The influence of aerosols – New study corrects previous research

Cloud study illustrates the effect of aerosols.

According to a recent study, aerosol particles in the atmosphere have a greater impact on cloud cover than previously thought, but a smaller impact on cloud brightness. Aerosols, which are tiny particles floating in the atmosphere, are essential for cloud formation.

Numerous assessments by the Intergovernmental Panel on Climate Change (IPCC) have shown that increasing aerosols due to human activities could have a significant impact on climate change as clouds reflect sunlight and sustain lower temperatures.

However, it is difficult to measure the cooling effect of aerosols on clouds, which has led to significant uncertainties in climate change projections.

The new research, led by the University of Exeter in collaboration with national and international academic partners and the UK Met Office, examined this using the Icelandic volcanic eruption of 2014.

“This massive aerosol cloud in an otherwise nearly pristine environment provided an ideal natural experiment to quantify cloud responses to aerosol changes, namely the aerosol-on-cloud fingerprinting,” said lead author Dr. Yingchen.

“Our analysis shows that the aerosols from the eruption increased cloud cover by about 10%. Based on these findings, we can see that more than 60% of the climate cooling effect from cloud-aerosol interactions is caused by increased cloud cover. Volcanic aerosols also brightened the clouds by reducing the size of the water droplets, but this had a significantly smaller impact than cloud cover changes in reflecting solar radiation.”

Previous models and observations indicated that this brightening was responsible for most of the cooling caused by cloud-aerosol interactions.

Water droplets often develop in the atmosphere surrounding aerosol particles, so a greater concentration of these particles facilitates cloud droplet formation.

However, because these cloud droplets are smaller and more numerous, the resulting clouds can hold more water before rain hits – hence more aerosols in the atmosphere could result in greater cloud cover but less rain. The study used satellite data and computer learning to examine cloud cover and brightness.

It used 20 years of satellite imagery of clouds from two different satellite platforms in the region to compare the periods before and after the volcanic eruption. The results will provide observational evidence of the climate impacts of aerosols to improve the models used by scientists to predict climate change.

Jim Haywood, Professor of Atmospheric Sciences at the University of Exeter and part of the Global Systems Institute, and a Met Office Research Fellow, said: “Our previous work had shown that model simulations could be used to unravel the relative contribution of aerosol clouds. Climate impacts and potentially confusing meteorological variability.”

He continues: “This work is radically different in that it does not rely on models; It uses cutting edge machine learning techniques applied to satellite observations to simulate what the cloud would look like without the aerosols. Clear differences between predicted and observed cloud properties are observed, which can be used to assess aerosol cloud climate impacts.”

Reference: “Machine Learning Shows Aerosol Climate Forcing Is Dominated by Increased Cloud Cover” by Ying Chen, Jim Haywood, Yu Wang, Florent Malavelle, George Jordan, Daniel Partridge, Jonathan Fieldsend, Johannes De Leeuw, Anja Schmidt, Nayeong Cho , Lazaros Oreopoulos, Steven Platnick, Daniel Grosvenor, Paul Field and Ulrike Lohmann, August 1, 2022,