Joint Seminar: Distinguishing climate signals from climate noise using pattern recognition methods

A primary goal of climate science is to separate the influences of external forcing and internal variability on the global temperature record, as is needed to attribute observed climate changes, to estimate the climate response to future changes in radiative forcing, and to characterize and understand internal climate variability. Ensembles of climate model simulations are commonly used for this purpose. 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. I will demonstrate novel pattern-recognition methods – forced pattern filtering (FP filtering) and low-frequency pattern filtering (LFP filtering) – that can more efficiently separate climate signals from climate noise, based on differences in their spatial patterns. These methods are particularly effective at filtering out spatially coherent internal variability such as El Niño and the North Atlantic Oscillation (NAO). I apply FP filtering to single-model large ensembles and show that it can identify the spatiotemporally variable forced climate response with up to ten times fewer ensemble members than a simple ensemble average. In the 40-member CESM Large Ensemble, this analysis elucidates forced responses that were not otherwise apparent, such as an El-Niño-like response to volcanic eruptions and a forced trend in the NAO over the period 1950-1990. I apply LFP filtering to pre-industrial control simulations and show that it helps to clarify the mechanisms of Atlantic multi-decadal variability, isolating them from mechanisms relevant at shorter timescales. Across CMIP5 models, Atlantic multi-decadal variability is confined to the subpolar gyre and is associated with anomalous ocean heat transport. Finally, I will discuss how these pattern-recognition methods may help us to identify the forced component of observed temperature changes. In observations, a key open question is on the extent to which anthropogenic aerosol forcing, forced ocean circulation changes, and multi-decadal variability have contributed to observed variations in the hemispheric temperature contrast.




13:30 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Robert Jnglin Wills, University of Washington


Maria Rugenstein

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