Earth system evolution

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The Global Warming and Climate Change issue dominates the present day political, social and scientific agenda, with the Intergovernmental Panel for Climate Change (IPCC) predicting an average global temperature rise of 1.5 - 5.5°C by the end of the century, attributed to greenhouse gases, principally CO2, released into the atmosphere by human activities. Yet, the always present natural greenhouse of ~33°C is due mainly to water vapour, not CO2. The theoretical idea underpinning all IPCC model "scenarios" is that the addition of energy, attributed to the CO2 greenhouse ("prescribed CO2"), causes more water to evaporate, thus causing a major temperature rise. However, this "positive feedback" may be strongly compensated for by the "negative feedback" of cloud formation, an intractable drawback of the present day climate models. In addition, water and carbon cycle are coupled, with the former at least as important as the latter for climate considerations. The question now arises, is it the carbon cycle that is the "driver" of the water cycle (as in the IPCC models) or is the carbon cycle mostly "piggybacking" on the water cycle? The outcome of model "scenarios" can be tested only against the past record, on geological and human time scales. I propose to study 1) isotopic evolution of past seawater, and 2) the role of terrestrial ecosystems (river watersheds) as the sources/sinks of atmospheric CO2. The study of ancient sediments (topic 1) enables us to constrain past climates, their causative factors and their CO2 budgets. Understanding the water budget of watersheds (topic 2) and its relationship to biological productivity can help to answer the question of what is really driving the photosynthetic capacity of ecosystems to absorb atmospheric CO2. Both approaches aim at the same fundamental question: is CO2 the "driver" of the water and climate cycles or is it the other way around?