Abstract

The concentration of methane trapped in Antarctic ice shows large variations over the last 800,000 years that appear to track changes in temperature. Our work focuses on the increase in methane from about 360ppbv at the last glacial maximum (approximately 20,000 years ago) to roughly 700ppbv in the pre-industrial era (approximately 200 years ago). Fundamentally, methane sources (e.g. emissions from wetlands) and/or sinks (e.g. oxidation by OH) must have changed during this period, however, the balance between changes in sources and changes in sinks remains uncertain. As methane is strongly radiatively forcing, we need to understand what caused the increase in methane if we are to fully understand the accompanying change in climate. To this end, we have carried out a number of sensitivity experiments using a global atmospheric chemistry-transport model, the aim being to identify any atmospheric chemical signal which could be used to differentiate between changes in methane emissions and changes in oxidising capacity. We have subsequently assessed whether any such signal could be derived from ice-core data. The results to this work will be presented, in addition to preliminary results regarding experiments designed to explore the influence that past changes in temperature and humidity could have had on oxidising capacity.