Hot Summer Nights

Summer 2010 set temperature records across the country and around the world. NRDC’s analysis of June, July, and August 2010 US temperature data from the National Oceanographic and Atmospheric Administration’s (NOAA’s) Historic Climatology Network reveal that this summer set heat records in many parts of the country. In fact, of the 1,218 weather stations in the contiguous United States, with data going back to 1895, 153 locations recorded their hottest summer on record and nearly one in three stations recorded average temperatures among their five hottest on record.

Even more telling is that nighttime lows were the hottest ever recorded at nearly one in four weather stations in NOAA’s Historic Climatology Network. This means that at 278 stations the average nighttime low temperatures for June, July and August 2010 were hotter than at any time since 1895. More than half the stations recorded average nighttime low temperatures among their five hottest on record. Nighttime temperatures are more sensitive to the buildup of heat-trapping pollution in the atmosphere than daytime temperatures because increases in atmospheric aerosols and cloud cover have counteracted some of the warming effect of greenhouse gases during the day. Hot, stagnant nights can prove even more harmful than daytime highs as vulnerable populations (particularly the elderly) are unable to cool down and get relief from the stress of the daytime heat.