Research Needs for Decadal to Centennial Climate Prediction: From observations to modelling

1. Research Needs for Decadal to Centennial Climate Prediction: From observations to modelling Julia Slingo, Met Office, Exeter, UK & V. Ramaswamy. GFDL, Princeton, USA

2. Climate Change Projections and Uncertainties IPCC AR4

3. Quantifying uncertainties – setting research priorities 2020’s 2080’s Winter rainfall in south east England Improved model physics e.g. clouds Benefits of initialisation for near-term projections Higher resolution global models Increased understanding of earth system processes – more uncertainty?

4. Challenges for Centennial Projections: Earth System Modelling

5. Moving from Climate to Earth System Models: Balancing the carbon cycle Atmospheric circulation and radiation Climate Model Sea Ice Land physics and hydrology Ocean circulation Atmospheric circulation and radiation Allows interactive CO2 Earth System Model Sea Ice Plant ecology and land use Ocean ecology and biogeochemistry Land physics and hydrology Ocean circulation

6. Carbon-climate feedback and centennial climate change

7. More Earth System Modelling challenges • How can we reduce the uncertainties in current estimates of the carbon-climate feedback? • How do missing or poorly represented processes such as the nitrogen cycle, plant adaptation to climate change, vegetation dynamics, and plankton dynamics affect current model results? • What other biogeochemical feedbacks involving methane, ozone and aerosols play a significant role on the centennial timescale? • How can Earth System Modelling inform decision-making when climate change is one of many drivers for environmental change (e.g. food security, water resources and quality, biodiversity, air quality)?

8. Earth System Modelling:Combining the needs of adaptation and mitigation

9. Quantifying uncertainties – setting research priorities 2020’s 2080’s Winter rainfall in south east England Improved model physics e.g. clouds Benefits of initialisation for near-term projections Higher resolution global models Increased understanding of earth system processes – more uncertainty?

10. Challenges for Decadal Prediction: Initialisation and Evaluation

11. Observations Forecast/hindcast Forecast from 2008 Forecast from 2009 Decadal predictions of global annual mean surface temperature Smith et al., 2007

12. Impact of initialisation on hindcast skill5 year mean (JJASON) surface temp15x15 degrees DePreSys anomaly correlation DePreSys-NoAssim correlation • HadCM3 • 9 member perturbed physics ensemble • Starting every Nov from 1960 to 2005

13. Improved predictions of multi-year Atlantic hurricane frequencies 5-year mean JJASON number of model storms (coloured) and observed hurricanes (black) DePreSys NoAssim Normalised anomaly Skill comes from SSTs in tropical Pacific and N. Atlantic sub-polar gyres, and from wind shear in hurricane development regions

14. Sub-surface ocean observations: A limiting factor in estimating skill and predictability 1960 2007 1980 • Need historical tests to assess likely skill of forecasts • Far fewer sub-surface ocean observations in the past Doug Smith, Met Office Hadley Centre

15. Temperature at 300m : June 2007 from 1960 observational base June 1960 obs June 2007 obs Analysis using all obs Analysis using sub-sampled (1960) obs

16. Variability versus Anthropogenic Forcing of the Physical Climate System

17. 20 centuries of NINO3 SSTs annual means & 20yr low-pass

18. Major uncertainty in Chemistry-Climate Interactions

19. Coupled Chemistry-Aerosol-Climate model Precipitation Evaporation Surface Flux SST Clear Sky Cloudy Sky SW Radiation Activation Aerosols and Climate Droplets Aerosols Atmosphere LW Radiation Land Sea Ice Ocean Mixed-Layer Deep Ocean Global Air Quality and Climate

20. Aerosol-Cloud Interactions in GFDL’s Newest Physical Climate Model (CM3) ‏ Comparison of Simulated Aerosol Properties with Observations Radiative Flux Perturbation w/m2 M O D E L Observations (AERONET) M O D E L Observations (AERONET) 20

21. Capturing High-Resolution Phenomena

24. Atlantic Hurricanes in a Warming World

25. Most recent GFDL downscaling study (Bender et al, Science, 2010) see https://www.gfdl.noaa.gov/21st-century-projections-of-intense-hurricanes Uses two downscaling steps: Global CMIP3 models => regional model of Atlantic hurricane season regional model => operational GFDL hurricane prediction system

26. Conclusion: Best estimate is for doubling of cat 4-5 storms in Atlantic by end of century, despite decrease in total number of tropical cyclones Much of the uncertainty arises from global model input

27. Conclusions I Emerging need for centennial and decadal projections. They pose similar and differing challenges. Earth system processes potentially increase uncertainty in centennial projections, especially in the upper range of warming. Initialising decadal projections can reduce uncertainty at least for a few years ahead.

28. Conclusions II Observations of the sub-surface ocean and the full earth system may limit our ability to provide more confident projections. Natural variability in the context of forced change is challenging. High resolution modelling is opening up new avenues for more detailed projections of regional climate change and high impact phenomena.