Why intense heat waves are more likely because of climate change

The scorching heat across five continents in recent days, scientists say, provided yet more proof that human-caused global warming has so raised the baseline of normal temperatures that once-unthinkable catastrophes have become commonplace.

The suffering came despite predictions that a year-long surge of global heat might soon begin to wane. Instead, in the past seven days alone, billions felt heat with climate change-fueled intensity that broke more than 1,000 temperature records around the globe. Hundreds fell in the United States, where tens of millions of people across the Midwest and Eastern Seaboard have been sweltering amid one of the worst early-season heat waves 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. “People will die because of global warming on this very day.”

That much of this week’s heat unfolded after the dissipation of the El Niño weather pattern — which typically boosts global temperatures — shows how greenhouse gas pollution has pushed the planet into frightening new territory, researchers say. Scientists had expected this summer might be somewhat cooler than 2023, which was the hottest in the Northern Hemisphere in at least 2,000 years.

But with summer 2024 just getting started, there are ominous signs that even more scorching conditions may still be on the horizon.

June is already all but sure to set a 13th-consecutive monthly global average temperature record, said Zeke Hausfather, a climate scientist who works for the payments company Stripe. Next month, he added, the planet could approach or surpass the highest global averages ever measured.

Whether the unyielding trend of record heat will ease soon, with an expected transition from El Niño to its cooler counterpart, La Niña, isn’t yet clear, scientists said. Scientists are also still analyzing individual extreme weather events to determine how much climate change influenced them, if at all.

What is obvious: The way humans have caused baseline temperatures to surge.

“We’ve got the highest greenhouse gas concentrations in the last 3 million years. Carbon dioxide traps heat, so the temperature of the planet is rising,” said Michael McPhaden, a senior scientist at the National Oceanic and Atmospheric Administration. “It’s real simple physics.”

‘Exceptional’ heat is arriving sooner and lasting longer

Though not all temperatures seen around the world this week were unprecedented, they were nonetheless evidence of how the climate has shifted in a way that makes hot weather more likely to arrive earlier and last longer.

For some 80 percent of the world’s population — 6.5 billion people — the heat of the past week was twice as likely to occur because humans started burning fossil fuels and releasing greenhouse gases into the atmosphere, according to data provided to The Washington Post by the nonprofit Climate Central.

Nearly half that number experienced what Climate Central considers “exceptional heat” — conditions that would have been rare or even impossible in a world without climate change.

“What is really standing out is how many [heat waves] are happening at the same time,” said Andrew Pershing, the nonprofit’s director of climate science.

All week long, “exceptional” conditions could be found across much of Africa, the Middle East, southern Europe and southeast Asia. Surging air conditioning demand crippled power grids in Albania and Kuwait. According to the National Oceanic and Atmospheric Administration, the past week has seen more than 1,400 high temperature records fall around the globe.

Since the start of the industrial era, human activities — mostly burning 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 hotter, averaging about 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels.

To assess how warming increases the likelihood of a given heat event, Climate Central uses multiple global climate models to calculate how often that temperature would have occurred in the preindustrial climate and how frequently it is reached today. The technique, which has been peer reviewed and published in an academic journal, underscores how warming has juiced the chance of temperatures at the edge of what people can tolerate.

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

Peter Fousek, secretary-treasurer for the Connecticut Tenants’ Union, spent the last few days going door to door in overheated buildings to check on low-income residents who were unaccustomed to such prolonged and severe heat. He recalled one East Hartford man who came to the door dripping with sweat, while the aged air conditioner wheezing in the background did little to keep his apartment cool.

“It’s really kind of terrifying to watch the way these heat waves are happening in this increasingly volatile climate,” Fousek said.

Climate change isn’t just making high temperatures and other extreme events more likely, Wehner said. It also makes every disaster that does occur more intense.

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

“We have been predicting for at least the past two decades that extreme weather would become yet more dangerous as the world warms,” Wehner said. “This is not a surprise.”

Early summer heat could hint at more global records

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

But this time, eight more years of greenhouse gas emissions warming the planet means the otherwise natural boost in global warmth is pushing the planet even further into uncharted territory, McPhaden said. That is despite the fact that the latest El Niño was “not in the same league” as the supercharged pattern of 2015-2016.

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

El Niño, during which unusually warm Pacific waters rise to the surface and transfer vast amounts of heat into the atmosphere, has fingerprints around the globe, including heat across southern and eastern Asia and heavy rainfall in eastern Africa. Those fingerprints were especially pronounced not because this El Niño pattern was excessively strong, but because it developed in a world where greenhouse gas emissions continue to rise, McPhaden said.

“Those effects we typically associate with a stronger El Niño event were much stronger simply because this El Niño occurred in a much warmer world,” he said. “It’s not just the temperature of the Pacific that matters anymore. It is, what’s the global temperature baseline on which El Niño is developing?”

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

For the month of June, global temperatures are likely to be slightly warmer than 1.5 degrees Celsius (2.7 degrees Fahrenheit) above preindustrial levels, Hausfather said.

Last July brought the hottest average global temperatures scientists had ever seen — the hottest, they estimate, in more than 100,000 years. It’s possible the planet surpasses that milestone next month, Hausfather said, and it’s almost certain to come close to it.

Climate scientists have been predicting the end of El Niño will bring a global cooling trend, but they haven’t seen it arrive yet.

“If temperatures stay at current elevated levels, we’d roughly tie last July,” Hausfather said. “Either way, it’s super hot. It’s just a question if, is it hotter than we expected, or not?”

A month or so ago, Hausfather said he estimated relatively slim odds of the planet hitting another record high average temperature next month. The chances have more recently appeared to reach about 50/50, he said. And after seeing such shocking warmth over the past year, he said he is too “humbled” to bet against another record.

John Muyskens contributed to this report.