last 7000 years. RSL (relative sea level) records indicate that from ~7 to 3 ka, GMSL likely rose 2 to 3 m to near present-day levels. Based on local sea level records spanning the last 2000 years, there is medium confidence that fluctuations in GMSL during this interval have not exceeded ~ ±0.25 m on time scales of a few hundred years.

Holocene Climatic Optimum

Of particular interest is the so-called ‘mid-Holocene highstand’ between about 6000 and 3000 years ago, with substantial regional variations. I don’t see any mention of this in the AR5. Here are a few local examples from the recent literature:

  • Rio de la Plata, Argentina and Uruguay:  the peak of the sea level high stand c. +4m [above present] between 6000 and 5500 cal yr BP Prieto et al. (2016)
  • Southeast Australia: during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today’s level Lee et al. (2016) 
  • Japan:   The Holocene-high-stand inferred from oyster fossils is 2.7 m at ca. 3500 years ago, after which sea level gradually fell to present level. Yokoyama et al. 2016 
  • Western Australia. possibly corresponding to the mid-Holocene sea-level highstand of WA of at least 1-2 m above present mean sea level. May et al. (2016)
  • Strait of Makassar. Radiometrically calibrated ages from emergent fossil microatolls on Pulau Panambungan indicate a relative sea-level highstand not exceeding 0.5 m above present at ca. 5600 cal. yr BP Mann et al. 2016 _
  • Scotland:   RSL [relative sea level] was <1 m above present for several thousand years during the mid and late Holocene before it fell to present. Long et al. (2016) 
  • Japan: Relative sea level during Holocene highstand reached 1.9 m [higher than today] during 6400–6500 BP Chiba et al. (2016) 
  • Denmark: The data show a period of RSL [relative sea level] highstand at c. 2.2 m above present MSL [mean sea level] between c. 5.0 and 4.0 ka BP Sander et al. (2016) 
  • China: sea level rising steadily to form a highstand of ~2-4 m [above present sea level] between 6 and 4 kyr BP Bradley et al. (2016) 
  • Africa: maximum 5 to 4 ka BP [5000 to 4000 years before present] (Ramsay, 1995) during a highstand about 3.5 m above the present sea level, Accordi and Carbone (2016)
  • Persian Gulf: a highstand of > 1 m above current sea level shortly after 5290–4570 cal yr BP before falling back to current levels by 1440–1170 cal yr BP Lokier et al. 2015 
  • French Polynesia: we find that local rsl was at least 5 ± 0.4 m higher than present at 5.4 ka Rashid et al. 2014 

The sea level high-stand was associated with the so-called Climatic Optimum or the Holocene Optimum, during 8000 to 4000 BC when average global temperatures reached their maximum level during the Holocene and were warmer than present day.

Last 2500 years

Since the AR5, an important new paper has been published on global sea levels over the past 2500 years (Kopp et al. 2016).  They compiled a global database of regional sea level reconstructions from 24 localities, many with decimeter-scale vertical resolution and subcentennial temporal resolution. Also included are 66 tide-gauge records.

The key figure summarizing their results is shown below.

The paper concluded that global sea level (GSL) varied by ∼ ± 7-11 cm over the pre-Industrial Common Era (CE), with a notable decline over 1000–1400 CE coinciding with ∼0.2 °C of global cooling.

Despite the incomplete coverage and regional variability, sensitivity analyses of different data subsets indicate that key features of the GSL curve are not dependent on records from any one region. By contrast, the rise over 1400–1600 CE and fall over 1600–1800 CE are not robust to the removal of data from the western North Atlantic.

Kopp et al. found that 20th century rise was extremely likely faster than during any of the 27 previous centuries.  Because their model is insensitive to the small linear trends in GSL over the Common Era, the relative heights of the 300-1000 CE and 20th century peaks are not comparable.

The Kopp et al. estimates differ markedly from previous reconstructions of Common Era GSL variability. For example, Grinsted et al. (2009) predicts GSL swings with ∼4 times larger amplitude (with much higher sea levels during the Medieval Warm Period).

Credibility of the Kopp et al. analysis is enhanced by semi-empircal prediction based on these rates that is close to model results using a budget approach.

An evaluation of the status of late Holocene sea level rise constructions is provided in a recent proposal by an international group of sea level experts (including Kopp), entitled:  Towards a unified sea level record: assessing the performance of global mean sea level reconstructions from satellite altimetry, tide gauges, paleo‐proxies and geophysical models.  Excerpts:

Furthermore, pre‐industrial reconstructions of GMSL based on sea level proxies are limited to one single study (Kopp et al., 2016). The approaches and datasets used in the different published estimates of past GMSL change differ considerably, and there has been no consistent assessment of the differences between the individual reconstructions.

Their proposal for improving our understanding of pre-industrial sea level:

Following the same approach as in WP1, a series of surrogate synthetic proxy records will also be created. Since the focus is on Late Holocene time scale, the synthetic sea level fields will be created using a millennial simulation with the Earth System model MPI‐ESM‐P AOGCM. The point‐wise information will correspond to the locations and temporal resolution of all available proxy records from paleo sea level studies (Kopp et al. 2016) and random noise will be added to each mimicking the limitations of actual proxy records. Gaussian process regression will be used to convert the non‐equidistant proxy records and their climate model surrogates into the required temporal resolution. Paleo‐sea level reconstruction techniques from Kopp et al. (2016) and Dangendorf et al. (under review) will be then applied to the surrogate time series and compared to the a priori known modelled GMSL curves.

Historical and archaeological records (pre-instrumental)

The Kopp et al. analysis does not settle the issue of whether sea levels during the Medieval and Roman Warm Periods were higher than current levels, or whether there were any large decadal-scale periods with large rates of sea level rise. Here we consider historical and archaeological information.

Hubert Lamb’s book Climate History and the Modern World offers his analysis on this issue (excerpts extracted by Paul Homewood):

1) The most rapid phases [of sea level rise] were between 8000 and 5000 BC, and that the rise of general water level was effectively over by about 2000 BC, when it may have stood a metre or two higher than today.

2) The water level may have dropped by 2 metres or more between 2000 and 500 BC. What does seem certain is that there was a tendency for world sea level to rise progressively during the time of the Roman Empire, finally reaching a high stand around 400 AD comparable with, or slightly above, present.

3) The slow rise of world sea level, amounting in all probably to one metre or less, that seems to have been going on over the warmer centuries in Roman times, not only submerged the earlier harbour installations in the Mediterranean, but by 400 AD produced a notable incursion of the sea from the Wash into the English fenland, and maintained estuaries and inlets that were navigable by small craft on the continental shore of the North Sea from Flanders to Jutland.

4) The existence of pre-Norman conquest salterns – saltpans over which the tide washed and from which salt-saturated sand was taken – outside the later sea dykes on the Lincolnshire coast may point to a period of slightly lowered sea level between the late Roman and the medieval high water periods. 

5) Our survey of the European scene during the warmer centuries of the Middle Ages would not be complete without mention of the things that suggest a higher stand of the sea level, which may have been rising globally during that warm time as glaciers melted .

Fig 60 [not shown] draws attention to the greater intrusions of the sea in Belgium, where Bruges was a major port, and in East Anglia where a shallow fjord with several branches led inland toward Norwich. [Bear in mind that the land here has been sinking due to isostatic forces since the ice age. If relative sea levels were as high then as now, it would mean absolute levels were higher than.]

In a previous post at Climate Etc., Historic variations in sea levels. Part I: Holocene to Romans, Tony Brown assessed some anecdotal, local evidence for higher sea levels during the Roman era.

JC note: TonyB et al, please let me know if you have any information/references on sea levels during the medieval warm period

Summary

The geological record for sea level rise provides important context for recent sea level rise. However, the uncertainties in the geological sea level  record are substantial, associated with sparse sampling, uncertainties in the proxy methods and uncertainties in the analysis methods.

Is the 20th century sea level rise unusual? Sea level was apparently higher at the time of the Holocene Climate Optimum (~ 5 ka), at least in some regions. I have not seen an overall assessment of this, but there have recently been numerous publications providing local evidence for higher sea levels during this period.

Whether or not sea level was higher during the Medieval Warm Period than current levels remains uncertain, and there is substantial disagreement among different reconstructions on the sea level during the MWP, with the Grinsted et al finding substantially higher sea level values during the MWP (around 1150 AD).

Kopp et al. find the 20th century rate of sea level rise to be the highest in the last 27 centuries. However, since their data is barely resolved at 100 year time scales (with decimeter vertical resolution), I would not place  high confidence in their conclusion. Eyeball examination of Grinsted et al.’s Figure 7 shows possibly higher rate of sea level rise between ~1000 and 1100 AD. Overall, I find Kopp et al.’s analysis to be more convincing (apart from overconfidence in the relative rate of 20th century sea level rise).

The pace of interesting and important paleo sea level rise research seems to have accelerated since publication of the AR5, I will be following this closely.

Forthcoming Part III: The observational (historical) record

 

 

 

 

 

 

107 responses to “Sea level rise acceleration (or not): Part II – The geological record

  1. Acceleration of SLR is not sufficient evidence of its anthropogenic cause
    https://ssrn.com/abstract=3023248

  2. Read Kopp 2016.I think very poorly of it. Spliced 66 high resolution long record tide gauges onto low resolution proxies. That is a repeat of Mike’s Nature trick. Done deliberately to create CAGW alarm, because they use impossible RCP8.5 to project 0.5-1 meter SLR by 2100.
    The other logic flaw is ~75% of the 20th century had no AGW. Up through ~1945 there wasn’t enough delta CO2 (ref. AR4 WG1 SPM figure 4). So the linear rate from ~1850 to beyond 2000 cannot be attributed to AGW as both the abstract and the conclusions expressly do. The old lack of acceleration problem only ‘solved’ by splicing a sat alt estimate of SLR onto a CORS (diff GPS) corrected tide gauge SLR that does close. See guest post SLR, acceleration, and closure for details.

    • You are tempting fate ristvan. JD and JCH will soon be along with their cut and paste tactics showing that there was no Nature trick and there are so many peer reviewed papers showing the Koop is right.
      The critical phrase seems to be “Because their model is insensitive to the small linear trends in GSL over the Common Era, the relative heights of the 300-1000 CE and 20th century peaks are not comparable.” Another case of inappropriate splicing and data being tortured into submission?

    • Grinsted 09 in very alarming commie red:

    • I find the “no acceleration” claim a bit mystifying. Even if the satellites are overstating SLR by 50%, 25 years at 2mm/year *is* unusual. Certainly 2mm/year hasn’t the rate of SLR for the last millenia, or even centuries. The rate of 3mm/year is also roughly equivalent to the SLR budget from land ice melt and thermal expansion, though admittedly there is a lot of uncertainty specially about Antarctica.

      Even assuming the correct rate was 2mm/year, for the 100-year SLR to return to a “normal” range of 1mm/year SLR would have to average 0.6-0.7mm/year over the next 75 years. There is no indication of any slowdown in SLR, let alone one that large. Such a slowdown would also imply essentially a stop to land ice melt, as ocean thermal expansion alone amounts to 0.5-1mm/year. If it’s not going to happen, we can declare pretty confidently this century (or the 100-year period starting in 1993) will see well over 1mm/year in SLR. Combined with a rise also of 1mm or more in the XX century, that’s definitely an acceleration over the previous centuries.

      • AZC, the mysterious problem is simple. All the pre Moerner CORS corrected tide gauge estimates relied on samples of long record tide gauges. No two samples were the same. The assumption apparently (implicitly only) was that vertical land motion would cancel in sufficiently large samples. That assumption simply is not true, the reason being the geographically very uneven distribution of long record tide gauges to the northern hemisphere still undergoing isostatic rebound from the LGM.

      • Actually 25 years at 2mm/yr *is not* unusual. Church and White show similar rates for any 25 yr period between 1925 thru 1965.

      • It is 7.5 cm in the last 25 years, or 3 mm/yr, which is twice the 20th century average, and that is just the satellites. Tide gauges tend to be even faster since 1990 in all the comparison I have seen, and I am still waiting for someone to post an image of a contrary comparison for the post-satellite era.

      • They’ll do, while acting deeply offended, the two-step side steps: funny math, bad data, manipulated data, etc. Then they squeak about how hard it is to measure, citing all sorts of physical complications, all of which they could only know about if not for the work of the very same scientists they are impugning. Tis a sight to behold.

        1900 to 1990 – 1.2 mm per year, now backed up multiple times, from the most advanced group of sea level scientists on the planet.

        1993 – 1.8 mm per year, backed up

        1993 to November 2017 – 3.3 mm per yr

        10-year trend – 4.26 mm per yr – going upward during the 2-year stasis
        5-year trend – 4.60 mm per yr – going upward during the 2-year stasis

        It’s not going to back off because of some ocean cycle; it just blew through one of those. That was the 300 ppm world: the past.

      • Berényi Péter

        Acceleration, as measured by satellites, is an overstatement.

        There are two online resources on satellite sea level data.

        1. CU Sea Level Research Group
        2. AVISO Mean Sea Level

        Last published data point at the former site is of 2016-07-20, while for the latter one it is 2017-11-17.

        Sea level rise due to acceleration (if it remains the same as measured since the beginning of 1993) in the next 100 years (till the beginning of 2118) is 17 cm at CU and 28.5 cm at AVISO.

        However, if data are cropped at the end of 2014, it is -14.7 cm at CU (deceleration) and 1.8 cm at AVISO.

        First of all, uncertainty in sea level rise acceleration, as measured by satellites is quite large. Second, acceleration is negligible anyway. And last, but not least, most of the acceleration measured is due to the giant El Nino during the past couple of years, so it is cherry picking.

      • The current science on the rate of sea level rise in 1993 is ~1.8 mm per yr. I do not think AVISO has included that in their graphs as of yet, and I know CU has not.

  3. Lorraine Lisiecki and Maureen Raymo (2005) @ 18O benthic cores:
    http://onlinelibrary.wiley.com/doi/10.1029/2004PA001071/epdf
    The data correlate with sea level only in the sense of thermal response. Benthic 18O correlates well with ice core 18O where they overlap.

  4. “Hence, at any location around or within the oceans, the observed sea level trend can differ significantly from the global average…”

    This gives new meaning to, all weather is local.

  5. Amid all these vagaries and conjectures one cannot but conclude that there is NO detectable signal of influence relating to CO2.

  6. Pingback: Sea level rise acceleration (or not): Part II – The geological record — Climate Etc. – NZ Conservative Coalition

  7. Yes, we have been in the Neoglacial for thousands of years, the Holocene Optimum was roughly 9,000 to 5,000 years BP. Glaciers are advancing, climate is cooling, sea level is falling. That’s the big picture.
    There may be some slr acceleration in the late 20th century, but there was similar acceleration in the early 20th century. It is NO evidence of AGW.

    • SLR is a predicted effect of warming
      1. It is warming
      2. We can predict a rise in SLR
      3. We see a rise in SLR.

      The cause of the warming? Nobody ever argued that SLR IN AND OF ITSELF was evidence about the Attribution of the warming.

      It is warming. We expect SLR as a result. We observe SLR.

      Now, why is warming? simple. We have been adding c02 to the atmosphere.

      Has SLR been higher before? Perhaps.
      Does that matter to the present day argument
      Not at all.

      It is warming
      We predict SLR
      We observe SLR, as predicted.
      Why is it warming NOW ( the past is not relevant)?
      Its warming now because of c02.
      How much more will warm ? Good question
      How much more SLR will we see? Good question
      Does that past matter in these questions? Not really

      • “it is warming”

        “In fact, as NASA’s Dr Gavin Schmidt has pointed out, the IPCC’s implied best guess was that humans were responsible for around 110% of observed warming (ranging from 72% to 146%), with natural factors in isolation leading to a slight cooling over the past 50 years.”
        https://www.carbonbrief.org/analysis-why-scientists-think-100-of-global-warming-is-due-to-humans

        Y’all need to get on the same hymnal.

      • I think I would stick to crypto currencies if I were you, mosh.

        Tonyb

      • Steven Mosher

        “It is warming. We expect SLR as a result. We observe SLR.”

        This statements seems to be an example of: correlation is not causation.

        “Now, why is warming? simple. We have been adding c02 to the atmosphere.”

        If the answer were simple, there wouldn’t be much discussion for most people. Throwing AGW into the calculus has made the discussion worse, not better. We’re back to the question: What is the contribution of adding CO2 to the atmosphere causing warming? enough to cause sea level rise? This seems like some “drive by shooting” best left to those mired in a culture of “respect”, or, more to the point, lack there of.

      • Mosher

        It all becomes much simpler when ignoring 3,000 years of history.

      • We are in the Neoglacial now. The multi-millennial temperature trend is negative (cooling).

        You just claimed that ‘we’ expect and predict SLR because it is warming, and it is warming because of CO2. You see SLR as evidence of AGW. If it’s accelerating, it’s even better evidence. Well, I say that’s nonsense!

      • Has SLR been higher before? Perhaps.
        Does that matter to the present day argument
        Not at all.

        Not even a hill of beans.

      • Steven
        At the onset of the medieval Warm Period
        around 900-1000CE,
        from much cooler preceding centuries,
        Why did it warm?
        What caused it?

      • The past is relevant.
        What caused warming in the past could be causing it again now.
        Parsimony.

      • Does that past matter in these questions? Not really

        Does that future matter in these questions? Not really.

        Slow levels of future rise are not relevant to current humans.
        And future SLR is probably not significant in the face of all other change ( population, technology, etc. ).

        Not only is climate change exaggerated ( and SLR would seem to be the marquee issue ), so too is climate in general.

        After lunch I’ll fetch you a great quote from the great big book of horrible things.

      • A perfect example of why fire marshals fired silly white men and replaced them with ever more insistent robots. Try ignoring a fire alarm in a multiple story building. You have to flee. The noise is just horrible. Human nonresponse is no longer tolerated.

      • “…there’s a tendency in popular science writing to overemphasize the role that Nature plays in shaping history. To hear some scientists talk, mankind is constantly being knocked around helplessly by every high-pressure system over the Pacific Ocean, or cut down by every bug that lurks in the jungle. Empires rise or fall according to wavering sunshine or annual rainfall. Civilizations are immortal without tsunamis to take them down. It sometimes sounds like societies don’t budge unless weather or disease force them to.”

        Humans face a much greater threat from one another than from climate.

        And humans face a still much greater threat from themselves than from one another.

        A very good read:

      • JCH “A perfect example of why fire marshals fired silly white men and replaced them with ever more insistent robots…Human nonresponse is no longer tolerated.”

        Your statement implies fire marshals are Leftist racists. It’s a bizarre extrapolation, a typically simplistic Leftist hate mongering concoction. It’s hardly the rationale for how fire marshals think.

        Robots aside, there’s actually little firing in fire departments and instead a retention and recruitment problem throughout the U.S. Over 70% of firefighters are volunteers.

        Your simplistic linear thinking aligns to CAGW alarmist pablum though: more people = more CO2 = more hot = rising seas, therefore; more robots = less people = less CO2 = less heat, etc. etc. The equation is such a common sense prediction sequence, right? Time to manufacture another paper to save the world from numerous white men.

      • Steven Mosher

        you guys persist in the silly notion that understanding the past is necessary to prediction. its not.
        it would be nice to understand it better but un necessary.

        physics tells us ghg warm the planet.
        our recent history confirms this.
        physics tell us that warmer water expands.
        our recent history confirms this.
        physics tell us warmer climate melts ice.
        duh.

        everything we know says warmer world higher ocean.

        pretty simple.

        no amount of ignorance about the deep past can erase what we know.

        you realize that this your argument.
        you appeal to ignorance.

        doesnt work.

        sorry

      • “you guys persist in the silly notion that understanding the past is necessary to prediction. its not.”

        Not at all; understanding the past or present doesn’t change physics, it’s not the point, it does continue to add to our basic understanding though of dynamic ranges, and it’s all based on physics and complex systems:

        ~20k years ago, 2 mile thick glacial ice over N.Y
        ~10k years ago, the last glacial ice retreats from N.Y.
        ~Circa 5-6k years ago what is now the Sahara was savannah
        ~Through to 20th century, quickening glacial retreat

        Definitely a pattern of dramaticly increasing warming, same physics. What combination of physics is the question.

        So you guys “persist” in the silly notion of CAGW, from 150 year granularity, in attempting to understand the relationship of CO2 to 1.5 degree global warming is all that’s necessary for prediction using crappy models. It’s not.

        As the argument moves into solutions is where the REAL silly notions are revealed. I’d prefer CAGWists to go into a square corner of the world and brood while the real science continues.

      • M

        You sound like one of the adolescents at Huffington Posts who dumbs down the debate and oversimplifies it. It’s all about attribution. We know the effect warming has on SLR. The issue is the proportionality between natural variability and AGW. Ignore the past if you want but there is a vast record of historical warming and cooling. If SLR had started in 1950 with not a scintilla of evidence of rise before that you would have a point. But it started since the LIA ended. It is not all about CO2.

      • A quarter of the GHG forcing occurred before 1950 and it was already 0.5 W/m2 by then. This is several times larger than typical solar variations in the sunspot cycle, so a noticeable sea-level response before 1950 is not surprising.

      • I hope you’re not tying the end of the LIA to CO2. I would enjoy seeing the citations.

      • This is Jim’s model:

      • Conversely, the LIA was at the end of the multi-millennial Milankovitch downward trend, after which CO2 forcing started to dominate.

      • Didn’t pack much of a punch during the Minoan, Roman and Medieval Warm Period.

      • Yes, indeed, because those weren’t CO2. CO2 is very effective. When it is added, it is noticed. Nothing subtle about it. Exactly one degree C per 100 ppm at the current rate of addition. This works out to be an effective rate of 2+ C per doubling.
        http://woodfortrees.org/plot/best/from:1950/mean:12/plot/esrl-co2/scale:0.01/offset:-3.25

      • Steven Mosher | January 25, 2018
        “you guys persist in the silly notion that understanding the past is necessary to prediction. its not.
        it would be nice to understand it better but un necessary.”

        To be able to predict one must have had a past.
        And a language to predict in.
        The past was where Mosher learned English, geography, science, maths and imagination.
        Taleb says one cannot predict anything new. We can only work with what we know, from the past and anything we can predict can only include things we know of using our imagination on those things.
        New things can happen, but since they do not dwell in our present or past experience, we can only know and predict about them after they have occurred.

        Where is Mosher coming from? His no models are perfect but they can be useful ideology. That said he is trying to say that one does not have to use reason to make a prediction, and that some airy fairy predictions can be right.
        Of course if one is trying to make a serious prediction the past, and as much knowledge as possible, is essential.

      • Steven Mosher | January 25, 2018

        “physics tells us ghg warm the planet.”
        One right
        “our recent history confirms this.”
        Pass. This comment from the man who does not use the past?
        “physics tell us that warmer water expands.”
        Not even wrong.
        It actually contracts as it gets warmer in part of its range.
        our recent history confirms this.
        “physics tell us warmer climate melts ice.”
        duh.
        Did I just see a big polar vortex cross America and freeze Niagara Falls due to, I’m told, global warming?
        Must have been dreaming

        “everything we know says warmer world higher ocean.”
        Grasshopper
        You missed the bit about rainfall in Australia, due to a warmer ocean dropping sea levels globally by centimetres.
        And extra ice in Antarctica and Greenland from snowing more with warmer weather.
        I think it wa in the previous post.
        I will add it in for you later.

  8. Compare this:

    with the krypton-xenon bubbles:

  9. Zanclean flood of the Mediterranean (5.33 Ma)
    During the last deglaciation, global sea level rose at about 20 mm/year. For interest, when the Mediterranean sea flooded, its water level rose at a more spectacular 10s of m/year ~ 1000 times faster.
    Mediterranean Sea filled in less than two years: study Dec. 9, 2009

    This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than 10 metres a day,”

    https://phys.org/news/2009-12-mediterranean-sea-years.html
    See: Garcia-Castellanos, D., Estrada, F., Jiménez-Munt, I., Gorini, C., Fernàndez, M., Vergés, J., De Vicente, R. (10 December 2009) Catastrophic flood of the Mediterranean after the Messinian salinity crisis, Nature 462, pp. 778–781, doi:10.1038/nature08555

    The Mediterranean Sea became disconnected from the world’s oceans and mostly desiccated by evaporation about 5.6 million years ago during the Messinian salinity crisis. The Atlantic waters found a way through the present Gibraltar Strait and rapidly refilled the Mediterranean 5.33 million years ago in an event known as the Zanclean flood. The . . .incision in the early stages of flooding imply discharges of about 10^8 m3/s (three orders of magnitude larger than the present Amazon River) and incision rates above 0.4 m per day. Although the flood started at low water discharges that may have lasted for up to several thousand years, our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years. This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than ten metres per day.

    Compare the global sea level rise rate above:

    During deglaciation between 19,000 and 8,000 years ago, sea level rose at extremely high rates (Cronin, 2012). At the onset of the deglaciation, a ~ 500-year long, glacio-eustatic event may have contributed as much as 10 m to sea level with an average rate of about 20 mm/yr. . . .RSL (relative sea level) records indicate that from ~7 to 3 ka, GMSL likely rose 2 to 3 m to near present-day levels.

  10. There are other mechanisms acting on sea level changes that are different from esteric changes and ice melting. The issue is so complex that nobody has been able to reconstruct global sea level changes for the Holocene. They simply are different from one place to another.

    Mitrovica, J. X., & Milne, G. A. (2002). On the origin of late Holocene sea-level highstands within equatorial ocean basins. Quaternary Science Reviews, 21 (20), 2179-2190.

    “Late Holocene sea-level highstands of amplitude ~ 3 m are endemic to equatorial ocean basins. These highstands imply an ongoing and moderate, sub-mm/yr, sea-level fall in the far field of the Late Pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment (GIA; Clark et al., 1978). Mitrovica and Peltier (1991) coined the term ‘equatorial ocean syphoning’ to describe the GIA-induced sea-level fall and they provided the first physical explanation for the process. They argued that water migrated away from far-field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions. We provide a complete physical explanation for the origin of equatorial ocean syphoning, and the associated development of sea-level highstands, using numerical solutions of the equation that governs meltwater redistribution on spherical, viscoelastic Earth models. In particular, we separate the total predicted sea-level change into contributions associated with ice and meltwater loading effects, and, by doing so, isolate a second mechanism that contributes significantly to the ocean syphoning process. Ocean loading at continental margins induces a ‘levering’ of continents and a subsidence of offshore regions that has also long been recognized within the GIA literature (Walcott, 1972). We show that the influx of water into the volume created by this subsidence produces a sea-level fall at locations distant from these margins—indeed over the major ocean basins—that is comparable in amplitude to the syphoning mechanism isolated by Mitrovica and Peltier (1991).”

  11. An understanding of sea-level change requires maintaining a clear distinction between global (or eustatic) sea-level and local relative sea-level.

    “Eustatic” is not a proper synonym for “global.” In established oceanographic usage, eustatic sea level changes refer to changes in total water mass and/or basin volume in the oceans. This is in clear contradistinction to steric change of volume induced by changes in temperature and salinity. Both terms refer to global datums, unlike relative sea level of purely parochial interest.

  12. The rise of sea that matters most
    Is that which happens at the coast
    On oceans far to west or east
    Those millimeters matter least

  13. This paper covers the natural variability of SLR and the state of knowledge with particular emphasis on each ocean basin.

    https://link.springer.com/content/pdf/10.1007%2Fs10712-016-9386-y.pdf

    • Speaking of Greenland and new papers, here is yet another paper hot off the press covering Geothermal activity in Greenland which the authors suggest may be contributing to accelerated basal sliding of glaciers. This follows other recent papers, including a NASA writeup, that identified the same processes. I predict many more papers in the next decade, finding even greater impacts from geothermal activity in Antarctica and Greenland. Exciting times.
      https://www.nature.com/articles/s41598-018-19244-x

  14. There seem to be quite some books out there about sea level rise.
    e.g.

    Handbook of Sea-level Research by
    Ian Shennan, Antony J. Long, and Benjamin P. Horton, Wiley 2015
    seems to be more about method and less about data.

    Quaternary Sea-Level Changes, A Global Perspective,
    by Colin Murray-Wallace and Colin Woodroffe, 2014,
    data and method/theory

    Understanding Sea-Level rise and Variability, John A. Church et. al., Blackwell 2010, method and data

    World Atlas of Holocene Sea-Level Changes, Paolo Antonio Pirazzoli, Elsevier 1991, older data., typoscript

  15. All for it. Slide that ice sheet into the oceans.

    • Warming water = higher probability of hurricanes = more coastal flooding.

      “2018 Hurricane Prediction – Strongest Cycle in 70 Years”
      http://www.prweb.com/releases/2018/01/prweb15095592.htm
      “Global Weather Oscillations (GWO) was cited by news media as the only major hurricane prediction organization that correctly predicted the hyperactive 2017 Atlantic hurricane season from beginning to end, and the destructive United States hurricane landfalls… GWO has issued the most accurate predictions by any organization during the past 10 years.
      http://www.globalweatheroscillations.com/
      “GWO predicts that 2018 will be somewhat of a repeat of 2017 – and possibly another record breaker. Although it will be strikingly similar to last year- some hurricane landfalls will occur in different locations this year. You can expect 16 named storms, 8 hurricanes, 4 major hurricanes, potential for 4 United States hurricane landfalls – 2 of which will likely be major impact storms. There is the potential for 6 named storms making United States landfalls. On the average, the entire Atlantic Basin has 12 named storms, 6 hurricanes and 2.7 major hurricanes.

      The reason for another destructive hurricane season is 3-fold. The ocean water temperatures continue to run warmer than normal across most of the Atlantic Basin (red and orange in the graphic), and especially in the Caribbean region and the Atlantic near the United States. This is very similar to the ocean temperatures of last year, and this will again be conducive for tropical storms and/or hurricanes forming and/or strengthening close to the United States. Mr. Dilley also expects the Bermuda-Azores High Pressure Center will again be in a favorable location – thus allowing more named storms to maintain strength – or strengthen as they move from east to west across the Atlantic toward the United States.

      Then we come to the last item – El Niño. GWO’s Climate Pulse Technology model indicates that the Tropical South Pacific Ocean temperatures where El Niño events typically form – will warm significantly during late winter and approach weak El Niño conditions during the spring- much like the El Niño scare of last year. However, all years are not the same – therefore it could mature enough to form a very weak El Niño, but not strong enough to dampen the hurricane season. Historical records indicate that moderate to strong El Nino events dampen hurricane activity – whereas years with very weak El Niño conditions can be associated with active hurricane seasons if a Climate Pulse Hurricane Enhancement Cycle is in place – and it is.”

    • “…the temperature increase from 2014 to 2016 was so large because El Niño released excess heat the Pacific Ocean had been storing since the 1990s because of increased greenhouse gases in the atmosphere.”

      In English: GHGs made joules go into the oceans since at least 1999. GHGs will not lose that ability. That would be magical thinking.

      “If we continue to use the temporary slowed surface warming as an excuse to delay climate action, we’ll regret that decision when the surface warming kicks in with a vengeance.” – Dana

      Vengeance is mine sayeth the climate. The Pacific kicked starting in 2014. Now will it run around and kick everything like a vengeful mule? I think it’s kicked out for awhile.

      With the warmer GMST, the additional 0.24 C or what’s left of it will now look around and figure out where it wants to go? I think the CO2 will tell it to go back into the oceans. It’s been doing a pretty good job with that so far.

    • You better talk to JimD and get on the same page. He stated up thread:
      “A quarter of the GHG forcing occurred before 1950 and it was already 0.5 W/m2 by then. This is several times larger than typical solar variations in the sunspot cycle, so a noticeable sea-level response before 1950 is not surprising.” yet your middle figure for ocean heat content shows no significant rise until mid 80s. Why the contradiction.
      With regards the bottom map, it shows measured heat content where ARGO floats don’t go http://www.noaanews.noaa.gov/stories2011/images/argofloats_may2011.jpg
      or there still is permanent sea ice – more creative infilling?
      Oh and the trick of using Joules / heat content, rather than temperature is so obvious. Why isn’t the earth’s atmosphere quoted the same way?

  16. For the geological record the work of Vail was seminal
    https://en.wikipedia.org/wiki/Sea-level_curve

  17. The apparent acceleration in sea level rise in the first few years of the 20th Century is only a red-noise fluctuation as shown here: http://blackjay.net/wp-content/uploads/2018/01/EnvironmentalPredictions.pdf

  18. “On the decadal rates of sea level change during the twentieth century”
    GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L01602, doi:10.1029/2006GL028492, 2007
    On the decadal rates of sea level change during the twentieth century
    S. J. Holgate Proudman Oceanographic Laboratory, Liverpool, UK

    Abstract
    Nine long and nearly continuous sea level records were chosen from around the world to explore rates of change in sea level for 1904–2003. These
    records were found to capture the variability found in a larger number of stations over the last half century studied previously. Extending the sea level record back over the entire century suggests that the high variability in the rates of sea level change observed over the past 20 years were not particularly unusual.

    The rate of sea level change was found to be larger in the early part of last century (2.03 ± 0.35 mm/yr 1904–1953), in comparison with the latter part (1.45 ± 0.34 mm/yr 1954–2003). The highest decadal rate of rise occurred in the decade centred on 1980 (5.31 mm/yr) with the lowest rate of rise occurring in the decade centred on 1964 (−1.49 mm/yr). Over the entire century the mean rate of change was 1.74 ± 0.16 mm/yr.

    • dennis

      I have quoted Holgate numerous times here and have been in direct contact with him as well.

      jch and jimd will just pooh pooh him and his research I am afraid, as they seem to prefer far more dramatic scenarios that promise doom and gloom.

      tonyb

      • And Holgate is not alone in his findings. There are other papers that have found evidence contrary to the runaway scenario.

      • Where has he gone to? One thing appears to be improvement of the tide gauge record, and those improvements are being used by Kopp and Hay. Their is Holgate DNA in the studies dismiss as drama.

        Drama has zippo to do with it. A scientist said something you liked years ago, and you can’t let go of it. Science moves on.

      • ESTABLISHING HISTORICAL SEA-LEVEL TRENDS USING SALT-MARSH FORAMINIFERA. A NEW RECORD FOR THE CROATIAN COAST OF THE ADRIATIC SEA – coauthor – Simon Holgate, 2014

        The application of salt-marsh foraminifera to reconstruct historical sea-level trends was investigated for the Croatian coast of the Adriatic Sea using a transfer function approach. This technique, whilst well practiced from north Atlantic sites along the shores of America and UK, has previously evaded the Mediterranean region. The long-term tide gauges in the Mediterranean show sea-level trends for the 20th century in the range of 1.1 – 1.3mm/yr whilst more recent satellite altimetry data reveals much larger increases in sea-level throughout the basin towards the latter part of the century. Here, we present a comparable record of sea-level change using a modern dataset of foraminifera collected from two micro-tidal (<0.4m) salt-marsh sites along the central Croatian coastline. The relationship between modern foraminiferal assemblages and tidal level is well constrained and confirms their suitability as proxies for sea-level in transfer function reconstructions. Further quantitative analyses of species environment relationships suggested the use of linear regression models. Transfer functions were then created for both site specific and total combined datasets and applied to two sediment cores sampled for fossil foraminifera coupled with composite chronologies involving short-lived radionuclides and radiocarbon dating. A total combined dataset was chosen and screened to remove sample outliers improving model performance before being applied to core sediments to reconstruct mean sea-level. An inflexion observed at ~AD 1940 showed an acceleration in sea-level comparable to other proxy reconstructions. Indeed this trend was similar to instrumental records from the tide-gauge at Trieste. Similarly the transfer function reconstruction also identifies the sharp increase in mean sea-level observed in both instrumental and satellite data since the early 1990s.

        1.1 – 1.3 mm per yr is in agreement with Hay et al’s 1.2 mm per year, which confirms there is an acceleration in SLR from 1900 to present. Hay found an increase in that rate leading into of 1940 of just over 2.0 mm per year; sound like Holgate work found a similar rate increase.

        Moving on.

      • Holgate’s 2014 work with Shaw uses techniques that are similar to those used by Kemp, including in his North Carolina study, which is the green line on the above graph from Kopp 2016.

      • Is There Evidence of’Fingerprints’ in North Atlantic Tide Gauge Records?

        Abstract Sea level is rising but clear evidence of an increase in the rate of rise has proved elusive. Recent observations have suggested that there has been a marked increase in the rate of Greenland melting. Increased melting from high latitudes should produce an identifiable pattern of sea level change (‘fingerprints’) that may provide evidence of an acceleration in the rate of sea level rise. Here we show evidence of recent changes in the latitudinal pattern of sea level change from global and North Atlantic tide gauges. These gauges show a latitudinal pattern of sea level change over the past 60 years which is indicative of an acceleration in the rate of sea level rise but is inconsistent with a dominant role for either melting ice or steric changes.

      • The above is Holgate – “These gauges show a latitudinal pattern of sea level change over the past 60 years which is indicative of an acceleration”

      • So, JCH, what are you saying, that Holgate was giving Tony a bunch of BS, when they talked? I’ve got a bunch of bench strength in case we need to bring in the reserves.

  19. temperatures shall fall quite a bit and sea level shall stabilize in the current levels or less.

  20. I think the Holgate 9 is one of the better sources for relative sea level.
    Who (except some scientist) care for the amount of water in the ocean when you live by the sea. You should only care for your local relative sea level.

  21. JC “Kopp et al. find the 20th century rate of sea level rise to be the highest in the last 27 centuries. However, since their data is barely resolved at 100 year time scales (with decimeter vertical resolution), I would not place high confidence in their conclusion.”
    Ristvan | “Kopp 2016.I think very poorly of it. Spliced 66 high resolution long record tide gauges onto low resolution proxies. That is a repeat of Mike’s Nature trick. Done deliberately to create CAGW alarm”.

    The problem with data as it goes further back into the past is that short term trends are erased.
    We can all see a short term rise or fall in event data because the data itself is short term.
    So we cannot say that data a thousand or more years ago does not show rapid rises and falls of recent data because it cannot.
    If there was a rise twice as fast as today for twice as long surrounded by more normal deviations, it would be merged out of existence. Not even able to be shown.
    We are comparing decadal rates with at least an order of magnitude centennial rates.
    It is not right to even try.
    Kopp knows this so…….

    • Always the with insinuations. Smearing is so analytical.

      What decadal rates? Determined how? How did Grinsted determine decadal rates? Are the methodologies superior to Hays on fingerprinting and Mitrovica on all those wonderful thing you know about SLH and gravity, ice sheets, length of day, and vertical land motion?

    • I note the actual paper buried in your link
      https://link.springer.com/content/pdf/10.1007%2Fs00376-018-8011-z.pdf (your usual bad form JD not going for the actual paper or is the press all you bother reading if it agrees with your prejudices?)
      For 2017 data to get accepted by publication mid January seems a very rapid process through peer review – just one day. And most of their information is based on models infilling data. Similar problem to global air temperatures

      • Thanks for finding the paper Chris.

      • That’s how I knew you hadn’t read the paper as the link was in the article you posted. You are getting sloppy.

      • The paper is only 2 pages and the news item captured the bottom line adequately. Anyway, you’re in damage control mode and have to slash out at someone, I guess. I can take it.

    • Jim D:
      Do you know how many degrees that increase was?
      How not to communicate. Use total Joules instead of temperatures.

      • 10^22 Joules is a lot of energy to gain in one year. The imbalance since 2000 averages ~0.7 W/m2, which says how far behind the surface warming is relative to the forcing. Still playing catch-up. More in the pipeline.

      • Jim D:

        “Roemmich estimates that at depths from 500 to 2000 meters, oceans are warming by .002 degrees Celsius every year, and in the top 500 meters, they’re gaining .005 degrees C. annually.”

        Let’s use the top 500 meters as it’s 2 ½ times more than further down, ending at 2000 meters.

        0.5 per century. Looking at the plot from the paper, a continuation of these rates is not wildly off from that plot.

        This is good news, I thought it was worse. The driver zone, 0 – 500 meters will only warm 0.5 C? I thought we were in trouble. The oceans can punish us. They have huge thermal reserves, but I will not mind being punished by 0.5 C per century.

        I figured if we raised CO2 from about 280 ppm to 400 ppm, something would happen. I am a bit disappointed.

      • Further to what Ragnaar wrote, the temperature change since the baseline works out to about 0.13°C total rise since the 1981-2010 baseline (effectively since 1997) So we have the temperature probes doing a transit once a month of the column. And the next month’s transit is maybe a kilometre away from the previous record. The nearest probe is say 100km away. That means the temperature record is seen as representative of about 15-20,000 cubic kilometres of water. And people wonder why there is scepticism?
        The deep upwelling zones are in the North Indian and North Pacific Oceans. This is water that is generally been regarded as being in the deep abyss for tens of thousands of years. Yet the Argo probes show the North Indian as one of the hot spots, so this historic water is carrying the heat signature. And the deep Arctic is another hotspot despite no Argo probes ever going there. Likewise, the Banda sea, though at least that has had a few probes drift in and out.
        The ARGO data may be very good, but the extrapolation of its information using models is where the issue is. It is turtles all the way down.

  22. Judith Curry, thank you for the essay.

  23. May be of interest: Sarker, M. H., Choudhury, G. A., Akter, J., & Hore, S. K. (2012, December 22). Bengal Delta not sinking at a very high rate – A pragmatic assessment based on archaeological monuments. Daily Star. Retrieved from https://tinyurl.com/Sarkeretal2012

    This work has not (yet) been incorporated in the refereed literature, unfortunately.

    The first author, Maminul Haque Sarker, is a leading authority on the geomorphology of the Bengal Delta. He began his scientific career by arguing in his PhD thesis (2009) for a dominate role in in Delta development of the 1950 Assam earthquake http://eprints.nottingham.ac.uk/14566/1/606302.pdf

  24. Pingback: Weekly Climate and Energy News Roundup #301 | Watts Up With That?

  25. Pingback: Weekly Climate and Energy News Roundup #301 |

  26. Judith: I find it useful to express all data as both changes in sea level height AND average rate of change using the same units. If you look at most data for the last 5 millennia, the rate of rise is smaller than we measured in the early 20th century with tide gauges. However, this simple message is hard to find in your post above. Adding a sloping line or lines to the Figures of Rhode helps put them in context of 20th century SLR and projected 21st century SLR.

    I personally prefer cm/decade, because planners need to know how much SLR will rise in the next few decade. The longest period people and planners can contemplate is the next few decades. The IPCC wants us to think in terms of m/century, but no government planner should be concerned about the hopefully-much-richer people living a century from now. mm/yr and m/millennia aren’t very intuitive.

    I also like to remember acceleration in terms of inches/decade/decade, since it takes approximately 1 inch/decade/decade to reach 1 m of SLR by the end of the century. Assuming constant acceleration, the rate of SLR needs to have doubled a decade from now and tripled in another decade to be on track for a meter of SLR by the end of the century. That clearly isn’t happening right now. HOWEVER, it is interesting to ask how long it would take for us to DETECT a doubling of the rate of SLR with high confidence. There have been some disturbing publications on this subject. If the rate of SLR had doubled in 2025, we won’t be able to prove this with high confidence for at least another decade. There are some interesting publications on this subject.

    Individual tide gauge records can’t tell us about SLR in units of cm/decade, because it takes perhaps 5 decades of data to obtain a usefully narrow confidence interval.

    Satellite measurements give the illusion of far more reliable measurements because measurements are being made continuously and the noise averages out. However, the problem of systematic error is far greater with satellites. The record shows major systematic errors being discovered and corrected every few years, including software errors. AR3 didn’t draw any conclusions about the first eight years or so of satellite data because the best methods then for processing that data were showing almost no SLR. IIRC, that was because satellites draft about 1 cm in height per year. Then they started calibrating altitude versus ground stations. The latest version brought the overall rise down to about 2.4 mm/yr due to corrections in the first decade. The process of converting radar signals to sea level is exceptionally complex and long-term biases entering that process product long-term systematic errors.

  27. Ice melts when it gets warmer, and water flows downhill. We are causing the world to get warmer. Why is there a question that we are causing sea levels to rise?

    Is it accelerating? Well, sea level rise has been averaging near zero for several thousand years; it’s more than zero now. You don’t get from zero to more than zero without acceleration.

  28. Pingback: Sea level rise acceleration (or not): Part III – 19th & 20th century observations | Climate Etc.

  29. Judith: The Figures prepared by Rohde cover many millennia and therefore are hard to interpret in terms of 20th century SLR. It would be useful to add one or more lines with slopes relevant to the 20th century. For example, 20th century SLR was about 20 cm/century or 2 m/millennium. A line with that slope would run from (0,0) on the right hand axis of the graph of 9 millennia of SLR to (-7.5 millennia, -15 m) on the x-axis. On the 24 millennia graph, it would run from (0,0) on the right hand axis to (-24 millennia, -48 m) on the left hand axis. Many people need a visual cue to recognize that SLR slowed below the 20th-century rate about 7 millennia ago and has been comparatively negligible since.

    A more sophisticated series of slopes might include some of: 10 cm/century (earliest tide gauge records), 20 cm/century (20th-century average), 30 (current satellite estimates), 50 cm/century (IPCC central estimate for 21st-century average), 100 cm/century (highest projections for 21st century and central estimate of rate for 2090-2110?).

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