This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September 2009. Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole. (©UCAR, graphic by Mike Shibao.)

By Deborah Zabarenko, Environment Correspondent 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.” …

Record-high U.S. temps outpace record lows: study