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All of the IPCC reports and assessments are used to inform the international policy and negotiations on climate issues, which since 1992 have occurred under the Framework Convention on Climate Change.

It is important to note that although the IPCC is organized within a political institutional framework, it is fundamentally a scientific body—made up and led by leading scientists from around the world. In order to remain true to its scientific mandate and to maintain scientific objectivity, the IPCC is careful to avoid making policy recommendations or shaping research programs. However, because the assessments of the IPCC are the most comprehensive and balanced evaluations of the climate change issue, its work is probably the single most important foundation on which climate policy is built [2].

Historically, the IPCC has been organized into three working groups, a variety of task forces or special committees, and a small secretariat in Geneva, Switzerland. Scientists from 120 nations participate in the preparation of the IPCC reports. The topical assignments to the working groups have evolved somewhat over time. For the Third Assessment Report, Working Group I was charged with assessing the scientific aspects of the climate system and climate change. Working Group II was charged with addressing vulnerability of human and natural systems to climate change (i.e., the negative and positive consequences of climate change), and options for adapting to them. Working Group III was charged with assessing options for limiting greenhouse gas (GHG) emissions and other types of mitigation, as well as economic issues. A separate Task Force oversees a program to compile national greenhouse gas inventories. Each of these four bodies has two co-chairs -- one from a developed and one from a developing country.

Each working group publishes an in-depth technical report, a Technical Summary, and a short Summary for Policymakers (SPM). In addition, the major findings and conclusions from all three reports provide the basis for preparing a Synthesis Report. The Synthesis report addresses a broad range of key policy-relevant questions identified by the IPCC in consultation with governments and the Bodies of the UNFCCC.

Each working group holds a plenary session to resolve final questions raised during the review phases and to reach final approval of the Summaries for Policymakers. The entire IPCC Plenary met in April 2001 to approve the contributions of the three Working Groups, and then again in September 2001 to approve the Synthesis report.

The key findings of each of the three working groups of the TAR are listed below. For additional information on the findings of each of the working groups, or on the processes of the IPCC, please see the "Related Links" section above.

The Key Findings of each of the three working groups were:

Working Group One "Climate Change 2001: The Scientific Basis"

• The average global surface temperature is projected to rise by 2.5 to 10.4 degrees Fahrenheit over the period of 1990 to 2100.
  
  
• It is very likely that 1990 to 2000 was the warmest decade and 1998 the warmest year since 1861.
  
  
• There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.
  
  
• Global sea level in the past century has risen at a rate 10 times faster than during any time over the last 3,000 years and it is projected to rise by about 3.5 to 34.6 inches between 1990 and 2100.
  
  
• Northern Hemisphere snow cover and sea-ice extent are projected to decrease further.

Working Group Two "Climate Change 2001: Impacts, Adaptation and Vulnerability"

• Recent regional climate changes, particularly temperature increases, have already affected many physical and biological systems.
  
  
• There are preliminary indications that some human systems have been affected by recent increases in floods and droughts.
  
  
• Natural systems are vulnerable to climate change, and some will be irreversibly damaged.
  
  
• Many human systems are sensitive to climate change, and some are vulnerable.
  
  
• Projected changes in climate extremes could have major consequences.
  
  
• The potential for large-scale and possibly irreversible impacts poses risks that have yet to be reliably quantified.
  
  
• Adaptation is a necessary strategy at all scales to complement climate change mitigation efforts.
  
  
• Those with the least resources have the least capacity to adapt and are the most vulnerable.
  
  
• Adaptation, sustainable development, and enhancement of equity can be mutually reinforcing.

Working Group Three "Climate Change 2001: Mitigation"

• The nature of the climate change mitigation challenge is unique.
  
  
• There are many options to reduce greenhouse gas emissions and enhance sinks.
  
  
• The costs and ancillary benefits of mitigation options vary by various assumptions and measurement techniques.
  
  
• There are many ways and means to make mitigation effective and affordable.
  
  

For additional information on these working groups, please read the UCS in-depth briefings on each working group. (see links above)