Spring is a transitional season with both warm and cold days, even in a warming climate. But long-term trends show that the arrival of summer-like temperatures is starting sooner across much of the U.S. These changes are beginning to warp the seasons as we know themーsqueezing out the winter chill and stretching the summer heat long before us.
To investigate the onset of summer heat, Climate Central analyzed the first calendar day when local temperatures reach their average daily summer high, and how that first day may have changed since 1970. We found that 54% of cities recorded summer temperatures at least a week earlier, on average, than they did fifty years ago. The top 15 stations with the largest advances in the onset of summer temperatures all recorded summer heat arriving more than three weeks earlier.
With the current pandemic, we’re bracing ourselves for a summer quite unlike any other. There is continued uncertainty around public gathering areas across much of the countryーincluding not only pools, beaches and summer camps, but also cooling centers like the local libraries and malls which many rely on to stay safe during the hot months. Finding new ways to adapt to the challenges of this summer’s heat should remind us of the abundance of longer-term climate solutions at handーfrom introducing green infrastructure to switching to renewable energy sources for cooling.
Daily temperature data from 1970-2019 were obtained from the Applied Climate Information System. Thresholds were calculated by finding the average summer maximum temperature from 1970-2019 and rounding that number to the nearest five degrees. For example, the average summer maximum temperature (1970-2019) in Abilene is 93.4°F so the appropriate threshold would be 95°F. Only 242 of our 244 stations are included in summary statements due to large data gaps in St. Johnsbury, Vt. and Wheeling, W. Va.