Deborah Zabarenko, Reuters 12 Nov 09;
WASHINGTON (Reuters) - In another sign of a warming planet, there were twice as many record-high temperatures in the United States as record lows over the last decade, climate scientists reported on Thursday.
This does not mean there are no record lows, just that there are fewer of them, said Gerald Meehl of the National Center for Atmospheric Research in Boulder, Colorado.
A parallel study of temperatures in Australia showed about the same results over the same period, Meehl said in a telephone interview.
"In a climate where the average temperatures are warming, you'd expect that there would be more record highs," Meehl said. "There have also been decreases in frost days, when the nighttime temperature goes below freezing -- there are fewer of those documented for many areas of the world, including the United States."
However, he said, even at the end of the 20th century when some of the highest U.S. temperatures ever were recorded, there still was enough variability that record cold days occurred.
The ratio of record highs to lows is likely to increase in the coming decades if emissions of climate-warming greenhouse gases continue to increase, the scientists said in a statement.
"Climate change is making itself felt in terms of day-to-day weather in the United States," Meehl said. "The ways these records are being broken show how our climate is already shifting."
If the climate was not warming, the number of record highs and lows each year would be about equal. But for the period between January 1, 2000 and September 30 this year, the continental United States had 291,237 record highs and 142,420 record lows amid usually mild winters and intense summer heat waves.
Meehl and other scientists used data from thousands of weather stations across the country over the last six decades to capture longer-term trends.
Research by Meehl and other scientists at Climate Central, The Weather Channel and the National Oceanic and Atmospheric Administration has been accepted for publication in the journal Geophysical Research Letters.
(Editing by Chris Wilson)
