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Measurement of Aerosols Optical Thickness of the Atmosphere using the GLOBE Handheld Sun Photometer
Published on: May 29, 2019
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Invisible ship tracks show large cloud sensitivity to aerosol
Peter Manshausen1, Duncan Watson-Parris2, Matthew W Christensen3
1Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK. peter.manshausen@physics.ox.ac.uk.
Nature
|October 5, 2022
Summary
Even without visible ship tracks, aerosol emissions significantly alter cloud properties. A new method reveals increased droplet numbers and liquid water, suggesting a larger climate cooling effect from shipping than previously understood.
Area of Science:
- Atmospheric Science
- Climate Science
- Aerosol-Cloud Interactions
Background:
- Cloud reflectivity is influenced by aerosol particles acting as condensation nuclei.
- Human-caused aerosol increases impact cloud droplet number, liquid water, and cloud fraction, but with significant uncertainties.
- Ship tracks are used to study aerosol-cloud interactions, yet only a small fraction of polluted clouds exhibit them.
Purpose of the Study:
- To quantify the impact of shipping emissions on cloud properties, even in the absence of visible ship tracks.
- To develop a novel method for assessing aerosol-cloud interactions beyond satellite-visible ship track observations.
- To investigate shipping's influence on clouds in the Atlantic trade cumulus regions.
Main Methods:
- Development of a new methodology to quantify aerosol-cloud interactions from shipping emissions.
- Analysis of cloud properties in the Atlantic trade cumulus regions, focusing on areas with minimal visible ship tracks.
- Direct detection of shipping-induced changes in cloud properties.
Main Results:
- Aerosol emissions substantially alter cloud properties even when ship tracks are not visible.
- The new method detected increased cloud droplet number concentration and a positive liquid water response in the absence of visible tracks.
- Shipping-induced cloud property changes were directly observed in Atlantic trade cumulus regions.
Conclusions:
- Previous studies relying solely on visible ship tracks may have selection biases.
- The observed strong liquid water path response implies a greater aerosol cooling effect from shipping.
- This enhanced cooling effect could potentially mask higher climate sensitivity than current temperature trends suggest.
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