Natural and anthropogenic changes in atmospheric greenhouse gases over the past 2 millennia

Millennial changes in atmospheric trace gas composition are best determined from air enclosed in ice sheets. Air extracted from the open pores in firn and the bubbles in ice is measured to derive the past concentrations and isotopic ratios of the long lived trace gases. The significant increases observed in CO2, CH4 and N2O since about 1750 and the more recent appearance of synthetic gases such as the CFCs in the atmosphere are a key feature of the anthropocene. The millennia preceding the anthropocene, the Late Pre-Industrial Holocene (LPIH), show evidence of natural changes in trace gases that can be used to constrain models and improve their ability to predict future changes under scenarios of anthropogenic emissions and climate change. Precise measurements and ice core air samples that are accurately dated and highly resolved in time are required to record the small and rapid trace gas signals of this period. The atmospheric composition records produced by CSIRO and collaborators using the Law Dome, Antarctica ice cores are widely used in models of climate, atmospheric chemistry and the carbon cycle over the anthropocene and the LPIH. Results from these studies have been influential in informing global policies, including the Montreal and Kyoto Protocols. We will present the recently revised trace gas records from Law Dome and new measurements of tracers from these and other ice sites that reveal the causes of atmospheric changes over the anthropocene and the LPIH