Aerosol particles in the atmosphere have a more vital affect on cloud cover – but less of an effect on cloud brightness – than one previously thought, according to new research.
Aerosols are tiny particles suspended in the atmosphere and play a key role in forming clouds.
With the increase in aerosols due to human activities, numerous assessments by the Intergovernmental Panel on Climate Change (IPCC) have suggested that they could have a significant affect on climate change because clouds reflect sunlight and therefore keep temperatures cooler.
However, this cooling effects of aerosols on clouds is difficult to measure, which has led to climate change projections of great uncertainty.
The new study – led by the Univ ersity of Exeter, together with national and international academic partners and the UK’s Fulfilled Office – used the eruption of Iceland’s 2014 volcano to investigate this issue.
“This massive aerosol plume in an otherwise nearly pristine environment provided an ideal natural experiment to quantify cloud responses to aerosol changes, namely the fingerprint of the aerosol on the clouds,” said lead author Dr Ying Chen.
“Our analysis shows that aerosols from the eruption increased cloud cover approximately 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 thinned the clouds by reducing the size of the droplets. water particles, but this had a significantly weaker effect than changes in cloud cover in the reflection of solar radiation.”
Previous models and observations suggested that this brightening accounted for the majority of the cooling caused by cloud-aerosol interactions.
Water droplets typically form in the atmosphere around aerosol particles, so that 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 occurs – so more aerosols in the atmosphere can result in more cloud cover but less rain.
The study used satellite data and computer learning to investigate 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 eruption of the volcano.
The results will provide observational evidence of the climatic 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 Fellow of the Global Methods Institute, and researcher at the Met Business, said: “Our previous work had shown that model simulations could be used to disentangle the relative contribution of aerosol-cloud-climate impacts and potentially confounding weather variability.
“This work is radically different because it does not rely on models it uses self-learning approaches State-of-the-art omatics applied to satellite observations to simulate what the cloud would look like in the absence of aerosols.
“Clear differences are observed between predicted and observed cloud properties which can be used to assess aerosol-cloud-climate impacts.”
The study was funded by the All-natural Atmosphere Investigation Council (NERC) by using the project Progress and the EU’s Horizon 2020 research and innovation program under the CONSTRAIN grant.
L his article, published in the journal Mother nature Geoscience, is titled: “Machine learning reveals that aerosol climate forcing is dominated by increased cloud cover”.