Estimates of confidence in observed and projected changes in extreme weather and climate events
Climate Variability and Change
Estimates of confidence in observed and projected changes in extreme weather and climate events
Table 1, Summary for Policymakers, Climate Change 2007 – The Scientific Basis
Likelihood of future trends based on projections for 21st century using SRES scenarios| Phenomenon and direction of trend | Likelihood that trend occurred in late 20th century | Likelihood of a human contribution to observed trend | Likelihood of future trends based on projections for 21st century using SRES scenarios |
|---|---|---|---|
| Warmer and fewer cold days and nights over most land areas | Very likely | Likely | Virtually certain |
| Warmer and more frequent hot days and nights over most land areas | Very likely | Likely (nights) | Virtually certain |
| Warm spells/heat waves. Frequency increases over most land areas | Likely | More likely than not | Very likely |
| Heavy precipitation events. Frequency (or proportion of total rainfall from heavy falls) increases over most areas | Likely | More likely than not | Very likely |
| Area affected by droughts increases | Likely in many regions since 1970s | More likely than not | Likely |
| Intense tropical cyclone activity increases | Likely in many regions since 1970s | More likely than not | Likely |
| Increased incidence of extreme high sea level (excludes tsunamis) | Likely | More likely than not | Likely |
Judgemental estimates of confidence:
- Virtually Certain: Greater than 99% chance that a result is true.
- Very likely:90-99% chance
- Likely: 66-90% chance
- Medium likelihood: 33 – 66% chance
- Unlikely: 10-33% chance
- Very unlikely: (1-10% chance)
- Exceptionally unlikely: Less than 1% chance
Reference
IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.