Summer nights heating up, scientists say

WASHINGTON - America in recent years has been sweltering through three times more than its normal share of extra-hot summer nights, government weather records show. And that is a particularly dangerous trend.

During heat waves, like the one that now has a grip on much of the East, one of the major causes of heat deaths is the lack of night cooling that would normally allow a stressed body to recover, scientists say.

Some scientists say the trend is a sign of manmade global warming.

A top federal research meteorologist said he "almost fell out of my chair" when he looked over U.S. night minimum temperature records over the past 96 years and saw the skyrocketing trend of hot summer nights.

From 2001 to 2005, on average nearly 30 percent of the nation had "much above normal" average summertime minimum temperatures, according to the National Climatic Data in Asheville, N.C.

By definition, "much above normal" means low temperatures that are in the highest 10 percent on record. On any given year about 10 percent of the country should have "much above normal" summer-night lows.

Yet in both 2005 and 2003, 36 percent of the nation had much above normal summer minimums. In 2002 it was 37 percent. While the highest-ever figure was in the middle of America's brutal Dust Bowl, when 41 percent of the nation had much above normal summer-night temperatures, the rolling five-year average of 2001-05 is a record - by far.