CONTACT:  Patricia Viets, NOAA          FOR RELEASE RELEASE
          Lynn Simarski                 11/13/97                                 National Science Foundation

Human-generated increases in greenhouse gas concentrations have combined with natural forces to cause unprecedented warming in the cold Arctic in the 20th century, a phenomenon that could lead to significant changes in the Earth's natural environment, according to a study by U.S. and Canadian scientists, the Commerce Department said.

Between 1840 and the mid-20th century, the Arctic warmed to the highest levels of the past four centuries, causing dramatic retreats of glaciers, thawing of permafrost and sea-ice, and changes in terrestrial and lake ecosystems, according to the study published in the Nov. 14 issue of Science magazine, the department's National Oceanic and Atmospheric Administration said.

Although significant warming in the Arctic, particularly after 1920, may be related to increases in greenhouse gases, the initiation of the warming in the mid-19th century suggests that natural variations, such as increased solar irradiance, decreased volcanic activity, and factors internal to the climate system, also played roles in driving the post-1840's warming trend.

Much of the Arctic research was funded by the National Science Foundation through its Arctic System Science (ARCSS) Paleoclimates of Arctic Lakes and Estuaries (PALE) Initiative with support in Canada from the Natural Sciences and Engineering Research Council and the Polar Continental Shelf Project.

"The climate of the Arctic has been changing rapidly, with important consequences for many parts of the Arctic system," said Jonathan T. Overpeck, head of NOAA's Paleoclimatology Program and coordinator of the study. "The most notable pattern of change is the near ubiquitous transition from unusually cold conditions of the 19th century, to peak warm conditions of the 20th century."

To study climatic changes that occurred before instruments were widely available, the scientists used natural archives of past climate variations such as lake and marine sediments, ice cores from glaciers, and tree rings. Generation of these paleoclimatic data involved extensive field sampling of the lakes, glaciers and trees, followed by careful laboratory analyses. The use of multiple proxy sources allowed the scientists to get broad geographic coverage and also to cross-check among the different proxies. The results of this work summarize multi-century climate records at 29 locations around the Arctic, and furnish a new 400-year Arctic-wide average temperature record.

"Before these studies began, we had only a few decades of instrumental measurements from the Arctic, so our view of climate variations in this region was very limited," said Ray Bradley, head of the Department of Geosciences at the University of Massachusetts, and a major contributor to the research. "By extending the climate record through the use of these natural recorders of climate, we were able to place the recent changes in a longer term perspective."

The five-year effort provides scientists with significant insight into how climatic change has affected the Arctic in the past, and how the Arctic is likely to be impacted by climatic change in the future, as greenhouse gases continue to accumulate in the atmosphere.

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