Official IPCC estimates of future global warming may be overstated
Press Release
London, September 20 – A new paper reduces the estimate of climate sensitivity – how much warming is expected to double carbon dioxide concentrations – by a third. The results therefore suggest that future global warming will be much less than expected.
An article by independent scientist Nic Lewis has just appeared in the journal Climate dynamics. This is an important challenge to the official position of the Intergovernmental Panel on Climate Change (IPCC).
Lewis critiqued the 2020 assessment of climate sensitivity by Sherwood et al., which strongly influences the IPCC’s Sixth Assessment Report, due in 2021. Lewis commented:
“Unfortunately, Sherwood et al.’s assessment of climate sensitivity, which forms the basis of the United Nations Framework Convention on Climate Change, is severely flawed, inconsistent and shortcomings in its methods”.
After editing Sherwood et al. methods and modify the primary input to reflect, primarily, more recent evidence, the central estimate of climate sensitivity that decreases from 3.1°C for every doubling of CO2 concentrations in original study down to 2.16°C in the new paper.
This large reduction shows how climate-sensitive estimates remain for the input assumptions, and values between 1.5°C and 2°C are still quite reasonable.
- Climate sensitivity represents a long-term increase in global temperature due to a doubling of atmospheric CO2 concentrations. There are different measures of climate sensitivity. Both the Sherwood and Lewis papers estimate so-called ‘effective’ climate sensitivity, reflecting a new equilibrium formed from changes hundreds of years after CO2 concentrations doubled. . This measure is considered to be the most suitable measure to predict climate change over the next two centuries.
- Climate sensitivity has always been a very important but also highly uncertain parameter in the climate change discourse. Previous IPCC reports have assessed its value to be between 1.5°C and 4.5°C, with the best estimate being 3°C. However, suggested by the article Sherwood’s Sixth Assessment Report 2021 moved that range upwards, from 2.5 to 4°C. While this may sound boring to an outsider, for those insiders, it was a revolutionary change.
- Lewis corrections and modifications result in a possible range of 1.75 to 2.7°C, which is not only lower but also much less uncertain than the official 2021 IPCC or Sherwood assessment. et al. estimated (2.6 to 3.9°C).
- Nic Lewis is the lead or sole author of ten peer-reviewed papers on climate sensitivity. He was a participant in the 2015 workshop that kicked off the World Climate Research Program project that led to Sherwood et al. Report 2020, but he is not a co-author of that paper.
Lewis commented:
“The significant reduction in climate sensitivity assessed when updating key inputs indicates that an increase at the bottom of the IPCC’s Friday Assessment Report is unfounded”.
Lewis article titled ‘Objectively incorporate climate-sensitive evidence’. It can be downloaded for free here. A detailed explanation of the article is available here.
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