Observational and Model Evidence for Positive Low-Level Cloud Feedback

Positve Feedback The uncertain effect of feedback between climate and clouds is one of the largest obstacles to producing more confident projections of global climate. Clement et al. (p. 460) examined how clouds, sea surface temperature, and large-scale atmospheric circulation vary in the Northeast Pacific region. Change in cloud coverage was the primary cause of sea surface temperature variations, and clouds provided a positive feedback to temperature variations. Furthermore, regional atmospheric circulation patterns were linked to patterns of cloudiness. One model produced realistic covariability between cloud cover, sea surface temperatures, and atmospheric circulation for the 20th century. Decreased low-level cloud cover in the Northeast Pacific region amplifies increases in sea surface temperatures. Feedbacks involving low-level clouds remain a primary cause of uncertainty in global climate model projections. This issue was addressed by examining changes in low-level clouds over the Northeast Pacific in observations and climate models. Decadal fluctuations were identified in multiple, independent cloud data sets, and changes in cloud cover appeared to be linked to changes in both local temperature structure and large-scale circulation. This observational analysis further indicated that clouds act as a positive feedback in this region on decadal time scales. The observed relationships between cloud cover and regional meteorological conditions provide a more complete way of testing the realism of the cloud simulation in current-generation climate models. The only model that passed this test simulated a reduction in cloud cover over much of the Pacific when greenhouse gases were increased, providing modeling evidence for a positive low-level cloud feedback.

[1]  R. Seager,et al.  An Advective Atmospheric Mixed Layer Model for Ocean Modeling Purposes: Global Simulation of Surface Heat Fluxes , 1995 .

[2]  S. Klein,et al.  The Seasonal Cycle of Low Stratiform Clouds , 1993 .

[3]  R. Burgman,et al.  Evidence for atmospheric variability over the Pacific on decadal timescales , 2008 .

[4]  F. Schwing,et al.  A new climate regime in northeast pacific ecosystems , 2003 .

[5]  G. Vecchi,et al.  Global Warming and the Weakening of the Tropical Circulation , 2007 .

[6]  Yuqing Wang,et al.  Large-Scale Atmospheric Forcing by Southeast Pacific Boundary Layer Clouds: A Regional Model Study* , 2005 .

[7]  G. Martin,et al.  A New Boundary Layer Mixing Scheme. Part I: Scheme Description and Single-Column Model Tests , 2000 .

[8]  John F. B. Mitchell,et al.  THE WCRP CMIP3 Multimodel Dataset: A New Era in Climate Change Research , 2007 .

[9]  Andrew K. Heidinger,et al.  The Advanced Very High Resolution Radiometer Pathfinder Atmosphere (PATMOS) Climate Dataset: A Resource for Climate Research , 2003 .

[10]  Steven J. Worley,et al.  ICOADS release 2.1 data and products , 2005 .

[11]  Martin Wild,et al.  Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar “dimming,” and solar “brightening” , 2007 .

[12]  A. Lacis,et al.  Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data , 2004 .

[13]  C. Deser,et al.  Pacific Interdecadal Climate Variability: Linkages between the Tropics and the North Pacific during Boreal Winter since 1900 , 2004 .

[14]  S. Bony,et al.  Marine boundary layer clouds at the heart of tropical cloud feedback uncertainties in climate models , 2005 .

[15]  Michel Crucifix,et al.  The new hadley centre climate model (HadGEM1) : Evaluation of coupled simulations , 2006 .

[16]  Ronald L. Miller.  Tropical Thermostats and Low Cloud Cover , 1997 .

[17]  Taneil Uttal,et al.  Daytime Global Cloud Typing from AVHRR and VIIRS: Algorithm Description, Validation, and Comparisons , 2005 .

[18]  J. Norris.  Trends in upper‐level cloud cover and surface divergence over the tropical Indo‐Pacific Ocean between 1952 and 1997 , 2005 .

[19]  C. J. Hahn,et al.  Extended edited synoptic cloud reports from ships and land stations over the globe , 1999 .

[20]  A. Sterl,et al.  The ERA‐40 re‐analysis , 2005 .

[21]  J. Wallace,et al.  A Pacific Interdecadal Climate Oscillation with Impacts on Salmon Production , 1997 .

[22]  C. Bretherton,et al.  Aquaplanets, Climate Sensitivity, and Low Clouds , 2008 .

[23]  R. Allan,et al.  A new globally complete monthly historical gridded mean sea level pressure dataset (HadSLP2): 1850-2004 , 2006 .

[24]  C. J. Hahn,et al.  Extended Edited Synoptic Cloud Reports from Ships and Land Stations Over the Globe, 1952-1996 , 1999 .

[25]  Arpat Ozgul,et al.  The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda , 2009, Science.

[26]  S. Klein,et al.  On the Relationships among Low-Cloud Structure, Sea Surface Temperature, and Atmospheric Circulation in the Summertime Northeast Pacific , 1995 .

[27]  Vincent R. Gray.  Climate Change 2007: The Physical Science Basis Summary for Policymakers , 2007 .

[28]  J. Norris,et al.  Low Cloud Type over the Ocean from Surface Observations. Part III: Relationship to Vertical Motion and the Regional Surface Synoptic Environment , 2000 .

[29]  Richard G. Weiss,et al.  Molecular Gels: Materials with Self-Assembled Fibrillar Networks , 2005 .

[30]  L. Marx,et al.  Manifestation of remote response over the equatorial Pacific in a climate model , 2007 .

[31]  Minghua Zhang,et al.  Evidence of deceleration of atmospheric vertical overturning circulation over the tropical Pacific , 2006 .

[32]  A. Arakawa,et al.  Peruvian stratus clouds and the tropical Pacific circulation , 1996 .

[33]  R. Seager,et al.  How Can Tropical Pacific Ocean Heat Transport Vary , 2004 .

[34]  D. F. Young,et al.  Stratocumulus cloud properties derived from simultaneous satellite and island-based instrumentation during FIRE , 1992 .

[35]  B. Carlson,et al.  The Spatiotemporal Structure of Twentieth-Century Climate Variations in Observations and Reanalyses. Part II: Pacific Pan-Decadal Variability , 2008 .

[36]  Thomas M. Smith,et al.  Extended Reconstruction of Global Sea Surface Temperatures Based on COADS Data (1854–1997) , 2003 .

[37]  B. Soden,et al.  An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models , 2006 .

[38]  Tom M. L. Wigley,et al.  A Bivariate Time Series Approach to Anthropogenic Trend Detection in Hemispheric Mean Temperatures , 2003 .

[39]  D. Hartmann,et al.  The Effect of Cloud Type on Earth's Energy Balance: Global Analysis , 1992 .

[40]  宁北芳,et al.  疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A , 2005 .

[41]  J. Norris,et al.  interannual Variability in Stratiform Cloudiness and Sea Surface Temperature , 1994 .

[42]  A. Evan,et al.  Arguments against a physical long‐term trend in global ISCCP cloud amounts , 2007 .

[43]  S. Nigam.  The Annual Warm to Cold Phase Transition in the Eastern Equatorial Pacific: Diagnosis of the Role of Stratus Cloud-Top Cooling. , 1997 .

[44]  I. Musat,et al.  On the contribution of local feedback mechanisms to the range of climate sensitivity in two GCM ensembles , 2006 .

[45]  J. Norris,et al.  What Can Cloud Observations Tell Us About Climate Variability? , 2000 .

[46]  W. Rossow,et al.  Advances in understanding clouds from ISCCP , 1999 .

[47]  J. Norris.  On Trends and Possible Artifacts in Global Ocean Cloud Cover between 1952 and 1995 , 1999 .

[48]  B. Stevens,et al.  On the Structure of the Lower Troposphere in the Summertime Stratocumulus Regime of the Northeast Pacific , 2007 .

[49]  J. Norris.  Multidecadal Changes in Near-Global Cloud Cover and Estimated Cloud Cover Radiative Forcing , 2005 .