Sign up for our daily briefing

Make your busy days simpler with Axios AM/PM. Catch up on what's new and why it matters in just 5 minutes.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Catch up on the day's biggest business stories

Subscribe to Axios Closer for insights into the day’s business news and trends and why they matter

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Stay on top of the latest market trends

Subscribe to Axios Markets for the latest market trends and economic insights. Sign up for free.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Sports news worthy of your time

Binge on the stats and stories that drive the sports world with Axios Sports. Sign up for free.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Tech news worthy of your time

Get our smart take on technology from the Valley and D.C. with Axios Login. Sign up for free.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Get the inside stories

Get an insider's guide to the new White House with Axios Sneak Peek. Sign up for free.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Catch up on coronavirus stories and special reports, curated by Mike Allen everyday

Catch up on coronavirus stories and special reports, curated by Mike Allen everyday

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Denver news?

Get a daily digest of the most important stories affecting your hometown with Axios Denver

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Des Moines news?

Get a daily digest of the most important stories affecting your hometown with Axios Des Moines

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Twin Cities news?

Get a daily digest of the most important stories affecting your hometown with Axios Twin Cities

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Tampa Bay news?

Get a daily digest of the most important stories affecting your hometown with Axios Tampa Bay

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Charlotte news?

Get a daily digest of the most important stories affecting your hometown with Axios Charlotte

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Nashville news?

Get a daily digest of the most important stories affecting your hometown with the Axios Nashville newsletter.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Columbus news?

Get a daily digest of the most important stories affecting your hometown with the Axios Columbus newsletter.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Want a daily digest of the top Dallas news?

Get a daily digest of the most important stories affecting your hometown with the Axios Dallas newsletter.

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Sign up for Axios NW Arkansas

Stay up-to-date on the most important and interesting stories affecting NW Arkansas, authored by local reporters

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

Please enter a valid email.

Please enter a valid email.

Subscription failed
Thank you for subscribing!

A man quenches his thirst in New Delhi, India, May 27, 2020. Photo: Jewel Samad/AFP via Getty Images

Climate change and population growth have led to a worldwide surge in the number of people exposed to hazardous levels of heat, according to a sweeping study that examines 13,115 cities from 1983 to 2016.

Why it matters: Extreme heat is the top weather-related killer in the U.S. each year, and studies show that as the world continues to warm in response to greenhouse gas emissions, heat exposure will become so severe that it will reduce economic output in many regions.

  • The researchers measured the average annual rate of increase in heat exposure in cities using a measure of person-days per year, and they found that increases in temperature were responsible for the majority of that trend. Person-days indicates how many people experience extreme heat and for how long when accounting for temperature, humidity and population.
  • About 23%, or 1.7 billion, of the world's population saw their heat exposure increase in 2016, the study found.

The big picture: The new study, published Monday in Proceedings of the National Academy of Sciences, found that previous studies significantly underestimated extreme heat exposure, particularly in the tropics and rapidly growing parts of the world, such as sub-Saharan Africa, the Middle East and southern Asia.

What they did: The scientists had to overcome a paucity of data in parts of the globe, including India and sub-Saharan Africa. They used infrared satellite imagery along with ground instruments to find maximum daily heat and humidity levels in the cities they evaluated, and they defined extreme heat as having a wet bulb temperature of 30°C (86°F), which incorporates the effects of heat and humidity on the human body.

  • The researchers looked at population data during the same period in order to come up with a count of person-days in such extreme conditions. They also used population data to determine how much of an increase in heat exposure was due to population growth versus climate change-related trends.

What they found: According to the study, the number of person-days in which urban residents were exposed to extreme heat skyrocketed from 40 billion person-days in 1983 to 119 billion in 2016 — a threefold increase.

  • The city that fared the worst in terms of a sharp uptick in person-days was Dhaka, Bangladesh, which saw an increase of 575 million person-days of extreme heat over the study period, though much of that increase was due to population growth.
  • Cities that saw climate change drive much of the increase in exposure include Baghdad (Iraq), Lagos (Nigeria), Kolkata (India) and Mumbai (India).
  • The study period did not include the record-shattering heat waves that struck North America this year, killing hundreds in the U.S. and Canada.
  • The study repeatedly emphasizes the unequal burdens of extreme heat, with poorer residents often suffering the most due to lack of access to air conditioning, among other factors.
  • The research calls into question whether the urban poor will be able to rise to greater levels of prosperity, since extreme heat has been tied to drops in economic output.

What they're saying: "The most surprising thing our study found was the sheer scale of change in urban extreme heat exposure globally," study lead author Cascade Tuholske of Columbia University told Axios.

  • "Billions of people across thousands of urban settlements worldwide face increasing exposure since the 1980s. This isn't a problem of the future. Rather, urban residents, largely in Africa and Southern Asia, have had to deal with increasingly dangerous heat for decades and the problem is just getting worse."
  • Tuholske views this as hopeful research, since known strategies, from early warning systems to green roofs and planting trees in urban areas can all help reduce the effects of urban heat islands and cut down on any heat-related fatalities.
  • "Nearly half of all of the cities in this study experienced significant increases in heat exposure through climate warming or through rapidly growing populations, or both," Jeremy Hoffman, a climate scientist at the Science Museum of Virginia, told Axios. Hoffman was not involved in the new research.
  • "We know that heat kills, and it disproportionately affects residents suffering from social isolation, chronic illnesses, advanced age, and exposure to other urban-amplified threats like flooding and poorer air quality," he said.

Go deeper

Penn researchers score $10M grant to study racial health disparities

Photo courtesy of Perelman School of Medicine at the University of Pennsylvania

Philadelphia researchers scored a nearly $10 million federal grant to study how investments in predominantly Black neighborhoods in the city can affect racial health disparities and violent crime.

Why it matters: Philly's poverty rate — currently at 23% — has remained high for decades. And Black residents experience poverty at far higher rates than their white counterparts, according to 2019 U.S. Census data.

  • A recent study found that investing in repairs for even a single house on a Philadelphia block reduced crime on that block by nearly 22%.
Updated 1 hour ago - World

Reports: Up to 17 U.S. missionaries kidnapped in Haiti

Haitian soldiers guard the public prosecutor's office in Port-au-Prince earlier this month. Photo: Richard Pierrin/AFP via Getty Images

Children were among up to 17 American Christian missionaries and their relatives kidnapped by a gang in Haiti on Saturday, the New York Times first reported.

Details: The missionaries had just left an orphanage and were traveling by bus to the airport to "drop off some members" and were due to travel to another destination when the gang struck in Port-au-Prince, Haitian security officials said, per the NYT.

3 hours ago - World

Melbourne, "world's most locked-down city," to lift stay-at-home orders

Victorian Premier Daniel Andrews during a news conference in Melbourne, Australia, on Sunday. Photo: Quinn Rooney/Getty Images

Melbourne's stay-at-home orders will end five days earlier than planned, officials in Australia's second-biggest city announced Sunday.

Why it matters: The capital of the state of Victoria has had six lockdowns totaling 262 days since March last year. That means Melbourne spent longer under lockdown than "any other city in the world" during the pandemic, Reuters notes.