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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."

Frequently Asked Questions: Links and Resources

IPCC's Working Group I Frequently Asked Questions
[Click here to download the PDF] (11 MB)

The National Center for Atmospheric Research's (NCAR) Climate Change Frequently Asked Questions

Additional Climate Change Information from NCAR

National Aeronautics and Space Administration's (NASA) Earth Observatory Global Warming Questions & Answers

NASA's Earth Observatory Fact Sheet on Global Warming

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