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

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Presentation on theme: "Understanding Feedback Processes Outline Definitions Magnitudes and uncertainties Geographic distributions and priorities Observational requirements."— Presentation transcript:

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 ( T) that results from a specified radiative forcing ( Q). The sensitivity is a function of the feedback factors ( ).

3 Climate Feedbacks W/m 2 /K 3.6 Planck (temperature + lapse rate) -1.6 Water Vapor (mixing ratio) -0.4 Clouds (cloud amount, water path, particle size) -0.3 Albedo (snow, ice) Climate sensitivity is the equilibrium change in global mean surface temperature ( T) that results from a specified radiative forcing ( Q). The sensitivity is a function of the feedback factors ( ). Radiative Forcing 4 W/m 2 = 3 K

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

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

6 W/m 2 /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 TropicsMid-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 6.7 m Brightness Temperature Anomaly (K) GCM No Moistening GCM HIRS

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

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

12 Cloud Feedback GFDL: Strong positive low cloud feedback. NCAR: Weak negative low cloud feedback. 2x CO2ENSO

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

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

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

16 Extra Slides

17 Calculation of Feedbacks: Control SW at tropopause LW at tropopause Radiation Model sfc albedo temperature mixing ratio clouds CO 2

18 Calculation of Feedbacks: Perturbation SW at tropopause LW at tropopause Radiation Model sfc albedo temperature mixing ratio clouds CO 2

19 Colman (2003) PRP Method Cess et al. (1996) Δ CRF Method 1 of 10 models has negative cloud feedback 8 of 18 models have negative cloud forcing 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 CFMIP contribution from each feedback class LW CRF SW CRF LW CRF response SW CRF response Mark Webb

21 Observable Radiative Damping Rates Regional Seasonal Interannual

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


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