A new study finds that technologies already exist to solve the problem of global warming. It says strategies employing these technologies over the next fifty years could put the brakes on rising levels of carbon dioxide and other heat-trapping gases in the earth's atmosphere - a chief cause of global warming. But critics say the study fails to address the economic, social and political costs of such a plan.

The study says global warming could be prevented by deploying a wide array of technologies, from renewable energy sources like solar, wind and nuclear power, to alternative bio-fuels, and the capture and storage of climate-changing emissions of carbon from power plants. The study also identifies changes in forestry and farming techniques that could provide additional reductions in carbon emissions.

"Anybody that is out there can look at the paper and visit the things that we are talking about and see that they exist at an industrial scale in the marketplace today," says Steve Pacala, the study's author and Princeton University ecology professor. He says a scaling up of the technologies can work to stabilize carbon emissions, which otherwise are expected to double by mid-century. "And most of the science and most of the indicators that we have of what's happened in the past say that we start to encounter serious dangers at about the doubling mark. That means we have to act at the first half of the century because we would reach a doubling by mid-century otherwise, and we would be faced with an energy system that was emitting carbon like crazy and the momentum would carry us on to a tripling."

Mr. Pacala says that an excessively carbon- rich atmosphere will likely cause decreased crop yields, increased threats to human health and more frequent extreme weather events. But critics like Marlo Lewis, a senior fellow in environmental policy with the Competitive Enterprise Institute, say the Princeton University study is flawed because it fails to take into account the economic and social costs of its recommendations. "One of their strategies which they said would eliminate a billion tons of carbon dioxide emissions over the next fifty years would be to reduce the number of automobile miles traveled, in other words reduce the amount of driving by fifty percent. And, that is going to impose a horrendous cost in terms of people's time, convenience, and lifestyle choices. But then there are the political costs and the intangible costs, which all of us would experience if our driving were somehow limited," he says.

Marlo Lewis says the study also ignores political reality, as in the case of nuclear power. The study recommends doubling the current global nuclear capacity to replace coal-based electricity, a strategy that most environmentalists find troubling. "Who are the biggest boosters of the Kyoto Agenda [Kyoto Protocol on Climate Change] of forced de-carbonization? It is the environmentalist movement? [Yes] Is the environmental movement pro-nuclear? [No it is not.] We have spent over a decade in this country debating where to put spent nuclear waste and we still can't come up with an answer. And the environmental movement is still hostile to the transport and disposal of nuclear waste in Yucca Mountain, [New Mexico]. And, it is because the environmentalists have blocked it."

Steve Pacala says the study contributes to the on-going debate about how the Earth's complex ecosystems should be managed. "We have the technology to engage in wise stewardship of the earth now at a cost that is not prohibitive. So I just think that we have a responsibility as a species to do it," he says.

Study author Steve Pacala says aggressive action now would create new industries, improve air quality and decrease reliance on polluting fossil fuels. The research is published in the Journal Science.