Warming Trend

Earth warmest in 1,000 years?
Researchers cite evidence for records in 1998 and entire '90s.
MSNBC Staff and Wire Reports, March 4, 1999

The federal government has already declared 1998 the warmest year since temperature recordings began 120 years ago, but several researchers say other evidence "strongly suggests" 1998 was the warmest of the last 1,000 years. Using tree rings, ice cores and other indicators, the scientists also dubbed the 1990s the warmest decade of the millennium.

University of Massachusetts press release on the new climate study

NBC's Robert Hager reports on brutal winter weather slamming New England. Their study, published in the upcoming journal Geophysical Research Letters, adds to a growing body of evidence that the global climate has been getting steadily warmer especially the last half of the 20th century. "Temperatures in the latter half of the 20th century were unprecedented," Raymond Bradley of the University of Massachusetts said in a statement describing the research.

 

Proxy Indicators Used

Because human climate records only go back a few hundred years, and do not cover the whole globe, the team at the University of Massachusetts and the University of Arizona looked at measurements other scientists have made of tree rings, ice cores and other "proxy indicators" that record climate variations.

 

An MSNBC special section: Climate Change

They heavily relied on three sets of 1,000-year-long tree-ring records from North America, as well as tree rings from northern Scandinavia, northern Russia, Tasmania, Argentina, Morocco and France. The ice cores they studied came from Greenland and the Andes mountains in South America. “The cooling trend of over 900 years (before 1000 AD) was dramatically reversed in less than a century. The abruptness of the recent warming is key, and it is a potential cause for concern.”

 

Michael Mann

University of Massachusetts researcher "As you go back farther in time, the data become sketchier," Michael Mann of the University of Massachusetts said. "One can't quite pin things down as well, but our results do reveal that significant changes have occurred, and temperatures in the latter 20th century have been exceptionally warm compared to the preceding 900 years."

 

Cold Trend Earlier

He said the records were not perfect, but complete enough to show "startling revelations." "If temperatures change slowly, society and the environment have time to adjust," he said. "The slow, moderate, long-term cooling trend that we found (in the 900 years prior to 1000 AD) makes the abrupt warming of the late 20th-century even more dramatic. "The cooling trend of over 900 years was dramatically reversed in less than a century. The abruptness of the recent warming is key, and it is a potential cause for concern." In January NASA and the National Oceanic and Atmospheric Administration said they had established that 1998 was the warmest year on record. But their finding was based on records only going back 120 years. The American Geophysical Union, which publishes Geophysical Research Letters, has called for continued efforts to curb human-made carbon emissions to stop global warming.