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Evaluation of climate models, Attribution of climate change IPCC Chapters 7,8 and 12. John F B Mitchell Hadley Centre • • • • How well do models simulate present climate? How well do they simulate past climate change? Can natural factors explain the last 100 years? Can human factors explain recent changes? “Simulations of the response to natural forcings alone … do not explain the warming in the second half of the century” SPM Global mean temperature from an ensemble of 4 simulations using natural and anthropogenic forcing Stott et al, Science 2000 “Reconstructions of climate data for the last 1000 years also indicate that this warming was unusual and unlikely to be entirely natural in origin” SPM Arctic Sea Ice Cover: Observation and (Vinnikov et al., 1999, Science; Chapter 7) Simulation Glacier mass balance During the 20th century, glaciers and ice caps have experienced widespread mass losses and have contributed to sea level rise Decline of mountain glaciers projected to reduce water availability in many regions Cumulative balance of glacier mass in some regions “The warming over the last hundred years is very unlikely to be due to internal variability alone as estimated from current models” SPM Optimal detection • Based on spatial and temporal patterns, not global means • Different components can be scaled separately (e.g. greenhouses gases, aerosols) • “..most model estimates that take into account both greenhouse gases and sulphate aerosols are consistent with observations [over the last 50 years]” • The observations can be used to “correct” model predictions, with uncertainty limits Temperature Substantial GHG warming with small sulphate cooling Small sulphate cooling Greenhouse warming Greenhouse warming slightly larger than observed Observations Time Different Computer Models Key technologies to reduce emissions Key mitigation technologies and practices currently commercially available Energy Supply Efficiency; fuel switching; renewable (hydropower, solar, wind, geothermal and bioenergy); combined heat and power; nuclear power; early applications of CO2 capture and storage Transport More fuel efficient vehicles; hybrid vehicles; biofuels; modal shifts from road transport to rail and public transport systems; cycling, walking; land-use planning Buildings Efficient lighting; efficient appliances and aircodition; improved insulation ; solar heating and cooling; alternatives for fluorinated gases in insulation and appliances Key policies to reduce emissions Appropriate incentives for development of technologies Effective carbon price signal to create incentives to invest in low-GHG products, technologies and processes Appropriate energy infrastructure investment decisions, which have long term effects on emissions Changes in lifestyle and behavior patterns, especially in building, transport and industrial sectors A technological society has two choices. First it can wait until catastrophic failures expose systemic deficiencies, distortion and self-deceptions… Secondly, a culture can provide social checks and balances to correct for systemic distortion prior to catastrophic failures.