Cretaceous-Paleocene-Eocene: Exploring Climate and Climate Sensitivity

How sensitive is the planet to increasing concentrations of atmospheric carbon dioxide? This crucial question has been the subject of intensive research over the past two decades. Recently, increasing use is being made of past climates, both to evaluate models used for future prediction, and to provide observational constraints on climate sensitivity. However, the relevance of past climates for future sensitivity is yet to be tested. In particular, differing palaeogeography (i.e. continental positions, mountain extents and height, and ocean floor depth) will influence climate and climate sensitivity, but to an extent that is unknown. In this study, we will use a modelling framework to explore the role of palaeogeography in controlling climate and climate sensitivity during the most recent interval of 'greenhouse' climates from the Cretaceous to Eocene (145 to ~35 million years ago; 145-35 Ma). We will investigate uncertainties related to the reconstructed palaeogeographies and the models used. We will evaluate our findings by comparing the model results with observations - compilations of existing data which we will synthesise and re-interpret. The work will provide fascinating insights into how our planet operates on long (multi-million year) timescales, and assess the utility of observations of past warm climates for informing future climate sensitivity.

Three recent developments which make this study timely are: (1) Brand new palaeogeographic maps of the Cretaceous to Eocene which improve greatly on previous representations in terms of both accuracy and temporal resolution, (2) A step change in the computing power available means that for the first time we can spin up large ensembles of simulations climates to equilibrium, allowing us to explore uncertainties, and (3) New understanding of the controls and limitations on palaeoclimate proxies means that we can provide a state-of-the-art comparison of our model simulations with the geological record.

Our Impact Plan has five main components:

(1) An international workshop on using past climate records to inform future climate sensitivity. This will be planned from the outset in collaboration with the main stakeholders, including the scientific community, members of the IPCC, policymakers, and those working on impacts assessments.
(2) The commissioning of a painting, by artist Bob Nicolls, based on our climate and vegetation model simulations of the CPE, to be displayed in a local public space such as the Bristol Museum and Art Gallery. This will hang beside a description of our modelling work, and an short introduction to climate models.
(3) The PI, in his spare time, will carry out climate model simulations of J.R.R. Tolkein's Middle Earth, to coincide with the release of The Hobbit movie, part 2 or 3. This will provoke interest from the public, and highlight the applicability of climate models to geographies very different from modern. This will also be presented alongside our work on the CPE.
(4) We will accompany each publication with a summary document, to be published online, aimed at the general public. This will be highlighted in well-read blogs such as 'All Models Are Wrong'
(5) We will engage with the general public through standard protocols, such as Science fairs.