Modelling the evolution of natural climate variability: from the last persistently warm period to the first glacial cycles

The climate of the planet has changed due to natural forcings on all timescales. Humans have disrupted these natural cycles by emitting large amounts of greenhouse gases, such that atmospheric carbon dioxide concentrations are higher now than they have been for any time in the last 3 million years (IPCC WGI Report, 2021; Box TS.2, Figure 1). Studying these previous warm periods can help us to understand the potential future climate changes. The Early Pliocene (5.3-3.6 million years ago; Ma) is a period of very muted climate oscillations, persistently warm, with little contrast between the warmer and colder periods in benthic oxygen isotope records (Figure 1). The mid-Pliocene Warm Period (mPWP; ~3.3-3.0 Ma), when atmospheric CO₂ was around 400ppm (parts per million) and temperatures 3.2°C warmer than pre-industrial, has been extensively studied using climate models and proxy data (Dowsett et al., 2012; Haywood et al., 2020; McClymont et al., 2020). However, the mPWP is preceded by the enigmatic M2 glacial period (Dolan et al., 2015) and leads into the Plio-Pleistocene Transition and the beginning of the regular glacial-interglacial of the Quaternary (Figure 1).

There are many marine cores that record palaeoclimate throughout this time interval (~5-2.5 million years ago), but the long timespan of these changes makes running full transient climate model simulations impractical. However, by examining the peak glacial and interglacial temperatures, we can quantify the magnitude of natural climate oscillations during different Plio-Pleistocene climate fluctuations in the early Pliocene, mid-Pliocene and Plio-Pleistocene Transition. The very different nature of the benthic oxygen isotope curves in these three time periods are well established (Figure 1), but how this translates into climate is less well known. There are sea surface temperature datasets from all these time periods (Robinson and Dowsett, 2010; Dowsett et al., 2012; Shakun, 2017; McClymont et al., 2020), with more data being produced.

This project will use a fully coupled ocean-atmosphere general circulation model (HadCM3), to simulate the climate of the early Pliocene, the M2 glacial period, the mPWP and the end members of the first Pleistocene glacials (MIS100, MIS99, MIS98). For some of these, the climate forcings are well known, but for others significant work is required to quantify the model boundary conditions. The student will have the opportunity to run the HadCM3 climate model, an oxygen isotope model and an ice sheet model, be the first to simulate key periods of the Plio-Pleistocene transition and contribute to a large international climate modelling project, the Pliocene Model Intercomparison Project (PlioMIP; Haywood et al., 2020). There will also be the opportunity to collaborate with the Pliocene palaeoceanographic community and visit the laboratories that produce palaeoceanographic data.

References

Dolan, A.M., Haywood, A.M., Hunter, S.J., Tindall, J.C., Dowsett, H.J., Hill, D.J. and Pickering, S.J., 2015. Modelling the enigmatic Late Pliocene glacial event – Marine Isotope Stage M2, Global and Planetary Change, doi:10.1016/j.gloplacha.2015.02.001.

Dowsett, H. J., Robinson, M. M., Haywood, A. M., Hill, D. J., Dolan, A. M., et al., 2012. Assessing confidence in Pliocene sea surface temperatures to evaluate predictive models, Nature Climate Change, 2, 365–371.

Haywood, A.M., Tindall, J.C., Dowsett, H.J., Dolan, A.M., Foley, K.M., Hunter, S.J., Hill, D.J. et al., 2020. The Pliocene Model Intercomparison Project Phase 2: large-scale climate features and climate sensitivity, Climate of the Past, 16, 2095–2123.

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2391 pp.

McClymont, E. L., Ford, H. L., Ho, S. L., Tindall, J. C., Haywood, A. M., et al., 2020. Lessons from a high-CO₂ world: an ocean view from  ∼ 3 million years ago, Climate of the Past, 16, 1599–1615.

Robinson, M.M. and Dowsett, H.J., 2010. ePRISM: a case study in multiple proxy and mixed temporal resolution integration, Stratigraphy, 7, 177-187.

Shakun, J.D., 2017. Modest global-scale cooling despite extensive early Pleistocene ice sheets, Quaternary Science Reviews, 165, 25-30.