Global warming has neither stopped nor slowed in the past decade, according to a draft analysis of temperature data by NASA's Goddard Institute for Space Studies.
The analysis, led by Goddard director Jim Hansen, attempts to debunk popular belief that the planet is cooling. It finds that global temperatures over the past decade have "continued to rise rapidly," despite large year-to-year fluctuations associated with the tropical El Niño–La Niña cycles.
The analysis also predicts, assuming current El Niño conditions hold, that 2010 will go down in history as the hottest year on record despite an unusually snowy winter in the Northern Hemisphere.
"Communicating the reality of climate change to the public is hampered by the large natural variability of weather and climate," the Goddard scientists wrote in the draft, which was circulated by Hansen Friday evening and posted on the ClimateProgress.org blog shortly after.
"We conclude there has been no reduction in the global warming trend of 0.15 (to) 0.20ºC (per) decade that began in the late 1970s."
The new analysis combines sea-surface temperature records with meteorological station measurements and tests alternative choices for ocean records, urban warming and tropical and Arctic oscillations. It concludes the urban "heat island" impacts are small compared to the warming attributed to greenhouse gas emissions.
And it finds that, while this winter's unusually strong Arctic Oscillation - which funnels cold northern air to the East Coast and pulls warm mid-latitude air up to the Arctic - is predicted as atmospheric carbon dioxide levels rise, seasonal temperature anomalies associated with it aren't enough to blunt long-term warming trends.
"In the United States only one of the past 10 winters and two of the past 10 summers were cooler than the 1951-1980 climatology, a frequency consistent with the expected 'loading of the climate dice,' " the scientists wrote.
Hansen and other co-authors could not be reached for comment. The analysis has not been subjected to a peer review, though Hansen, in an email sent discussing the paper, said he intended to revise it for submission to a journal "within a month or so."
Michael Mann, director of the Earth System Science Center at Pennsylvania State University, called the analysis solid.
"Essentially he's just pointing out that we've come out of this short-term, relatively cool period," Mann said. "The globe clearly continues to warm."
Joe Romm, editor of ClimateProgress.org and a senior fellow at the liberal Center for American Progress, added that the study is "important for those who care about the science."
Whether it would quell the debate over global cooling - fueled in part by the East Coast's hard winter and the revelation of errors in the United Nation's Intergovernmental Panel on Climate Change synthesis report - is less certain.
Mann said many claims of global cooling are spurious and "intellectually dishonest."
"The question becomes can you confront those who are choosing to be intellectually dishonest with more facts and hope they become more honest? Unfortunately, that's not the case," he said.
"But hopefully, as evidence continues to come in, those who have genuinely, honestly skeptical views about climate change will be swayed by the fact that evidence continues to ... to be stronger and stronger."
Romm was hopeful the analysis might inspire media to become less prone to arguments the globe is cooling. "If journalists want to write their global cooling piece, they better get it out soon," he said.
In an e-mail that accompanying the study, Hansen suggested defrocking the cooling theory was a chief aim of the subject. "Somehow we have to do a better job communicating," he wrote. "The paper has relevance to current public discussions, but the usual scientific journals are not too accommodating for explicit discussion of that relevance."
The Goddard analysis challenges in particular a respected and widely quoted study by climatologist Susan Solomon and colleagues at the National Center for Atmospheric Research that states the trend in global surface temperatures "has been nearly flat since the 1990s."
Not so, Hansen and his co-authors write. "Climate trends can be clearly seen if we take the 60-month (five year) and 132-month (11 year) running means." The five year mean minimizes El Niño variability, while the 11-year mean minimizes solar-cycle variability. Solomon could not be reached for comment Saturday night.
The warming trend was visible, Hansen said, even in this year's bitter Northern Hemisphere winter, which blanketed Britain and the East Coast in snow and had Congressional Republicans mocking former Vice President Al Gore for his climate claims.
Winter weather will always be highly variable, Hansen wrote in an email. Areas cold enough to have snow can expect more from a carbon-rich atmosphere containing more water vapor. But while the Arctic oscillation over the past three months was remarkable, he said, the cold temperatures were relatively benign compared to the late 1970s.
Filtering that "noise" makes long-term temperature trends visible, the authors said. It is also what allows them to predict that 2010 will emerge as the hottest year on record.
At first blush, it doesn't seem likely: The sun is near the bottom of deepest solar minimum in a century; this year's El Niño, while strong, is nowhere near as powerful as the 1998 cycle that drove temperatures higher across much of the globe.
But the underlying trend, Hansen and colleagues conclude, is up. "This new record temperature will be particularly meaningful," they wrote, "because it occurs when the recent minimum of solar irradiance is having its maximum cooling effect."
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