Yet this does not mean that global warming is no longer a threat, they said. The analysis also showed that 2008 was the ninth warmest year since continuous instrumental records were started in 1880. The 10 warmest years on record have all occurred between 1997 and 2008.
"GISS provides the ranking of global temperature for individual years because there is a high demand for it from journalists and the public," said climatologist Dr. James Hansen, director of the Goddard Institute.
The Sun sets over the Pacific Ocean in this photo taken by an Expedition 15 crewmember on the International Space Station. (Photo courtesy NASA)
"The rank has scientific significance in some cases, such as when a new record is established," Hansen said. "But rank can also be misleading because the difference in temperature between one year and another is often less than the uncertainty in the global average."
Hansen says the Earth's cooler temperature last year is due in part to the fact that the Sun is just passing through solar minimum, the low point in its 10 to 12 year cycle of electromagnetic activity, when it transmits its lowest amount of radiant energy toward Earth.
The GISS analysis found that the global average surface air temperature was 0.44°C (0.79°F) above the global mean for 1951 to 1980, the baseline period for the study.
Most of the world was either near normal or warmer in 2008 than the norm. Eurasia, the Arctic, and the Antarctic Peninsula were exceptionally warm, while much of the Pacific Ocean was cooler than the long-term average.
The relatively low temperature in the tropical Pacific was due to a strong La Nina that existed in the first half of the year, the research team observed.
La Nina and Pacific Decadal Oscillation cool the Pacific Ocean. April 2008. (NASA image by Jesse Allen)
La Nina and El Nino are opposite phases of a natural oscillation of equatorial Pacific Ocean temperatures over several years. La Nina is the cool phase. The warmer El Nino phase typically follows within a year or two of La Nina.The temperature in the United States in 2008 was not much different than the 1951-1980 mean, which makes it cooler than all the previous years this decade.
"Given our expectation that the next El Nino will begin this year or in 2010, it still seems likely that a new global surface air temperature record will be set within the next one to two years, despite the moderate cooling effect of reduced solar irradiance," said Hansen.
The GISS analysis of global surface temperature incorporates three sources of information - data from the Global Historical Climatology Network of the National Climate Data Center; the satellite analysis of global sea surface temperature of Richard Reynolds and Thomas Smith of the National Oceanic and Atmospheric Administration; and Antarctic records of the international Scientific Committee on Antarctic Research.
Last year, GISS climatologists found that 2007 tied with 1998 for Earth's second warmest year in a century.
"It is unlikely that 2008 will be a year with truly exceptional global mean temperature," Hansen correctly predicted in January 2008. "Barring a large volcanic eruption, a record global temperature clearly exceeding that of 2005 can be expected within the next few years, at the time of the next El Nino, because of the background warming trend attributable to continuing increases of greenhouse gases."
"As we predicted last year," Hansen said then, "2007 was warmer than 2006, continuing the strong warming trend of the past 30 years that has been confidently attributed to the effect of increasing human-made greenhouse gases."
Dr. James Hansen (Photo courtesy NASA)
Dr. Hansen has been chosen by his peers to receive the 2009 Carl-Gustaf Rossby Research Medal, the highest honor bestowed by the American Meteorological Society.
Hansen earned the Rossby Medal for "outstanding contributions to climate modeling, understanding climate change forcings and sensitivity, and for clear communication of climate science in the public arena."
He was presented with the medal January 14 in Phoenix at the society's annual meeting.
"Jim Hansen is performing a tremendous job at communicating our science to the public and, more importantly, to policymakers and decision-makers," said Franco Einaudi, director of the Earth Sciences Division at NASA Goddard Space Flight Center in Greenbelt, Maryland.
"The debate about global change is often emotional and controversial, and Jim has had the courage to stand up and say what others did not want to hear," Einaudi said. "He has acquired a credibility that very few scientists have. His success is due in part to his personality, in part to his scientific achievements, and in part to his refusing to sit on the sidelines of the debate."
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