The IPCC’s Synthesis Report “ Summary for Policymakers” (Table SPM.6) finds that using the best estimate climate sensitivity, stabilizing at a warming of 2.0☌ to 2.4☌ requires stabilizing carbon dioxide emissions in the range of 350-400 ppm CO2, or 445-495ppm CO2-equivalent. Currently, concentrations are 383 ppm and rising at a rate of about 2 ppm a year, a rate that has been rising and is expected to continue doing so. Therefore, to have any plausible chance of avoiding 2☌ total warming and its effects, the nation and the world must keep CO2 concentrations substantially below a doubling from preindustrial levels, which were roughly 280 parts per million. Values substantially higher than 4.5☌ cannot be excluded.” The Working Group I summary report from the panel concludes that the best estimate of “equilibrium climate sensitivity,” which is “the global average surface warming following a doubling of carbon dioxide concentrations” is “likely to be in the range 2☌ to 4.5☌ with a best estimate of about 3☌, and is very unlikely to be less than 1.5☌. Intergovernmental Panel on Climate Change’s “ Fourth Assessment Report”represents the best review and analysis of the state of scientific knowledge on climate. Many groups and countries have embraced the 2☌ target, including the 2005 International Climate Change Taskforce (in its report “ Meeting the Climate Challenge”), the European Union (see “ EU action against climate change”), and more than 200 of the world’s leading climate scientists (see the Bali Declaration by Scientists). The 2050 target is based on the science-driven conclusion that the risks of dangerous impacts rise sharply as planetary warming exceeds 2☌ from preindustrial levels. Cutting emissions to 80 percent below 1990 levels by 2050 greenhouse gas emissions back to 1990 levels by 2020Ģ. policymakers, President-elect Barack Obama has endorsed two targets:ġ. The United States finally appears likely to adopt a domestic climate bill in the 111th Congress. The IPCC science behind emissions targets The United States has the technology and resources to reduce its emissions levels substantially below 1990 levels by 2020, and having already lost much of its credibility in the international community by failing to act, there is no time to lose in adoption of binding targets to avoid the risks of dangerous impacts of global warming. To achieve its goals, domestic climate legislation should limit the use of both international and domestic offsets. That conclusion is based on the latest science from the Intergovernmental Panel on Climate Change and NASA, among others, but it also involves matters of timing and U.S. greenhouse gas emissions 20 to 30 percent below 1990 levels by 2020. climate bill should set a target of reducing U.S. Download this paper (pdf) Executive summaryĪ U.S.

Climate change by joseph romm