Millions of Americans are feeling the heat again. Europe was blanketed in hot air last weekend, with parts of France and Spain feeling the same heat as it does in July and August. High temperatures scorched northern and central China even as heavy rains caused flooding in the country’s south. Some parts of India experienced extreme heat from March to the beginning of the monsoon rains, which has provided some relief.
It’s too soon to say whether climate change is directly to blame for causing severe heat waves in these four powerhouse economies — which also happen to be the top emitters of heat-trapping gases — at roughly the same time, just days into summer.
Global warming is making extreme heat more common, but scientists need to do deeper analysis to determine if certain weather events are more likely or more intense due to human-induced warming. (A team of researchers who studied this spring’s devastating heat in India found that climate change had made it 30 times as likely to occur.)
Concurrent heat waves still seem to be hitting far-flung locations with increasing frequency of late. This is due to the jet stream, and other rivers of air, that influence weather systems all over the globe.
Studies have shown this link between parts of North America, Europe, Asia. Scientists are still trying to determine how these patterns might change as the planet warms further, but for now it means simultaneous heat extremes will probably continue affecting these places where so much of the world’s economic activity is concentrated.
“To have a heat wave, we need the heat, and we need the atmospheric circulation pattern that allows the heat to accumulate,” said Daniel E. Horton, a climate scientist at Northwestern University. With global warming, he said, “we’re definitely getting more heat.” But climate change may also be affecting the way this heat is distributed around the world by globe-circling air currents, he said.
Simultaneous weather extremes in numerous locations aren’t just meteorological curiosities. Individual heat waves can result in crop failures, wildfires and illness. Concurrent ones can threaten global food supplies, which have been under perilous strain this year because of Russia’s invasion of Ukraine.
Scientists are now able to say that climate change is making heat waves worse. Heat waves are influenced by local factors like urbanization and land use. Soon, the world’s most devastating heat waves may simply have no historical analogue from the time shortly before humans starting pumping greenhouse gases into the atmosphere, some scientists argue, rendering obsolete the question of whether climate change is a main driver.
The warming of recent decades has already made it hard for scientists to know what to call a heat wave and what to treat as simply a new normal for hot weather, said Andrew Dessler, a climate scientist at Texas A&M University.
If the threshold for a heat wave is just the mercury exceeding 100 degrees Fahrenheit for days in a row, for instance, then it’s “not at all unexpected,” Dr. Dessler said, to see them occurring more regularly in several regions at once. “As time goes on, more and more of the planet will be experiencing those temperatures, until eventually, with enough global warming, every land area in the mid-latitude Northern Hemisphere would be above 100 degrees,” he said.
However, scientists still find an increase in simultaneous heat waves despite looking at how often temperatures exceed a specific level relative to a moving mean.
This was confirmed by a recent study, which found that the average number days in May and September with at most one heat wave in the Northern Hemisphere grew to around 152 from just 73 between the 1980s. However, the number of days with at least two heat waves per day was seven times more than it was 20 years ago. It grew to 143 from 73. That’s nearly every single day from May to September.
The study also revealed that concurrent heat waves were more severe in 2010s than in 1980s. Peak temperatures were nearly one-fifth higher now than they were in 1980s. The study found that there were an average of 3.6 heat waves per day in the Northern Hemisphere on days when there was at most one large heat wave.
These “dramatic” increases came as a surprise, said Deepti Singh, a climate scientist at Washington State University and an author of the study.
Dr. Singh and co-authors also examined the locations where concurrent heat wave events occurred most often during those four decades. One pattern stood out: Large simultaneous heat waves struck parts of eastern North America, Europe, and central and eastern Asia increasingly often between 1979 and 2019 — “more than what we would expect simply by the effect of warming,” Dr. Singh said.
She stated that the study did not attempt to predict whether heat wave patterns along this pattern will become more frequent with global heating.
Scientists are trying to determine how the jet stream’s meandering, which has long shaped weather patterns and influenced the lives of billions of people, might be changing with the advent of global warming. One factor is the rapid heating of the Arctic, which narrows differences in temperatures between the Northern Hemisphere’s northern and southern regions. It is still unclear how this could affect extreme weather.
These temperature variations are key drivers of the winds that keep weather systems on the planet moving. These air currents could be slowing down as the temperature differences shrink, according to Kai Kornhuber, a climate science researcher at Columbia University’s Lamont-Doherty Earth Observatory. Extreme events like heat waves, heavy downpours, and other extreme weather will likely last longer.
“The longer a heat wave lasts, the more you push natural and societal systems to the edge,” Dr. Kornhuber said.
He stated that climate change already means that the world will experience more extreme weather events and more extremes simultaneously. “These circulation changes, they will act on top of it,” he said, “and would make extremes even more severe and even more frequent.”
Source: NY Times
