The IPCC Third Assessment Report (TAR), Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. 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 Third Assessment Report (TAR) was completed in 2001 and consists of four reports, three of them from its Working Groups: Working Group I: The Scientific Basis; Working Group II: Impacts, Adaptation and Vulnerability; Working Group III: Mitigation; Synthesis Report. A number of the TAR's conclusions are given quantitative estimates of how probable it is that they are correct, e.g., greater than 66% probability of being correct. These are "Bayesian" probabilities, which are based on an expert assessment of all the available evidence. "Robust findings" of the Synthesis Report include: "Observations show Earth's surface is warming. Globally, 1990s very likely warmest decade in instrumental record". Atmospheric concentrations of anthropogenic (i.e., human-emitted) greenhouse gases have increased substantially. Since the mid-20th century, most of the observed warming is "likely" (greater than 66% probability, based on expert judgement) due to human activities. Projections based on the Special Report on Emissions Scenarios suggest warming over the 21st century at a more rapid rate than that experienced for at least the last 10,000 years. "Projected climate change will have beneficial and adverse effects on both environmental and socioeconomic systems, but the larger the changes and the rate of change in climate, the more the adverse effects predominate." "Ecosystems and species are vulnerable to climate change and other stresses (as illustrated by observed impacts of recent regional temperature changes) and some will be irreversibly damaged or lost." "Greenhouse gas emission reduction (mitigation) actions would lessen the pressures on natural and human systems from climate change." "Adaptation [to the effects of climate change] has the potential to reduce adverse effects of climate change and can often produce immediate ancillary benefits, but will not prevent all damages." An example of adaptation to climate change is building levees in response to sea level rise. Working groups 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