There are two fields of risk related to chemical substances.
One is called "environmental risk". It gives bad effect to the eco system and human through the environment. The key-point is that there are substances that affect the environment by small amount.
The other is the risk that we touch dangerous substances directly. For example, in a factory.
There are various indexes. We compare the quantity of risk with these indexes.
Climate Engineering is a study to control global warming. Many methods are scattring chemical substances to the atmosphea.
Old environmental problems are happened by the scattring chemical substances accidentally. But Climate Engineering aims to scatter intentionally.
Of course, there are many uncertain things and negative opinions. Scattering is easy. But the effect and influence are complex and uncertain.
We know Risk studies , Design of Experiments and Environmental Assessment . Even if we do Small Experiment of Climate Engineering, we use these studies by grand scale that we have not experienced.