Category Archives: Sensitivity & feedbacks

New paper suggests historical period estimates of climate sensitivity are not biased low by unusual variability in sea surface temperature patterns

By Nic Lewis

An important new paper by Thorsten Mauritsen, Associate Professor at Stockholm University[i] and myself has just been accepted for publication (Lewis and Mauritsen 2020)[ii]. Its abstract reads: Continue reading

Emergent constraints on TCR and ECS from historical warming in CMIP5 and CMIP6 models

By Nic Lewis

This is a brief comment on a new paper[i] by a mathematician in the Exeter Climate Systems group, Femke Nijsse, and two better known colleagues, Peter Cox and Mark Williamson. I note that Earth Systems Dynamics published the paper despite one of the two peer reviewers recommending against acceptance without further major revisions. But neither of the reviewers appear to have raised the issue that I focus on here. Continue reading

Greening the planet and slouching towards Paris?

by Patrick J. Michaels

A new paper finds higher than expected CO2 fertilization inferred from leaf to global observations.  The paper predicts that the Earth is going to gain nearly three times as much green matter as was predicted by the IPCC AR5.

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Plausible scenarios for climate change: 2020-2050

by Judith Curry

A range of scenarios for global mean surface temperature change between 2020 and 2050, derived using a semi-empirical approach. All three modes of natural climate variability – volcanoes, solar and internal variability – are expected to act in the direction of cooling during this period.

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Explaining the Discrepancies Between Hausfather et al. (2019) and Lewis&Curry (2018)

by Ross McKitrick

Challenging the claim that a large set of climate model runs published since 1970’s are consistent with observations for the right reasons.

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Two more degrees by 2100!

by Vaughan Pratt

An alternative perspective on 3 degrees C?

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3 degrees C?

by Judith Curry

Is 3 C warming over the 21st century now the ‘best estimate’?  A reframing of how we think about climate change over the 21st century, and my arguments for 1 C.

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Comment by Cowtan & Jacobs on Lewis & Curry 2018 and Reply: Part 2

By Nic Lewis

In an earlier article here I discussed a Comment on Lewis and Curry 2018 (LC18) by Kevin Cowtan and Peter Jacobs (CJ20), and a Reply from myself and Judith Curry recently published by Journal of Climate (copy available here). I wrote that I would defer dealing with the differences between observed and CMIP5 model-simulated historical warming, which formed the basis of CJ20’s numerical analysis, until a subsequent article. I now do so. Continue reading

Comment by Cowtan & Jacobs on Lewis & Curry 2018 and Reply: Part 1

By Nic Lewis

A comment on LC18 (recent paper by Lewis and Curry on climate sensitivity)  by Cowtan and Jacobs has been published, along with our response.

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Gregory et al 2019: Unsound claims about bias in climate feedback and climate sensitivity estimation

By Nic Lewis

The recently published open-access paper “How accurately can the climate sensitivity to CO2 be estimated from historical climate change?” by Gregory et al.[i] makes a number of assertions, many uncontentious but others in my view unjustified, misleading or definitely incorrect.

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What’s the worst case? Climate sensitivity

by Judith Curry

Are values of equilibrium climate sensitivity > 4.5 C plausible?

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Why climate predictions are so difficult

by Judith Curry

An insightful interview with Bjorn Stevens.

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Climate sensitivity calculator app

by Alberto Zaragoza Comendador

How sensitive is the Earth’s climate to greenhouse gases? Speaking about carbon dioxide in particular, how much would air temperatures increase if we doubled atmospheric concentrations of said gas?

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Reconstructing a dataset of observed global temperatures 1950-2016 from human and natural influences

by Frank Bosse

A demonstration that multidecadal variation since 1950 leads to overestimation of the Transient Climate Response (TCR).

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Climate sensitivity to cumulative carbon emissions

By Nic Lewis

An observational estimate of transient (multidecadal) warming relative to cumulative CO2 emissions is little over half that per IPCC AR5 projections.

AR5 claims that CO2-caused warming would be undiminished for 1000 years after emissions cease, but observations indicate that it would halve. Continue reading

Warming patterns are unlikely to explain low historical estimates of climate sensitivity

By Nic Lewis

A critique of of a new paper by Andrews  et al., Accounting for changing temperature patterns increases historical estimates of climate sensitivity.

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Hothouse Earth

by Judith Curry

We need to raise the bar on how we think about the possible worst case scenario for climate change.

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Impact of recent forcing and ocean heat uptake data on estimates of climate sensitivity

by Nic Lewis

We have now updated the LC15 paper with a new paper that has been published in the Journal of Climate “The impact of recent forcing and ocean heat uptake data on estimates of climate sensitivity“.  The paper also addresses critiques of LC15.

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Emergent constraints on climate sensitivity in global models. Part III

by Nic Lewis

The two strongest potentially credible constraints, and conclusions.

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Emergent constraints on climate sensitivity: Part II

by Nic Lewis

The four constraints that Caldwell assessed as credible.

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Emergent constraints on climate sensitivity: Part I

by Nic Lewis

Emergent constraints on climate sensitivity:  their nature and assessment of validity.

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Recent research on aerosol forcing of the CMIP5 models

by Frank Bosse

A few days ago a paper (Sato et al) dealing with some aspects of the “Aerosol Cloud Interactions”, (ACI, also called “aerosol indirect effects”) was released. It bolsters the conclusions of earlier papers: the effective radiative forcing from ACI (ERFaci) is smaller than thought, perhaps near zero .

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Nature Unbound VIII – Modern global warming

by Javier

Summary: Modern Global Warming has been taking place for the past 300 years. It is the last of several multi-century warming periods that have happened during the Neoglacial cooling of the past 3000 years. Analysis of Holocene climate cycles shows that the period 1600-2100 AD should be a period of warming. The evidence suggests that Modern Global Warming is within Holocene variability, but the cryosphere displays a non-cyclical retreat that appears to have undone thousands of years of Neoglacial ice advance. The last 70 out of 300 years of Modern Global Warming are characterized by human-caused, extremely unusual, rapidly increasing CO2 levels. In stark contrast with this rapidly accelerating anthropogenic forcing, global temperature and sea level appear to have continued their rising trend with no perceptible evidence of added acceleration. The evidence supports a higher sensitivity to CO2 in the cryosphere, suggesting a negative feedback by H2O, that prevents CO2 from having the same effect elsewhere.

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Marvel et al.’s new paper on estimating climate sensitivity from observations

by Nic Lewis

Recently a new model-based paper on climate sensitivity was published by Kate Marvel, Gavin Schmidt and others, titled ‘Internal variability and disequilibrium confound estimates of climate sensitivity from observations’.[1]

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Reply to Patrick Brown’s response to comments on his Nature article

by Nic Lewis

My reply to Patrick Brown’s response to my my comments on his Nature article.

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