There is no longer any serious debateabout whether greenhouse gas emissions from human activityare altering the earth's climate. There is also a broadconsensus that efficient mitigation of emissions willrequire carbon pricing via market based instruments (chargesor auctioned tradable permits). The remaining controversiesstem mostly from economic and technological forecastinguncertainties, disputes about global and intergenerationalequity, and political divisions over collective measures tocombat climate change. Near term closure seems unlikely onany of these fronts, but the science is now sufficientlycompelling that a global consensus supports concertedaction. Developing countries must be full participants,because they will be most heavily impacted by globalwarming, and because the scale of their emissions is rapidlyapproaching parity with developed countries.