Global warming wildcard

Copyright 1998 Associated Press
September 7, 1998

Surfers from Australia to Northern California thanked El Nino for the monster waves that made 1998 the best surfing season of the century. This periodic warming of ocean currents certainly had a lot to do with it. But recent discoveries about the sun suggest a climatic wildcard could also be at play, wrote Jim Wilson in an article in the September issue of Popular Mechanics. Good surfing years track with another natural phenomenon - sunspots, the blemishes that for three centuries have been observed to pockmark the brilliant face of the sun.

The number of sunspots rises and falls over an average 11-year period. One hint of a sunspot-climate connection is that when the sun is most spotted, its total energy output is about 0.1 percent greater than during the sunspot minimums.

A second hint is what happens when sunspots virtually disappear. Without sunspots, long, severe winters and short, wet summers appear.

Scientists still remained cautious about drawing a connection. "We have only the 11-year sunspot record for the last 300 years to link directly to today's sun, and we don't have direct measurements of the radiation before the 1970s," says Peter Fox, of the National Center for Atmospheric Research (NCAR), in Boulder, Colo.

However, while surfers were being pummeled, conventional wisdom that down-played the sunspot-climate link was taking a beating of its own, at the 1998 meeting of the American Association for the Advancement of Science (AAAS) in Philadelphia. Evidence was shown that sunspots are the driving force behind a 10-to-12-year oscillation in temperature in the lower stratosphere. The stratosphere extends from about 6 to 15 miles above sea level. Temperatures are very, very cold but also stable.

At the AAAS meeting, Brian A Tinsley, of the University of Texas at Dallas, explained a theoretical multistep process that begins when solar activity associated with sunspots intensifies the solar wind - electrically charged particles thrown out by the sun.

On contact with the earth's magnetic field, these particles trigger a cascade of lower-energy ions. Eventually, these charged particles hit droplets of water that make up high-altitude clouds. At cloud tops the droplets are generally supercooled, that is, at temperature below freezing but still liquid. A minute quantity of energy input can trigger freezing, as in cloud seeding. As the liquid water making up the clouds turns to ice, the clouds themselves become thinner, reflecting less of the sun's energy back into space. The net result is a rise in temperature.

NASA is stepping up its investigation. Its Office of Earth Science will soon begin evaluating proposals for the Total Solar Irradiance Mission (TSIM), an orbiting instrument package designed to monitor variations in the amount of radiant solar energy that reaches Earth. The TSIM should be developed in 36 months or less.

TSIM's most important contribution may be to help the scientific community decide if the sunspot wildcard should be dealt in the global warming debate. If there is a strong sunspot-climate relationship, the notion that global warming is caused primarily by a buildup of carbon dioxide and other "greenhouse" gases could wipe out as dramatically as the surfers.

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