Temperatures in Transient Climates: Improved Methods for Simulations with Evolving Temporal Covariances

• Activity Number: 525
• Type: Topic Contributed
• Date/Time: Wednesday, August 3, 2016 : 10:30 AM to 12:20 PM
• Sponsor: Section on Statistics and the Environment
• Author(s): Andrew Poppick* and David McInerney and Elisabeth Moyer and Michael Stein
• Companies: The University of Chicago and University of Adelaide and The University of Chicago and The University of Chicago
• Keywords: climate change ; climate variability ; transient climate ; nonstationary processes ; evolutionary spectrum ; observation-driven simulation

Abstract

Future climate change impacts depend on temperatures not only through changes in means, but also through changes in variability. General circulation models (GCMs) predict changes in both, but raw GCM output should not be used for simulations, because GCMs do not fully reproduce present-day temperature distributions. We address a need for simulations of future temperatures that combine the observational record and GCM projections of changes in means and variability. Our perspective is that such simulations should be based on transforming observations to account for GCM projected changes, in contrast to methods that transform GCM output to account for discrepancies with observations. Our methodology is designed for simulating transient (non-stationary) climates. Our simulation relies on GCM projected changes in covariance, so we describe a statistical model for the evolution of temporal covariances in a GCM under future forcing scenarios and apply this model to an ensemble of runs from one GCM, CCSM3. The model for variability changes is also of interest on its own as a summary of GCM projections of variability changes.