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Fossil plant remains for more accurate climate forecasts

Climate change and its effects are the focus of research by Professor Ralph R. Schneider from the Institute of Geosciences. He is researching vegetation from the distant past to assess the effects of global warming.

African savannah
© YayaErnst/iStock

Dark clouds over the African savannah: heavy rainfall events are increasing in frequency and severity, but periods of heat in summer are also becoming noticeably more frequent. Scientists at Kiel University are researching what effects global warming will have on the earth.

Global temperature rise of significantly under two degrees: in order to limit the negative effects of climate change, the European Union (EU) has committed to a clear reinforcement of its climate target through a further reduction in greenhouse gas emissions by 2030. "This step is essential,” stressed Ralph R. Schneider, Professor of Marine Geology and Paleoclimatic Research at the Institute of Geosciences at Kiel University. "If we carry on as before, there is the risk of sea levels rising, inundating and wiping entire islands and stretches of land off the map.” This affects human life and survival: will there be enough food if fertile arable land becomes scarce? "Extreme weather phenomena like cyclones, typhoons and heavy rainfall are already becoming more frequent and severe, but people are also noticing that there are more heat waves in the summer,” explained the Director of Kiel Marine Science (KMS) and the Centre for Interdisciplinary Marine Research.

Global climate models provide information on the effects of global warming of 1.5 to 2 degrees, primarily through mathematical projections based on climate and weather records from the past 100 to 150 years. Schneider now plans to underpin these projections with research results from studies of natural samples from the past. Fossil plant remains from a time when temperatures were two degrees higher than the current average offer information on the climate at that time and its effects. Schneider and his team hope to achieve results that can be applied to future climate development, especially in warm climate zones, which are expected to experience a significant change in annual precipitation rather than a marked increase in temperature.

Looking to the past creates knowledge for the future

With his three-year project "Veränderungen des Hydroklimas und der Vegetation im tropischen Südostafrika” (hydroclimatic and vegetation changes in tropical Southeast Africa), funded by the German Research Foundation (DFG), Schneider is travelling around 130,000 years back in time. Tropical Southeast Africa, or Mozambique to be precise, is the destination for this scientific time travel. This is where the Zambezi, the largest river in southern Africa, flows into the Indian Ocean. "The river collects plant remains, roots, stalks and leaves all the way along its 2,600 kilometre journey from its source in Zambia to the coast,” explained Schneider. These are left on the bed of the river delta. By drilling to a depth of 100 metres, we are able to find fossil leaves dating from the last interglacial period, which lasted around 6,000 years between two ice ages. "Around 130,000 years ago, the average temperature in the Indian Ocean was 26 to 30 degrees, which is two degrees higher than our current average temperature, and this was an important factor for evaporation and water absorption in the atmosphere over the continent, too. It affected plant growth and the condition of plants, especially of the leaf wax, the waxy layer found on certain leaves,” explained Schneider. This leaf wax was chemically released from the sediment and the isotope distribution of typical hydrocarbon molecules contained in it was determined – a task conducted for the paleoclimatic and paleoarchaeological research team by experts at the Leibniz Laboratory for Radiometric Dating and Stable Isotope Research.

"The plant type, whether it was a deciduous tree, grass or bush native to rainforest or savannah, can be determined from the carbon isotopes,” said Schneider, explaining the complex links. The experts can identify how much rain or water vapour fell on the plant from the neighbouring warm ocean from the hydrocarbon isotopes. "The hypothesis is that as temperatures rose, precipitation increased or became more extreme.” However, initial results from the ongoing study are surprising: the isotopes also revealed longer dry periods lasting 200 to 400 years. What these processes triggered, the extent to which atmosphere and wind circulation played a role in this and what it led to in terms of climate warming and its effects are currently being examined. "We are assuming that global warming will result in more and heavier precipitation, followed by extremely dry periods,” explained Schneider. Whether he is right or not will be revealed in about a year when the research is concluded.

Author: Jennifer Ruske