Earth has been experiencing the hottest summer globally over the past few months, with record heatwaves dominating the headlines these days. Autumn can also prove to be very hot, with some of the coolest days being above average. Much of the talk about the heat record is about extreme daytime temperatures, but nights are warming rapidly as well.
Warming at night has been a trend that has been observed across the country throughout the year for several decades since the late 20th century. And nights aren’t just getting hotter, they’re warming faster than the days. In the United States, summer daytime maximum temperatures have risen on average by 3.5 degrees per century since 1970. During the same time the night temperature rose by 4.8 degrees. Winter has become even warmer, with maximum temperatures rising by 5.6 degrees and minimum nighttime temperatures rising by 6.1 degrees.
Warmer nights have many effects not only on the environment but also on people’s daily lives. Water bodies, insects, plants, humans, and much of our daily life are affected by rising nighttime temperatures. Invasive insect species that breed in warmer climates can threaten previously cold regions because the threat of cold weather, which is usually deadly, is reduced. Even native insects die less in the winter, allowing them to maintain larger populations. More freeze-free days throughout the year will expand planting and harvest seasons, and agricultural patterns will change as nights get warmer. But crops also experience the negative effects of warm nights because plants respire (and produce sugar) more than usual at night. This has been shown to put pressure on carbon and water resources for some crops, reducing yields by more than a quarter. Sensitive plants are affected as well. The acidity of grapes used in winemaking can change due to climate changes, which can change the taste of the resulting drink.
Humans will notice more than just high nighttime temperatures. Warmer weather can disrupt your sleep patterns, as higher body temperatures are known to reduce deep sleep. And the changes in vegetation mentioned earlier can also affect us in unexpected ways. Spending more time in temperatures above freezing allows many plants to survive and continue producing pollen during unusual times of the year. Ragweed, in particular, can survive longer into the fall when nighttime temperatures are warmer, with an average of 11 more days above freezing in the U.S. and more time to keep allergy medications on hand.