Summers Are Becoming Unbearably Hot Before They Even Start

A heat wave topping 100°F set records in multiple European countries this past week. Similar temperatures hit northern China, as well as midwest and southern U.S. states.

These sweltering temperatures are remarkable on their own. But what makes them more striking is when they’re happening. As a sobering reminder, it’s not July or August. It’s mid-June. And the summer season only officially kicked off on Tuesday.

To illustrate what this early heat looks like in a historical context, we created a chart (below) that compares 25 years’ of daily high temperatures in June and July in Biarritz, a coastal city in southwestern France. As the heat moved through Spain and France, Biarritz was among the hottest cities on Saturday, June 18, hitting a high of 109°F. Prior to this year, the average maximum temperature for June 18 between 1997 and 2021 was 74°F, according to our calculations using historical temperature data from Weather Underground.

Of course, one wildly hot day in a single city doesn’t prove global warming. But such days are becoming more common around the world—and are raising the average temperature patterns overall. What’s more, these heat waves are happening on the fringes of the hot season, causing longer summers with extreme precipitation conditions—both more wet and more dry—around the world. In the U.S., for instance, the heat wave season has stretched from 22 days in the 1960s to nearly 70 days in the most recent decade.

Persistent heat waves are dangerous; Spain and Germany have been battling wildfires amid the scorching temperatures, France canceled outdoor festivities to limit heat exposure over the weekend, and Italy’s health ministry issued health alerts and emergencies for 18 cities between June 22 and June 24.

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Conditions on this side of the Atlantic are similarly alarming. In addition to the immediate risks of heat exposure, the U.S. drought monitor is currently showing extreme conditions across the West. Scorching temperatures are killing cattle and some states are bracing for power outages. And hotter nighttime temperatures are providing less relief to the oppressive days, which pushes average daily temperatures higher overall and impacts human health, including lost sleep.

London Meteorologist Scott Duncan, who posts climate facts and commentary on social media, made an Instagram video parodying skeptics who dismissed the European heat wave as normal summer weather. “We’re breaking all-time records in June. Does that mean nothing?” he asks, sardonically. “It’s never been this hot so early in the year. And we can’t compare this to July and August because it’s just not the same. But you’re quite happy just to call it ‘summer’?”