Down votes? I know physicist, who tell me in private, that they are afraid about a point of no return. That we heat the climate up to a point where the system gets unstable. This is, as far as I know, what could have happend on planet Mars and it could happen here. Yet, you barley see anyone mentioning this public.

A sane risk assessment number should be something like:

Gain / (Risk * Damage)

So if the, theoretical, damage on Earth could make it something like Mars, we should act, even if we loose a lot of gain, that is comfort, and though the risk might seem low. On a sight note, the same goes for other humanity threatening dangers, like big asteroids.