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PMEL Publications Abstract

FY 2026

Impacts of mean state ocean heat transport on climate and its response to CO2 forcing

Li, Q., J. Zhang, W. Cheng, K.C. Armour, L. Thompson, O.A. Garuba, J. Lu, and B.E. Harrop

Geophys. Res. Lett., 53(6), e2025GL120436, doi: 10.1029/2025GL120436, View open access article at AGU/Wiley (external link) (2026)

Simulations of the slab ocean configuration of the coupled Energy Exascale Earth System Model (E3SM) were used to isolate the role of poleward ocean heat transport (OHT) in shaping the climate and its response to CO2 forcing. Imposed changes to mean-state OHT produce compensating changes in atmospheric heat transport (AHT) that are mediated by changes in surface evaporation. A reduction of maximum OHT by 0.56 PW (32%) reduces the global mean surface air temperature by 3.6°C. However, this cooler mean state exhibits 1.2°C more warming under CO2 quadrupling, with the largest differences occurring at high latitudes. The amplified warming arises from stronger surface albedo and lapse rate feedbacks in polar regions and a shortwave cloud feedback in the southern midlatitudes. These results highlight the critical role of mean-state OHT in modulating mean-state climate, the partitioning between the OHT and AHT, and climate sensitivity.

Plain Language Summary. Earth's climate depends on how heat is moved around the planet by both the ocean and the atmosphere. In this study, we use numerical climate model simulations to study how different magnitudes of ocean heat transport affect climate. We find that when the ocean moves less heat toward the poles, evaporation strengthens in the tropics and weakens outside of the tropics, causing the atmosphere to transport more heat poleward. Although the total (atmosphere plus ocean) heat transport remains nearly constant, the reduced ocean contribution produces a cooler climate. This cooler mean-state climate, however, is more sensitive to changes in CO2 than in the case with stronger ocean heat transport and warmer mean-state climate. This enhanced warming occurs mainly in the polar regions, where CO2 forcing triggers greater sea ice loss than in the warmer-climate case, amplifying surface temperature increases. This suggests that the strength of ocean heat transport influences both the magnitude and the spatial pattern of surface temperature in the present climate and under future conditions.

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