Journal Article

Flickering gives early warning signals of a critical transition to a eutrophic lake state

Dearing, John A., Langdon, Peter G., Zhang, Enlou, Wang, Rong, Yang, Xiangdong, Scheffer, Marten, Dakos, Vasilis

2012

Overview

Critical transitions in experimental and theoretical systems can be anticipated on the basis of specific warning signs, with ‘critical slowing down’ being the best studied; long-term data from a real system, a Chinese lake, now show that a flickering phenomenon can be observed up to 20 years before the critical transition to a eutrophic state. Flicker of recognition is fair warning Critical transitions in experimental and theoretical systems can be anticipated on the basis of specific warning signs, raising the prospect that it might also be possible to predict future real-world events on the scale of the 2007 global financial crisis and Arab spring. But what to measure? Recent work has focused on critical slowing down, in which a system's recovery from perturbation is reduced as the transition is approached. Another possibility is flickering, in which increasing shifts between alternative stable states are seen in the run-up to the transition. This study uses long-term data from a real system, a Chinese lake, to show that flickering can be observed and that it occurs up to 20 years before a critical transition — in this case the deterioration of a lake towards a dead 'eutrophic' state as algal growth consumes the last available oxygen. There is a recognized need to anticipate tipping points, or critical transitions, in social–ecological systems 1 , 2 . Studies of mathematical 3 , 4 , 5 and experimental 6 , 7 , 8 , 9 systems have shown that systems may ‘wobble’ before a critical transition. Such early warning signals 10 may be due to the phenomenon of critical slowing down, which causes a system to recover slowly from small impacts, or to a flickering phenomenon, which causes a system to switch back and forth between alternative states in response to relatively large impacts. Such signals for transitions in social–ecological systems have rarely been observed 11 , not the least because high-resolution time series are normally required. Here we combine empirical data from a lake-catchment system with a mathematical model and show that flickering can be detected from sparse data. We show how rising variance coupled to decreasing autocorrelation and skewness started 10–30 years before the transition to eutrophic lake conditions in both the empirical records and the model output, a finding that is consistent with flickering rather than critical slowing down 4 , 12 . Our results suggest that if environmental regimes are sufficiently affected by large external impacts that flickering is induced, then early warning signals of transitions in modern social–ecological systems may be stronger, and hence easier to identify, than previously thought.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/158/47 / Algae / Animal and plant ecology / Animal, plant and microbial ecology / Aquatic ecosystems / Basins / Biological and medical sciences / China / Diatoms / Diatoms - isolation & purification / Ecological research / Economic statistics / Environmental aspects / Environmental Sciences / Eutrophic lakes / Eutrophication / Forecasting - methods / Fresh water ecosystems / Fundamental and applied biological sciences. Psychology / General aspects. Techniques / Geologic Sediments - analysis / Geologic Sediments - chemistry / History, 19th Century / History, 20th Century / History, 21st Century / Humanities and Social Sciences / Lake ecology / Lakes - chemistry / letter / Mathematical models / Methods and techniques (sampling, tagging, trapping, modelling...) / multidisciplinary / Phosphorus / Phosphorus - analysis / Plankton / Population density / Science / Social-ecological systems / Studies / Synecology / Time Factors / Time series / Variables / Water quality