Official IPCC estimates of future world warming could also be overstated
Press Launch
London, 20 September – A brand new paper reduces the estimate of local weather sensitivity – the quantity of warming anticipated for a doubling of carbon dioxide concentrations – by one third. The outcomes due to this fact counsel that future world warming will likely be a lot lower than anticipated.
The paper, by impartial scientist Nic Lewis, has simply appeared within the journal Local weather Dynamics. It is a vital problem to the official view of the Intergovernmental Panel on Local weather Change (IPCC).
Lewis has critiqued a 2020 evaluation of local weather sensitivity by Sherwood et al., which strongly influenced the IPCC’s Sixth Evaluation Report, in 2021. Lewis commented:
“It’s unlucky that Sherwood et al.’s evaluation of local weather sensitivity, which underpinned the UN Framework Conference on Local weather Change, contained such critical errors, inconsistencies and deficiencies in its strategies”.
After correcting the Sherwood et al. strategies and revising key enter information to mirror, primarily, newer proof, the central estimate for local weather sensitivity comes down from 3.1°C per doubling of CO2 focus within the unique examine to 2.16°C within the new paper.
This massive discount reveals how delicate local weather sensitivity estimates nonetheless are to enter assumptions, and that values between 1.5°C and a couple of°C stay fairly believable.
- Local weather sensitivity represents the long-term world temperature improve brought on by a doubling of atmospheric CO2 focus. There are completely different measures of local weather sensitivity. Each the Sherwood and Lewis papers estimate the so-called ‘efficient’ local weather sensitivity, which displays a brand new equilibrium state projected from centennial adjustments after a doubling of the CO2 focus. This measure is taken into account probably the most related one for predicting local weather change within the coming two centuries.
- Local weather sensitivity has all the time been an important, but in addition extremely unsure, parameter within the local weather change discourse. Earlier IPCC reviews assessed its worth as more likely to be someplace between 1.5°C and 4.5°C, with a finest estimate of three°C. Nonetheless, prompted by the Sherwood paper, the 2021 Sixth Evaluation Report moved that vary upwards, to 2.5 to 4°C. Though for outsiders this may sound boring, for insiders it was a revolutionary change.
- Lewis’s corrections and revisions result in a probable vary of 1.75 to 2.7°C, which isn’t solely decrease however can also be a lot much less unsure than both the 2021 official IPCC evaluation or the very comparable Sherwood et al. estimate (2.6 to three.9°C).
- Nic Lewis is the lead or sole writer of ten peer-reviewed papers on local weather sensitivity. He was a participant within the 2015 workshop that kicked off the World Local weather Analysis Programme mission that led to the Sherwood et al. 2020 paper, however he was not a co-author of that paper.
Lewis commented:
“The substantial discount in assessed local weather sensitivity upon updating key enter information means that the rise within the backside of the local weather sensitivity vary within the IPCC Sixth Evaluation Report was unjustified”.
Lewis’s paper is entitled ‘Objectively combining local weather sensitivity proof’. It may be freely downloaded right here. An in depth explanatory article concerning the paper is on the market right here.
