How Outer Space Helps Clouds Form On Earth

In elementary school, we learn that clouds form when water vapor from seas, oceans, and other bodies of water, the ground, and living things rises into the sky and condenses into a large mass of droplets suspended in the air. For simplicity, this explanation often omits the need for aerosols, suspended molecules that help with the condensation of clouds. Understanding the role of aerosols is critical, and it is done in a variety of ways. IFLScience visited CERN in Switzerland to speak to the people working on the Cosmics Leaving Outdoor Droplets (CLOUD) experiment to find out more.

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Scientists study the atmosphere directly, looking at gas composition and other properties. They can also create clouds in labs studying the process of nucleation: how the water vapor condenses around the aerosols. At CERN, the CLOUD experiment does the second one, but with a cosmic twist. 

“CLOUD is a meteorology experiment here at CERN and it's a collaboration of more than 12 international institutes,” member of the CLOUD collaboration, Pedro Da Costa Rato, told IFLScience. “The two main questions that we're trying to answer are: how do galactic cosmic rays impact cloud formation and aerosol nucleation in the atmosphere, and how trace gases – and what trace gases – are fundamental in the nucleation of aerosols in the atmosphere.”

Let’s start with the first question. Every second of every day, particles from space rain on our planet. Some interact very little, but others, in particular the charged and high-energy ones, can interact a lot, especially with the molecules in the atmosphere. Since 2011, researchers have found a link between cosmic rays and aerosol nucleation. When the celestial particles slam into the molecules of the air, they can create important ions that then become the aerosol building block of clouds.

In a large cloud chamber, which you can see in the video above, researchers can accurately recreate the composition of the atmosphere by mixing specific gases. They then bombard the gases with accelerated protons so that the conditions in the stratosphere can be recreated at ground level.

The experiment is also looking at how the presence of new gases from industrialization has affected nucleation. They can alter the gases in the chamber and recreate preindustrial conditions, such as those known thanks to air bubbles trapped in ancient glaciers. All of this is crucial to provide more insights into the unfolding climate crisis.

 “We know that human impact in the industrial times has increased the temperature by 0.8°C since 1750. We also increased the aerosol population, which creates more clouds, which actually contributes to cooling down Earth,” Da Costa Rato told IFLScience.

“We have to understand how clouds are formed, how nucleation happens in the atmosphere, not just us making nucleation forcefully. And by understanding these mechanisms, CLOUD is helping to understand the impact of humans on climate change.”

Catching lightning in a bottle is proverbially difficult, but scientists have worked out how to make clouds in them. And if you have a big enough bottle, you can unlock the secrets of their formation, even if they come from space.