SACRAMENTO, CA - California Governor Arnold Schwarzenegger grabbed the spotlight at the recent U.N. World Environmental Day in San Francisco when he declared, "the debate is over. We know the science, we see the threat, and the time for action is now.'' He ordered that California cut its emissions of greenhouse gases to 2000 levels by 2010, to 1990 levels by 2020, and by 80 percent below 1990 levels by 2050.

Almost all scientists agree that human emissions are having some effect on climate. But contrary to media reports, there is no consensus about how much warming we may have, or how quickly it may occur.

The level for greenhouse gases in the atmosphere is about half what the models forecast. And while recorded temperatures have increased over the last century by 0.6 degrees Celsius, most of the increase occurred in the first part of that century, before human greenhouse gas emissions could have had an effect.

The infamous "hockey stick'' graph, purporting to show the last 25 years as the warmest in the last 1,000, turned out to be an artifact of poor mathematics. It is likely the world was warmer a thousand years ago than now - before fossil fuels came into use. Still, why not deploy as much green technology as we can? Because the state of that technology is pre-industrial.

In Europe, where nations have saddled themselves with requirements under the Kyoto Protocol, companies are having a tough time finding the technology to help them meet their goals. So they are instead paying rising prices for emissions credits from countries such as Russia, whose economy and energy use have collapsed.

The U.S. Energy Information Agency has developed scenarios in which renewable technologies advance rapidly. But even the most generous estimates show that renewables' share of energy production will only increase from one percent now to 4.6 percent by 2020 - far short of what Governor Schwarzenegger imagines.

The difficulty of shifting an entire economy from fossil fuels was demonstrated by the Department of Energy when it found that even if the nation got 140 million cars converted to some alternative fuel by 2020, it would only reduce fossil fuel use of 5.4 percent. The most important thing could be what the mayors agreed to as their World Earth Day measure - planting trees and improving green space.

The United States has been doing that on a massive scale, adding a million acres of forest a year since 1910. This coincides with the mechanization of agriculture. As Clemson economist Robert McCormick has noted, richer nations plant trees rather than destroying them. Developed nations may produce more emissions, but they also take more carbon dioxide and other greenhouse gases from the atmosphere than poorer nations do. McCormick predicts with continued economic growth that "the growth rate of net carbon emission per person will soon be negative in the United States.''

But if we saddle ourselves with impossible emission mandates, as Europe has, or start cutting down forests to grow plants for ethanol production or to make space for wind farms or open up land for huge arrays of solar collectors, we can reverse that process.

In short, by trying to save the climate - which may prove to be an impossible task - we could make ourselves and our environment all the poorer.

Sally C. Pipes is President and CEO of the Pacific Research Institute in San Francisco. She can be reached via
email at spipes@pacificresearch.org