The National Oceanic and Atmospheric Administration (NOAA) says 1998, 1999 and 1997 were the "warmest years on record." Critical minds might ask, "How long is the record, and how accurate is it?"

Before 1900 there were no reliable temperature records for more than 50 percent of the globe. But measurements of temperatures in boreholes can be used to reconstruct climatic conditions at the surface for the past several thousand years.

Thus, a study by University of Michigan researchers, published in the August 1997 Geophysical Research Letters, estimated mean global temperatures for the last 10,000 years from temperature measurements in more than 6,000 boreholes around the world (see figure).

Similarly, in a study published in Science in October 1998, research scientists measured temperatures in two deep boreholes drilled near the summit of the Greenland Ice Sheet.

The two studies show:

• The temperature rise seen in the last 140 years is a recovery from a cold period in the 19th century.

• Even after the modest 1.0 degree F global warming of the last 140 years, present-day global temperatures remain cooler by about 1.0 degree F than they were when the Vikings settled Greenland in medieval times.

• For more than 7,500 of the last 10,000 years, temperatures have been higher than today.

• For at least 5,000 of the last 10,000 years, the mean planetary temperature was about 1.5 degrees F warmer than today.

Human beings have a tendency to take short-term trends and extrapolate them to ominous doomsday scenarios. For example, in 1975, Newsweek warned readers of "profound climatic change" leading to "catastrophic famines" and stated, "The central fact is that after three-quarters of a century of extraordinarily mild conditions, the Earth's climate seems to be cooling down."

Source: David Deming, "The Warmest Year on Whose Record?" Brief Analysis No. 337, August 31, 2000, National Center for Policy Analysis.

For text http://www.ncpa.org/ba/ba337/ba337.html