As 12,000 people gathered in Bali this week to begin framing a global response to Earth's warming climate, efforts to close a deal that would slow destruction of tropical forests appear to be the best prospect for a concrete achievement from the historic assemblage.

The deforestation issue is also Exhibit A for the disputes that have made climate negotiations lengthy and divisive despite widening agreement that global warming is real and largely man-made. While scientific dispute over what causes global warming has ended, the debate over how to address it has just begun.

Deforestation is one of the biggest drivers of the buildup of greenhouse gases in the atmosphere. Each year, tropical forests covering an area at least equal to the size of New York state are destroyed; the carbon dioxide that those trees would have absorbed amounts to 20 percent of the world's greenhouse gas emissions, about the same as total U.S. emissions.

The bargain is being championed by a dozen of the world's developing countries at the conference, whose ultimate goal is to map out a two-year path aimed at forging a global system for imposing and enforcing reductions in greenhouse gas emissions.