Once more into the big IPCC report, where we keep looking in vain for the Code Red. Instead, we find things like Box 11.2, which is a rather calm and cool discussion of the fact that when it comes to the future rate of unlikely but damaging events, your guess is as good as theirs. Herewith, the IPCC in its own words, with only a few changes (e.g. (---) to denote lists of references and “...” to denote jumping over some details). “SREX (Chapter 3) assigned low confidence to low-probability high-impact (LLHI) events. … The low confidence does not by itself exclude the possibility of such events to occur, it is instead an indication of a poor state of knowledge. Such outcomes, while unlikely, could be associated with very high impacts, and are thus highly relevant from a risk perspective (---). Alternatively, high impacts can occur when different extremes occur at the same time or in short succession at the same location or in several regions with shared vulnerability (e.g. food-basket regions ---).
The difficulties in determining the likelihood of occurrence and time frame of potential tipping points and LLHI events persist. However, new literature has emerged on unanticipated and low-probability high-impact events more generally. There are events that are sufficiently rare that they have not been observed in meteorological records, but whose occurrence is nonetheless plausible within the current state of the climate system, see (---). The rare nature of such events and the limited availability of relevant data makes it difficult to estimate their occurrence probability and thus gives little evidence on whether to include such hypothetical events in planning decisions and risk assessments. The estimation of such potential surprises is often limited to events that have historical analogues (including before the instrumental records began, ---), albeit the magnitude of the event may differ. Additionally, there is also a limitation of available resources to exhaust all plausible trajectories of the climate system. As a result, there will still be events that cannot be anticipated. These events can be surprises to many in that the events have not been experienced, although their occurrence could be inferred by statistical means or physical modelling approaches (---). Another approach focusing on the estimation of low-probability events and of events whose likelihood of occurrence is unknown consists in using physical climate models to create a physically self-consistent storyline of plausible extreme events and assessing their impacts and driving factors in past (Section 11.2.3) or future conditions (11.2.4) (---)
… In summary, the future occurrence of LLHI events linked to climate extremes is generally associated with low confidence, but cannot be excluded, especially at global warming levels above 4°C. Compound events, including concurrent extremes, are a factor increasing the probability of LLHI events (high confidence). With increasing global warming some compound events with low likelihood in past and current climate will become more frequent, and there is a higher chance of historically unprecedented events and surprises (high confidence). However, even extreme events that do not have a particularly low probability in the present climate (at more than 1°C of global warming) can be perceived as surprises because of the pace of global warming (high confidence).