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Attribution of Changes Primary Source: IPCC WG-I Chapter 9 - Understanding and Attributing Climate Change (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) 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 (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) 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”. (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) What is detection and attribution? Detection of climate change is the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Attribution of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence. (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Net RF: 1750 to 2005 (from Chapter 2) Note uncertainties (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Atmospheric Temperature Changes - PCM Model solar only volcanic only GHGs only O3 only direct sulphate aerosol all 1890 to 1999 (Mt/Ag/EnSc/EnSt 404/504 - Global Change) (˚C/100Y) Climate Models (from IPCC WG-I, Chapter 9) Reflected Solar Radiation Satellites Models Deceasing Cloud Cover? (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) NH T: Reconstructions vs. EBM (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) GCM Simulations: Natural Forcings 19 Simulations 5 Models (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) GCM Simulations: All Forcings 58 Simulations 14 Models Internal variability? Aerosols? Solar, volcanic effects? (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) 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) (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Land & Ocean Changes IPCC Statement IPCC: Most global warming very likely due to increase in anthropogenic GHG concentrations Likely anthropogenic warming on continental scale Spatial Distribution of Trends 58 Sim. 14 GCMs 19 Sim. 5 GCMs (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Changes in Tropopause Height ERA40: Observation-based analysis Model results (each 4 simulations by PCM): Red - All forcings (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Blue - Natural forcings only Climate Models (from IPCC WG-I, Chapter 9) Ocean-Change Signal Strength Observed Signal: Red dots Model results (individual basins from PCM): Green - All forcings (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Blue - Natural forcings only Climate Models (from IPCC WG-I, Chapter 9) Methods of Detection - Optimal Fingerprinting Linear Regression Observed climate patterns Scale factors Response patterns to forcings - from a GCM Earlier slide (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Internal variability (“noise”) solar volcanic GHGs O3 Aerosol All Climate Models (from IPCC WG-I, Chapter 9) 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 (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Scale Factors - 4 GCMs Bars: 5-95% uncertainty range Red: GHGs Green: Other human factors (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Blue: Natural Climate Models (from IPCC WG-I, Chapter 9) Inferred Climate Change - 4 GCMs 1990s minus 1900s (decades) Observed: Black line Trend: 1950 - 1999 (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Can Greenhouse Warming Cause a Climatic Extreme? Summer temperatures in Switzerland A single event cannot be attributed to a forcing factor, but … (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) 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. (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9) Attribution of Changes END (Mt/Ag/EnSc/EnSt 404/504 - Global Change) Climate Models (from IPCC WG-I, Chapter 9)