What is it about?
What happens to the climate system after carbon emissions cease? Climate models have been used to explore what happens to global surface temperature after carbon emissions cease. Most climate models cool after net zero, but a few climate models continue to warm. Our work is about trying to understand why there are different climate model responses. We have introduced a new framework to compare the importance of different processes in the climate models and reveal their relative importance.
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Why is it important?
Whether there is continued warming or cooling after net zero depends on a competition between thermal and carbon responses. The thermal response often contributes to a surface temperature rise due to either a weakening in ocean heat uptake leading to more of the radiative forcing warming the surface or through an amplification by climate feedbacks. The carbon response usually contributes to a surface temperature decrease as more carbon is held in the land or ocean, decreasing the atmospheric carbon and associated radiative forcing. There are differences in the thermal and carbon processes operating in different climate models, so that there are then different surface temperature outcomes after net zero.
Perspectives
The study draws upon a simple identity connecting temperature change to a product of different factors. Each of those factors are connected to theory that we understand, such as (i) how the atmospheric carbon inventory connects to carbon uptake by the land and ocean (after carbon emissions cease) and (ii) how the energy uptake at the top of the atmosphere (linking effectively to ocean heat uptake) connects to the radiative forcing from carbon emissions plus the radiative response (returning heat to space and affected by climate feedbacks). I set out these connections on some sheets of paper and then we used this identity to diagnose the response from different climate models. We found there were different climate model responses according to differences in how the land carbon system is modelled (whether there is nutrient limitation), how the ocean takes up heat and carbon, and whether climate feedbacks amplify changes in surface temperature.
Professor Richard G Williams
University of Liverpool Department of Earth Ocean and Ecological Sciences
Read the Original
This page is a summary of: A normalised framework for the Zero Emissions Commitment, Biogeosciences, November 2025, Copernicus GmbH,
DOI: 10.5194/bg-22-7167-2025.
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