Evolution of global climate and regional hot extremes following CO2 emissions cessation.

Reaching net zero greenhouse gas emissions is essential to halt the current global warming trend and attempt to stabilise global temperatures. However, uncertainties remain on the sign and the magnitude of the long-term responses of the climate system following anthropogenic emissions cessation.

This study contributes to constraining this uncertainty by exploring the global and regional temperature evolution under zero CO₂ emissions conditions in the UKESM1.2 projections following the TIPMIP protocol (Jones et al., 2025). Stabilised warming levels spanning +1.5°C to +5°C above pre-industrial conditions are analysed to understand the impact of antecedent conditions on post zero-emissions trends. We find that the global average surface air temperature (GSAT) keeps increasing in all stabilised warming scenarios. The increase is more pronounced in the +3°C to +5°C scenarios, where it approaches 0.25°C per century. Most of the warming is registered in the Southern Hemisphere, particularly in the Southern Ocean, while the Northern Hemisphere experiences a slight cooling trend over land.

These regional cooling trends are more marked for the annual temperature maxima, with several regions across 45-65°N experiencing cooling of >1°C per century. The strongest cooling trends emerge in the higher warming scenarios, and we investigate their drivers in North America, where the cooling magnitude exceeds 1.5°C per century. Using a method based on constructed circulation analogues, we find that the projected cooling trend is almost completely explained by thermodynamic drivers and we reconcile this finding with the model vegetation changes. Our findings serve a double purpose. On one hand, they show the significant contribution that land-use changes can have regionally for the attenuation of annual temperature maxima, supporting the case for their careful consideration in future mitigation and adaptation strategies. On the other, they highlight how highly idealised protocols like TIPMIP could bias climate projections post emissions cessation if they do not include realistic projections of land use changes.

 

Bibliography

Jones, Colin, Bossert, I., Dennis, D. P., Jeffery, H., Jones, C. D., Koenigk, T., Loriani, S., Sanderson, B., Séférian, R., Wyser, K., Yang, S., Abe, M., Bathiany, S., Braconnot, P., Brovkin, V., Burger, F. A., Cadule, P., Castruccio, F. S., Danabasoglu, G., … Ziehn, T. (2025). The TIPMIP Earth system model experiment protocol: phase 1. https://doi.org/10.5194/egusphere-2025-3604.