Injecting sulfate aerosols into the stratosphere to minimize changes in both surface temperature and rainfall over land may affect ocean circulation and may be less effective at cooling the deep and polar oceans than in cooling the atmosphere, suggests a paper published online this week in Nature Geoscience. These effects could result in geoengineering only slowing sea-level rise rather than halting it.

Managing incoming solar radiation by enhancing the Earth’s reflectivity has been discussed as a potential way to offset the climate warming caused by greenhouse gas emissions. However, this approach is controversial because it has the potential for significant side effects, such as reducing rainfall over land and shifting regional and seasonal temperature patterns.

John Fasullo and colleagues analyse simulations of a climate geoengineering scheme that aims to produce a stable climate by strategically injecting sulfate aerosols into the stratosphere at 15° and 30° latitude in both hemispheres. They find that the geoengineering would indeed reduce both surface warming and changes in temperature gradients, as well as minimize the adverse impacts on regional temperatures and rainfall levels. However, the simulations also produce a change in oceanic circulation that could lead to continued ocean warming, particularly near southern Greenland, compared to the present day. The authors caution that the impacts of climate geoengineering cannot be assessed with complete confidence at present.