Immodest perturbation

Incurious and Unread in this comment talked about a “modest perturbation” and positive and negative feedbacks:

I can’t help feel that Gaia is letting us down here. It seems that we keep on getting positive feedback effects on the climate rather than negative feedback.

That seems kind of odd. As I understand it, the climate has been fairly stable pre-AGW, which suggests that negative feedback effects dominated. We have what seems to me (probably in my ignorance) a modest perturbation and suddenly we are envisaging positive feedback and an uncontrollable excursion to a new Venusian equilibrium.

Is it just that it is the positive feedback stories which hit the headlines, or is there some underlying reason why there are more positive feedback than negative feedback effects?

First up, it’s forcings that change the temperature positively or negatively. Forcings are amplified by feedbacks, positive and negative. For a stable climate the net effect of forcings and feedbacks should be zero, they should cancel each other out. Continue reading Immodest perturbation