In point 4 - "..legitimate positive knock-on effects for the Earth's whole ecosystem?" Pull the other one Bobski! ?Ask any marine biologist about the effect of a one degree rise on plankton distribution or on corals, or in fact the whole marine ecosystem. Find out about the likely effects on the Amazon basin rainfall, and subsequently the whole rainforest, or about any one of a myriad of downsides to GW for global ecosystems. We have been so hung up about whether WE could cope with any relatively rapid change in global climate, that we often forget about the catastrophe it could cause to many other species of animals and plants. From polar bears to corals - it's far from being a "positive" for them. Those who talk about "no regrets" are blowing smoke from a place where they shouldn't!!