According to a new study, an area of intensely warm weather—dubbed a “extreme heat belt”—with at least one day per year when the heat index exceeds 125 degrees Fahrenheit (52 degrees Celsius) is expected to cover a US region home to more than 100 million people by the year 2053.
The nonprofit First Street Foundation conducted the study, which used a peer-reviewed model built with public and third-party data to estimate heat risk at a “hyper-local” scale of 30 square meters.
The mission of the First Street Foundation is to make climate risk modelling accessible to the general public, government officials, and industry representatives such as real estate investors and insurers.
The study found that heat exceeding the National Weather Service’s highest category—called “Extreme Danger,” or temperatures above 125 degrees Fahrenheit—was expected to affect 8.1 million people in 2023 and grow to 107 million people in 2053, a 13-fold increase.
This would encompass a geographical region extending from northern Texas and Louisiana to Illinois, Indiana, and Wisconsin—inland areas far from the more temperate weather typically found near the coasts.
The heat index, also known as the apparent temperature, is what the outside temperature feels like to the human body when relative humidity and air temperature are combined.
To develop their model, the researchers looked at satellite-derived land surface temperatures and air temperatures from 2014 to 2020 to better understand the relationship between the two measurements.
This data was further examined by taking into account elevation, how water is absorbed in the area, distance to surface water, and distance to a coast.
The model was then scaled to future climate conditions, using the Intergovernmental Panel on Climate Change’s “middle of the road” scenario, in which carbon dioxide levels begin to fall by mid-century but do not reach net zero by 2100.
After the “Extreme Danger” days pass, hotter temperatures are expected across the country, with varying degrees of resilience.
According to the report, “these increases in local temperatures have significant implications for communities that are not acclimated to warmer weather relative to their normal climate.”
Despite the higher absolute temperatures seen in Texas, a 10% temperature increase in the northeastern state of Maine may be as dangerous as a 10% increase in the southwestern state of Texas.
The most significant predicted shift in local temperature occurred in Miami-Dade County, Florida, which currently has seven days per year with temperatures above 103 degrees Fahrenheit. That number is expected to rise to 34 days at 103 degrees by 2053.
The report also warned that the increased air conditioning use that is likely to result from such temperature spikes will strain energy grids, leading to more frequent and longer-lasting brownouts.