Climate wonks with a key to get through Science’s gate should check out Andy Dessler’s excellent discussion in today’s issue of the water vapor feedback. For those who don’t, here’s the nut graph:
[A]lthough there continues to be some uncertainty about its exact magnitude, the water vapor feedback is virtually certain to be strongly positive, with most evidence supporting a magnitude of 1.5 to 2.0 W/m2/K, sufficient to roughly double the warming that would otherwise occur. To date, observational records are too short to pin down the exact size of the water vapor feedback in response to long-term warming from anthropogenic greenhouse gases. However, it seems unlikely that the water vapor feedback in response to long-term warming would behave differently from that observed in response to shorter-time scale climate variations. There remain many uncertainties in our simulations of the climate, but evidence for the water vapor feedback–and the large future climate warming it implies–is now strong.