Judith Curry writes:
Admittedly there are numerous definitions of ‘abrupt climate change’, but the IPCC chooses a fairly trivial one: seemingly, the climate shift circa 2001 would qualify as an ‘abrupt’ climate change.
But the real issue is this. The IPCC approach, using highly damped deterministic global climate models, is incapable of producing abrupt climate change (beyond the melting of Arctic sea ice, which is not irreversible even on timescales of a decade).
The most scientifically interesting, and societally relevant topic in climate change is the possibility of abrupt climate change, with genuinely massive societal consequences (the disappearance of Arctic sea ice and regional forest diebacks arguably don’t qualify here). The IPCC has high confidence that we don’t have to worry about any of the genuinely dangerous scenarios (e.g. ice sheet collapse, AMOC collapse) on timescales of a century. These collapses have happened in the past, without AGW, and they will inevitably happen sometime in the future, with or without AGW. Are the IPCC overconfident in their conclusions on these also?