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SUMMARY:What Can the Internal Variability of Climate Models Tell Us About 
 Their Sensitivity? - Dr Nicholas Lutsko\, Earth and Planetary Sciences\, M
 IT.
DTSTART:20180917T120000Z
DTEND:20180917T130000Z
UID:TALK109789@talks.cam.ac.uk
CONTACT:9780
DESCRIPTION:The relationship between climate models' internal variability 
 and their response to external forcings is investigated. Frequency-depende
 nt regressions are performed between the outgoing top-of-atmosphere (TOA) 
 energy fluxes and the global-mean surface temperature in the pre-industria
 l control simulations of the CMIP5 archive. Two distinct regimes are found
 . On sub-decadal frequencies\, the surface temperature and the outgoing sh
 ort-wave flux are in quadrature\, with the short-wave acting as a stochast
 ic forcing of surface temperature. The long-wave flux is linearly related 
 to temperature\, and acts as a negative feedback on temperature perturbati
 ons. On longer time-scales the outgoing short-wave and long-wave fluxes ar
 e both linearly related to temperature\, with the long-wave continuing to 
 act as a negative feedback and the short-wave acting as a positive feedbac
 k on temperature variability. In addition to the different phase relations
 hips\, the two regimes can also be seen in estimates of the coherence and 
 of the frequency-dependent regression co-efficients. The frequency-depende
 nt regression co-efficients for the total cloudy-sky flux on time-scales o
 f 2.5 to 3 years are found to be strongly (r^2 >0.6) related to the models
 ' equilibrium climate sensitivities (ECSs)\, suggesting a potential ``emer
 gent constraint" for Earth's ECS. However\, O(100) years of data are requi
 red for this relationship to become robust. A simple model for Earth’s s
 urface temperature variability and its relationship to the TOA fluxes is u
 sed to provide a physical explanation of these results.
LOCATION:MR 5\, Centre for Mathematical Sciences
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