Stratospheric aerosol injection geoengineering has the potential to increase land carbon storage and to protect the Amazon rainforest

Solar radiation modification (SRM) aims to artificially cool the Earth, counteracting warming from anthropogenic greenhouse gases by increasing the reflection of incoming sunlight. One SRM strategy is stratospheric aerosol injection (SAI), which mimics explosive volcanoes by injecting aerosols into the stratosphere. There are concerns that SAI could suppress vegetation productivity by reducing the amount of sunlight reaching the Earth's surface and by shifting rainfall patterns. Here we examine results from five Earth System Models that use SAI to reduce the global mean temperature from that of a high emissions world (SSP585), to that of a more moderate global warming scenario (SSP245). Compared to SSP245, the SAI simulations project higher global net primary productivity (NPP) values (+15.6 %) and higher land carbon storage (+5.9 %), primarily because of increased CO₂ fertilisation. The effects of SAI are especially clear in Amazonia where land carbon storage increases compared to both SSP245 (+8.6 %) and SSP585 (+10.8 %), even though the latter scenario has the same atmospheric CO₂ scenario as the SAI scenario. Our results therefore suggest that SAI could provide some protection against the risk of climate change induced carbon losses from the Amazon rainforest, though this is not universally observed in all tropical forests. Additionally, we observe decreases in NPP and land carbon storage in some regions, such as eastern Africa, the northern high latitudes, and Indonesia.