Cloud study demystifies the effects of aerosols

Aerosols are tiny particles that float in the atmosphere and play a key role in cloud formation.

As aerosols increase due to human activities, numerous assessments by the Intergovernmental Panel on Climate Change (IPCC) suggest they could have an important impact on climate change, as clouds reflect sunlight and therefore keep temperatures cooler.

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

The new study – led by the University of Exeter, with national and international academic partners and the UK Met Office – used the Icelandic volcanic eruption of 2014 to examine this.

“This massive aerosol cloud in an otherwise nearly pristine environment provided an ideal natural experiment to quantify cloud responses to aerosol changes, namely the fingerprinting of aerosol on clouds,” 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 of cloud-aerosol interactions is caused by increased cloud cover.

“Volcanic aerosols also brightened clouds by reducing the size of water droplets, but this had a significantly smaller impact than cloud cover changes in reflecting solar radiation.”

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

Water droplets normally form around aerosol particles in the atmosphere, so a higher concentration of these particles facilitates the formation of cloud droplets.

However, because these cloud droplets are smaller and more numerous, the resulting clouds can hold more water before rain hits — so more aerosols in the atmosphere can result in more 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 Met Office Research Fellow, said: “Our previous work had shown that model simulations could be used to unravel the relative contribution of aerosol cloud-climate impacts and possibly.” bewildering meteorological fluctuations.

“This work is radically different in that it doesn’t 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 are observed between predicted and observed cloud properties that can be used to assess aerosol cloud climate impacts.”

The study was funded by the Natural Environment Research Council (NERC) through the ADVANCE project and the EU research and innovation program Horizon 2020 under the CONSTRAIN grant.

The paper published in the journal nature geosciencesis entitled: “Machine learning shows that aerosol climate forcing is dominated by increased cloud cover.”

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