Climate Variability & Change - Past & Future Decades
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Climate Variability & Change - Past & Future Decades. Brian Hoskins Director, Grantham Institute for Climate Change, Imperial College London Professor of Meteorology, University of Reading. Observed climate system Projections for 21 st century Uncertainties in projections
Climate Variability & Change - Past & Future Decades
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Presentation Transcript
Climate Variability & Change- Past & Future Decades Brian Hoskins Director, Grantham Institute for Climate Change, Imperial College London Professor of Meteorology, University of Reading
Observed climate system • Projections for 21st century • Uncertainties in projections • Targets for climate related policy • Concluding comments
Comparison of Observed T since 1990 with IPCC projections 19 point filter on Observations Observed variability added to IPCC
Some measurements of the climate system Arctic sea ice Global sea level . Sept min in Arctic sea ice area
Projections: globally averaged surface warming Different scenarios IPCC 2007
Surface T projections for different periods and scenarios IPCC 2003 2011-30 2046-65 2080-99 B1 A1B A2
Change in average maximum number of dry days in year, 2081-2100 IPCC 2011
Normalised PDFs for 2100 Decadal T (A1B) Ed Hawkins
UNEP Emissions Gap Report Nov 2010 Cumulative carbon – Allen et al 2009
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
Contributors to uncertainty in trends in decadal T Hawkins 2011 Global UK
T % Contributions to uncertainty in different decades
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
Are extremes increasing at a surprising/damaging rate? Coumu & Rahmtorf 2012
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
Summer 2010 Model estimates of Return periods for T/Z Barriopedro 2011 Otto et al 2012 6 day rainfall in July - ECMWF analysis
20th Century Blocking in CMIP5 Models: NH Winter ERA40 Mean of models SD of models
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
Fractional uncertainty & Fraction of Variance Globe British Isles
S/N (b) & (d) assuming model uncertainty zero
Matsuno & Maruyama, 2012 CO2 emissions CO2 concentration
Number of Monthly Record High Temperatures Coumu & Rahmtorf 2012 from Benestad (2004) 17 stations, decadal smoothing
21st Century Blocking in CMIP5 Models: NH Winter 2056-99 for RCP8.5
