An international study led by the University of Eastern Finland and the Finnish Meteorological Institute has demonstrated that the formation and properties of lower-atmosphere clouds are highly sensitive to changes in atmospheric aerosol concentrations. This finding is significant as it impacts the assessment of how much human-induced fine particles have slowed down climate warming caused by greenhouse gases. The study was published in the prestigious Nature Geoscience journal.

Long-term measurements of atmospheric aerosol concentrations and cloud properties at ACTRIS measurement stations in Svalbard and Finland (at the Puijo Tower in Kuopio and in Pallas) revealed that clouds are more sensitive to aerosol changes than previously thought. Long-term observational time series on both aerosol and cloud properties are very limited. Since cloud properties vary greatly, long-term measurements are needed to determine how aerosols influence clouds.

"Emissions of anthropogenic fine particles have cooled the climate by modifying cloud properties and have thus partly counteracted greenhouse gas-induced climate warming. Based on these results, this cooling effect is at the upper end of previous estimates based on satellite data," says Professor Annele Virtanen from the University of Eastern Finland.

The study also evaluated the ability of climate models to describe the relationship between cloud properties and aerosol concentrations. Comparing models with observations revealed issues in how key processes are represented in the models. Additionally, the study identified significant differences between models in their predicted interactions between aerosols and clouds.

"These findings will help us develop more accurate climate models to predict future climate change. These models play a key role in assessing the climate impacts of different emission scenarios," says Research Professor Sami Romakkaniemi from the Finnish Meteorological Institute.

The study, led by the University of Eastern Finland and the Finnish Meteorological Institute, was the result of extensive European collaboration and involved several key European research institutions and universities.