Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme (UNEP) and the UN's World Meteorological Organization (WMO) "... to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation."[IPCC website] The Third Assessment Report (TAR) is the third of a series of assessments; it has been superseded by the IPCC Fourth Assessment Report (AR4), released in 2007.
Statements of the IPCC or information from the TAR are often used as a reference showing a scientific consensus on the subject of global warming, although a small minority of scientists take issue with the UN assessments (see also Global warming controversy and Politics of global warming).
The IPCC is organized as three working groups (WG) and a task force [1]:
WG I covers the same areas as the Second Assessment Report (SAR) of 1995, but WG II & III cover slightly different areas in the TAR.
The key conclusions of Working Group I (The Scientific Basis, Summary for Policymakers, in IPCC AR3 WG1 2001) were:
The TAR estimate for the climate sensitivity is 1.5 to 4.5 °C; and the average surface temperature is projected to increase by 1.4 to 5.8 Celsius degrees over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 metres over the same period. The wide range in projections is based upon several different scenarios that assume different levels of future CO2 emissions (see the section below on Projections in the TAR).
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