Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 11, 1621-1633, 2015
https://doi.org/10.5194/cp-11-1621-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
08 Dec 2015
Early warnings and missed alarms for abrupt monsoon transitions
Z. A. Thomas1,2, F. Kwasniok3, C. A. Boulton2, P. M. Cox3, R. T. Jones2, T. M. Lenton2, and C. S. M. Turney1 1Climate Change Research Centre and School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia
2College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4RJ, UK
3College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK
Abstract. Palaeo-records from China demonstrate that the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesized that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem δ18O records from Sanbao Cave and Hulu Cave, China, spanning the penultimate glacial cycle. We find that although there are increases in both autocorrelation and variance preceding some of the monsoon transitions during this period, it is only immediately prior to the abrupt monsoon shift at the penultimate deglaciation (Termination II) that statistically significant increases are detected. To supplement our data analysis, we produce and analyse multiple model simulations that we derive from these data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. However, signals of critical slowing down, which occur on the approach to a bifurcation, are only detectable in the model simulations when the change in system stability is sufficiently slow to be detected by the sampling resolution of the data set. This raises the possibility that the early warning "alarms" were missed in the speleothem data over the period 224–150 kyr and it was only at the monsoon termination that the change in the system stability was sufficiently slow to detect early warning signals.

Citation: Thomas, Z. A., Kwasniok, F., Boulton, C. A., Cox, P. M., Jones, R. T., Lenton, T. M., and Turney, C. S. M.: Early warnings and missed alarms for abrupt monsoon transitions, Clim. Past, 11, 1621-1633, https://doi.org/10.5194/cp-11-1621-2015, 2015.
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Short summary
Using a combination of speleothem records and model simulations of the East Asian Monsoon over the penultimate glacial cycle, we search for early warning signals of past tipping points. We detect a characteristic slower response to perturbations prior to an abrupt monsoon shift at the glacial termination; however, we do not detect these signals in the preceding shifts. Our results have important implications for detecting tipping points in palaeoclimate records outside glacial terminations.
Using a combination of speleothem records and model simulations of the East Asian Monsoon over...
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