Tim DelSole, Professor
Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University
Location: Haines Hall A25
Abstract:
In climate science, two questions arise repeatedly: (1) Has climate variability changed over time? (2) Do climate models accurately represent reality? Answering these questions requires a procedure for deciding if two data sets might have originated from the same source. While numerous statistical methods exist for comparing two data sets, most of these methods do not adequately consider spatial and temporal correlations and possible non-stationary signals in a comprehensive test. In this talk, I discuss a method that fills this gap. The basic idea is to assume that each data set comes from a vector autoregressive model. This model can capture typical spatial and temporal correlations in climate data in a parsimonious manner. Furthermore, non-stationary signals can be captured by adding suitable forcing terms. Then, deciding if two data sets came from the same source reduces to deciding if two autoregressive models share the same parameters. A decision rule and associated significance test is derived from the likelihood ratio method. In this talk, I discuss this procedure and additional procedures for isolating the source of any discrepancies. This procedure is applied to assess the realism of climate model simulations of North Atlantic Sea Surface Temperatures. According to this test, every climate model differs stochastically from observations, and differs from every other climate model, except when they originate from the same modeling center. In fact, differences among climate models are distinctive enough to serve as a fingerprint that differentiates a given model from both observations and any other model.
Bio:
Tim DelSole is a statistical climate scientist who studies the extent to which future climate changes can be predicted on time scales from weeks to years. he is also a senior research scientist at the Center for Ocean-Land-Atmosphere Studies. He serves as co-Chief Editor of the Journal of Climate. After completing my doctorate in 1993 from Harvard University, he became a Global Change Distinguished Postdoctoral Fellow for two years and a National Research Council Associate for two years at the NASA Goddard Space Flight Center. In 1997, he joined the GMU Center for Ocean-Land-Atmosphere Studies.