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Satellite & Model Evidence for Global Warming Being Driven by the Pacific Decadal Oscillation Dr. Roy W. Spencer Principal Research Scientist The University of Alabama in Huntsville 10 March, 2009 Overview • Satellite evidence of negative feedback has been obscured by radiative forcing due to natural cloud variations • Negative feedback means that incr. CO2 is too weak to cause observed warming • 7.5 Years of Terra satellite data, combined with a simple climate model, shows that the PDO can explain most of the temperature variability seen during the 20th Century There are TWO RADIATIVE WAYS to Cause Global Warming 1) INCREASE SOLAR RADIATION being absorbed, or 2) DECREASE INFRARED RADIATION (IR) being lost to space. Observe the Behavior of TODAY’S Climate System with NASA’s Aqua & Terra Satellites Traditional Way of Estimating Feedbacks From Satellite Data Simple Forcing-Feedback Model of Temperature Variability dDT/dt = [Forcing – Feedback]/ Cp Incr. CO2, aerosols, cloud changes, etc. (W m-2) lDT l = lsw + lLW (W m-2 K-1) ~ Ocean depth l= 5 W m-2 K-1; 50 m mixed layer Simple Model Forced with Random radiative forcing True FB (e.g. cloud variations) …leads to 100% error in diagnosed feedback! (Spencer & Braswell, Nov. 1, 2008 J. Climate) Diag. FB Even the IPCC Models Show Evidence of “radiative forcing spirals” GFDL Simple Model Forced with Random non-radiative forcing (e.g. evap/precip. fluctuations) 0% error in diagnosed feedback Feedbacks can ONLY be measured in response to non-radiative forcing, Not radiative forcing REAL WORLD: Both Radiative & Non-Radiative forcing …leads to an underestimate of diagnosed feedback depending upon ratio of radiative to non-radiative forcing This explains why previous satellite diagnoses of Feedback have been so variable… AND biased toward positive feedback. True FB Diag. FB Only a FEW IPCC models show “feedback stripes” Slopes of “feedback stripes” Corresponds to long-term Feedbacks diagnosed by Forster & Taylor (2006) So, Feedback Is ONLY Indicated by Linear Striations in the Data (feedback stripes) Terra Satellite: CERES vs. AMSU ch. 5 Suggests STRONGLY Negative Feedback Stripes (8 W m-2 K-1) Aqua Satellite: CERES vs. AMSU ch. 5 Suggests STRONG Negative Feedback …even without accounting for contamination by radiative forcing 5 W m-2 K-1 Strongly negative feedback (insensitive climate system) means radiative forcing from extra CO2 too weak to cause global warming. IF Manmade CO2 hasn’t Caused Global Warming over the last 100 years..then what has? HOW ABOUT MOTHER NATURE.. c. Pacific Decadal Oscillation, 1902-2006 1.2 0.8 PDO Index Natural Cloud Variations 2 1.6 Pacific Decadal Oscillation 0.4 0 -0.4 -0.8 -1.2 -1.6 -2 1902 1912 1922 1932 1942 1952 1962 1972 1982 1992 2002 ? 0.6 YEAR a. Global Mean Temperature, 1902-2006 Natural Temperature Variations T Anomaly (deg. C) 0.4 0.2 LAND + OCEAN 0 -0.2 OCEAN ONLY -0.4 -0.6 1902 1912 1922 1932 1942 1952 1962 1972 1982 1992 2002 Global Surface Temperature A Simple Model Forced by Cloud Changes Assumed Associated with the Pacific Decadal Oscillation: PDO Can explain 3/4 of 20th Century Warming 0.6 Simple Model of PDO Cloud Changes Causing Global Warming Thermometer data T Anomaly (deg. C) 0.4 0.2 PDO+CO2 0 PDO-only -0.2 -0.4 -0.6 -0.8 1900 1910 1920 1930 1940 1950 YEAR 1960 1970 1980 1990 2000 …and Recent Satellite Data Suggests that there Indeed IS a Connection between the PDO and Cloud Variations….PDO INDEX 2000 2.5 2001 2002 (monthly) 2003 2004 2005 2.0 1.5 PDO Index PDO Index 2000-2005 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 Terra Satellite Observed Cloud Changes 2000-2005 TOA Flux Anom. (W m-2 K-1) -1.0 CERES LW+SW YEAR Flux Anomalies 60N-60S Oceans -0.5 0.0 0.5 1.0 1.5 2000 2001 2002 2003 2004 2005 …and plotted here as Yearly Averages (updated thru 2007). 1.5 Radiative Forcing (W/m2) 1.0 (Rad. Forcing= Total Flux minus Feedback) LW+SW 2005 0.5 2003 Model predicted 0.0 2007 2001 y = 1.39x - 0.23 R2 = 0.67 -0.5 -1.0 SatelliteObserved -1.5 ? -2.0 2008 ? 2000 -2.5 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 PDO Index Note that PDO forcing is actually measured…. ..forcing from incr. CO2 must be computed theoretically The End Natural climate variability: Partly due to Natural Cloud Variations? 0.8 Medieval Warm Period Temperature Anomaly (deg. C) 0.6 0.4 0.2 0 Vikings arrive in Greenland -0.2 End of Viking colonization of Greenland -0.4 -0.6 Little Ice Age -0.8 0 200 400 600 800 1000 YEAR (AD) 1200 1400 1600 1800 2000 Conclusions: Satellite data & simple model suggest… 1. Feedbacks are strongly negative (low climate sensitivity) Previous feedback estimates were contaminated by radiative forcing due to cloud fluctuations CO2 increase too weak to cause warming 2. The PDO causes natural radiative forcing of climate change Enough to explain 75% of global warming IPCC assumes cloud cover always remains the same Atlantic Multidecadal Oscillation, Arctic Oscillation, El Nino, La Nina, etc. all need to be investigated as possible climate change mechanisms 1st SATELLITE TEST OF THE CLIMATE MODELS: How they gain and lose INFRARED energy GOOD AGREEMENT Between Models & satellites for EMITTED INFRARED Number of 5-Year Periods 1400 1200 Positive Feedback (clouds AMPLIFY warming) 1000 800 Negative Feedback (clouds REDUCE warming) 18 IPCC Models 600 400 200 Satellite 0 -4 -3 -2 -1 0 1 2 3 4 5 6 Feedback Parameter Estimate (W m-2 K-1) 7 2nd SATELLITE TEST OF THE CLIMATE MODELS: How they gain and lose SOLAR energy NO AGREEMENT Between Models & satellites for REFLECTED SUNLIGHT Number of 5-Year Periods 1400 1200 Positive Feedback (clouds AMPLIFY warming) Negative Feedback (clouds REDUCE warming) 1000 800 Satellite 600 18 IPCC Models 400 200 0 -4 -3 -2 -1 0 1 2 3 4 5 6 Feedback Parameter Estimate (W m-2 K-1) 7 TOTAL SATELLITE TEST OF THE CLIMATE MODELS: How they gain and lose SOLAR+INFRARED energy. NO AGREEMENT Between Models & Satellites for REFLECTED SUNLIGHT+ EMITTED INFRARED Number of 5-Year Periods 1400 1200 Positive Feedback (clouds AMPLIFY warming) 1000 800 Negative Feedback (clouds REDUCE warming) 18 IPCC Models 600 Satellite 400 200 0 -4 -3 -2 -1 0 1 2 3 4 5 6 Feedback Parameter Estimate (W m-2 K-1) 7