Science

Why longer heat waves are so dangerous

For tens of millions of Americans, summer begins this week with a multi-day blast of blistering heat. Temperatures in parts of the country are expected to reach the high 90s through the weekend. The National Weather Service has warned that the heat wave could longest Some places have been through this for decades.

Weather like this heat poses many health risks, even for people who only sweat through it for a few hours. But researchers have found that the dangers of heat can increase when conditions are sweltering day after day, night after night. With so much of the United States facing such dangers this week, it’s a good time to take a moment to reflect on what we know about heat that lingers.

In general, human-induced global warming is making heat waves even hotter, more frequent and longer. This year, India has already experienced what its top weather official described as the country’s longest hot spell on record, spanning 24 days in April and May. Greece is in its second week of deadly heat, less than a year after a 16-day heat wave, the longest on record.

For the planet as a whole, that was 2023 the warmest year in human history and global temperatures have continued to break monthly records well into 2024.

When it is very hot, the human body has to work harder to keep organs and tissues at their normal healthy temperature. The longer your body is forced to do this, the greater the strain on your cardiovascular system and the greater the risk of negative health effects, which in extreme cases can include heart and kidney failure.

How much more risk? Two researchersG. Brooke Anderson and Michelle L. Bell, analyzed the numbers for 43 American communities between 1987 and 2005. They found that for each additional day a heat wave lasted, the risk of non-accidental death increased by 0.4 percent. For every additional degree Fahrenheit above normal temperatures, the risk increased by 2.5 percent. Both effects were more pronounced in the Northeast than in the Midwest or South, the researchers found, possibly because people there were less accustomed to stifling weather conditions.

Other researchers have found a small additional increase in mortality risk that occurs after four consecutive warm days. Another study looked at heat waves in 400 communities in 18 countries and regions in Asia, Europe, and the Americas. That report did not find that longer heat waves were more deadly, although this may have been due to technical differences in the way the timing of deaths was recorded.

Dr. Anderson and Dr. Bell also found that heat waves earlier in the summer were more dangerous than those later. This, they wrote, could be because people physically get used to the warm weather or change their behavior, for example by buying an air conditioner or spending more time indoors.

According to researchers, there’s another bleak possibility: Early summer heat waves could lead to extinctions among the elderly and those with chronic conditions, leaving a smaller group of vulnerable people later in the season.

Long heat waves also cause warm nights, which gives the body less time to recover and makes it more difficult to sleep.

Weather forecasters have warned of record heat this week, with temperatures only dipping into the 70s in some places. The human body lowers its core temperature to trigger sleep, so if temperature regulation is disrupted, so can our sleep. This is more likely to be a problem in big cities, where it generally cools down less at night than in the countryside because of all the asphalt and other surfaces that absorb and radiate heat.

A 2017 study combined nighttime temperature data with survey results from 765,000 Americans surveyed by the Centers for Disease Control and Prevention about their sleep habits. A robust association was found between hot nights and restless sleep, especially among older and poorer people. Other studies have shown that higher nighttime temperatures are associated with a higher risk of heat-related death also.

Such findings are already shaping the way government agencies discuss heat hazards. new HeatRisk tool from the National Weather Service and the Centers for Disease Control and Prevention takes into account the duration of daytime and nighttime temperatures in its threat assessments.

The National Weather Service has been blunt about why the concern this week isn’t just about the mercury: “The early arrival of this magnitude of heat, its duration, abundant sunshine and lack of lighting at night will increase the danger of increasing this heat wave beyond what the exact temperature values ​​would suggest.”


Dozens of environmental, labor and health care groups met Monday submit a petition and prompting the Federal Emergency Management Agency to declare extreme heat and smoke from wildfires “major disasters,” such as flooding and tornadoes.

The petition is a major effort by the federal government to help states and local communities struggling with the growing costs of climate change.

If the petition is accepted, FEMA could free up money to help municipalities prepare for heat waves and wildfire smoke by building cooling centers or installing air filtration systems in schools. The agency can also help during emergencies by paying for water distribution, health checks for vulnerable people and increased electricity use.

The support from major labor groups such as the AFL-CIO and the Service Employees International Union is part of a broader union strategy to improve protections for the tens of millions of people who work outside or without air conditioning during heat waves. —Manuela Andreoni

read about the push to use FEMA funds to combat extreme heat.

Recycling can have huge environmental benefits. First, it keeps things out of landfills and incinerators, where they can produce powerful greenhouse gases and potentially dangerous pollutants.

More importantly, recycling allows us to extract fewer raw materials.

But recycling rates in the United States have remained stubbornly flat for years. And in some cases they are bleak. Just now 10 percent of plastics are actually recycled. Meanwhile, hundreds of thousands of tons of recyclable waste are exported, often to developing countries.

It’s no wonder that many readers have asked us whether individual efforts make any difference at all. So we took a closer look at that question in the latest edition of our Ask Climate column. — Winston Choi-Schagrin.

Read more about why recycling doesn’t work and what you can do about it.

Correction: An essay in the Thursday newsletter about a lawsuit in Hawaii incorrectly describes a point of contention in the case. Lawyers for oil companies argue that the case should be governed by federal law, not state law. They are not arguing that the case should be heard in a federal court instead of a state court.


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