New research finds greenhouse gas slowing heatwaves to a crawl, prolonging misery

The changes, attributed mostly to human-caused climate change, have sped up since 1997, a newly published paper says.

A blazing month-long heatwave throughout March has brought drought, parching the land in Vietnam's southern Ben Tre province, 130km south of Ho Chi Minh City. Picture: AFP

Climate change is causing heatwaves to slow to a crawl, exposing humans to extreme temperatures for longer than ever before, a study published in Science Advances said.

While previous research has found climate change is causing heatwaves to become longer, more frequent and more intense, the new paper differed by treating heatwaves as distinct weather patterns that move along air currents, just as storms do.

For every decade between 1979 to 2020, researchers found heatwaves slowed down by an average of 8km 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 said.

Millions of Australians sweltered during the 2023-24 summer as severe heatwaves hit throughout the country.

James Cook University scientists doing regular reef surveys have reported severe coral bleaching this summer in the waters around Great Keppel Island, Queensland.

The researchers divided the world into three dimensional-grid cells and defined heatwaves as a million square kilometre 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 man-made 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.

A vendor prepares crushed ice at a fresh market in Bangkok on March 29 as Thailand braces for more hot weather with temperatures expected to rise above 40 degrees during a severe heatwave period. Picture: AFP

Record temperatures in March drove Brazilian residents of Rio de Janeiro and Sao Paulo to pour on to beaches and parks. Picture: AFP

A heatwave aggravated water shortages in Mexico, with more than 20 million people suffering since January in many neighbourhoods. Picture: AFP

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 heatwaves 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-travelling and slower-moving large contiguous heatwaves 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 centres for some folks, in particular for the disadvantaged population, will be very dangerous,” he warned.