NCPA - National Center for Policy Analysis


December 2, 2004

The Earth's temperature may have fluctuated more wildly during the past 1,000 years than previously thought, according to a new study that challenges how researchers use tree rings and corals to give us a picture of the Earth's past.

If true, the study suggests that recent warming might not be as unique as was thought previously, and might partly be due to natural temperature cycles, rather than humans spewing carbon dioxide into the atmosphere.

According to scientist Hans von Storch and his colleagues:

  • Reconstructing climate change through tree rings, corals and ice cores (known as proxies) may underestimate past temperature fluctuations.
  • Temperature fluctuations dating back to medieval times may be underestimated by a factor of two or more.
  • Underestimating past temperature variation would make the 20th century warming trend of 0.6 degrees Celsius appear to be far different than any occurrences over the past 10,000 years.

Chris Forest of the Massachusetts Institute of Technology stresses that the earth is currently getting warmer, but von Storch's study poses a critical question as to how much of the warming, especially before 1980, is part of natural temperature fluctuations.

Source: Quirin Schiermeier, "Past Climate Change Questioned,", September 30, 2004; and Hans von Storch, "Models of Global and Regional Climate," GKSS Research Center, September 1, 2004.

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