I wonder if any else has noticed that we appear to have crossed a threshold in the usage of the phrase ‘tipping point’ in discussions of climate? We went from a time when it was never used, to a point (of no return?) where it is used in almost 100% of articles on the subject. Someone should come up with a name for this phenomenon….
Regardless of the recent linguistic trends, the concept has been around for a long time. The idea is that in many non-linear systems (of which the climate is certainly one), a small push away from one state only has small effects at first but at some ‘tipping point’ the system can flip and go rapidly into another state. This is fundamentally tied to the existence of positive feedbacks and is sometimes related to the concept of multiple ‘attractors’ (i.e. at any time two different ‘states’ could be possible and near a transition the system can flip very quickly from one to another). Another ‘tipping point’ in non-linear systems occurs when as some parameter varies, the current attractor changes character or disappears. However it is currently being used interchangeably a number of potentially confusing ways and so I thought I’d try and make it a little clearer.
But Hansen has also said we don’t know where the tipping points are for a runaway greenhouse effect, because we don’t know nearly enough about the various feedback systems involved.
Hansen discusses this in his recent book, “Storms Of My Grandchildren”.
He says that we do know enough, now, that if we continue to burn oil and coal as we’re doing, there’s a strong likelihood that the Earth’s surface will average 200 degrees Celsius by the 25th century.
And, Hansen says, burning the tar sands and oil shales too will “certainly” lead to that sterilized Earth.
But the politicians, economists, and executives who have the capacity to take action, all have strong personal interests in continuing burning fossil fuels.
So I see very little prospect of avoiding an end close to the worst-case scenario.