While previous research has found climate change is causing heat waves to become longer, more frequent and more intense, the new paper differed by treating heat waves as distinct weather patterns that move along air currents, just as storms do.
For every decade between 1979 to 2020, researchers found heat waves slowed down by an average of five miles (eight kilometers) an hour per day.
"If a heatwave is moving slower, that means heat can stay in a region longer, so that has effects on communities," senior author Wei Zhang of Utah State University told AFP.
The researchers divided the world into three dimensional-grid cells and defined heat waves as a million square kilometer zones where temperatures reached at least the 95th percentile of the local historical maximum temperature. They then measured their movement over time in order to determine how fast the hot air was moving.
They also used climate models to determine what the results would have looked like absent human-caused climate change, and found manmade factors loomed large.
"It's pretty clear to us that a dominant factor here to explain this trend is anthropogenic forcing, the greenhouse gas," said Zhang.
The changes have accelerated in particular since 1997 and in addition to human causes, weakening upper atmospheric air circulation may play a part, the paper said.
The duration of heat waves also increased, from an average of eight days at the start, to 12 days during the last five years of the study period.
"The results suggest that longer-traveling and slower-moving large contiguous heat waves will cause more devastating impacts on natural and societal systems in the future if GHG keep rising, and no effective mitigation measures are taken," the authors wrote.
Zhang said he was worried by the disproportionate impacts on less-developed regions.
"In particular, cities that don't have enough green infrastructure or not many cooling centers for some folks, in particular for the disadvantaged population, will be very dangerous," he warned.
Humanitarian orgs raise alarm on heat as summer nears
Washington (AFP) Mar 28, 2024 -
Extreme heat is one of the most deadly problems from climate change even though it receives less attention than other knock-on effects like hurricanes and flooding, two of the world's leading humanitarian organizations warned Thursday.
The year 2023 was the hottest on record, with rising temperatures affecting the most vulnerable populations in particular -- the elderly, outdoor workers and those without access to cooling systems such as air conditioners.
The Red Cross and the US Agency for International Development delivered their warnings against the "invisible killer" of extreme heat at a virtual summit, on the heels of the United States exiting its warmest-ever winter on record.
"We are calling on governments, civil societies, young people and all the stakeholders to take concrete steps around the globe to help prepare countries and communities for extreme heat," said Jagan Chapagain, secretary general for the International Federation of Red Cross and Red Crescent Societies.
USAID chief Samantha Power warned that in the United States, "heat is already deadlier than hurricanes, floods and tornadoes combined."
"We are calling on development agencies, philanthropies and other donors to recognize the threat that extreme heat poses to humanity, and to put resources towards helping communities withstand that threat," she said.
Highlighting ongoing efforts addressing extreme temperatures, Power said USAID was supporting a program to build "heat resilient schools" in Jordan, using "passive heating and cooling systems, thermal insulation, double glazed windows and air conditioning."
Climate change's effects aren't limited to already hot places like the Middle East: in Europe, the fastest-warming continent in the world, more than 60,000 people were estimated to have died in heat waves in 2022, noted US climate envoy John Podesta.
"Climate information and services including early warnings can save lives and assets," he added. "But one-third of the world's population doesn't have access to this life-saving information."
Other efforts include those in Freetown, the capital of Sierra Leone, where nearly a million trees have been planted since 2020.
"But we mustn't allow this conversation to let anyone off the hook when it comes to reducing emissions," Freetown Mayor Yvonne Aki-Sawyerr said.
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