Irish Skies Shaped by Distant Deserts, Study Finds

A major new study has revealed that tiny particles of desert dust drifting into the atmosphere from distant regions can trigger the freezing of clouds over the Northern Hemisphere.

This natural process plays a key role in how clouds reflect sunlight and release rain or snow, and could have significant consequences for future climate predictions.

Led by researchers at ETH Zurich in Switzerland, the study is based on 35 years of satellite data. It shows that when more mineral dust is present in the atmosphere, clouds are more likely to freeze at their tops. This is especially relevant in colder northern regions such as the North Atlantic, Siberia and parts of Canada, where clouds regularly form at temperatures just below freezing.

Speaking about the findings, lead author Diego Villanueva, a post-doctoral researcher in atmospheric physics, explained that the presence of dust can make a big difference to what happens inside clouds. When more dust is present, there is a greater chance of clouds freezing at their upper levels. This has a direct influence on how much sunlight the clouds reflect back into space, and how much precipitation they produce.

The team focused on what are known as mixed-phase clouds. These are clouds that contain both ice crystals and supercooled water, and they are common in mid- and high-latitude regions. These clouds are known to be very sensitive to environmental changes, particularly to particles in the air that can trigger ice formation. Most of these particles come from desert dust that has been picked up by the wind and carried across long distances.

By comparing satellite measurements of cloud ice with dust levels in the atmosphere, the researchers found a clear and consistent trend. In colder and dustier conditions, cloud tops were much more likely to be icy. The pattern closely matched what previous laboratory research had suggested would happen, providing one of the strongest real-world confirmations of lab-based findings.

According to senior co-author Professor Ulrike Lohmann, the study is one of the first to show that satellite data on cloud composition lines up with experimental results from the lab.

The way clouds freeze has a major impact on climate. Icy clouds reflect more sunlight and can release more precipitation, which in turn influences global temperature and rainfall patterns. Until now, many climate models did not have accurate data on how this freezing process works on a large scale. The new research provides a solid benchmark to improve those models.

While the link between dust and ice formation is clear in many regions, the same does not apply everywhere. In desert zones like the Sahara, clouds are often scarce, and the hot, rising air may prevent the freezing process. In the Southern Hemisphere, other particles such as marine aerosols could play a more dominant role.

The researchers say more studies are needed to understand how other factors, like rising air currents and humidity, influence cloud behaviour. For now, though, their conclusion is clear. Microscopic grains of desert dust, carried thousands of kilometres by the wind, can help shape the clouds we see overhead—and influence the future of our climate.