The summer solstice is right around the corner this Saturday and temperatures around the U.S. have started to rise to the occasion. But it’s not just a warmup from spring to summer that’s occurring: summer temperatures have been steadily rising since 1970.
On average, temperatures have increased at a rate of about 0.4°F per decade in the contiguous U.S. since 1970, or nearly 2°F overall. But some areas have been warming much faster, and others more slowly.
The fastest warming “climate divisions,” or localized areas within regions, are in southern California and Nevada in the western region. There, temperatures have risen by as much as 1.32°F per decade, or more than 5°F overall since 1970.
The Southwest has seen the fastest average rate of summer warming at roughly 0.6°F per decade, and some parts of the region have warmed as much as 0.9°F per decade. Some parts of the Northwest have also experienced summer warming at the rate of 0.92°F per decade. Meanwhile, the Upper Midwest is bringing up the rear, warming on average by only 0.1°F per decade. Even there, however, summers in some areas have been warming by 0.5°F per decade.
The increase is mostly due to the rise of heat-trapping greenhouse gases in the globe’s atmosphere due to human activities. According to the recent National Climate Assessment, annual average temperatures in the U.S. could rise another 10°F by century’s end if emissions aren’t abated.
Explore how your region compares by clicking on the map above.