Canopy Structure Amplifies the Role of Radiation in Vegetation Responses Under Stratospheric Aerosol Injection

Abstract. Stratospheric aerosol injection (SAI) is a climate intervention approach that would inject aerosols into the stratosphere, reflecting a fraction of incoming sunlight and reducing surface temperatures to mitigate impacts of climate change. While ecological studies of SAI have largely focused on temperature and precipitation, observations following volcanic eruptions suggest that radiation changes may be a primary driver of vegetation responses to atmospheric aerosols. Here, we leverage two global land surface models with different complexity to isolate the effects of radiation under SAI. The big-leaf model, which represents vegetation as a single bulk canopy, suggests that radiation has little influence on vegetation, whereas the cohort-based model, which resolves vegetation size structure and canopy stratification, finds that radiation changes are a major driver of plant responses. In the cohort-based model, radiation changes increase global net primary production by 3.9% for broadleaf trees, 9.7% for needleleaf trees, and 2.6% for C3 grasses, but reduce it by 1.3% for C4 grasses, while the big-leaf model shows little overall response to radiation. These findings suggest that vegetation and agricultural impact studies that do not explicitly account for changes in radiation, or rely on simplified big leaf models, may not capture the full response to SAI.