Coal is dirty. But coal is driving the U.S., Chinese and Indian economies. And therefore, coal is not going away. Renewable energy sources like solar and wind generate only 1 percent of the world's electricity. Do the math: Making coal burn cleaner might be the most pressing environmental problem that no one talks about.

Despite recent estimates that pollution from China's booming coal industry reaches U.S. shores in as little as five days, the green-tech investment boom that has funded the rise of biofuels has bypassed coal. Even the head of the World Coal Institute recently proclaimed the last 10 years "a lost decade" for clean coal, saying it's time to play catch-up.

Stanford's Jeremy Carl, a research fellow in the Program on Energy and Sustainable Development, couldn't agree more. He spoke on the phone with Wired News to discuss China, the holy grail of clean coal and how many coal plants he'd trade for Kyoto's accomplishments.

Stanford research fellow Jeremy Carl says, "Coal is as dirty as it gets," but warns against throwing the possibly cleaned-up baby out with the dirty bathwater.

Wired News: Why'd you get into clean coal?

Jeremy Carl: I looked at the numbers. It's a question of where the big sources of emissions are and where we can attack them.

WN: Can you give us an idea of the scale of coal power? Can you put coal in context as an energy source?

Carl: Only oil makes a bigger contribution to global energy. In terms of energy in the industrial world, it's about 40 percent of electricity production.

WN: How dirty is coal?

Carl: Coal is as dirty as it gets. Coal has every element in the periodic table. And depending where in the world you get it from, "coal" can mean 100 different substances. If you sent the sort of coal you might use in a typical Indian plant to a supermodern boiler in Japan, it would shut the place down.

WN: But there's got to be good things about coal.

Carl: It's cheap. And coal doesn't have the kind of extreme risk that nuclear power has. You're not going to build a dirty bomb out of coal. And unlike other fossil fuels, it is really widely distributed, so there is less of a coal OPEC.

WN: And that distribution would seem to make resource wars less likely to break out over coal?

Carl: Yes.

WN: Is there an energy source that could replace coal?

Carl: Natural gas is the only viable replacement, and it's not clear that the natural-gas supply could scale up to replace coal.

WN: So, how can we can make coal cleaner?

Carl: The most-well-known is flue-gas desulfurization, which takes sulfur dioxide out of smoke stacks, and came out of concerns about acid rain. There are other pollution-control devices for nitrogen oxide and mercury filters.

WN: What about up-and-coming technologies like carbon capture and sequestration? Can you tell us about that?

Carl: You're taking carbon from a smokestack and pressure-injecting it into a geological formation of some sort. We actually already do this process at an industrial level. We know how this works.

WN: Seems like we're spending a lot of time on the backend scrubbing pollutants out. Should we be designing in a cleaner process on the front end?

Carl: A lot of people point to integrated gasification-combined-cycle (IGCC) plants, which gasify coal before burning it, as the holy grail because they get you a cleaner process. It gives you a more concentrated stream of carbon that you can sequester underground more cheaply. The capital cost is very high, though, and we don't have a lot of experience in designing them.

WN: We hear a lot about China's coal industry. Can you compare it with the U.S. industry, which ranks second in the world?

Carl: We mine about (1.1 billion tons) of coal per year. China was at about 1.4 billion tons seven years ago. Now they are at 2.4 billion tons. So, they essentially took the second-biggest coal industry in the whole world and replicated it in seven years. And if you look at the Chinese plans, they plan to ramp it up even more in the future.

WN: Given the obvious environmental impacts of these plants, why don't we have better answers for these problems than the Kyoto Protocol (which the United States didn't sign, and which exempted China and India from emissions restrictions)?

Carl: I'll give you a speculative, personal answer. It has to do with the politics of the type of people who were negotiating Kyoto. And the pressure put on by environmental groups that were uncomfortable with coal. There was just so much pressure on the symbolic importance of getting a deal done.

WN: What would you have rather seen?

Carl: I think there has been some really good criticism that says, "Was the U.N. really a good forum for this? Or would it have been better to have taken the 10 countries who consume 60 percent of global energy and do something with real teeth in it?" I think that would have been a much better approach.

I would have happily traded every emissions gain from Kyoto for eight clean coal plants sequestering carbon in different countries. Because then we could have a real discussion that says, "This works. Now let's see who has to bear the cost."

WN: Why would that be such a big deal?

Carl: Because right now we're having a conversation with China and India where we're trying to get China and India to build clean coal plants by saying, "Here's this thing that's never been tried before at a mass scale. You should build one." And that's not going to work.