ANYONE CAN spot a tipping level after it’s been crossed. Also called important transitions, such mathematical cliff-edges affect all the pieces from the behaviour of economic markets and the unfold of illness to the extinction of species. The monetary disaster of 2007-09 is commonly described as one. So is the second that covid-19 went world. The true trick, subsequently, is to identify them earlier than they occur. However that’s fiendishly troublesome.