Extreme ocean warming near Japan is now at least twice as likely due to global warming

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According to the Japan Meteorological Agency, SSTs in August 2020 in the southern region of Japan and the northwest Pacific Ocean reached unprecedented heights (JMA). The record-breaking Pacific Northwest SST observed in August 2020 could not have happened without human-induced climate change, according to a recent study published in January 2021.

Since then, the JMA has once again reported that record SSTs were observed near Japan in July and October 2021 as well as from June to August 2022. However, it is still unclear to what extent climate change has affected the possibility that these regions of extreme warming episodes would occur. “The impacts of global warming are not uniform, but rather show regional and seasonal differences,” said co-author Hideo Shiogama, head of the Earth System Risk Assessment Section at the Earth System Division, NIES. . “A comprehensive analysis of regional SSTs over a long period can provide a quantitative understanding of the state of the ocean near Japan that has been and will be affected by global warming. This better informs policy makers to plan mitigation strategies. mitigation and adaptation to climate change.

The study, which was published in Geophysical Research Letters, examines the role that global warming plays in the distinct monthly intense ocean warming events occurring in Japan’s marginal seas that, in pre-industrial times, could have occur less frequently than once every 20 years. . The Sea of ​​Japan, the East China Sea, the islands of Okinawa, the east coast of Taiwan and the Pacific coasts of Japan were among the ten surveillance areas that the JMA uses in its daily operations. Except for the area east of Hokkaido, scientists confirmed that the SST variations observed between 1982 and 2021 were accurately simulated by 24 climate models participating in the project’s phase of coupled model intercomparison. (CMIP6sixth).

In order to determine the contribution, exceptional occurrences of ocean warming were then discovered in nine monitoring regions. Extreme ocean warming and climate change

“In today’s climate, every extreme ocean warming event is linked to global warming,” said corresponding lead author Michiya Hayashi, associate researcher at NIES. Scientists estimated the frequencies of occurrence of each event under current and pre-industrial climate conditions from January 1982 to July 2022 based on CMIP6 climate models. “We found that the probability of occurrence of almost all extreme ocean warming events has already at least doubled since the 2000s compared to the pre-industrial era. It has increased more than tenfold in important cases since the mid-2000s. 2010s, especially in southern Japan.”

For example, episodes of extreme ocean warming in July 2022 are identified as abnormally high SSTs detected in five monitoring areas, including the Sea of ​​Japan (areas 1, 3), East China Sea (areas 5, 8) and southern Okinawa near Taiwan (zone 10). Updated results based on preliminary data uploaded to the NEAR-GOOS RRTDB website on September 15, 2022 (not included in the published article) reveal that events are also identified in six monitoring areas south of 35° N for August 2022: the East China Sea (zones 5, 8), south and east of Okinawa (zones 10, 9), southeast of Kanto (zone 7) and seas off Shikoku and Tokai (zone 6 ).

“We estimate that, in all these events identified in July and August 2022, the frequencies of occurrence are increased at least doubled due to climate change, and more than tenfold for those south of 35°N except for the north of the ‘East China. Sea,’ Hayashi said. “The impacts of climate change on extreme ocean warming events in northern Japan began to appear relatively late compared to southern Japan,” Shiogama noted. The increase in global aerosol emissions until the 1980s tends to cool the Earth’s surface, which is greatest in the North Pacific, especially near northern Japan, via large-scale atmospheric circulation changes . In addition, the natural year-to-year variability of SST is large in northern Japan, so the global warming signal was less detectable than in southern Japan. Since over the past few decades global aerosol emissions have been reduced, the cooling effect becomes less dominant for human-induced greenhouse gas warming.

“Our study indicates,” continued Shiogama, “that the contribution of climate change to SST extremes has already been noticeable beyond natural variability, even in northern Japan under current climatic conditions.” What about predicted changes in ocean conditions? Using outputs from 24 CMIP6 climate models from 1901 to 2100, the researchers further examined the likelihood of exceeding monthly record SSTs around Japan at different levels of global warming from 0°C to 2°C. Tomoo Ogura, co-author and head of the Climate Modeling and Analysis Section at the Earth System Division, NIES, said: “Once global warming exceeds 2°C, the nine regions of monitoring will experience SSTs that are warmer than the last highest values ​​at least every two years.”

He continued, “It is important to limit global warming to below 1.5°C to prevent the new normal climate in Japan’s peripheral waters from becoming the record heat.” According to a quantitative SST survey near Japan, climate change is already the main cause of the majority of recent SST records. Future analysis of the dynamics of each significant warming event must consider both long-term climate change and annual natural variability, Hayashi said.

“However, we anticipate that our statistical results based on the most recent climate models will help in the implementation of climate change adaptation and mitigation strategies.” (ANI)

(This story has not been edited by the Devdiscourse team and is auto-generated from a syndicated feed.)

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