Soccer, beer and bratwurst were very likely the only things on fans' minds as they descended on Germany to celebrate the World Cup this June. But all that partying had a downside--pollution. One million soccer tourists consumed a lot of energy. Environmentalism is part of the German zeitgeist, so it is only fitting that the event had a "green goal," too. A consortium including FIFA, the international soccer federation, and the German football association DFB donated 1.2 million euros to make this year's play-off the first sporting event to offset its carbon dioxide emissions by investing in three renewable energy projects.

Among the environmentally savvy, carbon-offset programs are the latest rage. At least a dozen companies offer the promise to mitigate greenhouse gas emissions from activities such as flying and driving and from events such as weddings and record releases. Voluntary offset programs, however, are not regulated, so consumers cannot be sure that they are investing in environmentally sound projects. What is more, reductions do not help much, because emissions from such activities are tiny: for instance, Germany's total carbon dioxide emissions are about 800 million tons per year--the World Cup emitted a mere 100,000 tons extra.

But governments are starting to pay heed to offsets. Europe established a cap-and-trade system last year that limits carbon dioxide emissions from about 50 percent of industry to reach its emissions goals as dictated by the Kyoto Protocol. Officials modeled the system on the sulfur dioxide trading market established in the U.S. in 1995, which has successfully cut levels of acid rain. As the trading market evolves, some environmentalists think that voluntary offset programs could join existing cap-and-trade market schemes to cut emissions even more substantially.

Right now, however, groups involved in voluntary projects are busy establishing credibility. "We wanted to serve as a model," says Christian Hochfeld of the ko Institute in Berlin, an environmental think tank that developed the Green Goal project for the World Cup.

To that end, the institute chose projects that met criteria established by the World Wildlife Fund to better define high-quality development projects for industries affected by Kyoto. In Tamil Nadu, India, Women for Sustainable Development, a nonprofit organization, will oversee the installation of 700 to 1,000 biogas reactors--simple enclosed pits about the size of a well into which villagers dump cow dung. The fermenting mass generates gas, which fuels stoves and replaces kerosene. Two other sustainable energy projects will take place in South Africa. One will capture off-gas at a sewage treatment facility and burn it to supply electricity to Sebokeng, a township near Johannesburg. The other will replace a citrus farm's coal-fired heating system with one that burns sawdust--a by-product of wood processing usually discarded. The projects will offset all the soccer tournament's emissions.

World Cup organizers could have planted trees--as has been done by previous sporting events, such as the Super Bowl--or invested in other projects on home turf. But planting has been criticized because trees take years of growth to suck up an equivalent amount of released carbon. Also, not all renewable energy projects constitute an "offset." If an undertaking that would have happened anyway was jump-started through government subsidies--using wind power, for example--it cannot be considered a true offset, environmental groups say.

Currently, voluntary activities do not generate tradable emission credits. But imagine if they did. Suppose, for example, that anyone could earn credits for cutting consumption or increasing efficiency. Those villagers in India could earn credits for reducing their emissions that they could in turn sell, says Annie Petsonk, international counsel at Environmental Defense, a New York City-based nonprofit group. "How interesting would it be to have everyone participating? It would stimulate so much energy efficiency," she predicts. "We're talking about tapping economic power in favor of protecting the environment on a huge scale."