Changes to the Warming Pattern in the Tropical Pacific

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.