Hot and humid temperatures in South Asia, which contains one-fifth of the global population, will exceed the upper limit of human survivability by the late 21st century, scientists project, underscoring an urgent need to adopt alternative strategies on top of those currently proposed to alleviate climate change-induced temperature extremes. In 2015, the fifth deadliest heat wave in recorded history affected large parts of India and Pakistan, claiming around 3,500 lives. Many studies in South Asia have charted the trajectory of heat waves linked to climate change and their impact on human health; however, the forecast of "wet-bulb temperature," or a measure of temperature, humidity and the human body's ability to cool down in response, is not yet clear. After running high-resolution simulations under two climate scenarios, Eun-Soon Im and colleagues reveal wet-bulb temperatures are projected to approach the survivability threshold (35 degrees Celsius) over most of South Asia, and exceed it at a few locations, by the end of the century under a business-as-usual (BAU) scenario, while reaching dangerous levels (over 31 Celsius) under a mitigation scenario (roughly comparable to the goals pledged by the 2015 UN Conference on Climate Change). The authors also found that the population exposed to harmful wet-bulb temperatures will increase from zero in the present day to about 30% under BAU versus only 2% under the mitigation timeline – a substantial difference that points to the significant impact of climate change mitigation efforts. The increase in humid heat raises important questions of environmental justice in agricultural areas where the inhabitants – the majority of whom work outdoors and have poor access to air conditioning – are most vulnerable, the authors say.
Elfatih A. B. Eltahir