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Download Talk 5 - Research needs for decadal to centennial climate prediction
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Research Needs for Decadal to Centennial Climate Prediction: From observations to modelling Julia Slingo, Met Office, Exeter, UK & V. Ramaswamy. GFDL, Princeton, USA Climate Change Projections and Uncertainties IPCC AR4 Quantifying uncertainties – setting research priorities 2020’s Improved model physics e.g. clouds 25 2080’s Winter rainfall in south east England 22 Benefits of initialisation for near-term 35 projections 43 Higher resolution global models 15 31 9 Natural Variability Carbon Cycle Downscaling Model Uncertainty Increased 20of earth understanding system processes – more uncertainty? Challenges for Centennial Projections: Earth System Modelling Moving from Climate to Earth System Models: Balancing the carbon cycle Atmospheric circulation and radiation Climate Model Sea Ice Ocean circulation Land physics and hydrology Atmospheric circulation and radiation Allows interactive CO2 Earth System Model Sea Ice Ocean ecology and biogeochemistry Ocean circulation Plant ecology and land use Land physics and hydrology Carbon-climate feedback and centennial climate change 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)? Earth System Modelling: Combining the needs of adaptation and mitigation Quantifying uncertainties – setting research priorities 2020’s Improved model physics e.g. clouds 25 2080’s Winter rainfall in south east England 22 Benefits of initialisation for near-term 35 projections 43 Higher resolution global models 15 31 9 Natural Variability Carbon Cycle Downscaling Model Uncertainty Increased 20of earth understanding system processes – more uncertainty? Challenges for Decadal Prediction: Initialisation and Evaluation Decadal predictions of global annual mean surface temperature Observations Forecast/hindcast Forecast from 2008 Forecast from 2009 Smith et al., 2007 Impact of initialisation on hindcast skill 5 year mean (JJASON) surface temp 15x15 degrees DePreSys anomaly correlation DePreSys-NoAssim correlation • HadCM3 • 9 member perturbed physics ensemble • Starting every Nov from 1960 to 2005 Improved predictions of multi-year Atlantic hurricane frequencies 5-year mean JJASON number of model storms (coloured) and observed hurricanes (black) NoAssim Normalised anomaly DePreSys Skill comes from SSTs in tropical Pacific and N. Atlantic subpolar gyres, and from wind shear in hurricane development regions Sub-surface ocean observations: A limiting factor in estimating skill and predictability 1960 1980 2007 • Need historical tests to assess likely skill of forecasts • Far fewer sub-surface ocean observations in the past Doug Smith, Met Office Hadley Centre Temperature at 300m : June 2007 from 1960 observational base June 2007 obs Analysis using all obs June 1960 obs Analysis using sub-sampled (1960) obs Variability versus Anthropogenic Forcing of the Physical Climate System 20 centuries of NINO3 SSTs annual means & 20yr low-pass Major uncertainty in Chemistry-Climate Interactions Coupled Chemistry-Aerosol-Climate model Clear Sky Cloudy Sky SW Radiation Activation Droplets Aerosols Atmosphere LW Radiation Sea Ice Evaporation Surface Flux Ocean SST Mixed-Layer Deep Ocean Global Air Quality and Climate Precipitation Land Aerosols and Climate 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 Direct effects – Sulfate and organic carbon Observations (AERONET) Direct effects Black carbon CM3 CM2.1 ~0 -1.3 (assuming internal mixing of sulfate and black carbon) (external mixing) 0.5 (external mixing) M O D E L Indirect effects -1.3 Not included Observations (AERONET) 20 Capturing High-Resolution Phenomena Atlantic Hurricanes in a Warming World 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 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 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. 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.