On June 6, a special panel of top-ranking American climate scientists sent a great big clue to the 800-pound gorilla of global warming politics. I believe it is the most important document on this issue since 1995. Let's take a look at what it tells the party in power.

The American government has never been eager to set sweeping policies against greenhouse gas emissions. It's very expensive to make big reductions, and it's highly uncertain that they will work as advertised. The Clinton administration went along with the Kyoto Accords promising to make those reductions, but there was never a chance that the Senate would approve the treaty�too many interests opposed it. And few nations have actually ratified it.

When George W. Bush proclaimed Kyoto a dead letter earlier this year, he promised to bring forth new proposals for the nations to discuss in July. Hence the administration's request to the National Academy of Sciences last month: "We seek the Academy's assistance in identifying the areas in the science of climate change where there are the greatest certainties and uncertainties. We would also like your views on whether there are any substantive differences between the IPCC Reports and the IPCC summaries."

The administration's two-sentence request is an echo of that debate. The first sentence, on certainties and uncertainties, asks a very practical question, one for which science is best suited. Treaties can be negotiated more quickly and easily on matters that are relatively certain, and resources can be directed toward those that are most uncertain. The public is not widely equipped to appreciate this problem, but sound policy depends on it. Uncertainty is not just a dodge to avoid taking action; it's a genuine and serious obstacle.

The second sentence, in essence, asks whether the IPCC process is politicized. That has always been the fear of Kyoto opponents. The SPM is an unusual document, a simplification prepared by the scientific group along with various bodies in and out of government. And so far, that is all we have to work with.

1. Where are the greatest certainties and uncertainties in the science of climate change?

What is certain is that greenhouse gases are generally still rising due to human causes (although not at an accelerating rate as the IPCC assumed), that the world's surface temperature is rising (especially recently), and that the world's stratospheric temperature is falling (during the short period we've been able to observe it). It is certain that any changes in carbon dioxide levels will persist for centuries, while other greenhouse gases like methane and ozone can be affected much faster. It is certain that climate science has enormous room for improvement and that support for research is unreliable.

The uncertainties in climate science far outnumber the certainties. The magnitudes of many basic factors are poorly known: the production and destruction of greenhouse gases and aerosols, the effects and feedbacks of clouds, the sensitivities of the climate system to changes, the natural variations in global temperature, the history of world climate, the behavior of water vapor, the history and effects of human land uses, and the role of the ocean in absorbing energy and greenhouse gases. In addition, we know very little about how global climate changes translate into specific effects at the regional level, where people will have to respond in concrete ways.

2. What are the substantive differences between the IPCC Reports and the IPCC summaries?

The IPCC report, specifically the full Group 1 report on climate science, is scientifically credible and much like what a group of American scientists would produce. But the Summary for Policy Makers tends to speak of conclusions being "likely" or "unlikely" without explaining the basis for uncertainty; "however, a thorough understanding of the uncertainties is essential to the development of good policy decisions." By omitting the caveats, the SPM may make it seem that the science is settled when that is not the case.

The NRC panel went on to discuss an underlying question: whether the work of the IPCC will continue to be fair and representative. Participating in the IPCC process is important, but also a big time sink. Many scientists turn down invitations to join it, and the panel warns that "this could create a form of self-selection for the participants. In such a case, the community of world climate scientists may develop cadres with particularly strong feeling about the outcome: some as favorable to the IPCC and its procedures and others negative about the use of the IPCC as a policy instrument." Moreover, the role of government officials in preparing the SPM invites political influences when discussing things like treaties and emission controls. In sum, the panel says, "there is a risk that future IPCC efforts will not be viewed as independent processes."

Finally, the panel pointed out some specific issues for the U.S. scientific community. Paramount is the need for a long-term system of collecting observations instead of the current patchwork of programs. (A good example of a Bush administration mistake in this regard is its proposal to discontinue the century-old stream monitoring network of the U.S. Geological Survey.) The paper calls for more research aimed at helping society use scientific knowledge to respond to climate change.

Seeing that American science research is innovative, effective, and efficient is a public-policy job, not a partisan issue. Not just the Bush administration, but Congress too needs to do its part. The lessons in this report are for all sides in the climate debate, and for every citizen who understands science.