What’s happening? The use of the geoengineering technique of marine cloud brightening (MCB) to reduce high temperatures in California could make European heatwaves more severe, according to a study published in Nature Climate Change. MCB involves the spraying of reflective aerosols, such as sea salt or sea spray, into clouds above the oceans. This helps reflect greater amounts of solar radiation back into space. The study’s authors also claim to be the first to show that cloud brightening effects can decrease, or even reverse, when climate conditions alter. The paper calls for regulation to govern the use of geoengineering techniques. (The Guardian)

Why does this matter? The new study demonstrates that targeted interventions to temporarily lower temperatures in one area can have negative impacts elsewhere, while also becoming more ineffective over time. It also emphasises that there is currently little regulation to control the use of techniques such as marine cloud brightening, meaning that individual countries, cities, or even companies and individuals, could potentially attempt to change their regional climates.

A divisive topic – Supporters of solar geoengineering suggest that it could help combat climate change impacts such as extreme temperatures, variable water availability and intense tropical storms. Advocates claim that it could also be cost effective. A 2018 study argued that solar geoengineering projects could potentially cost just $2bn to $2.5bn per year. However, opponents, such as the Union of Concerned Scientists, argue that geoengineering “poses unacceptably high environmental, social, and geopolitical risks” while also constituting a “moral hazard” as it could hinder efforts to reduce emissions.

Knock-on effects – The new study used Earth system computer models of the climate under both current and predicted 2050 conditions to simulate the impacts of MCB experiments conducted on the subtropics close to California and the mid-latitudes near Alaska. Both experiments aimed to lower the risk of extreme heat on the west coast of the US. Under present-day conditions, MCB was found to reduce the risk of dangerous summer heat in the western US by up to 55%. However, it also significantly reduced rainfall both in this area and other regions, including the Sahel of Africa.

Under predicted 2050 conditions, where global warming reached 2C above pre-industrial levels, MCB proved ineffective and led to dramatic warming in all areas of Europe except the Iberian peninsula. Scandinavia, Central and Eastern Europe were particularly badly affected. The impacts resulted from shifts in large-scale atmospheric currents that generated unexpected consequences.

Current uses – Despite concerns about the technique, solar geoengineering is already in use in some parts of the world. For example, in 2020, the Australian government backed plans to trial the technique in order to protect the Great Barrier reef.  

Practical challenges – Other such projects have proved controversial. In March, Harvard University cancelled its Swedish Stratospheric Controlled Perturbation Experiment (SCoPEx) project, which aimed to gather information for solar geoengineering initiatives. SCoPEx was opposed by Swedish environmental groups and the Indigenous Saami Council. Similarly, in May a University of Washington geoengineering project that saw sea-salt particles sprayed across the flight deck of a decommissioned aircraft carrier in San Francisco Bay was halted by authorities who wanted to assess the safety of the spray.