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Understanding Feedback Processes

Understanding Feedback Processes. Outline Definitions Magnitudes and uncertainties Geographic distributions and priorities Observational requirements. Climate Feedbacks.

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Understanding Feedback Processes

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  1. Understanding Feedback Processes Outline • Definitions • Magnitudes and uncertainties • Geographic distributions and priorities • Observational requirements

  2. Climate Feedbacks • Climate sensitivity is the equilibrium change in global mean surface temperature (DT) that results from a specified radiative forcing (DQ). • The sensitivity is a function of the feedback factors (l) .

  3. Climate Feedbacks • Climate sensitivity is the equilibrium change in global mean surface temperature (DT) that results from a specified radiative forcing (DQ). • The sensitivity is a function of the feedback factors (l) . Radiative Forcing 4 W/m2 = 3 K 3.6 Planck (temperature + lapse rate) -1.6 Water Vapor (mixing ratio) -0.4 Clouds (cloud amount, water path, particle size) W/m2/K -0.3 Albedo (snow, ice)

  4. Range of Model Feedbacks Negative Feedback Positive Feedback Colman (2003)

  5. Range of Model Feedbacks Negative Feedback Positive Feedback + Colman (2003)

  6. 00.40.81.21.6 W/m2/K The Importance of Water Vapor Feedback

  7. Distribution of Water Vapor Feedback Vertical Contributions Boundary Layer Upper Trop (> 800 mb) (< 600 mb) ~10% ~70% Latitudinal Contributions Tropics Mid-Lat Polar ~65% ~30% ~5% Stronger feedback Weaker feedback

  8. Water Vapor Feedback Fractional Change in Water Vapor Concentration: GFDL GCM (SRES A1B) Pressure

  9. Water Vapor Trends GCM No Moistening GCM 6.7 mm Brightness Temperature Anomaly (K) HIRS

  10. Cloud Feedback Summer 2002 GFDL 2xCO2 Sensitivity (K) NCAR IPCC TAR Models Change in Low Cloud Amount (%/K)

  11. Cloud Feedback Fall 2003 GFDL Change in Low Cloud Amount (%/K) 2xCO2 Sensitivity (K) NCAR

  12. Cloud Feedback ENSO 2x CO2 GFDL: Strong positive low cloud feedback. NCAR: Weak negative low cloud feedback.

  13. Response to Transient Forcings Eruption of Mt. Pinatubo June 1991

  14. Cloud and Radiation Trends Verification requires redundancy Wielicki et al. (2002)

  15. Priorities • Free tropospheric temperature • Tropical upper tropospheric water vapor (1%/dec, DZ=0.5 km) • Low cloud cover (0.5%/dec, DZ=0.5 km) • TOA radiative fluxes • Redundancy • Climate OSSE to guide system design and requirements

  16. Extra Slides

  17. Calculation of Feedbacks: Control sfc albedo SW attropopause temperature RadiationModel mixing ratio clouds LW attropopause CO2

  18. Calculation of Feedbacks: Perturbation sfc albedo DSW attropopause temperature RadiationModel mixing ratio clouds DLW attropopause CO2

  19. 1 of 10 models has negative cloud feedback 8 of 18 models have negative cloud forcing Cess et al. (1996)ΔCRF Method Colman (2003)PRP Method Soden, B. J., A. J. Broccoli, and R. S. Hemler, 2004: On the use of cloud forcing to estimate cloud feedback, J. Climate, in press.

  20. LW CRF response SW CRF response LW CRF SW CRF CFMIP contribution from each feedback class Mark Webb

  21. Observable Radiative Damping Rates Interannual Seasonal Regional

  22. Cloud Changes in a Warmer Climate AM2p5 – AM2p9: Increased tropical high cloud amount. AM2p10: Reduced tropical high cloud amount. This weakens LW feedback and changes sign of SW feedback in model.

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