Late in 2006 several events moved the U.S. and other countries closer to serious global negotiations to control greenhouse gas (GHG) emissions. First, the signatories to the UN Framework Convention on Climate Change, including the U.S., agreed to initiate negotiations on the framework to follow the Kyoto Protocol, which ends in 2012. Second, the U.S. Supreme Court heard arguments that the Federal Government must control CO2 emissions under the Clean Air Act. Third, the new Democratic majority in Congress, with Senator Barbara Boxer in the lead as Chair of the Environment Committee, promised to put climate change to the fore. And fourth, the Stern Review, an excellent new report by the U.K. Treasury, provided ample evidence on the case for faster and comprehensive action.

It's therefore timely to ask what a meaningful global agreement would entail, and how the world can arrive at such an agreement. A solid starting point is the 1992 U.N. Framework Convention on Climate Change (UNFCCC), the international treaty that binds countries to act on the problem and under which specific measures such as the Kyoto Protocol are adopted. The Kyoto Protocol was a flawed but useful first step under the Framework Convention, though one that in practice was gravely weakened by the lack of U.S. participation.

The UNFCCC wisely focused on the nub of the climate issue. The signatories to the Framework Convention, including the U.S. and almost all other countries, declared the objective to be the "stabilization of greenhouse gas concentrations in the atmosphere at a level which would prevent dangerous anthropogenic interference with the climate system." The Kyoto Protocol, adopted in 1997, did not implement this idea very well: it took a short-term view of a long-term objective and as a result lost clarity, credibility and support along the way. The key now is to move beyond it.

The Kyoto Protocol calls on the high-income countries and the post-communist countries of Eastern Europe and former Soviet Union to reduce their GHG emissions as of 2012 by around 6 percent compared to the 1990 level. This commitment is far better than nothing (a fair description of the Bush Administration's non-policy), but it has two major flaws. First, it leaves out the developing countries, which soon will emit more than half of the world's GHGs. Without the active participation of China, India and other developing countries, stabilization of GHGs is simply impossible. Second, the Kyoto Protocol takes the long-term objective of stabilization of GHG concentrations and transforms it into a short-term target on emissions reductions, with no clear link between the two. The main actions for GHG stabilization will have to be long-term changes in technology, which exceed the 2012 horizon of the Kyoto Protocol.

This time around, it's better to start with a long-term view. On today's best scientific evidence, we must stabilize GHGs at a level far below the level that will be reached on a business-as-usual trajectory of energy use, deforestation and industrial growth (three main sources of greenhouse gases). "Dangerous anthropogenic interference" is likely to kick in when carbon concentrations in the atmosphere are at 450-550 parts per million (ppm). The world's current trajectory of energy use, deforestation and industrial growth could easily take us to twice that range by the end of the century. The Stern Review, an excellent new report by the U.K. Treasury, makes clear that the consequences could be catastrophic: melting of ice sheets, with huge rises of ocean levels; massive crop failures; increased transmission of diseases; and perhaps most shocking of all, a pervasive extinction of other species with potentially catastrophic effects on ecosystem services that support human life and wellbeing.

The world should therefore agree to stabilize GHG concentrations at a tentative target level, say 550 ppm as of 2100, with that target to be revised periodically as new scientific information emerges. A mid-century goal, say 500 ppm, would provide a 40-year target consistent with the end-century target. With those two long-term anchors and interim targets set, the world's governments could then agree on strategies for reaching them. These strategies would include market incentives to reduce GHG emissions (using taxes and tradable permits); greatly expanded research on sustainable energy use, land use and industrial development, and technology transfers from rich to poor countries.

The Stern Report makes clear that the costs of such control will be far lower than the costs of inaction. Lost-cost, high-benefit control efforts look promising in at least three major areas: improved energy efficiency (including high-mileage autos), energy technologies that reduce greenhouse gas emissions (non-fossil-fuel sources and sequestration of fossil-fuel emissions), and sustainable land use. Smart technologies can likely keep the long-term annual costs of GHG stabilization at below 1 percent of global GDP. The rich countries can help the poor countries to develop and adopt the needed technologies.

It's time, therefore, to aim for a sensible long-term framework in which all countries will participate. The economics are right. The U.S. Congress is set to back such a course. The White House will as well, soon after 2008, and with some luck, even before.