As a physicist, let me point out that our understanding of climate was not "settled more than a decade ago," as global warming alarmists argue. Science is never settled, as Albert Einstein spectacularly demonstrated.

Our knowledge of the interplay between atmospheric carbon dioxide and global temperature has gone through three stages over the past 20 years. Al Gore correctly points out that early ice-core data gathered from glaciers around the world showed a very strong correlation between carbon dioxide and temperature over 650,000 years. Because carbon dioxide is a greenhouse gas, most of us assumed that it regulated global temperature.

By 1999, improving ice-core techniques produced a stunning reversal, showing that the global temperature changed many centuries before carbon dioxide changed. This proved that natural climate cycles were causing changes in atmospheric carbon dioxide, probably by affecting how much remained dissolved in the oceans.

Using new ice-core evidence, Caillon, et al. (Science, March 2003), concluded that "CO2 is not the forcing that initially drives the climatic system."

This should have convinced alarmists that their scare was unwarranted. But too many would have been thrown out of work, and too many politicians would have lost a hot-button issue. So they ramped up the alarm, relying on ever-more-contrived theories to explain the ice-core data.