On the effective number of climate models

Update item information
Publication Type thesis
School or College College of Mines & Earth Sciences
Department Atmospheric Sciences
Author Pennell, Christopher J
Title On the effective number of climate models
Date 2009-12-15
Description Projections of future climate change are increasingly based on the output of many different models. Typically, the mean over all model simulations is considered as the optimal prediction, with the underlying assumption that different models provide statistically independent information evenly distributed around the true state. However, there is reason to believe that the assumption of model independence is unfounded. Coupled models are of comparable complexity and are constructed in similar ways. Some models share parts of the same code and some models are even developed at the same center. This contributes to the well-known problem of common model biases and, consequently, to a reduced spread amongst different predictions. This study attempts to quantify the extent of this problem by asking how many models there effectively are. Determining the effective number of models is achieved by evaluating 24 state-of-the-art models and their ability to simulate broad aspects of 20th century climate. Using two different methods, we quantify the amount of unique information in the ensemble and find that the effective ensemble size is much smaller than the actual number of models. As more models are included in an ensemble, the amount of new information diminishes in proportion. We further find that this reduction goes beyond the problem of "same-center" models and that systemic similarities exist across all models. Our results suggest that current methodologies for the interpretation of multi-model ensembles may lead to overly confident climate predictions.
Type Text
Publisher University of Utah
Subject Climatic changes; Climate forecasting
Dissertation Institution University of Utah
Dissertation Name MS
Language eng
Relation is Version of Digital reproduction of "On the effective number of climate models" J. Willard Marriott Library Special Collections QC3.5 2010 .P46
Rights Management © Christopher J. Pennell
Format Medium application/pdf
Format Extent 98,238 bytes
Identifier us-etd2,132545
Source Original: University of Utah J. Willard Marriott Library Special Collections
Conversion Specifications Original scanned on Epson GT-30000 as 400 dpi to pdf using ABBYY FineReader 9.0 Professional Edition.
ARK ark:/87278/s6st849n
Setname ir_etd
Date Created 2012-04-23
Date Modified 2012-04-23
ID 192187
Reference URL https://collections.lib.utah.edu/ark:/87278/s6st849n