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256. Survival Limit Temperature Rise in Tropical Regions due to Global Warming

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Spring has just arrived and summer is still ahead, but in recent summers, the intense heat and humidity add to the feeling of discomfort. A study published in Nature Geoscience in March 2021 focused on a measure called wet-bulb temperature, an integrated temperature–humidity metric for the health impact of heat, and predicted wet-bulb temperatures on a regional scale that were not covered by traditional climate change models. Cooling of the human body due to sweating is suppressed as the wet-bulb temperature (and relative humidity) of the surrounding air increases. The wet-bulb temperature is 35°C, which is the limit of survival for humans, and even healthy young people are at risk of life in environments above that. Currently, there are very few areas where the wet-bulb temperature has reached 35°C, but it is predicted that as global warming progresses, there may be days when dangerous high temperatures would be reached in South Asia and the Middle East in the 21st century.

Extremely high temperatures under global warming are a concern, especially in the tropics, where population growth is expected to continue. According to the paper, every time the average temperature in the tropics warms by 1°C, the wet-bulb temperature rises by about 1°C in the area between 20 degrees north and south latitudes. The paper argued for the need to minimize the possibility that tropical regions would exceed the human survival limit of 35°C wet-bulb temperature by limiting post-industrial temperature rise to 1.5°C.

As mentioned in a previous Pick Up article, according to The Lancet Health and Climate Change Countdown 2020 Report, climate change puts at risk the health of vulnerable people. Over the last 20 years, heat stroke-related mortality in groups aged 65 and over has increased by 53.7% compared to the previous 20 years, with 296,000 reported in 2018, most of them in Japan, eastern China, northern India and central Europe. In India and Indonesia, heat waves have reported a loss of economic productivity equivalent to 4-6% of GDP in terms of labor. In response to the global issue of climate change, the international community needs to share information on the risks associated with the issue and effective countermeasures, and take immediate mitigation and adaptation measures.


Projections of tropical heat stress constrained by atmospheric dynamics, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00695-3, dx.doi.org/10.1038/s41561-021-00695-3

Contributor: IIYAMA Miyuki (Research Strategy Office)