- 1University of Birmingham, School of Geography, Earth and Environmental Sciences, Birmingham, United Kingdom of Great Britain – England, Scotland, Wales (cycy1320@163.com)
- 2University of Exeter, Exeter, UK
- 3University of Edinburgh, Edinburgh, UK
- 4The Met Office, Exeter, UK
- 5NASA US
- 6University of Reading, UK
- 7ETH Zurich, Zurich, Switzerland
Aerosol-cloud-interactions (ACI) is a leading uncertainty in estimates of their radiative forcing and hence for climate projection. The aerosol radiative forcing obtained from climate models is poorly constrained by observations, because the ACI signal is frequently entangled with noise of meteorological co-variability.
The Iceland-Holuhraun volcanic eruption in Iceland in 2014 provided an unprecedented opportunity to examine ACI of marine low-level clouds and how well they are represented in climate models. Malavelle et al. (2017) used Collection 5 data from the MODIS Aqua satellite and provided an assessment of the impact of the large release of sulfur dioxide on cloud effective radius (reff) and cloud liquid water path (LWP), finding a considerable impact on the former, but no impact on the latter. We revisit this eruption with a considerably extended satellite record which includes new Collection 6 data from the Terra and Aqua satellite and additional years of data from 2015-2020. This tripling of satellite data allows using novel data-science approach for a more rigorous assessment of ACI, including the impacts not just on cloud micro-physical properties (reff and LWP), but also on the macro property cloud coverage (Chen et al., 2022).
These results show that cloud fraction is significantly increased by 10% and appears to surpass cloud brightening and to be the dominant factor in aerosol indirect radiative cooling. The ACI cooling effect via increasing of cloud cover is even more remarkable in tropics (Fig.1, upto 50%), as demonstrated by our recent study of Hawaii volcanic natural experiments (Chen et al., 2024). Climate models are unable to replicate such strong impacts on cloud cover. These results show that the ongoing debate about the cooling impact of aerosols is far from over while climate models continue to inadequately represent the complex macro- and micro-physical impacts of ACI. These researches point towards a direction and provide new constraints for improving model representation of ACI.
Figure 1. Aerosol-induced changes in cloud cover from volcano natural experiments. Source: Chen et al., (2024)
References:
Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Partridge, D., Fieldsend, J., De Leeuw, J., Schmidt, A., Cho, N., Oreopoulos, L., Platnick, S., Grosvenor, D., Field, P., and Lohmann, U.: Machine learning reveals climate forcing from aerosols is dominated by increased cloud cover, Nature Geoscience, 10.1038/s41561-022-00991-6, 2022.
Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Peace, A., Partridge, D. G., Cho, N., Oreopoulos, L., Grosvenor, D., Field, P., Allan, R., and Lohmann, U.: Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover, Nature Geoscience, https://doi.org/10.1038/s41561-024-01427-z, 2024.
Malavelle, F., Haywood, J., Jones, A. et al. Strong constraints on aerosol–cloud interactions from volcanic eruptions. Nature 546, 485–491 (2017). https://doi.org/10.1038/nature22974
How to cite: Chen, Y., Haywood, J., Wang, Y., Malavelle, F., Jordan, G., Peace, A., Partridge, D., Cho, N., Oreopoulos, L., Grosvenor, D., Field, P., Allan, R., and Lohmann, U.: Observational evidence of strong aerosol fingerprints on clouds and effect on radiative forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-27, https://doi.org/10.5194/egusphere-egu25-27, 2025.
