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SUMMARY:Climate Response and Sensitivity: Timescales and Late Tipping Poin
 ts - Peter Ashwin (University of Exeter)
DTSTART:20220831T083000Z
DTEND:20220831T085000Z
UID:TALK177668@talks.cam.ac.uk
DESCRIPTION:Climate response metrics are used to quantify the Earth's clim
 ate response to anthropogenic changes of atmospheric CO2. Equilibrium Clim
 ate Sensitivity (ECS) is one such metric that measures the equilibrium res
 ponse to CO2 doubling. However\, both in their estimation and their usage\
 , such metrics make assumptions on the linearity of climate response\, alt
 hough it is known that\, especially for larger forcing levels\, response c
 an be nonlinear. Such nonlinear responses may become visible immediately i
 n response to a larger perturbation\, or may only become apparent after a 
 long transient. In this paper\, we illustrate some potential problems and 
 caveats when estimating ECS from transient simulations. We highlight ways 
 that very slow timescales may lead to poor estimation of ECS even if there
  is seemingly good fit to linear response over moderate timescales. Moreov
 er\, such slow timescale might lead to late abrupt responses ("late tippin
 g points") associated with a system's nonlinearities. We illustrate these 
 ideas using simulations on a global energy balance model with dynamic albe
 do. We also discuss the implications for estimating ECS for global climate
  models\, highlighting that it is likely to remain difficult to make defin
 itive statements about the simulation times needed to reach an equilibrium
 . [joint work with Robbin Bastiaansen and Anna von der Heydt]
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