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

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

6. Simulated annual global mean surface temperatures IPCC S/PM 2001 In the light of evidence and remaining uncertainties, most of the observed warming in the last 50 years is likely = 66-90% chance due to the increase in greenhouse gas concentrations.

7. 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 20 th climate trends Exploit: Expensive AOGCM calculations -> calibrate simpler climate simulations -> mass produce climate predictions for different future scenarios

8. Special Report on Emissions Scenarios 1.Population peaks mid century. A1: technology-led economy, F fossil fuels vs ( B “balanced” ) vs T non-fossil fuelled. not predictions, but a range of plausible assumptions 2.Population continues to increase. A2: very heterogeneous world (“business as usual”) B2: lower growth rate; emphasis on local solutions (smart but laissez-faire) B1: info & service economy; sustainability & global sol’ns. B2

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

10. Projected temperatures

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