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April 7, 2013

Climate change: A clear and present danger

The phrase “clear and present danger” was first articulated by Supreme Court Justice Holmes in 1919 in a case involving the limits of free speech that arose during World War I.

This phrase became popular after the 1994 film of the same title, based on a Tom Clancy novel.

It seems appropriate to use it again after reading a recent peer-reviewed journal article published in the March 8 edition of the magazine Science. The title is “A Reconstruction of Regional and Global Temperatures for the Past 11,300 Years” by S. Marcott, et al. The authors are from Oregon State University and Harvard University. 

The critical conclusion is that global temperatures today are the highest in at least 4,000 years. 

It’s an impressive research effort and builds on an earlier effort in 1998 by M. Mann et al. at Penn State University. In that case, Mann was able to use biological markers (pollen, tree rings, lake sediments) for estimating Earth’s temperature variation over the past 1,000 years. That work showed that today’s global temperatures are exceptional and higher than at any other time during that period.

By 2005, more than 12 additional peer-reviewed research studies supported that conclusion. 

Let’s look at one graph from the Marcott study labeled “Years (BP).” Temperature changes are noted on the vertical axis. The average temperature of the 30-year period from 1961 to 1990 is taken as the “0” degrees centigrade baseline (dotted), with temperature changes lower or higher measured relative to it. The graph’s shaded area on either side of the center line incorporates the statistics and uncertainties of the measurements. 

The time in years (from today to 11,300 years ago) is measured along the horizontal axis.

Both the new Marcott data and the Mann data, where they overlap on the right, agree very well. Note that the temperatures today are higher than at any time in at least the past 4,000 or more years.

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