Palaeo Constraints on the 1.5°C World: What does the Pliocene tell us about the long-terms effects of atmospheric CO2 at ~400 ppmv

This Project has been filled

The issue: Our ability to limit the rise in global temperature in line with the Paris Agreement is uncertain due to an inadequate understanding of the long-term sensitivity of the Earth and Climate System to CO2.

The goal: Constrain the long-term sensitivity (multi-centennial to millennial) of the Earth System to CO2 using a uniquely suited time interval in the geological past.



By the end of the 21st century global temperatures will have increased, the oceans will be more acidic and the hydrological cycle will be invigorated (IPCC, 2013). Understanding the geographical patterns, magnitudes and societal impacts associated with these changes is a huge challenge and responsibility. Success in this endeavour is crucial in order to develop robust policy-driven mitigation and adaptation strategies. Prior to the 2015 Paris Agreement the policy position, based on the best available scientific evidence of environmental and societal impacts, was that CO2 emission and stabilisation scenarios should not permit a global annual mean temperature increase of more than 2°C by the end of this century. This target was reaffirmed as an outcome of the Paris Agreement. However, due to more recent studies that demonstrated the likely impacts associated with a 2°C warmer world, a tougher policy stance was adopted, whereby the global annual mean surface temperature increase should be brought below 1.5°C of the pre-industrial era’s baseline by 2100 AD. This scientifically informed decision has rapidly developed into a nexus for research across all disciplines that share the common aim of understanding climate change and its societal impacts (Mitchell et al., 2016).


One of the greatest challenges in understanding what society must do in terms of emissions to limit global temperature change to a specific value (i.e. 1.5°C) is resolving the long term sensitivity of the climate system to a given change in CO2 forcing. Warm intervals in the geological past provide science with a unique natural laboratory in which to investigate long-term environmental change, and climate models have been used to simulate past climate, greatly enhancing our understanding of atmospheric, oceanic and ice sheet behaviour (Haywood et al., 2016a; Haywood et al. 2019). The most recent interval in the past known to have had a comparable atmospheric carbon dioxide (CO2) level to today (~410 ppmv) was the Pliocene epoch (~3 million years ago). It was an interval known to be warmer than the pre-industrial era, and shares a number of parallels to model predictions of climate for the end of this century (Haywood et al., 2016a; Burke et al., 2018; Tierney et al. (2019).

In the context of an international climate modelling effort (see international partners section below), this project will use a new suite of climate model simulations, and perform new experiments as needed, to investigate the nature of the critical components of the Earth system during the Pliocene to greatly enhance our knowledge and understanding of the long term consequences of atmospheric CO2 being at or above 400ppmv.


The student will be given significant academic freedom to follow their interests and explore different components of the long-term climate and Earth system response to CO2 forcing. Potential avenues for investigation include:

  • Analysis of the behaviour and variability of the jet stream and Arctic climate change
  • Behaviour of the hydrological cycle and variability in the global monsoon
  • The nature of, and changes to, temperature gradients and patterns of large-scale atmospheric and oceanic circulation
  • Modes of climate variability, such as the El Niño Southern Oscillation (ENSO)
  • The analysis of seasonality, climate and weather extremes
  • Terrestrial environmental/vegetation responses in the tropics and high latitudes

Potential for high impact outcomes

Understanding the long-term sensitivity of the climate system at different CO2 stabilisation targets is critical in order to inform society about prudent mitigation and adaptation pathways. The student will be guided by a brand new science plan recently formulated for the 2nd Phase of the Pliocene Model Intercomparison Project (Haywood et al., 2016b). Phase 1 led to the publication of many high impact papers in Nature journals. PlioMIP Phase 2 experiments are underpinned by the very latest syntheses of geological information available by the United States Geological Survey. The proposed research has the potential to contribute to the next Intergovernmental Panel on Climate Change Assessment Report.


The PhD student will be embedded within a vibrant and dynamic research group in the School of Earth and Environment (Palaeo@Leeds).  Palaeo@Leeds has experts in past climate and ice sheet modelling, as well as specialists in marine and terrestrial environments of the past. The student will be supported and fully trained in coupled ocean-atmosphere modelling. The student will analyse existing climate model simulations, learn to perform new experiments, learn how to compare results from different models, and learn appropriate methods for diagnosing the behaviour of different components of the climate system. The student will attend the Urbino Summer School in Palaeoclimatology (in Italy) and have the opportunity to attend various conferences during the project (e.g. American Geophysical Union Fall meeting in San Francisco and European Geoscience Union General Assembly in Vienna). Through our established collaborations the student will also have opportunities to visit and work with scientists from the Unites States Geological Survey as well other international modelling groups involved in the Pliocene Model Intercomparison Project Phase 2 (led by the University of Leeds and the U.S. Geological Survey) in the U.S., France, Germany, Norway and China.

Student Profile

It is necessary for the candidate has an undergraduate degree (2.1 or better) in Atmospheric/Climate Science, Environmental Science, Earth Sciences, Mathematics or Physics. A keen interest in climate modelling is required, although previous experience of climate modelling is not required as our training will equip the student with the skills necessary.

International Partners

Through our established collaborations the student will have an opportunity to interact and work with scientists from the Unites States Geological Survey as well other international modelling groups involved in the Pliocene Model Intercomparison Project Phase 2 in the U.S., France, Germany, Norway and China.


Haywood A.M., Valdes, P.J., Aze, T., Barlow, N., Burke, A., Dolan, A.M., von der Heydt, A.S., Hill, D.J., Jamieson, S.S.R., Otto-Bliesner, B.L., Salzmann, U., Saupe, E., Voss, J. (2019). What can palaeoclimate modelling do for you? Earth Systems and Environment, 3, (1), pp. 1-18

Haywood, A,M., Dowsett, H.J., Dolan, A.M. (2016a). Integrating geological archives and climate models for the mid-Pliocene warm period, Nature Communications, 7, doi: 10.1038/ncomms10646

Haywood, A,M., Dowsett, H.J., Dolan, A.M., Rowley, D., Abe-Ouchi, A., Otto-Bliesner, B., Chandler, M.A., Hunter, S.J., Lunt, D.J., Pound, M., Salzmann, U. (2016b). The Pliocene Model Intercomparison Project (PlioMIP) Phase 2: Scientific objectives and experimental design, Climate of the Past, 12, pp.663-675. doi: 10.5194/cp-12-663-2016.

IPCC (2013). Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.

Mitchell, D., James, R., Forster, P.M., Betts, R.A., Shiogama, H & Allen, M. (2016). Realizing the impacts of a 1.5 °C warmer world. Nature Climate Change 6, 735–737. doi:10.1038/nclimate3055.

Tierney, J.E., Haywood, A., Feng, R., Bhattacharya, T., Otto-Bliesner, B.L. (2019). Pliocene Warmth Consistent With Greenhouse Gas Forcing. Geophysical Research Letters.