When heatwaves swept across large parts of the planet last summer, oppressive temperatures lasted for days or even weeks in lots of places. According to researchers, as climate change warms the planet, heatwaves have gotten slower and last more study published Friday.
The study found that in each decade between 1979 and 2020, the pace of warmth waves, pushed by air circulation, slowed by about 5 miles a day. Heatwaves now last on average about 4 days longer.
“This really has a big impact on public health,” said Wei Zhang, a climate scientist at Utah State University and one in every of the authors of the study, which appears within the journal Science Advances.
The longer heatwaves last in a single place, the longer persons are exposed to life-threatening temperatures. As employees decelerate during extreme heat, economic productivity also declines. Heatwaves also dry out soil and vegetation, harming crops and increasing the danger of wildfires.
Dr Zhang says these changes in heat wave behavior have been more noticeable because the late Nineteen Nineties. He attributes these changes largely to human-caused climate change, but in addition partly to natural climate variability.
The study is one in every of the primary to trace how heatwaves move each in space and time.
Rachel White, an atmospheric scientist on the University of British Columbia who was not involved within the paper, said she had been waiting for such research.
“We know that climate change is increasing the intensity of heatwaves. We know that climate change is increasing the frequency of heatwaves,” Dr. White said. “But this study really helps us better understand how it happens.”
Dr. Zhang and his colleagues analyzed temperatures around the world from 1979 to 2020. They defined heatwaves as contiguous areas totaling at least 1 million square kilometers (247 million acres) in which temperatures rose to at least the 95th percentile of the local historical maximum temperature (essentially huge blobs of extremely hot air). Heatwaves also had to last at least three days. The scientists then measured how far these giant air masses moved over time to calculate their speed.
Over all the years they studied, heat waves slowed by about 5 miles a day each decade, or nearly 5 miles a day each decade.
The average duration of heatwaves has also increased: they lasted an average of 12 days in 2016-2020, compared with eight days in 1979-1983. These longer-lasting heatwaves also travel further, increasing the distance they travel. they cover approximately 226 kilometers per decade.
Scientists also found that heatwaves are becoming more frequent, with an average of 98 per year between 2016 and 2020, up from 75 per year between 1979 and 1983.
There are some regional differences. Heat waves last longer, especially in Eurasia and North America. They travel further, especially in South America.
To investigate the role of climate change, researchers used models to simulate temperatures under scenarios with and without warming caused by human greenhouse gas emissions. They found that a scenario that included these emissions best matched the actual pattern of heatwaves, indicating that climate change is the main driving force behind these trends.
Scientists have begun to detect a larger pattern of air and wind circulation in the upper atmosphere, such as a weakening jet stream, at least in summer at higher latitudes in the Northern Hemisphere. This can cause all kinds of extreme weather events to stop and prolong their hospitality.
“It’s clear that this is able to decelerate the speed of warmth waves,” said Stephen Vavrus, Wisconsin’s state climatologist. Dr. Vavrus studies atmospheric circulation but was not involved in this research.
A new study has found a correlation between weaker jet streams and slower heatwaves. However, Dr. White believes that further research is needed to determine whether jet stream is indeed the cause.
Regardless of the exact causes of the slowdown, the harmful effects remain.
“It’s kind of a confluence of factors,” Dr. Vavrus said. If heatwaves become more frequent, more intense, last longer and cover a larger area, “that basically increases our concern about their impacts,” he said.
Dr. Zhang is particularly concerned about cities, which are often warmer than their neighborhoods due to the urban heat island effect. “If these heat waves proceed in town for much longer than before, it would create a really dangerous situation,” he said.
In addition to atmospheric research, Dr. Zhang is helping local efforts plant more trees and grasses around bus stops in Salt Lake City, where people must wait in the sun during increasingly hot summers. He suggested that cities build more cooling centers, especially for people experiencing homelessness.
“There are some things the community can do,” he said.
While waiting for international leaders to make progress on reducing greenhouse gas emissions and stopping climate change, Dr. Zhang said local adaptation efforts are important to keep people safe.
