Solar geoengineering methods that inject aerosols into the atmosphere may have regionally diverging effects on tropical cyclone frequency, suggests a modelling study in Nature Communications. These results suggest the uncertain effects of solar geoengineering - a proposed approach to counteract global warming - should be considered by policymakers.
A solar geoengineering approach known as stratospheric aerosol injection is expected to effectively cool the Earth’s surface by reflecting some sunlight before it reaches the surface. Observations of volcanic eruptions, which are the natural analogue of stratospheric aerosol injection, suggest that aerosol enhancements modulate tropical cyclone activity: eruptions in the northern hemisphere decrease North Atlantic tropical cyclone activity, and those in the southern hemisphere enhance it.
As similar outcomes are expected for stratospheric aerosol injection, it would be informative to assess the implications of this approach. Thus, Anthony Jones and colleagues run simulations with a fully coupled atmosphere-ocean model to investigate the effect of hemispheric stratospheric aerosol injection on North Atlantic tropical cyclone frequency. They find injections of aerosols in the northern hemisphere would decrease North Atlantic tropical cyclone frequency, while injections contained to the southern hemisphere may potentially enhance it. However, abrupt cessation of injections in 2070 would rapidly lead to a rebound of tropical cyclone activity to its base state.
The authors caution that while tropical cyclone activity in the North Atlantic could be suppressed by northern hemisphere injections, this would, at the same time, induce droughts in the Sahel. Therefore, unilateral geoengineering to control the climate response of a particular region should be considered carefully, as this approach may have negative effects elsewhere.