摘要：Anthropogenic greenhouse gas emissions are warming the global climate at an
unprecedented rate. Significant emission reductions will be required soon to avoid a rapid
temperature rise. As a potential interim measure to avoid extreme temperature increase, it
has been suggested that Earth's albedo be increased by artificially enhancing
stratospheric sulfate aerosols. We use a 3D chemistry climate model, fed by aerosol size
distributions from a zonal mean aerosol model, to simulate continuous injection of 1–10 Mt/a into the lower tropical stratosphere. In contrast to the case for all previous work, the
particles are predicted to grow to larger sizes than are observed after volcanic eruptions.
The reason is the continuous supply of sulfuric acid and hence freshly formed small aerosol
particles, which enhance the formation of large aerosol particles by coagulation and, to a
lesser extent, by condensation. Owing to their large size, these particles have a
reduced albedo. Furthermore, their sedimentation results in a non-linear relationship
between stratospheric aerosol burden and annual injection, leading to a reduction
of the targeted cooling. More importantly, the sedimenting particles heat the
tropical cold point tropopause and, hence, the stratospheric entry mixing ratio of
H2O increases. Therefore, geoengineering by means of sulfate aerosols is predicted to accelerate
the hydroxyl catalyzed ozone destruction cycles and cause a significant depletion of the
ozone layer even though future halogen concentrations will be significantly reduced.
