This summer has been a scorcher for much of the Northern Hemisphere. June and July marked the hottest two-month stretch in Europe since record-keeping began. The contiguous US endured its hottest month on record in July, breaking a record held by July 1936 for nearly a century. South Korea saw its highest-ever recorded temperature.

Why has it been so hot? Climate change makes heat waves more likely and more intense. Europe is the world's fastest-warming continent. One study found that a similar May heat wave in 1976 would have been about 3.5 °C (6.3 °F) cooler than under today’s conditions.

Looking ahead, El Niño could make things worse. We’ve already entered an El Niño phase, defined by a 0.5 °C temperature increase in a specific part of the Pacific Ocean. This El Niño is expected to be especially strong—some forecasts predict it could peak over 3.5 °C above average. Climate scientist Zeke Hausfather notes it represents “one of the fastest onsets in the observational record.”

El Niño’s effect lags; 2024 is the reigning hottest year on record, but next year could be even hotter. As UN Secretary-General António Guterres said, “El Niño conditions will pour fuel on the fire of a warming world.” Immediate steps include buying air conditioners, installing solar, and upgrading insulation. But long-term, ending our addiction to fossil fuels is the only effective response.