Category Archives: Sensitivity & feedbacks

A pertinent climate question

by Michel de Rougemont

Not so innocent as it looks, a pertinent question is asked by Judith Curry on Twitter:

How much of a change in cloudiness would it take to account for the 0.53 W/m2 increase in TOA radiative forcing since 2003?
https://twitter.com/curryja/status/1375144537522204672

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Compensation between cloud feedback + ECS and aerosol-cloud forcing in CMIP6 models

By Nic Lewis

An important paper, Wang et al.[1], on the relationships between cloud feedback, climate sensitivity (ECS) and aerosol-cloud interaction in the latest generation of global climate models (CMIP6) has just been published. The key conclusion of the paper is:

The seeming consistency of global-mean temperature evolution between more positive cloud feedback (high ECS) models and observations requires a strong aerosol indirect cooling effect that leads to an interhemispheric temperature evolution that is inconsistent with observations.

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CO2 sensitivity: the polar solution

by Alan Longhurst

Natural climate variability in the polar regions.

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Committed warming and the pattern effect

By Nic Lewis

A critique of the paper “Greater committed warming after accounting for the pattern effect”, by Zhou, Zelinka, Dessler and Wang. Continue reading

Disconnect in the relationship between GMST and ECS

by Kenneth Fritsch

Abstract. An analysis is presented of  he disconnection between the CMIP5 and CMIP6 Historical and Future periods when considering the relationship of the individual model GMST changes and the climate sensitivity. I have included a simple model that can account for the period disconnection using the negative forcing of aerosol/cloud effects in the Historical period that is carried forward into the Future period.   I attribute some of the uncertainty in simulations of this simple model to endogenous model decision (selection) uncertainty that leads to variations in the changes of the negative forcing in the Historical period carried forward into the Future period.

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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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