Climate surprise

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A climate surprise is defined by the IPCC as a rapid, non-linear response of the climatic system to anthropogenic climate forcing (global warming). Climate surprises are low-probability, high-consequence extreme events, such as a collapse of the "conveyor belt" thermohaline circulation in the North Atlantic Ocean or rapid deglaciation of polar ice sheets. Because the global climate is made up of a number of complex subsystems which interact in complex and chaotic ways, climate change may lead to relatively few changes up to a tipping point, beyond which the system may tip into a new equilibrium.

Because of the high uncertainty regarding climate surprises, they are typically excluded from standard climate change scenarios. According to the International Climate Change Taskforce, the risks of surprises may increase above a 2°C temperature rise compared to the pre-industrial level, of which 0.8°C has already taken place and another 0.5 is already committed. The 2°C rise is typically associated in climate models with a carbon dioxide concentration of 400ppm; the current level is 379ppm, and rising at 2ppm annually. (The 2°C rise would not happen immediately, but would effectively be inevitable.)

Around 11,600 years ago, the earth's climate shifted from ice age to an age of warmth in the space of just 20 years.[1]