Climate policies commit us to a calamitous 2.9C of global heating, but catastrophic changes can occur at even 1.5C or 2C
If there’s one thing we know about climate breakdown, it’s that it will not be linear, smooth or gradual. Just as one continental plate might push beneath another in sudden fits and starts, causing periodic earthquakes and tsunamis, our atmospheric systems will absorb the stress for a while, then suddenly shift. Yet, everywhere, the programmes designed to avert it are linear, smooth and gradual.
Current plans to avoid catastrophe would work in a simple system like a washbasin, in which you can close the tap until the inflow is less than the outflow. But they are less likely to work in complex systems, such as the atmosphere, oceans and biosphere. Complex systems seek equilibrium. When they are pushed too far out of one equilibrium state, they can flip suddenly into another. A common property of complex systems is that it’s much easier to push them past a tipping point than to push them back. Once a transition has happened, it cannot realistically be reversed.