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South America’s Winter Hot Spell Was 100 Times More Likely With Climate Change

August and September mark the end of winter in the Southern Hemisphere, but a large swath of South America spent much of that period in deadly heat that felt much more like summer. Late in this past winter, millions of people in Brazil, Bolivia, Argentina and Paraguay experienced temperatures that exceeded 40 degrees Celsius (104 degrees Fahrenheit)—an event that was made 100 times more likely, and significantly hotter, by climate change, according to a new rapid analysis.

“Worryingly, temperatures above 40 degrees C in spring are becoming common in many parts of the world,” said Izidine Pinto, a researcher at the Royal Netherlands Meteorological Institute and a member of the international World Weather Attribution (WWA) team that conducted the analysis, in a press release. “This is the reality of our rapidly warming climate. We’re now experiencing more and more dangerously hot days each year.”

South America’s unseasonable heat wave has significantly affected crops such as coffee and has killed at least four people—but likely many more because the full scope of the heat-related deaths will take weeks or months to become clear. It has been just one of the many punishing heat events that have affected tens of millions of people around the world in recent months. Such soaring temperatures have combined to help set several global records this year: July was the hottest month in human history, the three months from June to August were the hottest three-month period, and September was likely the most anomalously warm month (meaning its temperatures were the most above a given month’s long-term average).

A tendency toward more extreme heat events and fewer extreme cold ones is a hallmark of the changing climate as humans continue to burn fossil fuels and add to the heat-trapping greenhouse gases in the atmosphere. In parts of South America, the whole winter period was punctuated by intense heat dome events, in which an atmospheric pattern that ushers in extreme heat becomes entrenched. July and August were the hottest such months for the whole continent, and August was the most anomalously warm month on record there. The latter measured a stunning 2.4 degrees C (4.3 degrees F) above average, according to the U.S. National Oceanic and Atmospheric Administration.

In looking for the fingerprints of climate change in extreme weather events, the WWA researchers focused on one of the heat domes that settled over the continent in late September. They looked at the 10 hottest consecutive days in the region where the heat was most extreme, which broadly included Paraguay, central Brazil, and parts of Bolivia and Argentina.

For each of its studies, the WWA looks for trends in historical data and uses computer models to compare today’s climate with a theoretical world without human-caused climate change.

The researchers found climate change made the recent South American event at least 100 times more likely and from 1.4 to 4.3 degrees C (2.5 to 7.7 degrees F) hotter. (There is some uncertainty because of the sparseness of weather records in some of the areas covered by the study.) Such an event would be expected about every 30 years in today’s climate.

But because the world continues to burn fossil fuels, the climate isn’t static. If worldwide average temperatures climb to two degrees C (3.6 degrees F) above the preindustrial period, such an event would be expected to happen every five to six years and would be another 1.1 to 1.6 degrees C (two to 2.9 degrees F) hotter still, the analysis found. The planet has already warmed by about 1.2 degrees C, or 2.2 degrees F, since the preindustrial era.

For the recent South American event, the WWA researchers also considered the possible influence of El Niño, which is a natural climate pattern that features warmer than normal ocean waters in the eastern tropical Pacific Ocean. Those hotter waters release heat into the atmosphere and unleash a cascading impact on atmospheric circulation patterns. This affects weather around the planet and often particularly does so in South America because of its proximity to the eastern Pacific. The current El Niño has been gaining steam and is expected to be a strong one. But the WWA analysis showed El Niño had only a minor effect on South America’s unseasonable weather. “A developing El Niño would have contributed some heat, but without climate change, spring heat this intense would have been extremely unlikely,” said WWA team member Lincoln Muniz Alves, a researcher at the Brazil National Institute for Space Research, in the press release.

Other recent WWA research found climate change exacerbated heat waves in China, North America and Europe earlier in the Northern Hemisphere’s just concluded summer. The team even concluded that the latter two heat waves would have been virtually impossible without the influence of climate change. Another analysis by nonprofit research organization Climate Central found that nearly every person on Earth experienced high temperatures that were made at least twice as likely by global warming, and half of the world’s population felt at least 30 days of extreme heat between June and August.

Extreme heat is a major public health threat, especially when it is unseasonable and where people are less acclimated to higher temperatures. Among the most vulnerable populations are the very young, the elderly, those with existing health conditions such as heart disease and those without access to air-conditioning. People who work outdoors are also particularly susceptible to heat illness and heat stroke.

The WWA researchers additionally found that the most affected South American countries lacked mechanisms to help warn people of the impending heat and connect them with resources such as cooling centers. “Good planning for heat can save lives,” said Julie Arrighi, a WWA team member and interim director of the Red Cross Red Crescent Climate Center, in the press release. “It is absolutely critical that every country and city develops a heat plan.”

The weight of climate science also underscores that it is critical for governments and companies to act rapidly to reduce the emissions of greenhouse gases that are causing such heat extremes.

Source: Scientific American