Just weeks after a 3rd of the US inhabitants was hit with air-quality alerts due to smoke from climate-change-fueled fires in Canada, 100 million Americans at the moment are below warmth alerts. A cap of extra-hot air, often called a warmth dome, has settled over the West and South, pushing temperatures relentlessly larger. 

The map under exhibits extreme warmth warnings in purple and warmth advisories in orange, and the forecast is that things will get worse via the weekend. Highs will keep above 110 degrees Fahrenheit in Phoenix; California’s Death Valley is flirting with 130 degrees; and Texas’s grid is struggling to keep the AC on. 

This follows the hottest June on record globally. “With an evolving El Niño event, that is certain to further increase global temperatures,” says Howard Diamond, local weather science program supervisor on the National Oceanic and Atmospheric Administration’s Air Resources Laboratory. (El Niño is a band of heat water that develops within the Pacific Ocean and influences weather around the world.) “Canada has also experienced multiple bouts of prolonged heat this summer, contributing to the worst wildfire season the country has ever seen,” Diamond provides.

A warmth dome is basically stagnation. It varieties as a robust high-pressure system. As that air descends to the bottom, it compresses and considerably warms up: Just a few thousand toes up, air is likely to be 80 levels, however it could possibly attain 100 levels as soon as it hits the land. 

This descending cap of scorching air self-perpetuates for days and even weeks. It discourages the formation of clouds, permitting the solar’s vitality to hit the panorama full power, additional elevating floor temperatures. At the start of a warmth dome, moisture within the dust and crops evaporates away, considerably cooling the panorama—it’s sweating, principally. But as the warmth continues for days on finish, that moisture runs out and temperatures climb larger. 

In different phrases, the warmth dome feeds on itself. “There is no cloud cover, there is a lot of solar radiation coming in, there is no precipitation,” says Claudia Tebaldi, a local weather scientist on the Pacific Northwest National Laboratory. “You also trigger this feedback—you dry the soil, and there is no way for things to cool down by evaporation.”

That self-perpetuation makes warmth domes extraordinarily harmful. It’s bad enough when temperatures rise above 110 for a single day, particularly for folks with circumstances like bronchial asthma, as a result of the warmth results in the formation of ozone, which irritates the airways. But if temperatures soar for days—and particularly if temperatures keep excessive in a single day—the physique has no time to recuperate. The stress retains piling up.