It's a reasonable concern, but whether to modify the biosphere is not a choice we have any longer. We are modifying it -- that's what all that CO2 that we are

It's a reasonable concern, but whether to modify the biosphere is not a choice we have any longer. We are modifying it -- that's what all that CO2 that we are already putting into the atmosphere amounts to. Geoengineering is about looking for ways that we can modify it intentionally along with the unintentional modifications we are already making. Caution is certainly warranted, and there is some danger of hubris, but running screaming from the room is not a productive response either.