Atmospheric CO2 concentrations have risen rapidly since pre-industrial times and our current climate is not yet in equilibrium with this; it will change. To obtain insight in the type and magnitude of this change and to validate climate models used to project these changes, we need to look back at past climates. The most recent time in Earth history with CO2 levels that were similar to today is the Pliocene. The Pliocene thus provides a unique window into a world that exhibited many of the climate characteristics that we might experience. These are documented by proxies locked into sedimentary archives, especially marine sediments. It remains a challenge for palaeoclimatologists, however, to quantify past terrestrial temperatures. I have recently developed a novel proxy for quantitative annual mean air temperature reconstruction, which is based on the distribution of membrane lipids synthesised by soil bacteria. Upon soil erosion these molecules are transported to the marine realm where they become part of the marine sedimentary archive.
The PlioProx project aims at a quantitative reconstruction of continental temperatures and latitudinal temperature gradients for the Pliocene. This will be achieved by applying this new palaeothermometer to high resolution marine sediment records near river outflows to generate river-basin integrated records of continental air temperature. This approach also allows for a direct comparison to reconstructed sea surface temperatures. Using globally distributed sediment records, latitudinal temperature gradients will be constructed which will be compared to moisture transport and rainout, reconstructed using stable hydrogen isotopes from plant wax lipids. Results will provide vital new insights in climate evolution on land under elevated atmospheric CO2 concentrations. It will also contribute to improving the next generation earth system models that are used to predict future climate.
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