Greenhouse Gas Concentrations in Ice Cores (T. Stocker and H. Fischer)
Today the concentrations of the major greenhouse gases in the atmosphere are significantly higher than during pre-industrial times. This is caused by the emissions of greenhouse gases by human activities, primarily by the burning of fossil fuels, land use change, and deforestation. An important question is whether and when the Earth System may have experienced comparable greenhouse gas concentrations in the past and how that may have influenced climatic conditions on our planet. It is now an established fact that today the atmospheric CO2 concentration is more than 30% higher than anytime during the past 800,000 years. The concentrations of methane and nitrous oxide have also increased significantly: they are now 150% and 20% higher, respectively. These key results are obtained by the analysis of air that is enclosed in bubbles trapped in polar ice cores, a research speciality that has been developed more than 40 years ago at our division and that has been refined and perfected in numerous projects since then. The focus of our research today is in three areas: greenhouse gas levels during warm epochs of the past 800,000 years, highly resolved time series of greenhouse gas concentrations during rapid climatic shifts during the late Pleistocene, and the greenhouse gas evolution during glacial-interglacial transitions.
The measurement of climate signals in ice cores requires the combination of custom-made extraction techniques with the latest analytical equipment. For CO2 concentrations we employ dry extraction using our novel centrifugal ice microtome. The concentration of CO2 is determined using a LICOR instrument. Thanks to the high extraction efficiency for all ice types and the precision of the analytical device we are able to produce high-resolution records of past CO2 concentrations. For CH4 and N2O we extract the gas by melting the ice core sample and analysing the air in a gas chromatograph. A completely redesigned device has been recently developed. Novel laser spectroscopic analyses for all three greenhouse gases and the stable isotopes of CO2 are currently developed within the ERC Advanced Grant deepSLice of Hubertus Fischer (see also Past Climate and Biogeochemical Studies on Ice Cores).