In 1997, Eileen Claussen, a former assistant secretary of State and onetime EPA official, received an intriguing call from officials at the Pew Charitable Trusts: if they wanted to spend a lot of money to address global warming, how should they spend it? Claussen drew up a blue-print--collect scientific data, search out practical solutions, get businesses onboard, work with policymakers. In May 1998, the Pew Center on Global Climate Change was launched with Claussen as president. Since then, she has been a forceful advocate for reducing greenhouse-gas emissions and has reached out to corporations, states, cities and members of Congress to help develop clean-energy policies. Claussen spoke recently with NEWSWEEK's Anne Underwood.

UNDERWOOD: Is there any doubt now that global warming exists?

CLAUSSEN: Let me put it this way. A few determined skeptics don't accept it, but the overwhelming majority of scientists do. When President Bush took office, he asked the National Academy of Sciences to study the issue. The report they issued was very balanced. They noted some uncertainties--for example, when and where impacts might be felt and to what degree. But the conclusion was that the Earth is warming, this change is induced by human activity, and it will get worse.

Do a few degrees of warming really matter?

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The Earth has warmed about 1 degree Fahrenheit in the last 100 years--more in some places, like the Arctic, where there has been an increase of 4 to 5 degrees since the 1950s. Polar bears are having a ter- rible time there and may be extinct by the end of this century. Already we're seeing changes in Alaska, where roads are buckling in places and some major pipelines no longer fit together. Coldwater fish that used to be found off the Alaskan coast are no longer there, because the waters are too warm.

Do you expect a similar amount of warming in the next century?

Estimates range from 2.5 to 10.4 degrees.

What will the effects be here in the United States?

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As the sea level rises, some areas, particularly in Louisiana, could be submerged because of their low-lying coastal plains. There will be more floods. But some regions [that are already parched] will have even less precipitation, so drought in the Southwest would likely increase. There are theories--and I would keep them in the category of theories--that ocean currents will change, as fresh water from melting ice in the Arctic mixes with salt water, slowing circulation of ocean currents. While most of the Earth would get warmer, Europe would get colder from the disruption of the Gulf Stream.

Do we have enough information now to take action?

Given what we know now, it would be irresponsible not to act. The costs are not huge, but the downside of not acting is potentially enormous.

Can a new energy policy help?

Energy policy is climate policy, since fossil fuels are the main source of greenhouse gases. So the question becomes, where do we get our energy? In the United States, 51 percent of electricity comes from coal; 20 percent, nuclear; 16.5 percent, natural gas; 7 percent, hydroelectric; 3 percent, oil, and the rest, renewables--geothermal, wind and solar.

How much power can we realistically expect to derive from renewable sources?

Ten percent by 2020 is realistic--or, with a concerted effort, 30 percent by 2050. Without major breakthroughs, it's hard to get beyond a third, because most renewables are intermittent. You need better ways of storing the energy.

Do we need to increase reliance on nuclear energy?

It's hard to imagine getting to zero carbon emissions without some nuclear. But it's expensive. The issue of dealing with radioactive waste has not been resolved. And I worry about proliferation overseas.

So, if a major portion of energy will continue to come from coal, how do we reduce emissions?

Gasification of coal--technically known as the integrated gasification combined cycle (IGCC)--could lead to cleaner burning. But the plants themselves are expensive, and it's not clear if states will allow companies to build them, given that costs would be passed on to the consumer. American Electrical Power and Cinergy both want their next plants to be IGCC, but they need to get it through their public-utility commissions. The other necessary ingredient is developing the technology for carbon capture and sequestration. That involves removing the carbon from emissions, using a chemical process for gas separation, and then piping it someplace or injecting it underground. Some experiments show that it can be done. In Norway, where there's a carbon-dioxide tax, one com- pany does it to avoid the tax.

It seems businesses are ahead of the government on this issue.

There are 39 companies working with us in our Business Environmental Leadership Council. Most of these are major multinational firms. Outside the United States, even in developing countries, there is a demand for cleaner technology, so it makes sense for them. Others have said that if they didn't have a forward-looking policy, they couldn't attract the best and brightest talent.

How does the council work?

We meet four times a year. These companies walk the walk; they don't just talk the talk. The most ambitious target was set in 1999 by DuPont, which set a goal of reducing emissions 65 percent below 1990 levels by 2010. They actually reached 67 percent by 2002 by reducing emissions from nylon manufacturing. They also brought down their energy consumption, even while growing the business. None of these companies found it cost them money to reduce greenhouse-gas emissions, because in the process, they became more energy-efficient.

But our primary focus is policy. What kind of legislation do we want nationally and at the state level? If a bill comes up, we share that with the companies, so we get the best product.

Are the states out ahead of the federal government on this?

It's an interesting picture on the state level. The California effort on auto emissions is being challenged by the automotive industry and may or may not survive. But if it does, New York and other states will follow. Then you will almost have de facto national limits on greenhouse gases from cars.

In the Northeast and mid-Atlantic, nine states, led by Gov. George Pataki of New York, are trying to fashion a program of trading between states to get the most cost-effective measures for reduction of emissions taken first.

Nineteen states plus the District of Columbia have requirements for renewable energy. For example, Montana passed a law calling for 10 percent of energy to come from renewables by 2010.

The states are motivated by different things. North Carolina is worried about the barrier islands [being submerged]. Arizona is starting to figure out what will happen with droughts and forest fires. The Western Governors' Association is studying this. We're starting to see some real momentum, and it's a nonpartisan effort.

Even cities seem to be getting into the act.

Seattle took the lead. There are now 165 cities who have said they will meet the targets of Kyoto--reducing emissions 70 percent below 1990 levels.

Are you encouraged by recent actions in the Senate?

[Last month] the Senate voted on four climate amendments to the energy bill. The strongest--from Senators John McCain and Joe Lieberman--did not pass. But a nonbinding resolution did, urging the Congress to enact mandatory, market-based limits to slow, stop and reverse the growth of emissions. Though it's nonbinding, the fact it passed with the word "mandatory" in it is encouraging. Most important, Pete Domenici, chair of the Senate Energy Committee, voted for it. I don't know if I'd call it a turning point. If I were making predictions--which is maybe not a business I should be in--I would say it will take another House and another president to see real changes. But we're about to enter a phase where the debate will not be about whether to deal with climate change, but how.