This is part of a series of candidate interviews produced jointly by Grist and Outside.

In his two and a half years in the U.S. Senate, Barack Obama (D.-Ill.) has been active—even hyperactive—on matters of energy and the environment. The Democrat from Illinois has introduced or co-signed nearly 100 eco-related bills on issues ranging from auto fuel economy to lead poisoning to biofuels promotion, and racked up a notable 96 percent rating from the League of Conservation Voters.

But it hasn't been all hugs and kisses between Obama and enviros. Some green activists wrinkle their noses at Obama's overarching emphasis on bipartisan consensus, insisting that real environmental change won't happen without tough partisan battles against entrenched interests. Enviros have also criticized Obama for his support of corn-derived ethanol and liquid coal, both of which would benefit industries in his home state of Illinois but do little to solve climate and energy problems.

We reached Obama by phone in his office in Washington, D.C., between Senate votes.

Why should voters consider you the strongest candidate on environmental issues? What sets your green platform apart from the rest?
To begin with, people can look at my track record. I'm proud of the fact that one of the first sets of endorsements I received in my race for the U.S. Senate was from the Sierra Club and the League of Conservation Voters. I've since cast tough votes on behalf of the environment. For example, I voted against the "Clear Skies" bill that George Bush was promoting, despite the fact that the administration had heated up support for the bill in southern Illinois, which, as you know, is coal country. So I think people can feel confident that I don't just talk the talk, I walk the walk.

How central will energy and the environment be to your campaign?
I consider energy to be one of the three most important issues that we are facing domestically, along with revamping our education system and reforming our health-care systems. The opportunities for significant change exist partly because the awareness of the threat of climate change has grown rapidly over the last couple of years. Al Gore deserves a lot of credit for that, as do environmental activists and outlets like Grist. People are ready to recognize the magnitude of the climate problem and take it on.

They're also recognizing that our dependence on fossil fuels from the Middle East is distorting our foreign policies, and that we can't economically sustain our use of a resource that is getting more and more expensive over time. As all those things converge, we have to move boldly on energy legislation, and that's what I'll do as the next president.

How central of a role do you think the issues of energy and the environment will play overall in the 2008 campaign? Will they take a backseat to Iraq?
Bringing the war in Iraq to a responsible end is the most pressing challenge we face, but that doesn't mean it's the only challenge we face. Reducing our dependence on foreign oil and slashing our greenhouse-gas emissions will also be defining issues in this campaign.

You've consistently emphasized consensus and putting aside partisan battles. Many argue that, when it comes to climate change, the maximum of what's politically possible falls short of the minimum we need to do to solve the problem. In other words, consensus won't get us where we need to go. Will you fight the political battles needed to move the consensus on this issue, even if that means aggravating partisan rifts?
I am the cosponsor of the most aggressive climate-change legislation in the Senate, along with Barbara Boxer [D-Calif.] and Bernie Sanders [I-Vt.], which would reduce carbon emissions by 80 percent by 2050. We are going to have to make some big decisions to meet those goals. Consensus doesn't mean 100 percent consensus-there is undoubtedly going to be resistance from certain parts of the energy sector, and there may be ideological resistance within the Republican party, and we are going to have to attend to the regional differences in terms of how people get energy. But I believe that we can put together a strong majority to move forward, as long as we are thoughtful about the potential losers in any big piece of energy legislation.

Do you believe that we can achieve political consensus on this goal of 80 percent reductions by 2050?
I think with presidential leadership we can meet this goal, and it will be one of my top priorities. But it is going to require a thoughtful approach that accounts for the possibility that electricity prices will go up, and that low-income people may need to be compensated. We'll have to deal with the fact that many of our power plants are coal-burning, and consider what investments we're willing to make in coal sequestration. If we make sure that the burdens and benefits of a strong environmental policy are evenly spread across the economy, then people will want to see us take on this problem in an aggressive way.

Do you believe that we need a carbon tax in addition to a cap-and-trade program?
I believe that depending on how it is designed, a carbon tax accomplishes much of the same thing that a cap-and-trade program accomplishes. The danger in a cap-and-trade system is that the permits to emit greenhouse gases are given away for free, as opposed to priced at auction. One of the mistakes the Europeans made in setting up a cap-and-trade system was to give too many of those permits away. So as I roll out my proposals for a cap-and-trade system, I will price permits so that it has much of the same effect as a carbon tax.

You have personally addressed automakers with a call for more efficient car technologies. Is Detroit ready for this shift?
We made some progress recently in the Senate, with the first fuel-efficiency standards increase in 20 years . It only went up to 35 miles per gallon-far short of what we needed and what technology would allow.

We have to work not only to make our cars more efficient, but the fuel we put in those cars a lot cleaner. I believe I am the only candidate who has proposed a National Low Carbon Fuel Standard, something that California has already initiated

You've received a lot of criticism from enviros of your support for coal-to-liquids technology. You recently shifted your position somewhat, but haven't retracted it. Why?
I was always firm that if the life-cycle carbon emissions of coal-to-liquid were higher than gasoline, we couldn't do it, because it would contradict my position on reducing greenhouse gases. But I also believe that, because of the abundance of coal in the U.S., coal-based fuels could be a substitute for some of the oil we import from the Middle East, as long as we can reduce the resulting CO2 emissions to 20 percent below current levels from petroleum-based fuels.

How much should we be willing to pay in taxpayer money to make liquid coal that clean?
Our original bill on coal-to-liquids—which generated a lot of heat in the environmental community, no pun intended—proposed $200 million for demonstration projects, to see where this technology might take us.

If the technology exists for us to use coal in a clean fashion, then that is something all of us should welcome, particularly because China and India are building coal-fired power plants at a rapid rate, and they likely have lifespans of several decades. Coal is a cheaper resource, and they're going to be figuring out a way to exploit it, so we should help to find technologies that will ensure that if it is used, it is used cleanly. The U.S. is recognized as the global leader in understanding better coal and geologic sequestration technologies. If we abandon that leadership, we risk leaving the rest of the planet wide open to investing billions in polluting infrastructure.

But I stress again that my position has been consistent throughout: If we are using coal in the absence of these clean technologies, then we are going to be worsening the trend of global warming, and that is something that we can't do.

Do you support a freeze in the U.S. on new coal development until these clean-coal technologies are commercially available?
I believe that relying on the ingenuity of the free market, coupled with a strong carbon cap, is the best way to reduce carbon emissions, rather than an arbitrary freeze on development.

As president, would you oppose subsidizing any technology that increases global warming—even if it reduces our dependence on foreign oil?
As a general principle I would agree with that. I would not make huge investments or try to take technologies to scale that worsen the climate-change situation. But it may be appropriate for the federal government to make small investments in pilot projects to see if we can make dirty fuels cleaner.

I think that with nuclear power, we have got to see if there are ways for us to store the radioactive material in a safe, environmentally sound way, and if we can do that and deal with some of the safety and security issues, [nuclear power] is something that we should look at.

My general view is that we should experiment with all sorts of potential energy sources—don't prejudge what works and what doesn't, but insist that we have very strict standards in terms of where we want to end up, and enforce those standards vigorously.

Some argue that we should commit to a global climate treaty only if China and India do as well. Do you agree? How would you bring China and India to the table?
We shouldn't look at it as a single tit-for-tat exchange. The U.S. is the world's largest economy and the largest single source of the world's greenhouse-gas emissions, so it is our responsibility to take the first step. We cannot expect China and India, with a billion people each, to take the lead on this if we do not—but we can expect them to join us if we demonstrate leadership. If we must take the first step, our second and third steps must be conditioned on meaningful participation by all countries. This is also an enormous opportunity for us to provide our technological expertise to these nations so they can leapfrog to cleaner technologies.

You are a strong supporter of both corn and cellulosic ethanol, both of which would get a major boost from your proposed National Low Carbon Fuel Standard. How, specifically, will you structure policies that transition the U.S. away from corn ethanol and toward cellulosic?
No single feedstock is going to get us to energy independence, and none will be the perfect solution—each faces its own challenges. Corn-starch ethanol provides a critically important bridge toward energy independence, and corn remains a strong part of the domestic biofuels industry. But developing greater volumes of cellulosics is a critical next step in domestic biofuel development, and is the key component of my Low Carbon Fuel Standard bill.

Through greater fuel economy and the use of hybrid and plug-in vehicles, we can notably reduce our dependence on foreign oil over the next decade. It is important to note that domestic fuel security, environmental protection, and economic development all must be considered in unison as we progress. My National Low Carbon Fuel Standard provides a way for us to better understand the impacts of an advanced biofuels industry on the environment, so that as we move forward on cellulosics and other domestic fuels we do so responsibly.

What environmental achievement are you proudest of?
In 2006, I developed an innovative approach to gradually increase CAFE standards while protecting the financial future of American automakers. The resulting Obama-Lugar-Biden Fuel Economy Reform Act gained the support of senators who had never supported CAFE increases before. This, in turn, helped lay the foundation for Senate passage of updated CAFE standards last month.

After climate and energy, what do you think is the most important environmental issue facing the nation?
Restoring the strength of the EPA to adequately enforce our clean-air, clean-water, and other environmental-protection laws, after over six years of ruling by ideology rather than science and adherence to the law.

Who is your environmental hero?
If I think historically, Rachel Carson probably had as much to do as anybody in helping trigger an environmental consciousness in this country.

I also admire Teddy Roosevelt, who probably wouldn't have seen himself as an environmentalist in modern terms, but who had a great appreciation of the outdoors and the beauty of our land, and understood that part of the role of the president is sound stewardship.

If you could spend one week in a natural area in the U.S., where would it be?
I have very fond memories as a kid of traveling to Yellowstone, marveling at the scenery and chasing after bison, much to my mother's distress.

But when I think of my own connection to the earth, I think of my time in Hawaii, my birthplace. I think those of us who grew up in Hawaii have a particular attachment to the land and understand how fragile it is. When you are snorkeling through the coral reefs, you realize that a slight change in temperature or increase in sediment and runoff could end up destroying it all and making it unavailable for your children. That is something you worry about.

What have you done personally to lighten your environmental footprint?
We just bought a Ford Escape, so I traded in a non-hybrid for a hybrid. We are in the process of replacing our lightbulbs in our house and trying to limit the use of our air conditioning, trying to make sure that we unplug and turn off all of our appliances when we're not using them. It's a fun project to work on with my nine-year-old and my six-year-old.