Why intense heatwaves are more likely due to climate change

The scorching heat across five continents in recent days has provided further evidence that human-caused global warming has raised the baseline for normal temperatures so much that once-unthinkable disasters have become commonplace, scientists say.

The suffering came despite predictions that a year-long global heatwave could soon begin to ease. Instead, in the last seven days alone, billions of people have felt heat of an intensity fueled by climate change, which has broken more than 1,000 temperature records around the world. Hundreds fell in the United States, where tens of millions in the Midwest and East Coast were sweltered by one of the worst early-season heatwaves in memory.

“It should be obvious that dangerous climate change is already upon us,” said Michael Wehner, a climate scientist at Lawrence Berkeley National Laboratory. “Even today, people are going to die because of global warming. »

Researchers say much of this week’s heat occurred after the dissipation of the El Niño weather phenomenon – which typically raises global temperatures – shows how greenhouse gas pollution has pushed the planet into scary new territory. Scientists expected this summer to be a little cooler than 2023, which was the warmest in the Northern Hemisphere in at least 2,000 years.

But with summer 2024 just beginning, there are worrying signs that even more scorching conditions could still be on the horizon.

June is already almost certain to set a 13th consecutive monthly record for global average temperature, said Zeke Hausfather, a climatologist who works for the payments company Stripe. Next month, he added, the planet could approach or exceed the highest global averages ever measured.

It is not yet clear whether the unyielding trend of record temperatures will ease soon, with an expected transition from El Niño to its colder counterpart, La Niña, scientists said. Scientists also continue to analyze individual extreme weather events to determine how much, if at all, climate change has influenced them.

What’s obvious: how humans have caused baseline temperatures to rise.

“We have the highest greenhouse gas concentrations in the last 3 million years. Carbon dioxide traps heat, which increases the planet’s temperature,” said Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration. “It’s very simple physics.”

“Exceptional” heat arrives earlier and lasts longer

While not all of the temperatures seen around the world this week were unprecedented, they nonetheless reflect how the climate has changed in ways that make warm temperatures more likely to arrive earlier and last longer .

For about 80% of the world’s population, or 6.5 billion people, last week’s heat was twice as likely because humans had started burning fossil fuels and releasing greenhouse gases. greenhouse in the atmosphere, according to data provided to the Washington Post by the nonprofit organization. Climatic plant.

Nearly half of that number experienced what Climate Central considers “exceptional heat” – conditions that would have been rare, if not impossible, in a world without climate change.

“What really stands out is the number [heat waves] are happening at the same time,” said Andrew Pershing, director of climate science at the nonprofit.

Throughout the week, “exceptional” conditions could be observed across much of Africa, the Middle East, southern Europe and Southeast Asia. Growing demand for air conditioning has crippled power grids in Albania and Kuwait. According to the National Oceanic and Atmospheric Administration, last week, more than 1,400 high temperature records were recorded around the world.

Since the beginning of the era of industrial burning, human activities – primarily fossil fuels – have warmed the planet by about 1.2 degrees Celsius (2.2 degrees Fahrenheit). Earth’s temperature over the past 12 months has been even higher, averaging about 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels.

To assess how much warming increases the likelihood of a given heat event, Climate Central uses several global climate models to calculate how often this temperature would have occurred in the pre-industrial climate and how often it is reached today today. The technique, which has been peer-reviewed and published in an academic journal, highlights how warming has increased the risks of temperatures reaching the limit of what people can tolerate.

The mercury in Hartford, Connecticut, reached 98 degrees Fahrenheit on Thursday, the highest temperature ever recorded for that day. Climate Central’s analysis found that these conditions are twice as likely under current levels of warming – and they will only occur more often as the planet continues to warm.

Peter Fousek, secretary-treasurer of the Connecticut Tenants’ Union, spent the past few days going door to door in overheated buildings to see if low-income residents were accustomed to such prolonged and intense heat. He remembers an East Hartford man who showed up at the door sweating, while the old air conditioner whistling in the background did little to keep his apartment cool.

“It’s really terrifying to see the way these heat waves are occurring in this increasingly unstable climate,” Fousek said.

Climate change doesn’t just make high temperatures and other extreme events more likely, Wehner said. It also makes every disaster that occurs more intense.

Wehner’s research found that heat waves like the one currently unfolding in the United States are now about 2 to 3 degrees Celsius (3 to 5 degrees Fahrenheit) hotter because of how humans have altered the planet . Severe hurricanes are at least 14 percent wetter because the warmer atmosphere can hold more moisture. And storm surges are occurring in oceans that in some places are more than a foot higher than they were a half-century ago, allowing floodwaters to reach heights never seen before.

“We have predicted for at least two decades that extreme weather would become even more dangerous as the planet warms,” Wehner said. “It is not a surprise.”

Early summer heat could portend more world records

Global warmth is to be expected after a historically strong El Niño developed this winter and dissipated earlier this month, climate scientists said. The same thing happened in 2016, which was the hottest year observed since at least the 1850s – until a global heat wave began breaking those 8-year-old records ago a year.

But this time, eight additional years of planet-warming greenhouse gas emissions mean the natural increase in global heat is pushing the planet even further into uncharted territory, McPhaden said. This is despite the fact that the last El Niño was “not in the same category” as the supercharged phenomenon of 2015-2016.

“The impacts of this event were amplified by the warm background conditions,” McPhaden said. “What had been intense El Niño rain became extreme El Niño rain. »

El Niño, during which unusually warm waters from the Pacific rise to the surface and transfer large amounts of heat into the atmosphere, has footprints all over the world, including heat in the south and east of the Asia and heavy rains in East Africa. Those fingerprints were particularly pronounced, not because the El Niño phenomenon was excessively strong, but because it developed in a world where greenhouse gas emissions continue to rise, McPhaden said.

“These effects that we typically associate with a stronger El Niño were much stronger simply because this El Niño occurred in a much warmer world,” he said. “It’s no longer just the temperature of the Pacific that matters. The question is, what is the global reference temperature over which El Niño develops? »

Although El Niño is over, the echo of its warming influence appears increasingly likely to push 2024’s average annual temperatures above the record set in 2023, Hausfather said.

For June, global temperatures are expected to be just 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels, Hausfather said.

Last July, global average temperatures were the warmest ever observed by scientists – the hottest, they estimate, in more than 100,000 years. It’s possible the planet will pass that milestone next month, Hausfather said, and it’s almost certain it will get close.

Climatologists predict that the end of El Niño will lead to a global cooling trend, but they haven’t seen it happen yet.

“If temperatures remain at current high levels, we would be about on par with last July,” Hausfather said. “It’s super hot anyway. It’s just a question of whether it’s hotter than expected or not?

About a month ago, Hausfather said he believed the chances of the planet hitting another average temperature record next month were relatively slim. The odds more recently seem to be around 50/50, he said. And after seeing such shocking heat over the past year, he said he was too “humble” to bet against another record.

John Muyskens contributed to this report.