Signals of atmospheric pollution in polar snow and ice
In their upper layers, the polar ice sheets contain a detailed record of changes in the atmosphere over the industrial period. Measurements from air bubbles in ice have shown that the CO2 content of the atmosphere has increased by 25% in the last 200 years, and that of CH4 has more than doubled. Ice core records have demonstrated a close correspondence between greenhouse gases and temperature during the last glacial cycle. Profiles of radioactive species in snow clearly document nuclear bomb tests in the atmosphere, and the recent Chernobyl accident has also left a signal in Northern Hemisphere ice. Nitrate has more than doubled in Greenland snow over the industrial period, while sulphate has more than trebled. No significant trend is seen in Antarctic snow for these anions. Pb increased 100-fold until the 1970s in Greenland snow, but concentrations appear now to be declining. A small increase is also recorded in Antarctic snow. Organochlorine compounds offer great potential for pollution studies in snow. The ability to study global scale pollution in polar ice could be hampered if there is significant local pollution. In Antarctica, impact on the atmosphere from local human activities is still mainly confined to small areas near stations.