If it hasn't been hot enough for you during the day recently, wait until tonight. 

Communities across the country last week set all-time record highs for daytime temperatures, but it's the higher temperatures at night that have been quietly setting records.

So why is that a problem? Well, according to data from the National Oceanic and Atmospheric Administration, summer nights have warmed at nearly twice the rate of days, nationwide, with overnight low temperatures increasing 1.4 degrees Fahrenheit since 1895.

That compares to a daytime high temperature increase of 0.7 degrees per century. In other words, when you expect things to cool down at night during the summer, the climatic trend is that it isn't cooling as much as it used to. The data also show this trend of warmer nights isn't only during the summer.

Using climate change models, scientists believe this trend will continue. For people who don't have air conditioning, hotter nights could make it harder to sleep. Of more concern, for older people, infants or those with respiratory ailments, extended runs of hotter nights — during a heat wave, for example — could be lethal. 

Warmer summer nights combined with scorching summer days can be a bad combination "because the body doesn't have a chance to cool down during the nighttime hours," Lara Cushing, a professor of environmental epidemiology at San Francisco State, told The New York Times this week. 

Then, there are people on farms, in construction or whose jobs take place outdoors and who can't avoid the heat by shifting their work hours earlier or later in the day. This trend toward hotter nights means they'll have to adapt somehow, and that could affect productivity or their health.

If this news makes you sweat, it's important to keep in mind this nighttime warming is a very slow trend. As it continues, we will probably have more time to think about the future as we lie awake nights, hoping for a cooling breeze.

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