Topics


Our research interests can be divided into three distinct time frames, within which we tackle the following key scientific topics:

  1. Earth History: Long-term co-evolution of life and the Earth system, understanding Earth system dynamics through major transitions and events, thus developing the Gaia theory.

  2. Quaternary: The 'EPICA challenge' of Quaternary Earth system dynamics, understanding the coupled glacial-interglacial variations of Earth system variables including CO2, and hence the natural background behavior of the Earth system.

  3. Anthropocene: Past, present and future human-induced global change, simulating feedbacks on and within the human system (anthroposphere), projecting the long-term response of the Earth system to human activities.


Timescales and Transitions

We are particularly interested in the following time intervals and major transitions during Earth history (recently reviewed in Lenton et al., 2004 and Lenton, 2003):

  • Archean-Proterozoic (~4.0-2.0 Ga).

    After the origin of life >3.5 Ga, a biogenic methane greenhouse may have counteracted the faint young Sun, but extreme Huronian glaciations ~2.4 Ga indicate a breakdown of climate regulation. The evolution of oxygenic photosynthesis >2.7 Ga ultimately led to the Great Oxidation of the atmosphere 2.2-2.0 Ga, but why the long time delay? and what are the causal links between methane fall, extreme glaciations and the great oxidation? Colin Goldblatt is working on these questions for his PhD.

  • Neoproterozoic (1.0-0.54 Ga).

    After a billion years of relative stability, came the extreme ('Snowball Earth'?) glaciations, a rise in atmospheric oxygen, and the appearance of fossilized animals, culminating in the Cambrian explosion. A key question is what caused these dramatic changes? Richard Boyle, for his PhD, is working on the hypothesis that the evolution of photosynthesizing life on land (perhaps in the form of lichens) and its effects on weathering may have triggered planetary cooling and a rise in oxygen (Lenton and Watson, 2004).

  • Phanerozoic (542-0 Ma).

    After the Cambrian explosion, the rise of land plants, beginning ~420 Ma caused a final rise in oxygen and lowering of carbon dioxide and temperature. Subsequently plants became part of the negative feedback mechanisms that may account for the remarkable stability of atmospheric oxygen over the past ~350 Myr (Lenton, 2001; Lenton and Watson, 2000b). The oxygenation state of the ocean was more variable, with a series of Oceanic Anoxic Events occurring in the mid-Cretaceous (120-80 Ma) that may have been part of a self-sustaining oscillation of the Earth system (Handoh and Lenton, 2003). Noam Bergman developed the COPSE model of the coupled changes in atmospheric compositions and global biogeochemical cycles during the Phanerozoic for his PhD (Bergman et al., 2004).

  • Quaternary (2.6-0 Ma).

    The past 2.6 Myr are characterized by the onset of periodic glaciations and subsequent transitions to greater amplitude and lower frequency oscillations. During the recent ~100 kyr glacial-interglacial cycles, atmospheric carbon dioxide and methane co-vary with climate in ways that have yet to be satisfactorily explained. We are now in what orbital theory would predict to be an unusually long ~50 kyr interglacial. Understanding the natural Quaternary dynamics of the Earth system is central to improving confidence in our predictions of the impact of human activities. Sudipta Goswami is applying the GENIE model to examine a new hypothesis for the low glacial level of atmospheric carbon dioxide.

  • Anthropocene

    The carbon dioxide being added to the atmosphere by fossil fuel burning and land-use change is (with high confidence) making the largest contribution to observed global warming. If a significant fraction of known fossil fuel reserves are emitted in the future, thresholds are likely to be crossed in the Earth system, in particular the slow melt of the Greenland ice sheet. Less certainly, the thermohaline circulation of the ocean may be vulnerable to shut down (Marsh et al., 2004). On a millennial timescale, added CO2 will be redistributed among the atmosphere, ocean, and land (vegetation and soil) reservoirs (Lenton and Cannell, 2002; Lenton, 2000). The fraction remaining in the atmosphere will continue to cause long-term climate change (Lenton, submitted). It will only be removed over thousands of years, by the dissolution of carbonate sediments in the ocean and the slow replenishment of alkalinity from carbonate weathering. Mark Williamson is applying a version of GENIE with a closed carbon cycle to make millennial climate change projections. Clare Britton has added carbonate sediments and weathering to the simple Earth system model to look even further into the future.



Models


The models that we are using and/or developing and the time frames these are being applied to are:
  • COPSE: The Phanerozoic (550-0 Ma), Neoproterozoic (1000-550 Ma) and the future lifespan of the biosphere (the next ~1000 yr).
  • The Redfield model: The past ~120 Ma including the Mid-Cretaceous (120-80 Ma).
  • ESMdt: The Archean (4.0-2.5 Ga) and Paleoproterozoic (2.5-1.6 Ga) with plans to merge it with COPSE to span Earth history.
  • GENIE: The Quaternary, Anthropocene, and snapshots of Earth history.
  • Simple Earth System Model: The Anthropocene, from 1800 A.D. to the end of this millennium (3000 A.D.), soon to be extended to ~10 kyr into the future.


These can be placed within a wider spectrum of Earth system models:





The models span different timescales with differing degrees of complexity in terms of comprehensiveness (number of processes represented), dimensionality, and spatial resolution. The Redfield model, ESMdt, COPSE and SESM are all zero-dimensional box models at present, whereas GENIE has a 3D ocean, 2D land surface and either a 2D (single vertical layer) or 3D atmosphere.

GENIE

The Grid ENabled Integrated Earth system model (GENIE) project is coordinated by Tim Lenton and involves Sudipta Goswami, Mark Williamson, Chris Brockwell and Andy Watson. We are part of a UK and international network of researchers developing and applying GENIE.



GENIE is a modelling framework with which we can construct many instances of Earth system model. The key features of the framework are modularity, scalability and traceability. Modularity is the 'plug and play' capability to swap in and out alternative representations of each of the major components: atmosphere, ocean, sea ice, ocean biogeochemistry, sediments, land vegetation and soil, and ice sheets. Scalability is the ability to vary the resolution of the ocean and atmosphere components and hence the surface grid. In practice, our 3D ocean and 3D atmosphere are available in a range of spatial resolutions. Traceability refers to being able to link model process representation (i.e. equations) to more comprehensive models, in particular, basing model parameterizations of unresolved processes on accurate models that do resolve the processes. Traceability applies within the GENIE spectrum of variable atmosphere and ocean resolution where the fundamental equations remain unaltered. With GENIE we can span a region of 'model space' in terms of resolution, dimensionality, and comprehensiveness:





Bibliography


Marsh, R.J., Yool, A., Lenton, T.M., Gulamali, M.Y., Edwards, N.R., Shepherd, J.G., Krznaric, M., Newhouse, S., Cox, S.J. 2004. Bistability of the thermohaline circulation identified through comprehensive 2-parameter sweeps of an efficient climate model, Climate Dynamics, Online First.

Lenton, T.M., submitted. Climate Change to the end of the Millennium, Climatic Change.
For suggestions and corrections, contact Sudipta.
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