The Earth’s climate has changed ever since the Earth began, but the drivers of these changes are not clear. If solar luminosity drove climate change alone then the Earth would have started out much chillier than evidence suggests and gradually heated throughout its history – a pattern at complete odds with geological records. The effect of changing concentrations of greenhouse gases is a more likely driver, but the causes of these changes through time are not so certain.
PhD: ‘What were the drivers of carbon-climate system perturbations during the Cenozoic?’ (2011-2015)
Over the course of the Cenozoic (the last 66 million years) the Earth system has shifted from a CO2-rich ‘Greenhouse’ climate state to a CO2-poor ‘Icehouse’ climate state. This trend is punctuated by numerous perturbations to the carbon-climate system, but the extent of the coupling between the carbon cycle and climate system, the drivers of these perturbations, and their relationship to the longer-term Cenozoic trend is still debated.
In my PhD thesis I used biogeochemical modelling and numerical analysis to explore the key research question: ‘What were the drivers of carbon-climate system perturbations during the Cenozoic?’, with a focus on perturbations during the Eocene-Oligocene Transition and the mid-Miocene, the role of tipping points during these periods, and the long-term evolution of the ocean carbonate system.
So far I have published 2 papers from my PhD (see my writing page for details and links) on the impact of the Columbia River Basalt large igneous province eruptions on the carbon-climate system in the mid-Miocene (around 16 million years ago) and the drivers of the carbon cycle perturbation during the glaciation of Antarctica in the Eocene-Oligocene Transition (~34 million years ago). I also co-authored a paper on the likely extent of ocean acidification as a result of the dinosaur-killing asteroid impact at the Creataceous-Palaeogene boundary (~66 Ma) and the role of Methane Hydrate dissociation during the infamous Palaeocene-Eocene Thermal Maximum (PETM, ~55 Ma), and am currently preparing further papers from my Thesis.
Post-Doc 2: Can early warning signals be reliably detected in the Cenozoic palaeoclimate record? (2016)
My current research project is a 3 month Post-Doctoral Research Fellow position at the University of Southampton funded by the EPSRC/ReCoVER network, and follows on from my 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.  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’ll focus on these most promising events with additional analytical techniques and data and publish the results in due course.