The decade ending in 2009 was the warmest on record, new surface temperature figures released Thursday by the National Aeronautics and Space Administration show.
The agency also found that 2009 was the second warmest year since 1880, when modern temperature measurement began. The warmest year was 2005. The other hottest recorded years have all occurred since 1998, NASA said.
James E. Hansen, director of NASA’s Goddard Institute for Space Studies, said that global temperatures varied because of changes in ocean heating and cooling cycles. “When we average temperature over 5 or 10 years to minimize that variability,” said Dr. Hansen, one of the world’s leading climatologists, “we find global warming is continuing unabated.”
A separate preliminary analysis from the National Climatic Data Center, a unit of the National Oceanic and Atmospheric Administration, found that 2009 tied with 2006 as the fifth warmest year on record, based on measurements taken on land and at sea. The data center report, published earlier this week, also cited the years 2000 to 2009 as the warmest decade ever measured. The new temperature figures provide evidence in the scientific discussion of global warming but are not likely to be the last word on whether the planet’s temperature is on a consistent upward path.
Dr. Hansen, who has been an outspoken figure in the climate debate for years, has often been attacked by skeptics of global warming for what they charge is selective use of temperature data. The question of whether the planet is heating and how quickly was at the heart of the so-called “climategate” controversy that arose last fall when hundreds of e-mail messages from the climate study unit at the University of East Anglia in England were released without authorization.
Critics seized on the messages as evidence that, in their view, climate scientists were manipulating data and colluding to keep contrary opinion out of scientific journals. But climate scientists and political leaders affirmed what they called a broad-based consensus that the planet was growing warmer, and on a consistent basis, although with measurable year-to-year variations.
The NASA data released Thursday showed an upward temperature trend of about 0.36 degrees Fahrenheit (0.2 degrees Celsius) per decade over the past 30 years. Average global temperatures have risen by about 1.5 degrees Fahrenheit (0.8 degrees Celsius) since 1880.
“That’s the important number to keep in mind,” said Gavin Schmidt, a climatologist at Goddard. “The difference between the second and sixth warmest years is trivial because the known uncertainty in the temperature measurement is larger than some of the differences between the warmest years.”
Policy makers at the United Nations climate change summit conference in Copenhagen last month agreed on a goal of trying to keep the rise in average global temperatures to 3.6 degrees Fahrenheit, or 2 degrees Celsius, to try to forestall the worst effects of global warming.
New York Times has contributed to the report.