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Working Group II Definitions

Likelihood of an outcome or result
Virtually certain > 99% probability of occurrence
Extremely likely > 95%
Very likely > 90%
Likely > 66%
More likely than not > 50%
Very unlikely < 10%
Extremely unlikely < 5%.

Confidence in a statement
Very high confidence: At least a 9 out of 10 chance of being correct
High confidence: About an 8 out of 10 chance
Medium confidence: About a 5 out of 10 chance
Low confidence: About a 2 out of 10 chance
Very low confidence: Less than a 1 out of 10 chance

Confidence symbols in the text
*** Very high confidence
** High confidence
* Medium confidence

Key Assumptions

The Working Group II report discusses future impacts "for the range of unmitigated climate changes projected by the IPCC over this century judged to be relevant for people and the environment." Its different scenarios of future emissions of greenhouse gases "do not include additional climate initiatives, which means that no scenarios are included that explicitly assume implementation of the United Nations Framework Convention on Climate Change or the emissions targets of the Kyoto Protocol."

Please note: This website was created to support the 2007 IPCC Fourth Assessment Report and much of the content is now outdated. For current IPCC information, please visit www. ipcc.ch.

The IPCC Fourth Assessment Report

In addition to key excerpts from the IPCC reports, this website offers academic and journalistic resources to help journalists localize their coverage of the four IPCC reports being issued in 2007, including regional and state resources and contact information for scientists. Recordings of regional briefings with scientists held April 2-4, 2007, and a teleconference with Working Group III authors held on May 4, 2007, are also posted.

The IPCC's Fourth Assessment Report (AR4) is a series of four reports being released in 2007, which follows earlier IPCC Assessment Reports in 1990, 1995, and 2001. Assessment Reports express the world scientific community's updated understanding of global warming, based on research conducted since the previous report. The IPCC was established by the World Meteorological Organization and United Nations Environment Programme and represents the consensus science position on climate change, directly engaging more than 2,500 scientists from more than 130 nations.

The first three parts of the 2007 report summarize the findings of three IPCC working groups. The fourth part will synthesize the three working groups' findings in more detail. The four parts are:

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