Heatwave in India breaks records, still worsening
Since we&#x27;re talking about a deadly heat-wave, people will certainly ask what global warming has to do with this. Roughly speaking, global temperatures have increased by about 1 degree Celsius over the past century. So a simple answer is that global warming is responsible for about 1 degree of the 10-degree heat anomaly.<p>But it&#x27;s also important to recall that the human sensitivity to excessive heat depends on humidity. Because the vast majority of the heat burden from global warming is stored in the oceans, and evaporation rates are determined by sea surface temperatures, global warming tends to increase wet-bulb temperatures just as much as dry-bulb temperatures [1]. Since heat waves tend to occur under dry (sunny) conditions, the wet-bulb temperature anomaly is probably smaller than the dry-bulb anomaly, and global warming may play a larger role, perhaps 20%.<p>It&#x27;s also important to remember that the human sensitivity to heat stress has an extremely rapid onset. Under reasonable conditions (shade&#x2F;hydration&#x2F;ventilation), a Tw of 28 C is uncomfortable, but brief exposure (a few hours, while working) rarely causes health issues [2]. The risk of exertional heat injury doubles at 30 C, doubles again at 32 C, and doubles again at 34 C. Above Tw = 35 C, extended survival is not possible [1]. Historically, wet-bulb temperatures on Earth almost never exceeded 31 C [1].<p>So, are the people who die in this heat wave dying because of global warming? Probably some of them. Considering what we have learned about heat stress, it seems plausible that the &quot;rebrand&quot; of global warming to &quot;climate change&quot; was a mistake.<p>[1] S. C. Sherwood and M. Huber, An Adaptability Limit to Climate Change Due to Heat Stress, Proc. Natl. Acad. Sci. U.S.A. 107, 9552 (2010).<p>[2] X. P. Garzon-Villalba, A. Mbah, Y. Wu, M. Hiles, H. Moore, S. W. Schwartz, and T. E. Bernard, Exertional Heat Illness and Acute Injury Related to Ambient Wet Bulb Globe Temperature, Am. J. Ind. Med. 59, 1169 (2016).<p>[2 note] Wet-bulb globe temperature is an adjustment that incorporates sun exposure into heat stress calculations. However, sunlight is easily mitigated. Because humans avoid such conditions, there is not much evidence on human exposure to in-shade Tw above 32 C.