Doctoral defence: Heido Trofimov “Polluted clouds at air pollution hot spots help to better understand anthropogenic impacts on Earth’s climate”

On 25 August at 14:00 Heido Trofimov will defend his doctoral thesis “Polluted clouds at air pollution hot spots help to better understand anthropogenic impacts on Earth’s climate” for obtaining the degree of Doctor of Philosophy (in Physics).

Supervisors:
Associate professor Velle Toll, University of Tartu
Associate professor Piia Post, University of Tartu

Opponent:
Professor Risto Makkonen, Finnish Meteorological Institute (Finland)

Summary
It is unknown to what extent the cooling effect of the anthropogenic air pollution particles called aerosols offsets the warming effect of greenhouse gases. It is especially uncertain how strong is the cooling effect exerted by aerosol-induced changes in cloud properties. Clouds and precipitation can form in the Earth’s atmosphere thanks to the fine solid and liquid particles suspended in the atmosphere. Due to anthropogenic air pollution, there are more aerosol particles in the atmosphere leading to changes in cloud properties. Here, we compare the properties of clouds polluted by emissions from strong isolated aerosol sources to the nearby unpolluted clouds. We show that strong anthropogenic cloud perturbations occur intermittently and only in the case of favourable meteorological conditions. We challenge the assumption of unidirectional increases in cloud thickness in contemporary climate models and show that the cloud thickness does not increase in response to aerosols on average. This indicates that the cooling effect of anthropogenic aerosols on Earth’s climate might not be as strong as previously assumed. Our results will ultimately lead to more reliable climate projections.