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- Title
Uncertainty quantification of climate sensitivity: State-dependence, extreme values and the probability of tipping.
- Authors
Ashwin, Peter; von der Heydt, Anna
- Abstract
The Equilibrium Climate Sensitivity (ECS) remains not very well constrained, either byclimate models, observational, historical or palaeoclimate data. In addition to the classicalnotion of uncertainty (of measurement or model), the spread in ECS values finds its origin invarious dynamical aspects:(i) The climate system exhibits strong internal (and forced) variability on many timescalesmeaning that the 'equilibrium’ will only be relative to fixing the slow feedback processes.The implicit assumption here is that time scale separation (fast and slow) exists and ECSvalues from palaeoclimate (model or data) time series can be compared to shortmodel simulations. Palaeoclimate records instead can also give insight into theso-called Earth System Sensitivity (ESS), which includes the integrated effect of slowprocesses and boundary conditions (e.g. geography, vegetation and land ice). (ii) Thebackground state dependence of the fast feedback processes: Information from the latePleistocene ice age cycles indicates that the ECS varies considerably between regimebecause of fast feedback processes changing their relative strength over one cycle. (iii)Tipping elements in the climate system: Extreme values of palaeo-derived ECSsuggest that the climate response is in a region where there is a breakdown of theassumption of a linear response to perturbations. Here we show that for models of theclimate system with more than one regime and occasional switches between theseregimes, we can empirically determine probability of change in regime and confirmthat extremes of climate sensitivity are associated with very high probabilities oftipping.
- Subjects
EXTREME value theory; PROBABILITY theory; UNCERTAINTY; TIME series analysis; GLACIAL Epoch
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article