In a recent post, I highlighted an interview with Michael Mann in which he discusses possible tipping points. These are essentially rapid and irreversible (at least on short timescales) changes to our climate system. Judith Curry, however, has a recent post called did the AR5 take the dangerous out of AGW in which she discusses the section in the recent WG1 report that discusses potentially abrupt or irreversible changes.
The basic conclusions of the report are in the table below. It only shows potential changes that could happen in the 21st century. A number of things are possible, but quite few are unlikely. A number, however, seem to have a low confidence which I take to mean that they’re not sure. It does seem likely that the summer Arctic sea ice will disappear by mid century (at least under high forcing scenarios).
So, what does Judith make of this? Her post ends with
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?
So, the disappearance of the summer Arctic sea ice and regional forest diebacks don’t qualify as societally relevant. Okay, I would regard these as significant, but what do I know – I’m not a climate scientist like Judith. Fortunately, according to Judith, there is high confidence that we don’t need to worry about any of the genuinely dangerous scenarios on the timescales of a century (and, apparently, such things happen anyway without AGW).
So, it seems that Judith thinks that nothing too catastrophic will happen during the 21st century. The 22nd on the other hand …..