The tropical Pacific Ocean plays an important role in the global climate system. El Niño events wreak havoc worldwide by causing extreme weather and droughts. To better prepare for future changes in this region, it is crucial that climate models can accurately simulate changes in the mean state of the tropical Pacific. Unfortunately, most state-of-the-art climate models fail to reproduce the observed warming pattern of sea surface temperatures in the tropical Pacific over the last century.
To further evaluate the performance of these models under different atmospheric CO2 levels, IONTU’s postdoctoral researcher Alicia Hou (currently at University of Bordeaux) and associate professor Sze Ling Ho, along with their collaborators from the University of Bremen and Queen Mary University of London, collated paleotemperature estimates from past climates characterized by contrasting atmospheric CO2 levels for comparison with model simulations (Fig. 1). Before performing proxy-model comparison, they first used ARGO data to ensure that several temperature indices commonly used in paleoclimate reconstruction can indeed capture changes in the upper ocean thermal conditions of the tropical Pacific. The team then generated a multi-model ensemble using simulations from seven state-of-the-art models based in institutions in North America, Europe, and Asia under the auspices of the Paleoclimate Modelling Intercomparison Project (PMIP). The proxy-model comparison results indicate that, similar to the warming observed over the last century, these models were unable to reproduce the tropical Pacific cooling pattern when atmospheric CO2 levels were about half of today’s levels. The discrepancies between proxies and models may stem from the fact that the models overestimate sea surface temperature changes in the eastern tropical Pacific. The proxy results also suggest that the western Pacific may warm more than the eastern Pacific if greenhouse gas emissions continue unabated in the future.
The study was published in Nature Research journal Communications Earth and Environment:
Hou, A., Jonkers, L., Ford, H.L., Ho, S.L. (2024) El Niño-like tropical pacific ocean cooling pattern during the last glacial maximum. Commun Earth Environ 5, 587.
https://www.nature.com/articles/s43247-024-01740-w
Fig. 1: Proxy-model comparison of glacial-interglacial upper ocean temperature changes in the tropical Pacific, with the locations of proxy sites (filled circles) and the areas used for computing regional means from model simulations (black box).
