WASHINGTON -- America in recent years has been sweltering through three times more than its normal share of extra-hot summer nights, government weather records indicate.
And some scientists say the trend is a sign of manmade global warming.
From 2001 to 2005, nearly 30 percent of the nation had ``much above normal" average summertime minimum temperatures, according to the National Climatic Data Center in Asheville, N.C.
By definition, ``much above normal" means low temperatures that are in the highest 10 percent on record.
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 Dust Bowl in the 1930s, the rolling five-year average of 2001-05 is a record, by far.
Figures from this year's sweltering summer have not been tabulated yet, but they are expected to be just as high as recent years.