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Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming Patrick T. Brown Carnegie Institution for Science, Stanford CA Stanford EE Computer Systems Colloquium January 17, 2018 Combining


  1. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming Patrick T. Brown Carnegie Institution for Science, Stanford CA Stanford EE Computer Systems Colloquium January 17, 2018

  2. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming

  3. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical Observations Relative Global Temperature (C) 4 3 2 1 0 -1 1900 1950 2000 2050 2100 Year

  4. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical Observations Relative Global Temperature (C) 4 3 2 1 0 -1 1900 1950 2000 2050 2100 Year

  5. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical Observations Relative Global Temperature (C) 4 3 2 1 0 -1 1900 1950 2000 2050 2100 Year

  6. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical + Observations Relative Global Temperature (C) 4 3 2 1 0 -1 1900 1950 2000 2050 2100 Year

  7. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical + Observations Relative Global Temperature (C) 4 3 2 1 0 -1 1900 1950 2000 2050 2100 Year

  8. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Modeled Historical Observations Relative Global Temperature (C) 4 3 2 1 “The Agreement aims to respond to the global climate change threat by keeping a global temperature rise this century well 0 below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further -1 to 1.5 degrees Celsius” 1900 1950 2000 2050 2100 Year

  9. Combining Physical and Statistical Models in Order to Narrow Uncertainty in Projections of Global Warming a, pretty modeled and observed global temperature 6 Modeled Future RCP 2.6 Modeled Future RCP 4.5 Modeled Future RCP 6.0 5 Modeled Future RCP 8.5 Response Uncertainty Modeled Historical Observations Relative Global Temperature (C) 4 How much global warming should we Scenario Uncertainty expect for a given increase in the 3 atmospheric concentration of greenhouse gases? 2 Projections differ by a factor of 2 1 0 -1 1900 1950 2000 2050 2100 Year

  10. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Global Average Surface Temperature Perturbation (K) Net Energy Flux (W m -2 ) Heat capacity (W yr m -2 K -1 )

  11. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 Atmosphere Net Energy Flux (W m -2 ) Ocean

  12. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 Atmosphere Net Energy Flux (W m -2 ) Ocean

  13. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 “Feedback” (W/m 2 ) Atmosphere Climate Feedback Parameter (W m -2 K -1 ) Ocean “Forcing” (W/m 2 )

  14. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 Atmosphere Climate Feedback Parameter (W m -2 K -1 ) Ocean

  15. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 Atmosphere 0 Small uncertainty for CO 2 Large uncertainty Ocean Large uncertainty

  16. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? 240 W/m 2 76 W/m 2 24 W/m 2 Space 340 W/m 2 Atmosphere 0 Ocean

  17. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Strategy #1: estimate F and ∆ T over some time in the past

  18. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Strategy #2: Increase greenhouse gas concentrations in a physical climate model and have it calculate ∆ T

  19. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Mathematical / greenhouse gas mechanistic concentrations models of the in a physical entire Earth climate model system run on and have it supercomputers calculate ∆ T • Typically about a million lines of code

  20. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Developed greenhouse gas at many concentrations centers in a physical around the climate model world and have it calculate ∆ T

  21. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Developed greenhouse gas at many concentrations centers in a physical around the climate model world and have it calculate ∆ T

  22. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Developed greenhouse gas at many concentrations centers in a physical around the climate model world and have it calculate ∆ T

  23. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Discretize the greenhouse gas Earth system in concentrations space and time in a physical climate model and have it calculate ∆ T

  24. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Use laws of greenhouse gas physics to concentrations calculate state in a physical of Earth system climate model at every 3D and have it location calculate ∆ T • March forward in time with time steps of ~30 minutes

  25. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Number of greenhouse gas processes explicitly concentrations represented has in a physical increased over time climate model and have it calculate ∆ T

  26. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Spatial greenhouse gas resolution has concentrations increased over in a physical time climate model and have it calculate ∆ T

  27. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase • Spatial resolution not sufficient to greenhouse gas represent many important processes concentrations • These processes must be in a physical ‘parameterized’ climate model • Calculated based on a formula that and have it is only semi-physical and has calculate ∆ T tunable parameters that are poorly constrained • Example: Cloud fraction

  28. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: Increase greenhouse gas concentrations in a physical climate model and have it calculate ∆ T

  29. How much global warming should we expect for a given increase in the atmospheric concentration of greenhouse gases? Physical Global Climate Models Strategy #2: • Most of uncertainty in future Increase warming comes from greenhouse gas uncertainty in feedbacks ( 𝝻 ) concentrations that stems from important in a physical processes being ‘parameterized’ climate model and have it • The primary goal of our study calculate ∆ T was to narrow this range of model uncertainty and to assess whether the upper or lower end of the range is more likely.

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