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Deadly heat stress threat…

Deadly heat stress threat… 17 July 2017

Deadly heat stress could threaten hundreds of millions even if climate targets are reached
(via Acclimatise)

By Tom Matthews

Deadly heat stress is projected to affect hundreds of millions more people each year under relatively little additional climate warming. The Paris Agreement commits the international community to limit global warming to no more than 2? above pre–industrial (late 19th century) air temperatures, with an aspirational target of 1.5?. In our latest research, which looked at the impact of global temperature rises on megacities, we found that even if 1.5? is achieved, large increases in the frequency of deadly heat are expected.

By 2050 about 350m more people living in megacities could be exposed to deadly heat each year.

Humans become “heat stressed” when the body absorbs more heat than is tolerable. If core body temperature rises just a few degrees above 37?, deadly heatstroke can result. By using its cooling system – sweating – the human body can maintain a safe temperature even if air temperatures rise above 37?. This mechanism works better in a drier atmosphere (which is why steam rooms feel hotter than saunas – even at the same air temperature). The heat index is a measure that combines this humidity effect with air temperature to provide a “feels like” temperature. A heat index in excess of about 40.6? is considered dangerous to human health.

As global air temperatures rise, observations and experiments with climate models suggest that atmospheric moisture content also climbs. This means that the heat index (and how hot it feels) rises faster than air temperature. Also, because the amount of moisture the atmosphere can hold increases more rapidly at higher temperatures, the heat index rises faster too (a non–linear response).

Read more via Acclimatise…