Environment
Climate models suggest that a possible scheme to cool the western US by geoengineering clouds could work, but may have severe consequences in Europe,
A CLOUD-modifying technique could help cool the western US, but it would eventually lose its effectiveness and, by 2050, could end up driving heatwaves around the planet towards Europe, according to a modelling study.
There is growing interest in alleviating some impacts of global warming by using geoengineering techniques. These include marine cloud brightening (MCB), which aims to reflect more sunlight away from Earth’s surface by seeding the lower atmosphere with sea salt particles to form brighter marine stratocumulus clouds.
Small MCB experiments have already taken place in Australia on the Great Barrier Reef and in San Francisco Bay, California. Proponents hope this approach could be used to reduce the intensity of extreme heatwaves in particular regions as the climate continues to get hotter.
Katharine Ricke at the University of California, San Diego (UCSD), and her colleagues modelled the impact that a possible MCB programme to cool the western US might have under present climate conditions and projections for 2050.
The team modelled the impact of MCB in two locations in the northern Pacific Ocean: one in temperate latitudes and another in subtropical waters. The modelling applied MCB for nine months out of every year for 30 years, essentially altering the long-term climate.
The researchers found that under present-day climate conditions, MCB reduces the relative risk of dangerous summer heat exposure in parts of the western US by as much as 55 per cent. However, it dramatically reduces rainfall in the western US and in other parts of the world, such as the Sahel of Africa.
STOCKTREK/ALAMY IAN C. BATES/THE NYT/REDUX/EYEVINE
They also modelled the impact MCB would have in 2050, in a predicted scenario where global warming reaches 2°C above pre-industrial temperatures. Under these conditions, the same MCB programme was ineffective and instead dramatically warmed almost the entirety of Europe, except the Iberian peninsula. Ricke says the modelled temperature increase was especially large in Scandinavia, central Europe and eastern Europe.
These far-reaching impacts were caused by changes to large-scale atmospheric currents leading to unexpected consequences (Nature Climate Change, doi.org/m45d).
Team member Jessica Wan at UCSD says a big takeaway is that the impacts of regional MCB aren’t always intuitive: “Our results provide an interesting case study illustrating the unexpected complexities in the climate system you can uncover through regional geoengineering because o
