Resilience, Tipping Points, & Early Warnings

Resilience is the ability of a dynamical system (such as the Earth System) to quickly recover from short-term perturbations and return to its previous state. High resilience implies an ability for a system to withstand shocks, whereas declining resilience would leave a system vulnerable to passing ‘tipping points’ beyond which a regime shift to an alternative stable state (if it exists) becomes inevitable. It has been hypothesised that these tipping points may under certain circumstances be preceded by ‘early warning signals’ (EWS) that are detectable through statistical analysis, which could in theory provide invaluable alerts to humanity prior to future environmental regime shifts. However, reliably detecting EWS has proven tricky in practice, and producing robust measures of changing resilience and EWS remains a major research challenge. Measuring and predicting changes in Earth System Resilience has become a major theme in my research, and has played a central role in several projects:

Post-Doc 1.2: Can early warning signals be reliably detected in the Cenozoic palaeoclimate record? (2016)

In the summer of 2016 I received early career researcher funding from the EPSRC/ReCoVER network for a 3 month Research Fellow position at NOCS, University of Southampton, which follows on from some preliminary tipping point / early warning research in my PhD. There are many points in Earth’s history where the Earth System is hypothesised to pass a ‘tipping point’ beyond which a rapid transition to a new and very different state occurs. These critical transitions are common in other complex dynamical systems and are often preceded in datasets by ‘early warning signals’ (EWS) such as critical slowing down (i.e. the system’s recovery time in response to perturbations slows down) and increasing variability (as the data gradually contains more extreme values). Dakos et al. [2008] and subsequent studies found that EWS can be detected prior to several past climate shifts, suggesting that critical transitions can successfully be detected in the palaeorecord and that palaeo tipping points can be identified. However, doubts have been raised about the reliability of EWS analysis on palaeoclimate records, the degree to which parameter selection can affect the results, and the risk of committing the ‘prosecutor’s fallacy’ when analysing suspected critical transitions. In my PhD I did a pilot study in which I analysed the highest-resolution palaeorecords currently available across a number of perturbations to the Cenozoic carbon-climate system, and found some promising results even when using a cautious approach to counter potential problems. In this Post-Doc I extended these analyses, and found evidence of significant declines in carbon cycle resilience prior to several Cenozoic climate events. The first batch of results are now under review (see the academic publications page for updates).

Outreach: The point of no return? An Interactive Stall and Website Starting Conversations on Climate Tipping Points (Uni. Southampton 2016)

As part of the above Post-Doc project, I also received funding from the ReCoVER Network to run a public outreach project about Climate Tipping Points, for which I set up the website, commissioned a youtube animation, and gave a series of public talks. See the website for more information!

Post-Doc 1.4: Agent-based models for the analysis of early warning signals of ecosystem tipping points (Uni. Southampton, 2017)

In this pilot study project (also funded by the ReCoVER Network), we aimed to extend our understanding of ecosystem functioning in lakes undergoing eutrophication, and how it is affected by changes in biodiversity prior to the critical transition to a eutrophic state. As part of this I have developed a new prototype resilience metric based on reconstructing ecosystem community structure from diatom palaeoabundance data and inferring network stability, and helped to develop a prototype Agent-Based Model of diatom community dynamics during the eutrophication process. Work on this is ongoing, and a paper is in progress.

Post-Doc 2: Earth Resilience in the Anthropocene (Stockholm Resilience Centre, 2018-present)

I am now working at Stockholm Resilience Centre (SRC) on the Earth Resilience in the Anthropocene project, working on modelling nonlinear climate-biosphere feedbacks that could affect the resilience of the Earth System during the next century. See the Earth System Models of the Anthropocene page or my SRC bio for more information.