Tree rings establish temperature fluctuations over the centuries
A new study of old tree rings shows that 1,000 years ago long before power plants and sport utility vehicles temperatures across North America and Asia rose in a period of unusual warmth. Temperatures were known to be warm in Europe between 900 and 1100 during what is known as the Medieval Warm Period.
Collecting wood samples in 14 locations that cover a large part of the globe from New Orleans to the top of Alaska, researchers from Columbia University's Lamont-Doherty Earth Observatory and the Swiss Federal Research Institute found evidence that the warm temperatures extended to much of the Northern Hemisphere.
Writing in the current issue of the journal Science, scientists say the data demonstrate that temperatures naturally rise and fall over the centuries.
The peak temperatures in the Medieval Warm Period are similar to those seen in the first half of the 20th century and that warming, many scientists contend, was induced naturally, by a brightening of the sun.
The scientists add that their data do not argue against the view that artificial emissions so-called greenhouse gases have set off global warming in recent decades.
Source: Kenneth Chang, Tree Rings Show a Period of Widespread Warming in Medieval Age, New York Times, March 26, 2002.
For text http://www.nytimes.com/2002/03/26/science/earth/26TREE.html
For more on global warming http://www.ncpa.org/iss/env/
FMF Policy Bulletin/03 April 2002
Publish date: 09 April 2002
The views expressed in the article are the author’s and are not necessarily shared by the members of the Foundation.