Pairing a lethal summer heat wave with a winter so mild that in some places daffodils bloomed out of season and bears forgot to hibernate, 2006 was the warmest year on record for the 48 contiguous states, government climate experts reported yesterday.
Based on an analysis of readings from 1,200 weather stations across the country, the average annual temperature in the 48 states last year was 2.2 degrees warmer than the mean temperature for the 20th century and fractionally warmer than 1998, which previously held the temperature record, the researchers reported.
Seven months last year were much warmer than average, concluded the scientists at the National Climatic Data Center in Asheville, N.C., a branch of the National Oceanic and Atmospheric Administration.
Last January was the warmest on record in the U.S., and December was the fourth-warmest since recordkeeping began in 1895. In five states, December temperatures set records: Minnesota, New York, Connecticut, Vermont and New Hampshire.
"We are breaking warm records all over the place," said climate scientist Gavin Schmidt at NASA's Goddard Institute for Space Studies in New York, who was not involved in the NOAA analysis.
Each of the past nine years has been among the 25 warmest years on record nationally - an unprecedented hot streak historically, the scientists said.
Overall, annual temperatures in the United States and around the world are one degree warmer than a century ago, and the rate of warming has accelerated threefold in recent decades. Eight of the past 10 years were the warmest on record worldwide.
Last week, climate experts at the British Meteorological Office predicted that 2007 could easily become the warmest year globally on record.
"Global warming is pushing these temperatures ever upward," said meteorologist Michael Mann, director of the Earth System Science Center at Pennsylvania State University. "We are loading the dice."
The warming temperature trends of recent years appear to closely track the general predictions of computerized climate models analyzing the effects of greenhouse gases on global climate patterns, several scientists said.
"It looks pretty much like what the climate models of global warming expected," said Penn State climate analyst Richard Alley, who was not part of the research effort. "We have turned up Earth's thermostat."
Rising levels of carbon dioxide and other greenhouse gases, which can trap heat in the atmosphere, were a key factor in the warming trend, the climate center researchers acknowledged.
The rate at which carbon dioxide is being released into the atmosphere has doubled since than 1990s, Australian researchers recently reported, with 7.85 billion tons of CO2 released into the atmosphere in 2005 alone.
But other influences, such as a mild El Nino current stirring in the Pacific Ocean, also played a role in blocking Arctic air that might normally chill the country, as did warmer conditions in the Indian Ocean, they said.
Robert Lee Hotz writes for the Los Angeles Times.