Poll workers. Pilgrims. Tourists on a hike.

All have died in blistering heat in recent weeks around the world, a harrowing reminder of the global dangers of extreme weather as a severe heat wave bears down on more than 70 million Americans this week.

Dozens of cities in Mexico broke heat records in May and June, killing more than 100 people. India has been under an extraordinarily long heat wave that killed several election workers, and this week, in the capital, Delhi, even overnight temperatures remained in the mid-90s Fahrenheit, or in the mid-30s Celsius. Greece is bracing for wildfires this week, right after back-to-back heat waves killed several tourists. In Bamako, the capital of Mali, hospitals reported more than 100 excess deaths on the first four days of April, The Associated Press reported.

Between May 2023 and May 2024, an estimated 6.3 billion people, or roughly 4 out of 5 people in the world, lived through at least a month of what in their areas were considered abnormally high temperatures, according to a recent analysis by Climate Central, a scientific nonprofit.

The damage to human health, agriculture and the global economy is just beginning to be understood.

Extreme heat killed an estimated 489,000 people annually between 2000 and 2019, according to the World Meteorological Organization, making heat the deadliest of all extreme weather events. Swiss RE, the insurance-industry giant, said in a report this week that the accumulating hazards of climate change could further drive the growing market for insurance against strikes and riots. “Climate change may also drive food and water shortages and in turn civil unrest, and mass migration,” the report said.

As for the world’s two rival economic powers, China and the United States, both face a common peril this summer. As one-fifth of all Americans were under an extreme-heat alert this week, several areas in China’s north broke maximum temperature records. And earlier in the week the capital, Beijing, was under a heat alert as temperatures reached 99 degrees Fahrenheit (37 degrees Celsius).

The two countries are also the two biggest producers of greenhouse gases warming the planet. China’s current emissions are by far the highest in the world, and the United States’ cumulative emissions over the past 150 years of industrialization are the highest in the world.

Emissions like these, produced by the burning of fossil fuels, are what drive these bouts of abnormally high temperatures, scientists have repeatedly found. “Unsurprisingly, heat waves are getting deadlier,” said Friederike Otto, a climate scientist at Imperial College in London, in a statement on Thursday.

Global temperatures in the first five months of the year have been the highest since modern record-keeping began. That puts 2024 on course to be the hottest year in recorded history, eclipsing last year’s record.

Saudi Arabia, a petrostate that has opposed diplomatic efforts to phase out fossil-fuel use, experienced a harrowing event this week. Agence France-Presse reported Thursday that 1,000 people had died while on the hajj pilgrimage to Mecca, the holy city in Saudi Arabia. In central Algeria, another oil-rich state, riots erupted over water in mid-June as rising temperatures and a lack of rain dried up drinking-water supplies.

Doctors around the world have increasingly pointed to heat’s often underappreciated effect on health.

Many hospital systems have no adequate way to count heat illnesses or deaths because heat can aggravate a host of other conditions, like kidney disease or asthma, which means that deaths due to heat sometimes end up attributed to other causes and show up as a pattern of excess deaths.

“A transition away from fossil fuels is the best way to prevent deaths and illness from heat in the future — everything else is just a Band-Aid on a bullet wound,” said Renee Salas, an emergency-room doctor at Massachusetts General Hospital and the lead author of a special issue of The Lancet, the medical journal, on climate change and health.

Heat isn’t the only extreme weather hazard affecting the world.

High temperatures dried out soils in China’s northern agricultural provinces, prompting emergency-response measures against an expanding drought, including cloud-seeding operations to cause rain. Meanwhile, heavy rains inundated the country’s south, with landslides blocking roads and power outages affecting 100,000 households.

Last week, three days of tropical rains in Florida wreaked havoc on airports and highways.

On Thursday, the Atlantic hurricane season’s first named storm, Alberto, barreled into the northeastern coast of Mexico. Amid the lashing wind and rain, three children were killed, local officials said. One drowned trying to rescue a ball in a fast-moving river. Two others were electrocuted when a cable made contact with a pond.

The hurricane season is projected to be unusually strong this year, according to the National Oceanic and Atmospheric Administration, because the ocean is extraordinarily hot. That, too, is in part because of the burning of fossil fuels.

John Liu contributed reporting.