An intense heat wave has brought unusually high temperatures to the Western United States — some of the highest of the season — and broken heat records.

Millions of Americans from Phoenix to Los Angeles to Seattle are under heat warnings. Even before this latest wave of extreme weather, which began Wednesday and is expected to last through the weekend, the summer of 2024 was considered the hottest summer on record.

In California, the desert city of Indio recorded its hottest on September 5, reaching 121 °F (49.4 °C), beating the previous record of 120 °F set in 2020. Palm Springs set its daily high at 121 °F. The city recorded its all-time high of 124 °F in July. The Los Angeles area hasn’t broken any records yet—though Burbank hit the all-time high at 114 °F—but the region is bracing for several days of triple-digit temperatures.

This week, Phoenix recorded 100 consecutive days of temperatures above 100 degrees Fahrenheit, with its hottest day at 115 degrees Fahrenheit on Sept. 5. In the Pacific Northwest, schools around Portland closed early because of the heat, and normally cool Seattle broke its daily temperature record on Thursday with 90 degrees Fahrenheit.

This summer was the hottest on record globally, and on July 22, the Earth experienced its hottest day in recorded history, breaking the previous day’s record.

Heatwaves are becoming more frequent, more extreme and longer lasting in the western US and around the world as the climate crisis leads to increasingly severe and dangerous weather conditions. Heatwaves are the weather event most directly affected by the climate crisis, an expert told the Guardian in July.