On the fever chart of rising temperatures, 2006 was the warmest year on record for the 48 contiguous states, 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, government climate experts reported Tuesday.
Based on an analysis of readings from 1,200 weather stations around the country, the average annual temperature in the Lower 48 states last year was 2.2 degrees higher than the mean temperature for the 20th century and fractionally warmer than in 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.
Indeed, January 2006 was the warmest on record in the U.S. and December was the fourth warmest since record-keeping began in 1895. In five states, December temperatures set record highs: 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.
Even cities now in winter's stranglehold were relatively balmy. Denver, paralyzed by blizzards during its third snowiest December on record, still basked in a monthly temperature 1.7 degrees higher than the average from 1971 to 2000, the researchers said. In Minneapolis-St. Paul, the temperature was 17 degrees above normal for the last three weeks of December.
Temperatures in California, which experienced a searing heat wave in the summer, ran above normal for the year, but not as high as most of the country.
Each of the last nine years all has been among the 25 warmest years on record in the U.S. -- an unprecedented hot streak historically, the scientists said.
Overall, annual temperatures in the U.S. and around the world are one degree higher than a century ago and the rate of warming has accelerated threefold in recent decades. Eight of the last 10 years are the warmest on record worldwide. Climate experts at the British Meteorological Office last week predicted that this year could easily become the warmest year globally on record.
If global temperatures continue to rise as projected, melting icecaps could raise sea level worldwide by up to 3 feet by 2100, swamping coastal communities that are home to millions of people, according to estimates from the United Nations. At the same time, rising temperatures could fuel more powerful storms, while disrupting subtle seasonal patterns of plant growth and animal habitats around the world.
"Global warming is pushing these temperatures ever upward," said meteorologist Michael Mann, director of the Earth System Science Center at Penn State University. "We are loading the dice."
The rising 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 University 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 said. 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, they said.
In 1998, record high temperatures were driven by an unusually powerful El Nino current that disrupted weather patterns worldwide. The current El Nino, a periodic warming current that took shape last summer, is far weaker and has had only a moderate effect on global climate, several experts said.
"What we are seeing is much more than El Nino," said climate analyst Kevin Trenberth at the National Center for Atmospheric Research in Boulder, Colo. "The overall pattern is consistent with our concepts of global warming."
To those who analyzed last year's temperature records, the effort to attribute the higher temperatures to relatively transitory minor perturbations in the planet's weather systems missed a more crucial trend.
"The important thing is that, in the long term, warmer temperatures are becoming the norm," said Jay Lawrimore, chief of the climate monitoring branch at the National Climatic Data Center, the federal center that prepared the study. "The expectation is that temperatures will continue to warm in the U.S. and globally."