Global warming has neither stopped nor slowed in the past decade, according to a draft analysis (pdf) of temperature data by NASA's Goddard Institute for Space Studies.
The analysis, led by senior scientist James 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.
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 Saturday. The 34-page analysis has not been subjected to a peer review, though Hansen, in an e-mail sent discussing the paper, said he intended to revise it for submission to a peer-reviewed scientific journal soon.
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. It challenges in particular a respected and widely quoted study by noted 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 immediately reached late Saturday night.
The warming trend was visible, Hansen said in an e-mail, even in this year's bitter Northern Hemisphere winter, which blanketed Britain and the East Coast in snow and had some Republicans claiming that the Snowmageddon proved global warming as a hoax.
Winter weather will always be highly variable, Hansen said. 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, the cold temperatures were relatively benign compared to the late 1970s.
Supporters say that filtering of such "noise" makes long-term temperature trends visible. It also allows the NASA team 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 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."
Douglas Fischer is editor of Daily Climate, one of The Daily Green's trusted sources of information. This post is republished with permission.
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