In his book Heat, George Monbiot looks at the possibility of a climate change catastrophe. He argues that a 2°C rise in global average temperature would precipitate such a disaster, as it would cause many ecosystems to begin to collapse. They would become CO2 emitters rather than the CO2 sinks that they are at present, and runaway global warming would follow, regardless of what we humans might do.
In order to be sure of avoiding that scenario, Monbiot estimates that humanity must achieve a 90% reduction in its CO2 output by 2030. Is it at all possible? In his book, Monbiot attempts to show that it is.