THE CLOUD CHASER
If we learn how to influence the weather, climate change could be slowed. Anna Possner is crunching the numbers to find out what the consequences might be
“Could spraying tiny droplets of seawater into clouds brighten them enough to cool the planet – without nasty side effects?”
Ie see them almost every day, but there’s a lot we don’t know about clouds. Even to meteorologists, their inner workings are somewhat hazy. And that matters, because clouds play an important role in regulating the planet’s temperature – both reflecting radiation from the Sun and acting like a blanket, keeping the Earth’s heat in. In fact, some clouds are so effective at the reflecting bit that ‘supercharging’ them by making them even brighter and whiter has been suggested as a way to reduce temperatures and fight global warming.
It’s an idea that atmospheric scientist Anna Possner is very familiar with. Her research at the Carnegie Institution for Science in Stanford, California, will help to answer the question of whether ‘cloud brightening’ might actually work. She’s part of the Marine Cloud Brightening Project, an initiative that’s brought together cloud experts in the US and UK with a bunch of retired Silicon Valley engineers to find out whether spraying tiny droplets of seawater into clouds can brighten them enough to cool the planet – and do so without any nasty side effects.
Possner runs experiments with clouds, looking to see what happens when she injects droplets of seawater into them. But the clouds Possner works with are made up of numbers – they are numerical representations of the real thing created using algorithms that model how atmospheric systems work. So complex are these models that they require supercomputers – such as those at the National Center for Atmospheric Research’s (NCAR) centre in Wyoming – to run. “You run your models and you get output files that are usually four-dimensional – time and 3D space of various fields such as temperature, pressure, cloud water and cloud reflectivity,” says Possner.
Now a postdoctoral research scientist at Carnegie, it was Possner’s research for her PhD at ETH Zurich, Switzerland, that led to her connection with cloud brightening. Here she studied ship tracks, which are the shipping equivalent of aircraft contrails. These slender strips of brightened cloud form as ships crossing oceans belch out tiny aerosols, such as sulphate particles, from their smoke stacks. It’s around these tiny particles that water vapour in the atmosphere condenses, making the clouds more reflective. It’s exactly the same principle behind cloud brightening, except the particles that would supercharge the clouds would be saltwater.
Cloud brightening, like most geoengineering projects, is controversial. The biggest concern being that meddling with our weather systems might have unforeseen knock-on effects, and could actually make things worse. This controversy makes funding for such research hard to come by. It also makes young atmospheric scientists like 30-year-old Possner tentative about getting involved. “I’m not saying I’m in support or against it really, we have just got to start this now in terms of research. This is an idea that’s out there, and if people expect the scientific community to make a qualified statement about the possibilities and limitations of this method, it requires coordinated research.”
Possner’s virtual clouds are helping to plan the next stage of the project – where seawater will be sprayed into real clouds, rather than numerical ones, to measure what happens. At first, the plan is to run experiments on land at Moss Landing on the Californian coast before starting trials out at sea. Exactly when these experiments will happen is dependent on funding. “If you want to see whether this will work, you’ve got to test it in the field,” says Possner. “That’s where marine cloud brightening has a benefit – you can test it in the small scale without it having a long-term impact. Sea salt sediments out of the atmosphere quickly, and you’re not spraying anything that isn’t there already.”
For Possner, the big draw of cloud brightening research is understanding the basic physical process of how microscopic particles, such as sea salt and dust, interact with the atmosphere to generate and grow clouds. These aerosol-cloud interactions, as they are known, are one of the biggest unknowns in climate science, and figuring them out will give scientists a much better idea of what’s in store for our fragile planet.