Monday, June 19, 2017

Half of World Could See Deadly Heat Waves by 2100

Average daily surface air temperature and relative humidity during lethal heat events (black crosses) and during non-lethal heat event of equal duration from the same cities (the red to yellow shading indicates the number of such non-lethal events). The blue line broadly separates lethal and non-lethal heatwave events, but the red line is a conservative estimate beyond which all events were deadly. [Source: Mora et al. (2017)] Click to Enlarge.
Even with drastic cuts to the emissions of greenhouse gases that are driving up Earth’s temperature, more than half of the world’s population could be exposed to deadly heat waves by century’s end.

If emissions continue on their current path, that proportion will jump to three-quarters of the world’s residents, due to both rising temperatures and humidity, a new study detailed Monday in the journal Nature Climate Change, finds.

That future is what study author Camilo Mora calls a choice between “bad and terrible,” but crucially, it is still a choice.  If the world reduces emissions, it can reduce the impacts of warming as much as possible.

Societies will also have to adapt to rising temperatures and the higher risks to human health they bring, but it is the developing countries that are least able to adapt that are likely to be hit the hardest.

“The projections of future risk to human health are sobering,” Michael Wehner, a senior staff scientist at Lawrence Berkeley National Laboratory who wasn’t involved in the study, said in an email, citing the particular risk to developing nations.  “I welcome this paper for highlighting this inequity and for its novel demonstration that changes in the combination of heat and humidity are critical to understanding the effect of global warming on human health.”

A shift to more, and more extreme, heat is one of the clearest outcomes of global warming:  as overall temperatures rise, extreme heat becomes more likely, and extreme cold less likely.  Several studies have shown that warming is already influencing such heat waves.
Using historic data, the team found that 30 percent of the world’s population sees at least 20 days each year that surpass the temperature and humidity thresholds for a deadly event at a given location.

Under even the most stringent cuts to emissions — cuts that are virtually unfeasible at present — that proportion would increase to half by 2100.  If emissions aren’t curtailed at all and continue to increase, 75 percent would be under threat.

In particular, New York City would see 50 days over the threshold considered deadly, while Los Angeles would see 30, and Orlando and Houston would be above those conditions for the entire summer under the latter scenario.

Read more at Half of World Could See Deadly Heat Waves by 2100

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