Opportunistic experiments to constrain aerosol effective radiative forcing

Opportunistic experiments to constrain aerosol effective radiative forcing

Christensen, Matthew W. (University of Oxford; Pacific Northwest National Laboratory)
Gettelman, Andrew (University Corporation for Atmospheric Research)
Cermak, Jan (Karlsruhe Institut für Technologie)
Dagan, Guy (The Hebrew University of Jerusalem)
Diamond, Michael (University of Washington; National Oceanic and Atmospheric Administration; University of Colorado)
Douglas, Alyson (University of Oxford)
Feingold, Graham (National Oceanic and Atmospheric Administration)
Glassmeier, F. (TU Delft Atmospheric Remote Sensing)
Goren, Tom (University of Leipzig)
Grosvenor, Daniel P. (University of Leeds)

2022

Aerosol-cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due to human activities. The nonlinearity of cloud-state changes to aerosol perturbations make it challenging to attribute causality in observed relationships of aerosol radiative forcing. Using correlations to infer causality can be challenging when meteorological variability also drives both aerosol and cloud changes independently. Natural and anthropogenic aerosol perturbations from well-defined sources provide "opportunistic experiments"(also known as natural experiments) to investigate ACI in cases where causality may be more confidently inferred. These perturbations cover a wide range of locations and spatiotemporal scales, including point sources such as volcanic eruptions or industrial sources, plumes from biomass burning or forest fires, and tracks from individual ships or shipping corridors. We review the different experimental conditions and conduct a synthesis of the available satellite datasets and field campaigns to place these opportunistic experiments on a common footing, facilitating new insights and a clearer understanding of key uncertainties in aerosol radiative forcing. Cloud albedo perturbations are strongly sensitive to background meteorological conditions. Strong liquid water path increases due to aerosol perturbations are largely ruled out by averaging across experiments. Opportunistic experiments have significantly improved process-level understanding of ACI, but it remains unclear how reliably the relationships found can be scaled to the global level, thus demonstrating a need for deeper investigation in order to improve assessments of aerosol radiative forcing and climate change.

http://resolver.tudelft.nl/uuid:6a004e04-0321-4aff-8346-53bebd395e6c

https://doi.org/10.5194/acp-22-641-2022

1680-7316

Atmospheric Chemistry and Physics (online), 22 (1), 641-674

Institutional Repository

review

© 2022 Matthew W. Christensen, Andrew Gettelman, Jan Cermak, Guy Dagan, Michael Diamond, Alyson Douglas, Graham Feingold, F. Glassmeier, Tom Goren, Daniel P. Grosvenor, More Authors