EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Eastern equatorial Pacific warming delayed by aerosols and thermostat response to CO2

Ulla K. Heede1 and Alexey V. Fedorov1,2
Ulla K. Heede and Alexey V. Fedorov
  • 1Earth and Planetary Sciences, Yale University, New Haven, CT, USA (
  • 2LOCEAN/IPSL, Sorbonne University, Paris, France

Understanding the tropical Pacific response to global warming remains a challenging problem due to discrepancies between models and observations, as well as a large intermodel spread in future projections. Here, we assess the recent and future evolution of the equatorial Pacific east-west temperature gradient, and the Walker circulation within the CMIP6 dataset. Using 40 models, we compare simulated tropical climate change across a wide range of experiments with varying CO2 and aerosol forcing. In abrupt CO2-increase scenarios, many models generate an initial strengthening of the east-west gradient resembling an ocean thermostat (OT), characterized by lack of warming in the central Pacific, followed by a small weakening; other models generate an immediate weakening that becomes progressively larger establishing a pronounced eastern equatorial Pacific (EP) warming pattern. The initial response in these CO2-only experiments is a very good predictor for the future EP pattern simulated in future warming scenarios, but not in historical simulations showing no multi-model trend. The likely explanation is that recent CO2-driven changes in the tropical Pacific, which are relatively small compared to future projections, are masked by aerosol effects. In future warming scenarios, however, the EP warming pattern emerges within 20-40 years as greenhouse gases overcome aerosol forcing. These findings highlight the need to understand the largely overlooked, but possibly significant role of aerosols in delaying sea surface warming in the tropical Pacific, and the implications for predicting future climate change across the tropics.

How to cite: Heede, U. K. and Fedorov, A. V.: Eastern equatorial Pacific warming delayed by aerosols and thermostat response to CO2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13946,, 2021.


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