New Paper Out: Reduced Carbon Cycle Resilience across the PETM

Much like buses, after a waiting a while for new papers to be published two have come along in short succession. This time though we’re back in the palaeoclimate domain, with a paper based on my work on a ReCoVER-funded Early Career Research award hosted at Ocean & Earth Science at Southampton which applied ‘early warning signal’ methodology to Cenozoic palaeoclimate records. It’s now available open access from Climates of the Past, and as with other papers I’ll summarise it here on my blog as well.

CP cover enlarged
My first EGU journals paper , and a pleasant public review process!

The setting of this paper is the Palaeocene-Eocene Thermal Maximum (i.e. the PETM), which is a natural case of carbon cycle disruption and linked rapid global warming that happened about 56 million years (My) ago. The triggers of this event are still being investigated, but palaeorecords point to the release of several thousand gigatonnes of carbon being released over a few thousand years driving ~5oC of global warming. As a comparison to today, this is a similar amount of carbon as humans are likely to emit from fossil fuel burning but over ~10 times the time, making it a partial but limited analogue to current climate change. The PETM was then followed by several smaller ‘hyperthermal’ events on a regular timescale into the warm Eocene.

As with many other big ancient climate shifts, the PETM was preceded by more gradual changes before a rapid shift, which has led many to hypothesise that it involved some sort of ‘tipping point’ (i.e. when gradual changes can eventually lead to a sudden shift in a system after reaching a critical threshold – see for more info!) that led to lots of carbon from parts of the Earth system like methane hydrates or peat being suddenly released. Alternatively, the PETM also coincided with a time of mass volcanism associated with the opening of the North Atlantic (of which Iceland is now the distant hangover of), and so could have been directly triggered by volcanic eruptions without any sort of tipping point involved.

Theory suggests that tipping points are often preceded by small but detectable ‘early warning signals’ (EWS), which can be found using statistical analysis of data. After an early proliferation of EWS techniques a few years ago though researchers have found them to have important limitations, with data quality being a big constraint and a propensity for false or missed alarms. Despite this, using multiple EWS indicators of different types along with strong statistical significance testing can still give us a pretty good idea of changes in a system’s overall resilience, with increasing variability and system ‘memory’ indicating the weakening of the system’s stabilising negative feedbacks and therefore a greater risk of being disturbed.

In our study we put this to the test by analysing some good quality long palaeorecords covering 5 My before the PETM and ~2 My after in order to look for any significant changes in carbon-climate system resilience that might help explain the origins of the PETM. We found consistent evidence from several different methods of a gradual destabilisation of the geological carbon cycle in the ~2 My before the PETM, and long-lasting carbon-climate system instability in the aftermath. This period coincides with the North Atlantic volcanism, leading us to suggest that these eruptions helped to gradually destabilise the carbon cycle by suppressing organic carbon burial (in particular either the marine biological pump or peat on land) as the result of volcanism-driven warming .

However, although this could mean the PETM itself was a tipping point resulting from this destabilisation it cannot solidly prove it, and we find no evidence of a tipping point in just the climate system either. Despite this, a decline in carbon cycle resilience would’ve still made it easier for the PETM to occur and last longer than it would’ve been otherwise, as weaker negative feedbacks would slow down the carbon cycle’s recovery to pre-PETM conditions. We also find evidence that the subsequent hyperthermal was preceded by slightly different dynamics than the PETM itself, which fits with the hypothesis that the PETM required an extra “push” from say volcanism but that the later events were more traditional tipping points.

To find out more, the full article is open access and free to read for all, and direct questions are welcome. Future follow-up work include a similar analysis of the Cretaceous/Palaeogene boundary and the Deccan Traps (paper TBC), and other Cenozoic climate shifts as more long and high-resolution records become available. Thanks also go to EPSRC/ReCoVER for funding the initial project, OES at Uni. Southampton for hosting the project back in Summer 2016, SRC where I did the final revisions/reanalyses, and Stockholm University for funding the open access publication.

New paper out on the extent of Sustainable Intensification in England

I’ve had a paper accepted over at Science of the Total Environment called “To what extent has sustainable intensification in England been achieved?” – click here for free access to the final published version (open until 18/19/2018), and after that you can find a free pdf of the accepted post-print manuscript over on my publications page. This is the final product of the first postdoc I took on at Southampton’s Geography department in 2015-16, so it’s good to see it finally out there! It’s also my first paper branching out into Sustainability Science & Socio-Ecological Systems from my Geological/Earth System roots. Here’s a blog summary:

The background to the paper is the drive for the Sustainable Intensification of Agriculture (SI) – the goal being to produce more food with a smaller environmental footprint, as agriculture remains one of the biggest global drivers environmental degradation while global population is projected to substantially grow by mid-century. This has been a hot topic over the last couple of decades in agricultural & environmental sciences, and there’s evidence for some progress in some places. However, the process of SI itself is not sufficient if the environmental footprint is still too big to be truly sustainable – we need to make sure that SI leads to global and regional agroecosystems reaching a ‘safe operating space‘ in which no ecosystem service is degraded beyond acceptable planetary/regional boundaries. In other words, making intensification a bit more sustainable or efficient isn’t enough if the environment that agriculture depends on is still being degraded in some way.

In this study we used publicly available data to determine the progress of SI in England and two sub-regions (mostly arable Eastern England & mostly pastoral South-Western England), using it as a case study of a rich, developed country with some signs of SI occurring. We use the data to produce metrics and indices of various important ecosystem services important for keeping the English agroecosystem in a safe operating space, such as river contamination by agricultural nutrients (water quality), atmospheric emissions (air quality), the farmland bird index (proxy for wider biodiversity), and soil erosion, as well as how much food is produced (wheat yield, and meat & dairy) and socio-economic context (e.g. farm income, subsidies, labour, etc.). [It’s worth noting here that even in a rich country there are some things we just couldn’t get enough data for, making this only a partial analysis]. From this we looked at their relative trends, performed some statistical analyses to explore these trends, and then built a simple system dynamics model of the agroecosystem and make some future projections.

Here’s a key summary figure of our main results (from the graphical abstract to the paper):

Armstrong McKay et al - Graphical Abstract
Graphical Abstract from Armstrong McKay et al. (2018) showing some key intensification trends in the English agroecosystem between 1950 and 2013.

The trends above (shown as z scores, i.e. relative changes rather than the absolute values) can be split into two main phases. Prior to the mid 1990s, Wheat Yield increases as a result of conventional Agricultural Intensification driven by increased fertiliser use, with livestock population and outputs also increasing. This results in greater food self-sufficiency (i.e. less food imported), but also leads to increased environmental degradation (the thick brown line) primarily due to pollution and falling farmland biodiversity (the dot-dashed green line). However, after the mid 1990s fertiliser use decouples from yield and starts to fall (while yield stays stable), which along with falling livestock population (mostly due to the 2001 foot-and-mouth disease outbreak) leads to a fall in pollution and therefore in overall degradation.

This seems like good news, and it partially is (especially for river-water and air quality, the biggest improvers), but this fall in overall degradation masks the fact that farmland biodiversity fails to recover at all. The parallel decline in self-sufficiency also means more food is being imported to the UK, and indicates that some of the UK’s agricultural degradation is simply being ‘offshored’ to other countries to deal with instead. These trends were further analysed and confirmed by the statistical analyses and modelling, and can also be plotted against GDP per capita to show a partial ‘Environmental Kuznets Curve’ (a reduction in degradation relative to yield beyond a certain level of prosperity – implying that prosperity leads to less degradation – but critically not for biodiversity, and could also be the result of using prosperity to pay others to degrade instead). Another interesting outcome from the analysis is the despite there being some evidence of ‘land sparing’ – i.e. intensification allowing the transfer of marginal agricultural land to conservation areas, here primarily from rough grazing areas – this has not stopped biodiversity decline so far despite being mooted as a key conservation strategy (see the paper for thoughts as to why).

Overall, these trends indicate that SI has indeed begun in England, but with major negative trade-offs on biodiversity and offshored degradation. These trade-offs undermine the general SI trend, and so must be dealt with before the English agroecosystem can reach a safe, or just, operating space. In future there’ll also be the challenges of climate change (which is likely to reduce yields and biodiversity overall) and post-Brexit subsidy changes (which might affect the financial viability of farming), which will require even more SI to counteract. What this future SI will look like is hard to say, but it’ll certainly require new approaches to subsidies and agri-environment schemes that better encourage both biodiversity restoration and reduced offshoring of degradation.

For more details, go read the paper and feel free to ask me questions!

Moving to Sweden


Some big (and late) news from me: as of this April and after ~10 years I’ve finally left Southampton to move to Sweden for a new Post-Doc (along with my partner Rachael – see her blogs about moving to Sweden)!

The last time I posted on this blog I had just started a new Post-Doc project in Southampton – since then I moved on to a new project (using Agent-Based Models to design agroecological microinsurance co-ops to improve the resilience of smallholders in coastal Bangladesh) and have now taken up a new Post-Doc at Stockholm Resilience Centre (a cutting-edge research institute within Stockholm University promoting ‘Sustainability Science for Biosphere Stewardship’). I’ll be working on modelling nonlinear climate-biosphere feedbacks as part of the Earth Resilience in the Anthropocene project for the next 2 years – you can find some more details at my SRC bio or on my newly updated Research pages. It’s also nice to have a longer project to get my teeth into compared to the rather short-term and precarious small pots of funding I’ve had since the end of my PhD – ~2 guaranteed years of job and housing seems like quite the luxury compared to the uncertainty of the last few years! We’ll be living in Solna in Stockholm county for the duration, and I’m hoping to get out and about exploring around the Nordic/Baltic regions and getting some good travelling and bushcrafting in.

New Project: Agent Based Models & Ecosystem Tipping Points

Things continue to keep rapidly changing this year, and I’ve started on another new academic project!

Back in May I started a new Post-Doc Research Fellowship in the Global Environmental Change and Earth Observation group in the Geography and Environment dept. of the University of Southampton, working on the ReCoVER Network-funded pilot study project “Agent-based models for the analysis of early warning signals of ecosystem tipping points” with PI James G. Dyke. In this project we’re working on some new potential early warning signals for ecosystems near tipping points – in particular looking at the ecosystems’ compositional disorder and food web dynamics and replicating these using Agent Based Models (ABMs) – using lake eutrophication as a case study. We’re hoping this 6 month pilot study will lead to some new useful metrics for detecting potential tipping points in ecosystems (and socio-ecological systems) developed through a bigger project in future. Thanks again to the ReCoVER Network for funding this project! This means I’ll still be In Southampton for the rest of 2017, but beyond that who knows…

In other news, I’ll be giving a Winchester Café Scientifique talk on Monday 4th September about Climate Tipping Points (linked to my outreach project) – I’ll be talking about what climate tipping points are, how they might affect us, and whether we can predict them, as well as considering how they make climate change more of a “wicked problem” to deal with. Come along if you’re around!

February Update: Climate Tipping Points and Current Research

My ReCoVER-funded outreach project on Climate Tipping Points has mostly come to an end now, and it’s gone really well. We’ve done some public events including a school science day and some public conversation sessions, and I’ve written a collection of articles over at and an article for The Science Room responding to their community question of “Why is Climate Change so Hard to Address?” (also posted over at my new Medium page where I’ll try to post my non-academic writing). We’ve also made an animated guide to Climate Tipping Points, with thanks going to Rachael for lending us her voice and Ciarán for animating:

There’ll also soon be a podcast chat with my friend Jess on the same material too, alas featuring my own voice instead of Rachael’s (and it turns out the only way to make my voice sound more posh is for me try and sound less posh…).

Since I last posted I’ve also moved on to a new Postdoc based at Geography at the University of Southampton with Prof. John Dearing, once again moving from ancient climate change to modern sustainability to study macroscale controls on how Ecosystem Services and Poverty Alleviation are interlinked. This position has been intense and led to some interesting outcomes (paper now in progress) but as another short contract is now nearly finished, so the hunt for a new position continues!

ReCoVER Outreach Project on Climate Tipping Points

I’m pleased to announce that I’ve been giving funding by the ReCoVER network to do some Outreach linked to the end of my current Research Fellowship, and so we’re now launching the project: The Point of No Return? An Interactive Stall and Website Starting Conversations on Climate Tipping Points”.

title-pageIn this project we’ll be hosting conversations about climate tipping points at a series of stalls, public discussions, and online during October and November 2016, focusing on how they happen, why they’re important to our lives, and how researchers are trying to understand and predict them.

We’ll be running stalls at Southampton Sustainability Week (8th-16th October) – including at the Family Festival of Science at Thomas Hardye School on October 8th (tomorrow!) and at Researchers Café at Mettricks on October 14th – and at TEDx Southampton (5th November). We’ll upload materials from the stall on the website along with additional articles, blog posts, interactive discussions, integrated social media feeds, a podcast, and videos (in collaboration with local film-maker global documentary and a local animator) about climate tipping points.

So please pay a visit to, on twitter at @climatetippoint, and on facebook – we look forward to starting the conversation and invite you to join in!

NEWS: New Post-Doc on Palaeo Early Warning Signals (funded by ReCoVER)

I’m pleased to announce that I’ve just started a new Post-Doc today at the University of Southampton, funded by the EPSRC/ReCoVER Network’s Early Career Researcher fund. I’ll be working for the next few months as a Research Fellow at Ocean and Earth Sciences in the National Oceanography Centre on a project entitled “Can early warning signals be reliably detected in the Cenozoic palaeoclimate record?” along with Co-Is Toby Tyrrell, James Dyke, and Tim Lenton. This will continue with research on the same topic that I started during my PhD, with the aim of extending the data and techniques used and write up some papers.

Some background: 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’ll focus on these most promising events with additional analytical techniques and data and publish the results in due course.

I’d like to thank the ReCoVER network and EPSRC for funding this research, and I look forward to sharing the results here in future!

NEWS: New Website!

I’ve finally gotten round to setting up a new website, which will act as my online home for my academic work and other interests and where I’ll post news on my current projects. I’ve also brought across some older stuff from defunct blogs, some more of which I may upload in due course. Stay tuned for new updates on my next project starting in the near future!