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SUMMARY:Inferring causality in the atmosphere - constraining aerosol-cloud
  interactions from observations - Edward Gryspeerdt\, Imperial College\, L
 ondon
DTSTART:20170206T141500Z
DTEND:20170206T151500Z
UID:TALK70624@talks.cam.ac.uk
CONTACT:Michael Herzog
DESCRIPTION:Atmospheric aerosols are known to modify cloud properties\, wi
 th a net\ncooling effect on the earth.  However\, the magnitude of this co
 oling\neffect is highly uncertain\, largely due to the difficulty of separ
 ating the changes aerosols cause in cloud properties from those of other m
 eteorological factors.  For example\, both aerosol optical depth (AOD - us
 ed as a proxy for aerosol number) and cloud fraction (CF) are strongly aff
 ected by relative humidity\, such that the correlation between AOD and CF 
 is not a good indicator of the causal effect of aerosols on CF.  As CF is 
 strongly correlated to many other cloud properties\, this in turn obscures
  the causal effect of aerosols on these cloud properties.\n \nThe standard
  method for separating causal effects is direct experiment.  Unfortunately
 \, direct experiments on the atmosphere are often difficult\, expensive an
 d even unethical\, requiring approaches based only on observation.  In thi
 s talk\, several possible methods for separating the effect of aerosols on
  clouds from those of the surrounding meteorology are demonstrated.  These
  observational results are compared to results from global climate models 
 to assess how well they can actually constrain causal aerosol-cloud relati
 onships. Finally\, techniques more common to economics and public health a
 re used to evaluate the effect of aerosols on CF at a global scale\, reduc
 ing the uncertainty in the anthropogenic forcing of the climate.
LOCATION:Pfizer Lecture Theatre\, Department of Chemistry
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