This century, heat waves are moving slower and lasting longer Premium

Study shows global heat waves are slowing down, lasting longer due to human-induced climate change, impacting health and environment.

Growing up in the 1990s in India meant having seen an ad for a glucose-based drink on television in which the Sun literally sucks the life-force out of children with a giant straw as they are playing. This ad has started to hit closer to reality. India has increasingly been in the grip of more frequent and intense heat waves, with outdoor workers especially struggling with the rising mercury.

A recent study published in Science Advances showed that it wasn’t just India: the whole world is grappling with slower and longer heat waves.

Heat waves have a terrible impact on human and animal life, with increased risk of wildfires, damaged crops, and worse health. Analysing temperatures around the world from 1979 to 2020, Wei Zhang, a climate scientist at Utah State University, and his colleagues studied how they have changed over time.

On average, they found, heat waves have slowed down nearly 8 km/day each decade and lasted longer by about four days — the effects being particularly drastic in North America and Eurasia. Heat waves have also increased in frequency, from about 75 events averaged over 1979-1983 to about 98 over 2016-2020.

“In thinking about heat waves and how they would change in the future, there are two pieces of the puzzle that climate scientists think about,” Rachel White, an atmospheric scientist at the University of British Columbia, said. “One of them is thermodynamics: it’s just about the temperature. As temperatures are getting warmer, heat waves are going to get warmer. The second piece is the dynamics: the atmospheric circulation patterns that cause heat waves.”

There are still some open questions around how those might change in a warming world.”

Previous studies have mostly focused on how frequent heat waves are or how hot it gets during one. In this study, the researchers classified contiguous heatwaves as events with extremely high temperatures, covering more than a million square kilometres, and lasting for longer than three days. They then tracked the movement of these huge masses of hot air over space and time, studying how far and how fast they were moving – one of the first groups of scientists to do so.