Clouds: bright and with a fresh pine scent

A new study has shed light on the first step of cloud formation, revealing that organic oxides - such as the molecule responsible for giving pine forests their smell - are a vital ingredient. The CLOUD experiment (Cosmic Leaving OUtdoor Droplets), conducted at the CERN laboratory in Switzerland by an international team, including academics from the University of Leeds, will help scientists to better understand the effect that clouds have on climate change. “Clouds have a major cooling effect on climate, but we don’t have a good understanding yet of how pollution has affected natural clouds, and what this means for climate change,” said study co-author Professor Ken Carslaw from the School of Earth and Environment at the University of Leeds. Indeed, the latest report of the Intergovernmental Panel on Climate Change (IPCC) has once more pointed at clouds as the largest source of uncertainty in current climate models. A large share of the uncertainty stems from the complexity of cloud formation. Cloud droplets form when water vapour in the atmosphere condenses, but the process requires the helping hand of solid or liquid particles to which water vapour needs to attach before a cloud droplet is born. While such particles can be emitted directly from sources like sea spray, dust or vehicle emissions, most of them form in the atmosphere from gases emitted by natural sources or human activity.