Changes to the Warming Pattern in the Tropical Pacific

The Earth is rapidly warming in response to human-induced greenhouse gas emissions. The warming is however not uniform, with some areas of the Earth warming much faster than others. The tropical Pacific Ocean is an area that is rather unique: While the western tropical Pacific has been warming rapidly as predicted, the eastern tropical Pacific experienced a slight cooling in recent decades, together with a strengthening of the trade winds – similar to a phenomenon called “La Niña”. However, the long persistence of this regional La Niña-like temperature pattern over several decades has not been predicted by most of the climate models, creating a puzzle for scientists that study the underlying physical processes of warming patterns. Predicting how this pattern will continue to evolve over the next few decades will be critical for regional climate change projections including changes in weather extremes such as the pathways and intensities of typhoons.

An international group of researchers based in Japan, Germany, the UK, Taiwan, Australia, and the USA published this week in Nature a comprehensive assessment of the physical mechanisms behind the historical sea surface temperature pattern change in the tropical Pacific and based on this assessment provide a perspective on how these processes together will shape its future evolution.

“Climate change simulations through the end of this century indicate that warming will be greater in the eastern tropical Pacific than in the western tropical Pacific. However, observational data for the past approximately 40 years show larger warming in the western Pacific and slight cooling in the eastern Pacific,” said Masahiro Watanabe, one of the lead authors of the study and professor at the University of Tokyo in Japan.

“Currently, global warming due to human activities has exceeded 1°C and one of the very few regions where we see a mismatch between the model predictions and our observations is the eastern tropical Pacific. To explain this misalignment, researchers have conducted many different studies and proposed different mechanisms that could explain the mismatch,” adds Sarah Kang, the other lead author of the study and director of the Max Planck Institute for Meteorology in Germany.

In this review, the group of researchers answered the following two key questions based on their evaluation of more than 150 scientific studies:

  • If the observed recent temperature trends in the tropical Pacific are at least partially due to human activities, how can they be reconciled with the future pattern changes predicted by the climate model simulations?
  • Furthermore, what are the reasons that most climate model simulations did not predict these recent trends?

The authors identified several mechanisms that are key to warming patterns in the tropical Pacific Ocean (Figure 2). “We concluded in our assessment that some of the processes that caused the La Niña-like warming pattern in recent decades are likely temporary in nature and will weaken as the Earth continues to warm,” said Malte Stuecker, one of the co-authors and assistant professor at the University of Hawaii at Manoa in the USA.

“We think that the processes that will switch the pattern to more warming in the eastern tropical Pacific – a so-called El Niño-like warming pattern – will likely dominate in the future,” explained Masahiro Watanabe.

Among the mechanisms that lead to a La Niña-like warming pattern, the authors identified several processes that are potentially underestimated in most climate simulations, such as the connectivity between the Southern Ocean and the tropical Pacific.

“This assessment highlights that more research focus is needed on improving the representation of physical processes that control tropical warming patterns. To contribute and help coordinate research efforts we recently founded an international research group called TROPICS under CLIVAR – the Climate Variability and Predictability Program,” added Sarah Kang.

Original publication

Watanabe, M., Kang, S.M., Collins, M. et al. Possible shift in controls of the tropical Pacific surface warming pattern. Nature 630, 315–324 (2024).


Masahiro Watanabe
Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan
hiro@we dont want

Sarah M. Kang
Max Planck Institute for Meteorology
sarah.kang@we dont want