Wallace Climate Paper Summary

Start Date/Time: Thursday, August 27, 2009, 1:05 PM
Ending Date/Time: Thursday, August 27, 2009, 1:20 PM
Location: ATG 310C

After the Norden Huang seminar, in the last 15 minutes of the hour, Mike Wallace, UW Department of Atmospheric Sciences, will present a summary of a recently submitted paper, an application of EEMD in which he, Norden Huang, former UW student, Zhaohua Wu, and current student, Brian Smoliak are co-authors.

A summary of that paper follows:

The Earth has warmed at an unprecedented pace in recent decades. In assessing how much of this warming is natural and how much of it is induced by the buildup of greenhouse gases it is useful to partition the temperature time series into the secular trend and the (oscillatory) multidecadal variability. In a paper published in PNAS two years ago, Huang and Wu showed that the rapidity of the warming in recent decades was a result of concurrence of a secular warming trend and the warming phase of a multidecadal (~65-year period) oscillation and they estimated that the contribution of the former has been about 0.08°C per decade since ~1980. Here, we demonstrate the robustness of those results and focus upon their physical interpretation, considering in particular the spatial patterns associated with the secular trend and the multidecadal variability. We find that the pattern associated with the secular trend tends to be more globally uniform, suggestive of a response to the buildup of well-mixed greenhouse gases. In contrast, we find that multidecadal variability tends to be concentrated mostly over the extratropical Northern Hemisphere and particularly over the North Atlantic, suggestive of a possible link to low frequency variations in the strength of the Atlantic meridional overturning circulation. Depending upon the relative importance of the contributions of ocean dynamics and the time-varying emissions of aerosols by human activities to the observed trends in global-mean surface temperature, we estimate that up to half of late 20th century warming could have been a consequence of natural variability.