Tipping Points in the Arctic: Eyeballing or Statistical Significance?
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Arctic ecosystems have experienced and are projected to experience continued large increases in temperature and declines in sea ice cover. It has been hypothesized that small changes in ecosystem drivers can fundamentally alter ecosystem functioning, and that this might be particularly pronounced for Arctic ecosystems. We present a suite of simple statistical analyses to identify changes in the statistical properties of data, emphasizing that changes in the standard error should be considered in addition to changes in mean properties. The methods are exemplified using sea ice extent, and suggest that the loss rate of sea ice accelerated by factor of ~5 in 1996, as reported in other studies, but increases in random fluctuations, as an early warning signal, were observed already in 1990. We recommend to employ the proposed methods more systematically for analyzing tipping points to document effects of climate change in the Arctic.
KeywordsChange point detection Global warming Ecological regime shift Sea ice retreat Threshold response
We thank the National Snow and Ice Data Center, University of Colorado in Boulder, for their open access data services. This research is a contribution to the Arctic Tipping Points project (http://www.eu-atp.org) funded by FP7 of the European Union (contract #226248). The manuscript was improved with the constructive comments from Paul Wassmann and two anonymous reviewers.
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