Every region of the world needs to prepare for unprecedented heatwaves, warns research published today in the journal Nature Communications. The study also pinpoints which places are most at-risk of record-breaking heat in the future and urges people to start preparing now for weather events they might not have thought possible in the past.

The researchers identified which locations are probably past due to seeing their temperature records shattered. They also considered factors that make certain communities more vulnerable than others, like booming population growth and limited access to air conditioning or healthcare.

Crucially, they find that communities facing the most risk have never dealt with such extreme heat in the past. That means they might not be prepared to handle the consequences since emergency response plans tend to take shape after a similar disaster has already taken place.

“They’ve had no reason to adapt, to learn how to live with it yet,” says Vikki Thompson, lead author of the paper. She’s now a climate scientist at the Royal Netherlands Meteorological Institute but completed the study as a researcher at the University of Bristol.

“The key thing that we find is that anywhere in the world could experience one of these heat waves beyond what is currently seen as possible from the observational record … everywhere needs to be prepared for them.”

The spark for this study was a 2021 heatwave declared the “most extreme” on record for North America. The record-shattering heat in the northwest US and southwest Canada that year buckled roadways and led to a spike in emergency department visits. Local infrastructure just wasn’t built to withstand temperatures that soared some 20 degrees Celsius (or 36 °F) hotter than the average in some places that June. In British Columbia, the village of Lytton hit 49.6 degrees Celsius (121 degrees Fahrenheit), a record high for Canada. In Seattle, a city used to a cooler climate, many homes lacked air conditioning.

A heat spell that severe would have been “virtually impossible” without climate change, researchers later found. So Thompson and her colleagues were surprised to find that as stunning as that disaster was in the US and Canada, similarly implausible events have already happened around the world without garnering as much attention.

She and her team studied data sets spanning from 1959 to 2021 to gauge how likely it would be for an event as drastic as the 2021 North American heatwave to occur. That particular heatwave was beyond a 1-in-10,000-year event, the research team determined. And yet, they found that heatwaves so extreme that they’re beyond a 1-in-10,000-year event have also struck 31 percent of the regions they studied, which encompassed a majority of the world, excluding Antarctica and some scattered areas lacking consistent data. Climate models suggest that the same could happen pretty much anywhere.

Some places are likely overdue for a record-smashing heatwave since they have yet to even experience a more likely 1-in-100-year event. The “region of most concern,” according to the study, is Afghanistan. While the region already has hot summers, something like a 1-in-10,000-year event would be unlike anything it’s seen in modern history, potentially reaching temperatures that test the limits of the human body.

Climate change is often called a “threat-multiplier” because of how it can make an already precarious situation even worse. That’s a big concern in Afghanistan, one of the poorest countries in the world following years of conflict. The country has also had to cope with the whiplash from severe drought and sudden floods, another hallmark of climate change. A rapidly growing population exacerbates the risks posed by extreme weather, including hotter temperatures than it’s seen in the past.

Another area facing the most risk from unprecedented heat, according to the study, is Central America — particularly Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, and Panama. What’s unique here is that there’s a bigger gap between temperature records set in the past and maximum temperatures possible in the future. The bigger the change is from the norm, the more difficult it can be to adapt.

Germany, Netherlands, and Belgium are also similarly overdue for record-smashing heat projected to affect a growing population, the study finds. But as more affluent countries, they’re likely to have more resources to prepare in advance. And preparation — making sure people can find places to cool down and that healthcare systems can respond to heat-related illness — saves lives.

“There’s lots and lots of climate research coming out saying that heatwaves are going to happen more often,” Thompson says. “Policymakers need to make sure that they are prepared and that they are prepared for events beyond what we think could happen.”