John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
This generation is doomed to more frequent and extreme heat waves, but researchers say the next one can benefit if we act on emissions now.
Hot weather during 2012, in a word, sucked. Unprecedented high temperatures pushed the planet to one of the top-10 warmest years on record; in the United States, it was the hottest year known to humankind, with a particularly brutal heat wave punishing citizens in the summer. Dozens of people died, highways buckled, and farmers kicked at barren fields during the worst drought in 50 years.
Well, guess what: There could be plenty more of these awful heat waves waiting in the pipeline. Even if humanity immediately takes drastic steps to reduce greenhouse-gas emissions, periods of extreme heat will be commonplace until at least 2040, according to a new study in Environmental Research Letters.
The gears are already in motion for more frequent, more severe heat waves, say European climatologists Dim Coumou and Alexander Robinson. They used a computerized climate model to suss out how many bad and how many really bad heat waves – dubbed "3 sigma" and "5 sigma" events, respectively – could arrive in the future. Their results indicate that three-sigma scorchers, equivalent to the one that hit the U.S. last year, will likely cover four times more global-land surface in 2040 than they do today. And the peak-of-misery 5 sigmas will go from "being essentially absent in the present day" to cover 3 percent of the planet's surface by 2040.
To condense their message, millions of people are in for decades of discomfort and premature death (like the 650 who reportedly died due to this July's heat wave in Britain). The amount of misery we want to put up with in the second half of the century is up to us, the researchers say:
After then, the rise in frequency of extreme heat waves becomes dependent on the emission scenario adopted. Under a low emission scenario, the number of extremes will stabilise by 2040, whereas under a high emission scenario, the land area affected by extremes will increase by one per cent a year after 2040....
Under a high emission scenario, the projections show that by 2100, 3-sigma heat waves will cover 85 per cent of the global land area and five-sigma heat waves will cover around 60 per cent of global land.
This incoming swarm of heat waves has already started to manifest itself, the scientists say, especially in tropical areas that had abnormally hot stretches from 2000 to 2012. Noting that these meteorological events kill crops and livestock, drive up human mortality, and set the stage for impossibly fierce forest fires, they add that the heat is "likely to pose serious challenges to society."
Top image: A dried-up riverbed during this August's heat wave in Zhejiang Province, China. (William Hong / Reuters)