1. Climate Variability & Change - Past & Future Decades Brian Hoskins Director, Grantham Institute for Climate Change, Imperial College London Professor of Meteorology, University of Reading

2. Observed climate system Projections for 21 st century Uncertainties in projections Targets for climate related policy Concluding comments

3. Some measurements of the climate system. x

4. Comparison of Observed T since 1990 with IPCC projections 19 point filter on ObservationsObserved variability added to IPCC

5. Mean Central England T 1772 to 22 July 2012

6. Some measurements of the climate system Global sea level. Arctic sea ice Sept min in Arctic sea ice area

7. Projections: globally averaged surface warming IPCC 2007 Different scenarios

8. B1 A1B A2 2011-302046-652080-99 Surface T projections for different periods and scenarios IPCC 2003

9. Change in average maximum number of dry days in year, 2081-2100 IPCC 2011

10. Normalised PDFs for 2100 Decadal T (A1B) Ed Hawkins

11. UNEP Emissions Gap Report Nov 2010 Cumulative carbon – Allen et al 2009

12. Matsuno & Maruyama, 2012 CO2 emissions CO2 concentration Impact of post 2100 global emissions level Atm CO 2 TSL Atm CO 2 SL T 450ppm CO2 stabilisation Zero emissions floor

13. Contributors to uncertainty in trends in decadal T Hawkins 2011 GlobalUK

14. T % Contributions to uncertainty in different decades

15. “Dangerous Climate Change” e.g. 2C Is 1.9C fine and 2.1C disastrous? Policy makers could do with a ceiling on ΔT or GHGs Atmospheric CO2 level e.g. 450ppm Cumulative emissions e.g. 1trillion t of carbon

16. Thresholds (“Tipping Points”)

17. Are extremes increasing at a surprising/damaging rate? Coumu & Rahmtorf 2012

18. Attribution of extremes Basic physics/theory More heat waves & less cold periods: shift of distribution & change in local T/D balance More heavy rainfall events can be expected – Clausius-Clapeyron More intense storms? Latent heating+, baroclinicity +/- Model attribution studies Analogues of synoptic situations e.g. Cattiaux et al 2010 for extreme cold European winter 2009/10

19. Summer 2010 Barriopedro 2011 6 day rainfall in July - ECMWF analysis Otto et al 2012 Model estimates of Return periods for T/Z

20. 20 th Century Blocking in CMIP5 Models: NH Winter ERA40Mean of modelsSD of models

21. Concluding Comments Very strong evidence that we are performing a very dangerous experiment with our planet Very long time-scales of atmospheric CO 2 & the ocean imply a climate commitment, but also imply some very long term sensitivity to GHG emission floor next century Current models suggest emissions reductions in next few decades important only after 2050 Thresholds will probably exist in the climate system but we do not know where they are. For societies thresholds will certainly exist. Extreme weather events may be increasing more than simple shifts of distributions suggest but this has not yet been shown conclusively Uncertainties in climate models & their prediction of natural variability will be reducible to some extent Hard targets are not based on scientific evidence but softer ones to guide policy can be posed e.g. CCC 50% chance of not exceeding 2C by much & very small chance of reaching 4C

23. Fractional uncertainty & Fraction of Variance Globe British Isles

24. precip

25. S/N (b) & (d) assuming model uncertainty zero

27. Matsuno & Maruyama, 2012 CO2 emissionsCO2 concentration

28. Global temperatures and 10, 20 & 30 year running averages

29. Number of Monthly Record High Temperatures 17 stations, decadal smoothing Coumu & Rahmtorf 2012 from Benestad (2004)

30. 21 st Century Blocking in CMIP5 Models: NH Winter 2056-99 for RCP8.5

31. Date at which signal emerges from “noise”