Reading "The Planetary Emergency" by John Bellamy Foster and Brett Clark in the current Monthly Review the consensus is that irreversible climate change sets in with a rise in temperature of 2 degrees C (3.6 degrees F), which corresponds to one trillion cumulative metric tons of carbon emissions. We're going to hit the one trillion metric ton mark in 2043. Three decades.
The answer? We've got to stop growing. But capitalism is based on growth, on constantly increasing consumption, on the American ideal of every Chinese family owning a car or two and eating meat three times a day. So get ready to rumble. Conflict is coming our way, either in the form of dealing with the catastrophic effects of climate change (imagine being a character in Cormac McCarthy's The Road) or in the many politically necessary battles required to radically change the status quo. It's more than likely that we'll be dealing with both at the same time.