Climate Variability & Change - Past & Future Decades

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 21st 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 Observations Observed variability added to IPCC

5. Mean Central England T 1772 to 22 July 2012

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

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

8. Surface T projections for different periods and scenarios IPCC 2003 2011-30 2046-65 2080-99 B1 A1B A2

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

13. Contributors to uncertainty in trends in decadal T Hawkins 2011 Global UK

14. T % Contributions to uncertainty in different decades

15. Policy makers could do with a ceiling on ΔT or GHGs “Dangerous Climate Change” e.g. 2C Is 1.9C fine and 2.1C disastrous? 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 +/- Analogues of synoptic situations e.g. Cattiaux et al 2010 for extreme cold European winter 2009/10 Model attribution studies

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

20. 20th Century Blocking in CMIP5 Models: NH Winter ERA40 Mean of models SD 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 CO2 & 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 emissions CO2 concentration

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

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

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

31. Date at which signal emerges from “noise”