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coupled O cean- A tmosphere G eneral/Global C irculation M odels

coupled O cean- A tmosphere G eneral/Global C irculation M odels. ~100km horizontal res’n; Finer (~2) for ocean than atmosphere. ~20 layers atmosphere; ~20 layers ocean. Geography inevitably coarse.

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coupled O cean- A tmosphere G eneral/Global C irculation M odels

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  1. coupled Ocean-Atmosphere General/Global Circulation Models ~100km horizontal res’n; Finer (~2) for ocean than atmosphere. ~20 layers atmosphere; ~20 layers ocean. Geography inevitably coarse. “Regionalisation”: redo simulation of one region only (e.g. Europe) matched onto cruder global simulation

  2. Basic Physics …

  3. Features and processes Moist processes: Evaporation & condensation: clouds and latent heat Radiation processes, light and IR Sub-resolution convection -> effective viscosity & dispersion Surface changes, e.g. of albedo and roughness Atmosphere-Surface exchange: heat, vapour, liquid, momentum

  4. <<10km: three dimensional >>10km: two dimensional Turbulence Sub-resolution convection -> effective viscosity & dispersion

  5. Major Volcanos State of art ca 1997 -> Major volcanic eruptions are a visible and predictable perturbation on the climate.

  6. Figure TS.23 “Greenhouse gas forcing has very likely [90%] caused most of the observed global warming over the last 50 years.” IPCC 2007 IPC 2007 ….likely [67%].. IPCC 2001

  7. IPCC 2007 Previous predictions … correct to show wide error bars

  8. =Temperature rise from doubling CO2 (equivalent) IPCC2007

  9. Predictability General claim: Weather chaotic (beyond ~two weeks) but wider/longer scale climate changes relatively predicable. Evidence: Correlation of ice ages with Milankovitch cycles (of earth orbit) Successful replication of response to largest sudden terrestrial perturbations: Volcanoes El Nino changes in ocean circulation Replication of 20th climate trends Exploit: Expensive AOGCM calculations -> calibrate simpler climate simulations -> mass produce climate predictions for different future scenarios

  10. SpecialReport on Emissions Scenarios B2 • Population peaks mid century. • A1: technology-led economy, • F fossil fuels vs ( B “balanced” ) vs T non-fossil fuelled. B1: info & service economy; sustainability & global sol’ns. • Population continues to increase. • A2: very heterogeneous world (“business as usual”) • B2: lower growth rate; emphasis on local solutions (smart but laissez-faire) not predictions, but a range of plausible assumptions

  11. The global climate of the 21st century IPCC S/PM 2001

  12. Figure TS.28 IPCC 2007: Scenario -> OAGCM -> Climate prediction

  13. Figure 10.4 IPCC 2007

  14. IPCC 2007

  15. Observed and projected changes in extreme weather and climate events. IPCC S/PM 2001

  16. OAGCM predictions (sample) annual mean change of the temperature (colour shading) and its range (isolines) (Unit: °C) for SRES A2 and B2 . period 2071 to 2100 relative to 1961 to 1990 B2 IPCC2001

  17. Projected temperatures

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