Satellite-based estimate of global aerosol-cloud radiative forcing by marine warm clouds

Changes in aerosol concentrations affect cloud albedo and Earth’s radiative balance. Aerosol radiative forcing from pre-industrial time to the present due to the effect of atmospheric aerosol levels on the micro- and macrophysics of clouds bears the largest uncertainty among external influences on climate change. Of all cloud forms, low-level marine clouds exert the largest impact on the planet’s albedo. For example, a 6% increase in the albedo of global marine stratiform clouds could offset the warming that would result from a doubling of atmospheric CO_2 concentrations. Marine warm cloud properties are thought to depend on aerosol levels and large-scale dynamic or thermodynamic states. Here we present a comprehensive analysis of multiple measurements from the A-Train constellation of Earth-observing satellites, to quantify the radiative forcing exerted by aerosols interacting with marine clouds. Specifically, we analyse observations of co-located aerosols and clouds over the world’s oceans for the period August 2006–April 2011, comprising over 7.3 million CloudSat single-layer marine warm cloud pixels. We find that thermodynamic conditions—that is, tropospheric stability and humidity in the free troposphere—and the state of precipitation act together to govern the cloud liquid water responses to the presence of aerosols and the strength of aerosol–cloud radiative forcing.

[1]  S. Twomey The Influence of Pollution on the Shortwave Albedo of Clouds , 1977 .

[2]  J. Coakley A Study of Climate Sensitivity Using a Simple Energy Balance Model , 1979 .

[3]  B. Albrecht Aerosols, Cloud Microphysics, and Fractional Cloudiness , 1989, Science.

[4]  Roy W. Spencer,et al.  SSM/I Rain Retrievals within a Unified All-Weather Ocean Algorithm , 1998 .

[5]  M. Kirkpatrick,et al.  The impact of humidity above stratiform clouds on indirect aerosol climate forcing , 2004, Nature.

[6]  M. Chin,et al.  Aerosol anthropogenic component estimated from satellite data , 2005 .

[7]  E. Vermote,et al.  The MODIS Aerosol Algorithm, Products, and Validation , 2005 .

[8]  M. A. Friedman,et al.  Retrieval of Cloud Properties for Partly Cloudy Imager Pixels , 2005 .

[9]  Yoram J. Kaufman,et al.  Satellite‐based assessment of marine low cloud variability associated with aerosol, atmospheric stability, and the diurnal cycle , 2006 .

[10]  C. Bretherton,et al.  Cloud droplet sedimentation, entrainment efficiency, and subtropical stratocumulus albedo , 2007 .

[11]  R. Wood,et al.  Cancellation of Aerosol Indirect Effects in Marine Stratocumulus through Cloud Thinning , 2007 .

[12]  Christian D. Kummerow,et al.  Multisensor satellite observations of aerosol effects on warm clouds , 2008 .

[13]  Andrew Gettelman,et al.  Global temperature stabilization via controlled albedo enhancement of low-level maritime clouds , 2008, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[14]  O. Boucher,et al.  Satellite-based estimate of the direct and indirect aerosol climate forcing , 2008 .

[15]  Johannes Quaas,et al.  Interpreting the cloud cover – aerosol optical depth relationship found in satellite data using a general circulation model , 2009 .

[16]  P. Chuang,et al.  Can aerosol decrease cloud lifetime? , 2009 .

[17]  J. Lamarque,et al.  Aerosol indirect effects – general circulation model intercomparison and evaluation with satellite data , 2009 .

[18]  B. Stevens,et al.  Untangling aerosol effects on clouds and precipitation in a buffered system , 2009, Nature.

[19]  Steven D. Miller,et al.  Rainfall retrieval over the ocean with spaceborne W‐band radar , 2009 .

[20]  R. Wood,et al.  Subseasonal variability of low cloud radiative properties over the southeast Pacific Ocean , 2009 .

[21]  E. Wilcox Stratocumulus cloud thickening beneath layers of absorbing smoke aerosol , 2010 .

[22]  Patrick Minnis,et al.  Relationships among cloud occurrence frequency, overlap, and effective thickness derived from CALIPSO and CloudSat merged cloud vertical profiles , 2010 .

[23]  G. Feingold,et al.  The scale problem in quantifying aerosol indirect effects , 2011 .

[24]  J. Pringle,et al.  The frequency and cause of shallow winter mixed layers in the Gulf of Maine , 2012 .

[25]  Philip Stier,et al.  Investigating relationships between aerosol optical depth and cloud fraction using satellite, aerosol reanalysis and general circulation model data , 2012 .

[26]  J. Seinfeld,et al.  Occurrence of lower cloud albedo in ship tracks , 2012 .

[27]  M. Christensen,et al.  Radiative Impacts of Free-Tropospheric Clouds on the Properties of Marine Stratocumulus , 2012 .

[28]  M. Christensen,et al.  Microphysical and macrophysical responses of marine stratocumulus polluted by underlying ships: 2. Impacts of haze on precipitating clouds , 2012 .

[29]  Johannes Quaas,et al.  Estimates of aerosol radiative forcing from the MACC re-analysis , 2012 .

[30]  T. Stocker,et al.  SBSTA-IPCC Special Event Climate Change 2013: The Physical Science Basis , 2013 .

[31]  G. Mann,et al.  Large contribution of natural aerosols to uncertainty in indirect forcing , 2013, Nature.

[32]  D. Rosenfeld,et al.  Decomposing aerosol cloud radiative effects into cloud cover, liquid water path and Twomey components in marine stratocumulus , 2014 .

[33]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .