"Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures to rise and subsurface ocean temperatures to rise," declared the recent National Research Council report, Climate Change Science, requested by President Bush. No one argues with any of the above claims, but they do not in themselves mean that the world is headed toward a climate disaster due to humanity's activities.

Let's briefly review the data on global temperature trends. Earth's average temperature has apparently gone up by about 0.6 degrees Centigrade (C) in the past century. According to the highly accurate measurements taken from satellites of the entire troposphere (the bulk of the atmosphere from the surface to five miles up) the earth's temperature since 1979 is increasing at a rate of 0.038 degrees C per decade. Weather balloon data from the same period show an increase of only 0.03 degrees C per decade. Taking the weather balloon data from 1958 to today, the average per-decade increase in temperature is 0.1 degrees C. Interestingly, weather balloon temperature data are essentially flat between 1958 and 1976. Between 1976 and 1978, global temperatures measured by weather balloons jumped dramatically, after which they essentially became flat again. No one knows why temperatures spiked in the mid-1970s, but such a spike is not consistent with human causation. Finally, the surface temperature measures on which those most concerned about global warming rely show an increase of 0.16 degrees per decade over the same period.

These actual data on temperature increases are interesting, since to reach an average global temperature increase of 3.0 degrees C by the end of the 21st century would imply that global average temperatures must increase by at least 0.3 degrees C per decade. (The U.N.'s Intergovernmental Panel on Climate Change projected an increase ranging from 1.4 to 5.8 degrees C by 2100.) That 0.3 degree per decade increase is evidently not happening. Climate alarmists claim that is because aerosols like soot and sulfur dioxide are shading the planet, causing a cooling countertrend. Perhaps, but even the National Research Council report admits, "The monitoring of aerosol properties has not been adequate to yield accurate knowledge of the aerosol climate influence."

Global warming alarmists often suggest that despite the uncertainties surrounding projected global warming, humanity should still suffer anything to cut back on greenhouse gas emissions, especially by cutting back on the carbon dioxide emitted by burning fossil fuels. They say such action is equivalent to buying an insurance policy -- sensible behavior in the face of uncertainty. Let's unpack that analogy a bit.

The Kyoto Protocol, which President Bush has rejected, would limit U.S. emissions of greenhouse gases to 7 percent below their 1990 levels by 2012. Given the current trajectory of energy and economic growth, meeting that target means the United States would have to cut energy consumption by as much as 30 to 35 percent below what Americans are now expected to be using in 2012. Some economists estimate that it would cost 3 percent of U.S. gross national product per year to achieve that lower level of emissions. How much would Kyoto-mandated emissions cutbacks benefit the global environment? Climatologists estimate that implementing the Kyoto Protocol would, by 2100, avoid only 0.14 degrees C of temperature rise. That means projected man-made greenhouse warming that might have been 3 degrees C by 2100 would instead be 2.86 degrees C.

So, suggests University of Alabama at Huntsville climatologist John Christy, if the Kyoto Protocol is an insurance policy, it is like one where you pay $3,000 per year (3 percent of GNP per year) on a $100,000 house for 100 years. The total cost of insuring the $100,000 house would be $300,000. In keeping with the insurance analogy, let's treat a projected 3 degree temperature increase as a total loss. Thus the payout on the insurance policy--the reduction in the damage caused by a projected temperature increase--is only about 5 percent (0.14 degrees is about 5 percent of a 3 degree increase.) The payout comes to a grand total of $5,000. Nobody sensible would buy such an insurance policy.

On Monday, President Bush correctly pointed out in a speech at the White House that "the Academy's report tells us that we do not know how much effect natural fluctuations in climate may have had on warming. We do not know how much our climate could, or will, change in the future. We do not know how fast change will occur, or even how some of our actions could impact it."

In the face of such scientific uncertainties, and the high costs of the even less certain benefits of reducing greenhouse gas emissions, ditching Kyoto's mandatory emissions reductions--while focusing on improving climate science and energy technologies--is the most reasonable path.