Runaway Cooling From Large Solar Reductions Modulated by Ocean Overturning Circulation and Heat Uptake

[Geoengineering News]

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GL117821

Authors: Maya V. Chung, Wenchang Yang, Gabriel A. Vecchi

First published: 03 October 2025

https://doi.org/10.1029/2025GL117821

Abstract

The climate system can respond asymmetrically to warming and cooling, yet this asymmetry remains underexplored. This study uses multi-century experiments with two coupled global climate models under idealized abrupt solar forcing changes of 

±1%, 2%, 4%, and 6%. In both models, cooling has a larger impact on surface temperature than warming, driven by the ice-albedo feedback. However, under strong cooling (−4%, −6% Solar), the models diverge significantly. One model undergoes runaway ice growth, while the other has slower ice expansion and even transient sea ice retreat in the north Pacific. The latter is linked to the development of a strong Pacific meridional overturning circulation, which transports heat northward and slows ice growth. The model with less ice growth also exhibits greater “cold uptake into” (or heat release from) the deep ocean. These findings motivate further investigation of inter-model differences in ocean-ice-atmosphere interactions and their impacts on climate feedbacks.

Plain Language Summary

Understanding both warming and cooling of the climate system is crucial for studying past climates, predicting climate changes under different greenhouse gas emission scenarios, and connecting past climates to future changes. This study compares how two climate models respond to sudden increases and decreases in incoming sunlight. While both models show similar warming and moderate cooling responses, they behave differently under strong cooling. In one model, sea ice rapidly expands and reaches the tropics within a few centuries, whereas in the other, ice growth never reaches that point even after running the simulations for nearly twice as long. We find that in the second model, an ocean overturning circulation develops in the Pacific that transports heat from the Equator northward. This process prevents sea ice from advancing by melting it from below. These findings emphasize the need to examine the ocean's role in climate change, run models for multiple centuries, and conduct more simple perturbation experiments including cooling scenarios to better understand discrepancies between climate models.

Key Points

Two climate models have different responses to extreme solar reductions driven by ice-albedo feedback

Ice cover and surface temperature differences are influenced by ocean heat uptake and one model's transient Pacific overturning

Pacific overturning formation associated with lower salinity stratification in the north Pacific

Source: AGU