It is very likely that efforts to prevent CO2 levels from soaring to 450ppm – the level we need to stop at to have any hope of limiting temperature rise to 2C or less – will fail. This will lead to a series of climatic “tipping points”, as Gaia’s stabilizing systems fail to check runaway warming and the Earth veers into a new hothouse steady state in which the Arctic remains unfrozen year round and “zones of uninhabitability” – places where it becomes physiologically impossible for humans to survive during summer days – spread out from the equator. The basic argument is as follows:
- The current atmosphere CO2 concentration (384ppm) correlates to the Pliocene 3mn years ago, when temperatures were 3C higher and the sea level was 25m higher. [No "hockey stick", no models even, involved; just paleoclimate].
- This degree of warming is now inevitable; if all emissions were to stop today, as a rule of thumb, it would take around 30 years for half of that projected warming to occur as the Earth system moves towards the new equilibrium. [Consequences of heat diffusion / laws of thermodynamics].
- Emissions aren’t stopping, but accelerating, and this will continue with the industrialization of China and India. [Economic growth as linchpin of the System].
- Global dimming, which had hitherto partially shielded us from the rising temperatures, will start playing a much lesser role. The effects of CO2 are cumulative, soot and SO2 particulates are washed out of the atmosphere within months.
- Beyond 2C of warming, the Earth will reach tipping points in which GW becomes self-sustaining. Such tipping points include the melting of the Arctic (reduces albedo), release of Siberian methane from melting permafrost, forests around the world turning from carbon sinks to carbon sources due to accelerated decomposition, the possible death of the Amazon rainforest, etc.
- Though geoengineering may work, as you point out, there are also many arguments against it. It will probably be tried in the end, but only as a last-ditch throw of the dice that cannot be guaranteed to succeed.
- Furthermore, innate human psychological features such as conservatism, denial, hedonism, and susceptibility to creeping normalcy and “landscape amnesia”, as well as the anarchic nature of the international system, means that the chances of any effective global action being taken in time is near zero.