We Know What’s Causing This Heat


It’s still very hot, and scientists are getting better at telling us why.

A firefighter running with a hose with a blaze in the background and a tree to the right. The image appears to be tinted orange.
A blaze in New Peramos, Greece, on July 19.Louisa Gouliamaki/Agence France-Presse — Getty Images

Some of the searing temperatures that scorched the United States, Mexico, Europe and China this month would not have happened without human-caused climate change, my colleague Delger Erdenesanaa reports.

Before humans began burning fossil fuels in enormous quantities, this month’s North American and European heat waves would have been “virtually impossible,” according to a newly released statistical analysis. China’s heat wave would have happened only about once every 250 years.

“Without climate change, we wouldn’t see this at all,” said Friederike Otto, a senior lecturer in climate science at Imperial College London and co-founder of World Weather Attribution, the group that produced a study released today, at a press briefing. “Or it would be so rare that it basically would not be happening.”

How can scientists like Dr. Otto be so sure?

Extreme weather was around long before humans were burning fossil fuels, of course. Yet over the past couple hundred years, man-made emissions have heated the planet. And when the world is warmer, heat waves, hurricanes, droughts and fires all get more intense.

The body of research that measures these odds — how much more likely certain weather events are thanks to climate change — is called attribution science. That’s a rather dry name that undersells the urgent detective work of figuring out a crucial question: When extreme weather happens, is climate change to blame?

To conduct attribution studies, scientists use powerful computers to compare two versions of the global climate. One version is a model of the real world we live in, where man-made emissions have warmed the planet an average of 1.2 degrees Celsius (2.1 degrees Fahrenheit). The other version, known as the “counterfactual world,” is a model without man-made emissions.

When events like this month’s blistering heat waves hit, the scientists compare the models and see if they can detect the fingerprints of human activity.

“A heat wave so severe could still have occurred even if humans hadn’t been heating up the planet,” my colleague Raymond Zhong, who reports on climate science, told me. “But the chances, in that world, would most likely have been slimmer. And a similarly rare heat wave would have been less intense.”

The first attribution study is generally considered to be a 2004 paper titled “Human Contribution to the European Heat Wave of 2003.”

Since then, scientists have gotten much better at figuring out the links between climate change and specific extreme weather events — and they’re doing it much more quickly.

World Weather Attribution, the scientific collaboration that conducted this latest study, “has boiled attribution analysis down to a set of standardized steps,” Zhong told me.

This has allowed researchers to study extreme weather “very quickly after it happens, sometimes within days, so people can understand, in near real time, the science behind the severe weather they’re experiencing,” he said.

The scientists affiliated with WWA aren’t the only ones out there who are doing this sort of analysis. Lots of other researchers around the world are conducting their own attribution studies, many of which are collected in a special report produced by the American Meteorological Society each year.

The field has been slower to grow in the developing countries suffering some of the harshest effects of climate change. Weather stations (and therefore, data) are scarcer in poorer nations, as are other scientific resources.

And attribution studies don’t always find the fingerprints of human activity in extreme weather events. Sometimes, they conclude that a heat wave, a storm or a drought was entirely natural.

For example, last year’s lack of rainfall that led to drought in Uruguay and Argentina was not made more likely because of man-made emissions, scientists concluded earlier this year. That’s valuable research, too.

“It’s a reminder that the weather can be scary and destructive and unpredictable enough even without the influence of global warming,” Zhong said.

Attribution studies offer us a peek into the future of our warming world.

“If scientists find that climate change made a particular weather event in a particular place much more likely, then we know to expect more of this kind of event there going forward, because humans are still warming the planet,” Zhong told me. “It tells us the kind of weather that today is considered exceptional but in the future will be more commonplace.”

Attribution studies are also being used as evidence in court cases.

Hundreds of lawsuits have been filed against fossil fuel companies, and a growing number of them cite attribution science as proof that human-caused climate change is to blame for costly extreme weather.

Two lawsuits (including the Puerto Rico case we covered last week) have recently gone even further, suing fossil fuel companies for damages from specific weather events.

“The science is there to make those claims in court and draw those connections,” said Michael Burger, the executive director of the Sabin Center for Climate Change Law at Columbia University. Much harder, he said, will be pinning the warming that led to a specific weather event on a single company.

Residents getting water from a tanker truck near the dried-up Lake Hamun in Zabol, Iran, in May.Mohammad Dehdast/DPA, via Getty Images

Taps across Iran are running salty or dry. One province is expected to run out of water entirely by September, my colleagues Vivian Yee and Leily Nikounazar reported this week.

Iran is especially vulnerable to global warming. Its sprawling desert combines with humidity coming from the nearby Persian Gulf to produce conditions that can surpass what humans can tolerate. Last Sunday, at the Persian Gulf Airport, the heat index — a measure of temperature and humidity — reached 152 degrees Fahrenheit, or 66.7 Celsius.

Climate shocks have added to what Kaveh Madani, a United Nations water expert, has called “water bankruptcy.” It’s the consequence of policies that were meant to make Iran self-sufficient in food but instead have depleted its water supplies beyond repair.

Iran’s stalled economy and double-digit inflation means much of its population is too poor to cope. Many can’t afford to buy water brought in from other parts of the country, and air-conditioning units are even farther out of reach.

Water shortages could fuel political instability in a moment when protest movements that started by targeting the morality police are still challenging the government. The Washington Post reported that, a few days ago, the head of Iran’s Islamic Revolutionary Guard Corps warned against demonstrations during a visit to Khuzestan Province, where water shortages incited protests in 2021. During a record-breaking summer, more discontent could be on the way. — Manuela Andreoni

  • An international agency delayed the start of industrial-scale seabed mining after pressure from environmental groups and a group of nations including Costa Rica, Chile and France.

  • Heavy rainfall and heat waves are causing food shortages in India.

  • Venezuela’s oil industry, hobbled by decades of mismanagement and U.S. sanctions, has become a major source of pollution.

  • London politics are being roiled by an expanding tax on polluting vehicles, Ali Griswold writes in Oversharing.

  • The Guardian explained the psychology behind why we aren’t more scared of climate change. It has to do with the way we experience fear and our tendency to adapt.

  • Community gardens in the Bronx are tempering the effects of climate change by absorbing water and emissions.

The brutal summer heat that has blanketed the Southwest into Texas and down to South Florida will expand to other parts of the country, first into the central United States and then farther east.

On Tuesday, the heat will move into the central United States with temperatures 10 to 20 degrees above normal. Heat index readings, which consider both temperature and humidity, will reach into the 100s. About 55.2 million people — 17 percent of the population of the contiguous United States — live in the areas expected to have dangerous levels of heat.

By Thursday and Friday, temperatures and humidity levels will rise in the Mid-Atlantic and Northeast, causing sweatier-than-normal conditions.

Yes, but probably not soon.

For weeks, the culprit in the Southwest has been a “heat dome” of high pressure. As it shifts east, temperatures in the region may ease by the weekend, but not before setting more records. Forecasters warn that Phoenix is likely to extend a streak of hitting at least 110 degrees, which is currently at 24 days.

Record streaks in the desert Southwest may come to an end this weekend or early next week, with forecast models hinting that temperatures may return to normal summertime readings.

But in the Central Plains and across the Southeast, forecasters see a moderately high likelihood of above-average temperatures next week. — Judson Jones and John Keefe

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