Duringone of the country's hottest summers, New Orleans quietly set a mind-boggling record.On43 nights, the temperature did not drop below 80 degrees in New Orleans, according to the Louisiana state climatologist.Itblows the previous record out of the water -13 nights in 2010. It's also incredible considering in an average summer, New Orleans has just 2.1 nights at or above 80 degrees.This recordshould be getting much more attention than it has been.Very warm overnight temperatures are hard on your body, let alone your utility bills. The elderly are particularly at risk during these times, as isthe entire homeless population and anyone with an illness. You might be inclined to raise a finger to mention that air conditioning negates these effects, but around 30 percent of New Orleans's population lives in poverty. If a family is lucky enough to own an air conditioner, they probably cannot afford to use it.Why is this happening? In short, man-madeclimate change.It's not just New Orleans and the South in general that are suffering through dangerously uncomfortable nights; this trend is obvious across theentire Lower forty-eight. And that's exactly what we expect in a climate-change world. In reality, very warm overnight low temperatures have been increasing in frequency since the 1970s.There are a couple of things that can explain this phenomenon.The air can hold more water vapor as it warms up. So as global temperatures increase, so does the humidity. That also means there's more moisture to create clouds. Even though clouds keep things cool during the day -they reflect sunlight -they act as a blanket at night, keeping the day's heat trapped near the ground.The humidity itself also acts like a warm, wet blanket. At night, the air doesn't cool down past the dew point, which is inherently linked to humidity. The more moisture that's in the air, the higher the dew point, and the warmer the overnight temperature."Well, the Gulf of Mexico [was] exceptionally warm this past summer, which has led to enhanced evaporation off the Gulf and higher than normal humidity levels and dew point temperatures across our fair city," wrote Barry Keim, the Louisiana state climatologist in a short essay posted Monday morning. "This has led to our minimum temperatures being exceptionally warm ... or hot ... or perhaps sweltering when you factor in the humidity. ..."All of this is to say that our nights are going to continue to warm up, and it wouldn't be surprising at all to see more cities topple records like New Orleans did in the near future.