What has prevented us from reducing the uncertainty in aerosol cloud mediated radiative forcing and what can we do about it? (Invited Presentation)

The estimated magnitude of aerosol cloud mediated radiative forcing has evolved during the IPCC assessments, but its large uncertainty remained essentially unchanged and constituted a major component of the total uncertainty in climate forcing. In fact, paradoxically, the advancements in understanding impacts of cloud aerosol interactions on radiation increase the uncertainty, because we discover additional pathways by which aerosols affects clouds much faster than developing our ability to quantify these effects observationally. In other words, we discover more of what we should know that we don't know. This inherently increases the known uncertainty. The presentation will review the various known and recently discovered aerosol cloud mediated radiative effects and the methods that may be used to quantify them. The major challenges in doing so are measuring CCN from satellites and disentangling the impacts of CCN and updrafts on cloud properties. New breakthrough capabilities that give hope that it may be achievable from current satellite measurements will be presented.