September 13, 2007
In understanding the present warming trend, it is absolutely essential to learn more about climate change in the distant past. But many scientists prefer to work only with data collected after 1975, says Syun-Ichi Akasofu, former director of the International Arctic Research Center at the University of Alaska.
This distorts the picture, says Akasofu. For example:
- During a period called the "Little Ice Age" -- from roughly 1400 to 1800 -- temperatures dropped by as much as 1.5 degrees Celsius.
- The anomaly of the Little Ice Age corrected itself through something called rebounding; the rebounding rate is estimated at 0.5 degrees Celsius per century.
- Since our present warming rate is roughly 0.6 degrees Celsius per century, the greenhouse effect caused by CO2 may represent only a 0.1 degree Celsius increase in temperature over the course of a century.
There is no doubt that global warming is in progress, says Akasofu. But much of it can be attributed to the rebounding effect from the Little Ice Age. Recovering from a cool period is, of course, warming. Ice core data from the Greenland ice sheet show many periodic warming and cooling periods during the last 10,000 years. The present warming phase is far from the warmest.
Ultimately, scientists have no clear knowledge of the cause of the Little Ice Age and of the subsequent rebound; or of the Big Ice Age; or of a warm period when the Arctic Ocean had no ice, say Akasofu. In fact, scientists do not understand the causes of the rapid increase of temperature from 1910 to 1945; or the decrease from 1945 to 1975, when CO2 levels were rising. Without understanding these recent changes, it is premature to jump to the conclusion that CO2 is the main cause of the last 30 years of global warming.
Source: Syun-Ichi Akasofu, "Climate Corrections," Wall Street Journal, September 12, 2007.
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