Japan has experienced , with experts raising alarm over their potential impact.
The summer of 2025 was the hottest ever recorded in , with the nationwide average 2.36 degrees Celsius hotter than average since records began in 1898. The city of Isesaki, in Gunma Prefecture, setting a new national record high of 41.8 Celsius (107.2 Fahrenheit) on August 5.
The Japanese Meteorological Agency (JMA) said its network of more than 1,300 stations recorded 30 times when the temperature was above 40 degrees, far above the 17 occasions that was the last annual record, set in the summer of 2018.
And even though autumn has arrived across the archipelago, the heat has not entirely dissipated, with 35 degrees recorded in the southern city of Kagoshima this Sunday. More than 30 locations across the country also logged record highs for the month of October.
‘Abnormally high rises’ in temperature
“The most basic reason for the rising temperatures is global warming,” said Yoshihiro Iijima, a professor of climatology at Tokyo Metropolitan University.
“This year we have seen very high surface temperatures in both the Pacific Ocean and the Sea of Japan, so on both sides of the islands of Japan, which has contributed to higher-than-average humidity and warmer air temperatures over the land,” he told DW.
Ocean temperatures have been exacerbated by a persistent high-pressure system that lingered over Japan for an extended period this summer, Iijima said, while the subtropical jet stream over Eurasia after June shifted significantly towards the North Pole.
“These conditions combined are a sort of ‘perfect storm’ that have contributed to the record temperatures we have experienced so far this year,” Iijima said. “But we have broken records for three years in a row and this is an extremely worrying trend. I would have been worried about a gradual increase in temperatures, but we are seeing abnormally high rises.”
Global warming as a key factor
Conditions have been so dramatic this year that the JMA convened its Advisory Panel in Extreme Climatic Events, with the researchers also pointing a finger to .
“The record high temperatures observed around Japan in summer 2025 would virtually never have happened with the assumption of no effects from global warming,” they said in a study published in late September.
“The rate of temperature increase experienced under global warming has accelerated in recent years,” the panel added. “Record-high summer mean surface air temperatures over Japan have been observed in three consecutive years (2023 to 2025), far exceeding the projected linear trend of temperatures based in the period from 1995 to 2024.”
Hotter summers harm crops, bring more destructive typhoons
The soaring summer heat could have , Iijima points out.
“The effect on Japan’s agricultural sector will be serious, with rice production down as the crop cannot withstand the heat and there is inadequate water,” he said. Experts have also noted changes in the nation’s fishing sector, with catches down and species that have traditionally made up the bulk of the catch moving north in search of cooler waters.
But the heat also has a more direct impact on the Japanese population, with more than 100,000 people admitted to hospitals between May 1 and early October to be . This is up 4% compared to the last year’s figure — another record high — with the elderly particularly affected by a combination of high temperatures and high humidity.
Iijima also warns that tends to create more powerful typhoons.
Typhoon Nakri passed through the Izu island chain south of Tokyo on Monday, a week after Typhoon Halong hit the same area. The first storm caused one fatality but also damaged buildings across the islands and triggered landslides. The JMA said winds from Typhoon Nakri gusted up to 180 kilometers per hour (112 miles per hour) and brought unusually large amounts of rain.
“Sustained high surface water temperatures near Japan enable these typhoons to last longer and become more powerful and destructive,” said Iijima. “And as conditions get even hotter, then that will make them even more dangerous.”
No more spring and autumn?
Research conducted by a team led by Yoshihiro Tachibana, a professor in Mie University’s Department of Environmental Science and Technology, has determined that have become three weeks longer between 1982 and 2023 as a result of climate change.
“This is because of global warming and sea surface temperatures becoming warmer and warmer around Japan,” Tachibana said, pointing out that sea temperatures around Japan are rising two or three times faster than elsewhere on the planet.
“This is due to high summer temperatures, which are even higher here than elsewhere in the world because of warmer westerly winds, and the impact of the warm Kuroshio current, which brings water from the tropical Pacific to Japan,” he said.
While Japanese summers are now longer, winters have tended to remain of a similar duration due to the nation’s exposure to Arctic winds, Tachibana said. Autumn and spring, however, are contracting.
“I expect Japanese summers to continue to get longer because of global warming, which means that spring and autumn will get even shorter,” he said. “In as little as 30 years, they could effectively disappear unless something is done to halt the effects of global warming. But if not, then in 30 years Japan will become a nation of only two seasons.”
Edited by: Darko Janjevic
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