| Summary: | We first show why current climate forecasting techniques, based on continuous extrapolations, are unreliable in the case of complex arrangements of interacting entities like the atmosphere–ocean system. By contrast, according to the well-established theory of dynamical systems, the observed present increase of fluctuations (as heat waves, droughts, tornadoes, forest fires) is a warning signal for an impending discontinuous climate tipping. A comparison with paleoclimatic events suggests that the atmospheric temperature would be likely to increase in this case by 6–9 °C in the next few years. In the transient period, the succession of heavy snow-falls and thawing episodes would favor spontaneous full-depth avalanches with larger run-out distances. After tipping into a new equilibrium, significantly warmer temperatures would shift snow-covered areas towards higher altitudes, probably by more than 1000 m, resulting in closure of a number of ski resorts. Glacier retreat and permafrost thawing would also enhance both ice and rock-fall frequency.
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