The intensifying and expansive heat wave affecting around 150 million people in the United States from Wisconsin to Washington, DC, bears the hallmarks of human-caused global warming.

Extreme heat is only becoming more common. In the United States, heat waves now occur three times as often as they did in the 1960s, and one study, published in 2022 in the journal Copernicus, found that climate change is making heat domes 150 times more likely.

Extreme humidity and triple-digit temperatures are affecting around 250 million people across the United States. Here's the science behind the heat dome that’s stifling the nation.