WASHINGTON -- Climate change caused by greenhouse gases is warming the United States, though unevenly, government researchers said Thursday.
"The continent as a whole is warming, mostly as a result of the energy sources we are using," William J. Brennan, acting administrator of the National Oceanic and Atmospheric Administration, said at a briefing on the nation's climate since 1951.
But there is a "warming hole" where no change occurred in the center of the country, roughly between the Rocky Mountains and the Appalachians, added Martin Hoerling of NOAA's Earth System Research Laboratory.
Last year the International Panel on Climate Change, studying the planet as a whole, concluded that global warming is "unequivocal, is already happening, and is caused by human activity."
Thursday's report localized the analysis, concluding that average surface temperatures over the United States have increased 1.6 degrees Fahrenheit since 1951, nearly all in the last 30 years.
Weather observations are the Rosetta stone, Hoerling said, "We see a cause-effect relationship in data."
He said that human-induced warming is the overall driving factor and also is the major cause of changes in sea-surface temperature.
Sea temperatures, in turn, result in the uneven changes over land by affecting wind and storm movement. Climate experts have learned a lot about this effect in recent years by studying the periodic El Nino and La Nina patterns of unusual warming or cooling of the tropical Pacific Ocean and how those changes alter weather.
Currently the Pacific is in a neutral condition between the two extremes, and in a separate report Thursday NOAA's Climate Prediction Center said neutral conditions are likely to continue through early next year.
And in yet a third report released Thursday, NOAA's National Climatic Data Center reported that November's average temperature for the contiguous United States was 44.5 degrees, 2.0 degrees warmer than average. It was the warmest November on record for the Western states.
For the January-November period, the average temperature of 54.9 degrees F was 0.3 degree above the 20th century average.
The nation's January-November temperature has increased at a rate of 0.12 degrees per decade since 1895, and at a faster rate of 0.41 degrees each decade during the last 50 years.
NCDC said precipitation across the contiguous United States in November averaged 1.93 inches, which is 0.20 inch below the 1901-2000 average.
Meanwhile, in Poznan, Poland, U.N. Secretary-General Ban Ki-moon on Thursday warned the world against backsliding in the fight against climate change as it battles financial crisis. He called for a renewed sense of urgency in facing "the defining challenge of our era."
Ban spoke as some 145 environment ministers and other top officials gathered to help push efforts to secure agreement next year on a new worldwide treaty to cut greenhouse gas emissions, which would take effect in 2013.
In addition to the 1.6 degree warming since 1951, key findings of the North America climate change report included:
-- Six of the 10 warmest summers in the continental United States since 1951 occurred between 1997 and 2006.
-- The largest yearly average regional temperature increases have occurred over Northern and Western North America, with up to 3.6 degrees warming in 56 years over Alaska, the Yukon Territories, Alberta, and Saskatchewan.
-- No significant yearly average temperature changes have occurred in the Southern United States and Eastern Canada.
-- More than half of the warming averaged over all of North America is probably the result of human activity.
-- Regional temperature trends are likely to have been influenced by regional variations in sea surface temperature.
-- There has not been a significant trend, either up or down, in North American precipitation since 1951, although there have been substantial changes from year to year and even decade to decade.
-- It is unlikely that a fundamental change has occurred in either how often or where severe droughts have occurred over the continental United States during the past half-century.
-- However, overall drought impacts over North America have become more severe in recent decades.
-- It is likely that warming resulting from human activity has increased drought impacts over North America in recent decades through increased water stresses associated with warming land surface temperatures.