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Attribution of Changes

Attribution of Changes. Primary Source: IPCC WG-I Chapter 9 - Understanding and Attributing Climate Change. What is climate?.

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Attribution of Changes

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  1. Attribution of Changes Primary Source: IPCC WG-I Chapter 9 - Understanding and Attributing Climate Change

  2. What is climate? Climate is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. WMO period: 30 years

  3. What is climate change and variability? Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean or variability of its properties, and that persists for an extended period, typically decades or longer. Climate variability refers to variations beyond individual weather events in the mean state and other statistics of the climate (such as standard deviations, the occurrence of extremes, etc.) on all spatial and temporal scales. This includes “internal variability”.

  4. What is detection and attribution? Detection of climate changeis the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Attributionof causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence.

  5. Net RF: 1750 to 2005(from Chapter 2) Note uncertainties

  6. Atmospheric Temperature Changes - PCM Model solar only volcanic only GHGs only O3 only direct sulphate aerosol all 1890 to 1999 (˚C/100Y)

  7. Reflected Solar Radiation Satellites Models Deceasing Cloud Cover?

  8. NH T: Reconstructions vs. EBM

  9. GCM Simulations: Natural Forcings 19 Simulations 5 Models

  10. GCM Simulations: All Forcings 58 Simulations 14 Models Internal variability? Aerosols? Solar, volcanic effects?

  11. Latitudinal Distribution of Trends Red: All forcings, middle 90% of GCM range (58 simulations by 14 GCMs) Blue: Natural forcings only, middle 90% of GCM range (19 simulations by 5 GCMs)

  12. Land & Ocean Changes

  13. IPCC Statement IPCC: Most global warming very likely due to increase in anthropogenic GHG concentrations Likely anthropogenic warming on continental scale

  14. Spatial Distribution of Trends 58 Sim. 14 GCMs 19 Sim. 5 GCMs

  15. Changes in Tropopause Height ERA40: Observation-based analysis Model results (each 4 simulations by PCM): Red - All forcings Blue - Natural forcings only

  16. Ocean-Change Signal Strength Observed Signal: Red dots Model results (individual basins from PCM): Green - All forcings Blue - Natural forcings only

  17. Methods of Detection - Optimal Fingerprinting Linear Regression Internal variability (“noise”) Observed climate patterns Scale factors solar volcanic Response patterns to forcings - from a GCM GHGs O3 Earlier slide All Aerosol

  18. Methods of Detection - Inferring Change Are at least some of the scale factors significantly different from zero? DETECTION Is a forcing distinguishable from others? Can it (or some combination) explain the observed pattern? ATTRIBUTION

  19. Scale Factors - 4 GCMs Bars: 5-95% uncertainty range Red: GHGs Green: Other human factors Blue: Natural

  20. Inferred Climate Change - 4 GCMs 1990s minus 1900s (decades) Observed: Black line Trend: 1950 - 1999

  21. Can Greenhouse Warming Cause a Climatic Extreme? Summer temperatures in Switzerland A single event cannot be attributed to a forcing factor, but …

  22. Probability of extreme European summer temperatures(using the Hadley Centre GCM) No anthropogenic change With anthropogenic change … the probability (risk) of an occurrence can change due to external influences.

  23. END Attribution of Changes

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