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IMAGe Brown Bag Seminar

Four Million Years and Counting: Designing and analyzing the RAPIT GCM Ensemble
Peter Challenor

University of Exeter

As the concentration of greenhouse gases in the atmosphere grows the risk of catastrophic events, such as the collapse of the AMOC increases. To guide policy we need to estimate the size of these risks. Estimating climate risks needs a combination of physics and statistics. In this paper we discuss the methods and results from the RAPIT project looking at the risk of AMOC slow down or collapse. We use a very large perturbed parameter (or physics) ensemble to investigate the effect of anthropogenic climate change on the strength of the AMOC. The model we use is HADCM3, and we run a very large (o20000) ensemble on volunteers’ computers using climateprediction.net. Each ensemble member, with one duplicate, is run with a different set of values for the uncertain model parameters. We now have almost 5 million years simulated in our ensemble. Even with such a large ensemble there are important questions of how we design the experiment. We discuss these issues and why we chose the design we did. Our design gives us a very wide range of possible HADCM3 climates most of which are not realistic. Using emulators and a measure of model discrepancy we use a method called ‘history matching’ to combine the model output and data. Unlike calibration where we try to find the ‘best’ parameter values, history matching rules out implausible climates. We thus restrict the range of not implausible HADCM3 models. All extra data further reduce the volume of Not Ruled Out Yet (NROY) space. I will discuss our initial results and show how calibration may allow us to produce better climate models.

Thursday July 25, 2013
Mesa Lab Chapman Room
at 12:00 PM
About you
First name: 
Carolyn
Last name: 
Mueller
Phone extension: 
2491
Announcement contact
First name: 
Carolyn
Last name: 
Mueller
Phone extension: 
2491
Announcement duration
Start: 
Thursday, July 25, 2013
End: 
Thursday, July 25, 2013