The countries that attended the second meeting of the Parties to the Kyoto Protocol in Nairobi agreed to review the pact in 2008. The Nov. 17 agreement is a step forward since it was feared that serious conflict between developed and developing countries might torpedo the conference. It is hoped that the review will lay the groundwork for creating a future international mechanism to combat global warming more effectively than Kyoto, but many obstacles remain to be overcome.

The pact, agreed in 1997 but not effective till 2005, requires 35 industrialized countries to reduce their emissions of greenhouse gases by an average 5 percent below 1990 levels by 2012, when the pact expires. But there are inherent weaknesses.

The United States, the No. 1 polluter, accounting for 25 percent of the world's carbon dioxide emissions, pulled out of the Kyoto Protocol in 2001, saying that remaining with the pact would damage its economy. Developing countries including China, the world's No. 2 emitter, India and Brazil are not obliged under the pact to reduce emissions. The U.S. and China together account for about 40 percent of greenhouse-gas emissions.