Our Hot Planet

Hurricane Harvey drowned south Texas in a year's worth of rain in just a few days, it left behind an estimated $150 billion in damage to sodden homes and inundated factories and claimed about 60 lives. Two weeks later, Hurricane Irma hit Florida, killing at least 33 people there and causing billions more in damages - as well as brutal loss of life in the Caribbean. But these storms may not be 2017's deadliest U.S. disaster. Instead, that title may go to a largely unseen killer: rising temperatures.

Over the last 30 years, increasingly broiling summer heat has claimed more American lives than flooding, tornadoes or hurricanes, according to the U.S. National Weather Service. And the problem has not been limited to the United States. More than 35,000 people died during a European heatwave in 2003, and tens of thousands perished in Russia during extreme heat in 2010.

Experts say heat remains underestimated as a threat by governments, aid agencies, and individuals. That's both because it's an invisible, hard-to-document disaster that claims lives largely behind closed doors - and because hot weather just doesn't strike many people as a serious threat.

"If you have a natural disaster like a cyclone or an earthquake or a flood, the impacts are immediate. Things get washed away, people drown. But heat is a silent killer," said Sarah Perkins-Kirkpatrick, a climate change researcher at Australia's University of New South Wales. "In Australia, heatwaves kill more people than any other natural disaster - but no one realises the destruction they can cause. The attitude is, 'It's hot, suck it up, get on with it'."

Around the world, heat is a neglected and poorly understood disaster, in part because few of the deaths it produces are directly attributed to heatwaves. Victims - many elderly, very young, poor or already unhealthy - often die at home, and not just of heat stroke but of existing health problems aggravated by heat and dehydration. In India, for instance, a major risk factor for women - who die of heat far more often than men, researchers say - is the lack of an indoor toilet. To avoid embarrassment or harassment, many women refrain from drinking water during the day to limit their trips to the toilet - a potentially deadly strategy during heatwaves.

"These deaths are recorded as normal deaths. But they wouldn't have happened if it wasn't so hot," said Gulrez Shah Azhar, an Indian heat researcher who works for the RAND Corporation, a global think tank.

To find the true rate of deaths during heatwaves, health officials look at "excess" deaths - how many more people died than would otherwise be expected during that period.

In places used to dealing with hot conditions, there is a "diagnostics failure" in recognising the risks of extreme heat, noted Eric Klinenberg, an American sociologist and expert on a deadly 1995 Chicago heatwave.

In steamy cities like Miami, "there's a sense we know how to deal with heat here, while everybody else is complaining", he said. "There's a will not to see the risk."

City dwellers, from Bangkok to Cairo, face particular - and growing - risks. In many rural areas, trees and open land planted with crops help daytime heat subside at night, providing some respite.

But in cities, acres of concrete and asphalt absorb warmth during the day and radiate it back at night, creating heat islands that can be nearly as hot at night as during the day.

During Chicago's three-day heatwave in 1995, more than 730 people died, many of them older people living alone and already facing health problems. With city services overwhelmed, hospitals turned away emergency cases, and the city's morgue had to rent refrigerated trucks to store the dead.

With more than half the world's population now living in cities - and two-thirds of people expected to live in them by 2050 - finding ways to reduce urban heat will be crucial to saving lives as climate change ramps up heat extremes.

India alone has 300 million people without a power connection, which means they cannot turn on a fan or air conditioning when temperatures soar. In New Delhi, some of the poorest of the poor, living on the streets, sleep near the curb of busy roads at night, hoping to catch a breeze from passing cars.

When Azhar was growing up in the Indian city of Lucknow, in a home without electricity, "there was no escape" from debilitating summer heatwaves. "You're trapped and there is literally nothing you can do," he said.

Experts say one clear way to reduce growing health risks from heatwaves is to provide more of the world's population with access to power, particularly in the hottest areas.

"The best way to mitigate (heat deaths) is to get electricity" to run fans or air conditioning, said Steven J. Davis, a University of California, Irvine earth system science professor and one of the authors of a 2017 report that predicted a growing risk of widespread deaths during Indian heatwaves.

Global efforts, including as part of the Sustainable Development Goals, to bring power to those without it could play a significant role in reducing heat deaths, experts say. But if action to curb climate change is not robust enough, heatwaves could more often overwhelm or breakdown power grids, leaving rich and poor without help to cool down, they warn.

Despite an international agreement to curb climate change reached in Paris in 2015, cuts in the use of fossil fuels around the world are not yet ambitious enough to meet the accord's goal of keeping warming to 1.5 to 2 degrees Celsius above pre-industrial times. Instead the world is on a path towards at least 3 to 4 degrees Celsius of warming by the turn of the century, scientists say.

"How is the global community going to respond to that?" Ibrahim asked. "Are we just going to accept millions of deaths? We do now around drought, but will we do that around heat exhaustion? And how are we going to manage the migration flows? We are not at all prepared globally for the big numbers that will be affected," she said.

An analysis by Climate Central, a U.S. non-profit science and media organisation, found that Houston by 2030 is likely to face "heat danger days" - when combined heat and humidity make temperatures feel like 105 degrees Fahrenheit (40 degrees Celsius) - 110 days a year. Miami will face 126 such days each year by 2030, it noted.

"A one-off every now and then we can recover from," said Perkins-Kirkpatrick. "But we'll be seeing this almost every summer in the next 40 or 50 years. We need to do something about it."