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  • Pattern Recognition Methods to Separate Forced Responses from Internal Variability in Climate Model Ensembles and Observations
Title: Pattern Recognition Methods to Separate Forced Responses from Internal Variability in Climate Model Ensembles and Observations
Ensembles of climate model simulations are commonly used to separate externally forced climate change from internal climate variability. However, much of the information gained from running large ensembles is lost in traditional methods of data reduction such as linear trend analysis or large scale spatial averaging. This paper demonstrates a pattern recognition method (forced pattern filtering) that extracts patterns of externally forced climate change from large ensembles and identifies the forced climate response with up to 10 times fewer ensemble members than simple ensemble averaging. It is particularly effective at filtering out spatially coherent modes of internal variability (e.g., El Ni˜no, North Atlantic Oscillation), which would otherwise alias into estimates of regional responses to forcing. This method is used to identify forced climate responses within the 40-member Community Earth System Model (CESM) large ensemble, including an El-Ni˜no-like response to volcanic eruptions and forced trends in the North Atlantic Oscillation. The ensemble-based estimate of the forced response is used to test statistical methods for isolating the forced response from a single realization (i.e., individual ensemble members). Low-frequency pattern filtering is found to effectively identify the forced response within individual ensemble members and is applied to the HadCRUT4 reconstruction of observed temperatures, whereby it identifies slow components of observed temperature changes that are consistent with the expected effects of anthropogenic greenhouse gas and aerosol forcing.  more » « less
Award ID(s):
1929775 1752796
PAR ID:
10161458
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Journal of climate
ISSN:
0894-8755
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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