Remember 2010? U.S. and international scientists reckon it tied for the warmest year on record, supporting findings of unequivocal global climate change. Climate skeptics remain unconvinced.
Those who study the climate skeptic position say this raises echoes of scientific controversies of the past, including the debate over the health hazards of tobacco.
In Washington, the most vocal denier of human-caused climate change is U.S. Sen. James Inhofe, an Oklahoma Republican who has repeatedly dismissed the idea as a hoax.
"Actually, right now we're in the third year of a cooling period," Inhofe said in December, before the January release of statistics from the U.S. National Climate Data Center, NASA, and the World Meteorological Organization showing 2010 tied for the hottest year since modern record-keeping began in 1880.
WMO showed it tied with 2005 and 1998.
NCDC and NASA had a tie with 2005.
The latest temperature data have not changed Inhofe's stance, said Matt Dempsey, Inhofe's spokesman.
"Why would one year, even if it was the hottest year on record, influence the senator's view?" Dempsey said in a phone interview. "There's a lot of factors that go into this. To have one hot year and use that to suggest that there's catastrophic man-made global warming sounds a little hollow."
Brenda Ekwurzel, a climate expert at the Union of Concerned Scientists, which maintains that human activity is a primary cause of global warming, agreed that one year is less significant than the record over decades, which she said conclusively showed a warming world.
"Any one year can vie with another year or be extremely hot and break all records," Ekwurzel said by telephone. "It's more important to look at the decadal average."
Looking at it on that time scale, she said, showed that 2001-2010 was the hottest decade since 1880. The previous decade, 1991-2000, was next-warmest, and 1981-1990 was the third-warmest. "This trend is undeniable," Ekwurzel said.
It's been a rough year or so for scientists and others who say that data shows human activities, especially the burning of fossil fuels, accelerate the climate-warming greenhouse effect. Climate skeptics are quick to point this out. To wit:
-- Skeptics allege scientists manipulated climate research, citing the so-called "climategate" scandal of December 2009, in which leaked e-mails from scientists at the University of East Anglia's Climatic Research Unit in Britain appeared to show scientists sniping at climate deniers and trying to block publication of articles critical of their findings.
At least four reviews of the case have exonerated the climate scientists but skeptics maintain it cast doubt on all climate research that showed a consistent warming trend.
-- In 2010, the U.N. Intergovernmental Panel on Climate Change had to correct a 2007 report used by government policymakers that exaggerated the melt of Himalayan glaciers by saying they might all vanish by 2035. Since then, however, independent reviews have reaffirmed the panel's main conclusion that it is at least 90 percent certain that human activities are the main cause of global warming in the past 50 years.
-- International meetings in 2009 and 2010 aimed at crafting global policy to stem greenhouse emissions have not brought major results.
-- The U.S. Congress failed to pass climate change legislation, and without U.S. involvement, any international agreement is unlikely to go forward.
-- President Barack Obama, who ran for the White House in 2008 on a platform that included tackling climate change, failed to mention the issue in his State of the Union address last month, though he did mention clean energy.
-- Fewer U.S. residents think there is solid evidence that human activities spur climate change than did five years ago.
Not all climate skeptics are as vociferous as Inhofe in denying that the phenomenon is occurring; many maintain the science is unsettled, and until it is, there's no point in acting.
Myron Ebell of the Competitive Enterprise Institute is a key proponent of this view. In a telephone interview, Ebell questioned NASA's climate data for the 1930s, which he said had been "monkeyed with" by scientists aiming to show anthropogenic climate warming.
As for data kept by the East Anglia Center for Climatic Research, Ebell said it had traditionally been considered better than statistics kept by NASA's Goddard Institute for Space Studies, but that the "climategate" scandal showed the CRU numbers were "such a mess" that they could not be relied upon. (Independent investigations reached a different conclusion.)
"I think we have a real problem now with the historical datasets," Ebell said. "I have more faith in the ones before global warming became the greatest cause of the day for these people and they adopted a political agenda and they've been twisting the scientific evidence to fit their story."
Ebell said large-scale weather patterns like El Nino/La Nina had more influence on recent temperatures than greenhouse emissions. He also questioned temperature readings from surface stations, saying many were improperly positioned and failed to take into account the "heat island" effect of major cities.
Naomi Oreskes, co-author of "Merchants of Doubt," which says that some key climate science deniers also denied the health risks of tobacco, said Ebell's stance was typical of climate skeptics.
Noting Ebell's affiliation with the pro-business Competitive Enterprise Institute, Oreskes said, "These are people committed to the defense of the free market as the foundation stone of American political liberty . . .
"It's not about the science," said Oreskes, whose book tracked scientists who questioned human-spurred global warming back to their previous opposition to curbing tobacco use. "It's about defending their ideological position; they attack anything that they fear could lead to more regulation of the marketplace."
Inhofe is reluctant to admit he could be wrong about the human impact on climate change. When asked to consider what would happen if he were wrong, he said, "If we find out I'm wrong in three years, we can do some things to make some changes. In the meantime, we have not caused the American people to pay $400 billion a year for however number of years that is."
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