His believes (and provides much supporting evidence) that the Earth's climate exhibits a negative feedback system. That is, the greenhouse effect constantly adjusts itself in a way that keeps temperatures in sync with the amount of heat received from the Sun. That winds, clouds, evaporation and precipitation react to temperature changes such that high temperatures weaken the greenhouse and lower temperatures strengthen it.
He points out that today's climate models do not take enough of these factors into account, so they incorrectly predict disasters.
Read the essay for all the details.