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Extreme ocean warming in Japan linked to human activities

Climate change doubled the likelihood of extreme ocean warming near Japan over the last two decades, according to new research from the National Institute for Environmental Studies. The experts report that record heat in the northwestern Pacific in August 2020 would not have occurred without human-induced climate changes.

The Japan Meteorological Agency (JMA) documented record high sea surface temperatures again in July and October 2021 and from June to August 2022.

“Impacts of global warming is not uniform, rather show regional and seasonal differences,” said study co-author Hideo Shiogama. “A comprehensive analysis on regional SSTs for a long period may provide a quantitative understanding of how much ocean condition near Japan has been and will be affected by global warming. This better informs policymakers to plan climate change mitigation and adaptation strategies.”

The research was focused on ten monitoring areas operationally used by the JMA. The scientists confirmed that the observed sea surface temperature changes from 1982 to 2021 were well reproduced by 24 climate models in all but one of the monitored regions. 

“In the present climate, every extreme ocean warming event is linked to global warming,” said co-lead author Michiya Hayashi. “We found that the occurrence probability of almost all the extreme ocean warming events has already at least doubled since the 2000s than the preindustrial era. It is increased more than tenfold in sizeable cases since the mid-2010s, especially in southern Japan.”

Using the 24 climate models, the researchers estimated the probability of exceeding the monthly record high sea surface temperatures around Japan at global warming levels from zero to two degrees Celsius.

“Once global warming reaches 2°C, all of nine monitoring areas are expected to experience SSTs warmer than the past highest levels at least every two years,” said study co-author Tomoo Ogura. “Limiting global warming below 1.5°C is necessary not to have the record warm conditions in Japan’s marginal seas as the new normal climate.”

The study is published in the journal Geophysical Research Letters.

By Chrissy Sexton, Editor

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