Pliocene Gateways ('PlioGate')

Lead Research Organisation: University of Bristol
Department Name: Geographical Sciences


In the wake of rising greenhouse gases, such as carbon dioxide (CO2) and methane, how will the climate evolve over the next 100 years? This question is paramount in the minds of scientists and politicians alike. However, despite over 100 years of research into climate sensitivity, the range of projected future warming remains startling wide; 1.5 to 6.1 degrees C for a doubling of atmospheric CO2. The disagreement between projections made by different climate models makes a considerable contribution to this uncertainty.

Because a compromise must be reached between the limits of technology and our knowledge of climate processes, climate models are necessarily approximations of reality. As a result, all models differ in terms of the processes they represent and the resolution they run at. This is why climate models produce different results even though they are based on the same mathematical principles. It is also why it is crucial to test the models, to make sure that they really are capable of simulating Earth's climate.

As there are no observations for future climate change, we look to the past to evaluate climate models. The instrumental record provides one such test of the model. However, throughout the short duration of our instrumental record, climate change has been small in comparison to projected changes for the next 100 years. This makes the instrumental record an inadequate definitive test of the models and we must test the models in other time periods too.

The last time atmospheric CO2 was as high as today was during a period known as the late Pliocene, specifically around 3 million years ago. Obviously there are no direct observations from so long ago, but evidence from fossil-remains of Pliocene fauna and flora show a climate-dependent chemical and biological signal, which we can use to reconstruct the climate conditions that these fauna and flora lived in. The conclusions from this work suggest that climate was 2 to 3 degrees C warmer than the Pre-Industrial era, with particularly large amplitude warming in the N.Atlantic and Greenland-Iceland-Norwegian Sea. Therefore, the parallels between the Pliocene and future scenarios makes the Pliocene an ideal test case for models used to project future climate change.

To date, model simulations for this period have been able to simulate the overall warmth of the Pliocene, but fail to reproduce the large amplitude warmth in the N.Atlantic GIN Sea. Recently, under the auspices of the international PlioMIP project, 14 different state-of-the-art climate models have been run for this period, but all have failed to reproduce the N.Atlantic/GIN Sea warming.

We suggest that this mismatch is symptomatic of inadequate representation of ocean gateways during the Pliocene, rather than a fundamental error in climate models during warm periods. Recent work at the University of Bristol has showed that changing the way ocean gateways are set-up in a model of modern climate can impact regional climates by 5 degrees C or more. This proposal will investigate the role of two key ocean gateways, namely the Bering and Gibraltar Straits. Nobody has ever investigated whether changes in their exchange could have had an impact on Pliocene climate, despite the fact that there is evidence that the gateways were different and that they can have a big impact on climate.

The results from the project will make a considerable contribution to improving our understanding of Pliocene climates and whether climate models work for past warm intervals.

Planned Impact

Who will benefit from this research and measures of this benefit:

There are several beneficiaries of the PlioGate project.

The named researcher (Ruza Ivanovic) will extend her current abilities and knowledge. It will strengthen her understanding and knowledge of past climates, but it will particularly strengthen her technical ability in mathematical modelling, and in adapting and developing climate models. This is especially important since there is a significant skill shortage for trained climate computer modellers who are able to actually change and develop models, as opposed to simply applying them.

Global modellers and oceanographers will benefit from our findings. Briefly but specifically, we expect the following scientific groups to benefit from our optimal representation of Pliocene ocean boundary conditions:
- Pliocene researchers: our improved model set-up will inform future Pliocene simulations. We will shed light on the cause of model-proxy data disparity (and reduce it), answering some of the outstanding questions in Pliocene research, not least "why don't our models get it right?"
- Palaeoclimate scientist more generally: we will elucidate the sensitivity of the current generation of climate models to model boundary conditions that evolve over geologic timescales
- Future-climate modellers and policy makers: reducing or eliminating proxy-model data disparity will improve the usefulness of the Pliocene as an analogue for future climate warming (the Pliocene was the last time atmospheric CO2 concentrations were as high as today, and temperatures were similar to those projected for the end of the 21st Century, yet worryingly, our models are unable to simulate the observed climate patterns). Crucially for improving confidence in projected future climate change, we will elucidate on whether this model-data disparity arises from flawed Pliocene model boundary conditions or deficient climate process representation.

The general public, school teachers and children will benefit from learning more about the science of climate, how we make projections of future climate change and how we validate these projections against ancient 'observed' climate. By establishing a truly interactive discourse between the general public (including children) and researchers on these political and topical issues, we will highlight the diversity of scientific research, encouraging critical thought and a research mentality. By keeping the flow of questions coming in, we will make sure that we (research scientists) address public concerns and queries, passing back the information these 'general' users want or need.

Knowledge transfer to beneficiaries:

We will publish results, recommendations and the technical details of model configuration in high profile papers, present this work at the high profile EGU General Assembly 2011, reformat and upload our results to the online BRIDGE, PlioMIP and PMIP databases for public access and personally communicate details of interest to specific PlioMIP, PMIP and PRISM researchers.

Public reactions to climate controversies highlight the strong influence of the bloggersphere. During this project, we will design, build and maintain a blog to communicate climate science (e.g. results and controversies) in a fast and responsible way for general public readership. We will also engage with the general public through the annual, interactive 'Discover!' event, run by University of Bristol scientists in Bristol City Centre, and through multiple school visits.


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Description The research project investigated the role of ocean gateways on climate change in the past, particularly during the Pliocene era (approximately 5 to 2.5 million years ago). For some of these gateways, such as the closing of the Panama isthmus about 4.5 million years ago, we had already shown that this could have a major impact on Northern hemisphere ocean circulation and hence climate in Europe and N. America. Our project investigated a number of other gateways such as the Bering Strait, Gibraltar Strait, and the flow through the Canadian archipelago of islands. Our computer modelling results have shown that opening/closing the Gibraltar straights and Canadian archipelago has very modest impact on climate, indicating that the Panama isthmus is the most important change. More generally, it appears that tropical gateways are potentially more important to climate than mid and higher latitude gateways.We are currently completing work for the Bering straights to confirm this result.
Exploitation Route Ocean gateways remain an important issue, with geological data often indicating greater importance than modelling studies. This paleoclimate enigma does need further work to reconcile the mismatch, which may be resolved by newer and better interpretations of the data, but may also be related to problems with the relatively coarse resolution (i.e. NOT eddy resolving) models used in this study.
Our preliminary results have informed the experimental design of the Pliocene Model lntercomparisonson Project (PlioMIP) Phase 2, where all groups are required to carry out simulations with a closed Panama Seaway, closed Canadian Archipelago, closed Bering Strait and open Gibraltar Strait. We refer to the recently released PlioMIP resources for more detail on the project and current experiment design:
Sectors Energy,Environment