1000-year records of southern hemisphere background concentrations of CO2 parts per million (ppm – orange), N2O parts per billion (ppb – blue) and CH4 (ppb – green) measured at Cape Grim Tasmania and in air extracted from Antarctic ice and nearsurface levels of ice known as firn. BOM

1000-year records of southern hemisphere background concentrations of CO2 parts per million (ppm – orange), N2O parts per billion (ppb – blue) and CH4 (ppb – green) measured at Cape Grim Tasmania and in air extracted from Antarctic ice and near surface levels of ice known as firn. Global CO2, methane (CH4), and nitrous oxide (N2O) concentrations have risen rapidly during the past two centuries. The amount of these long-lived greenhouse gases in the atmosphere reached a new high in 2011. The concentration of CO2 in the atmosphere in 2011 was 390 parts per million (ppm) – much higher than the natural range of 170 to 300 ppm during the past 800,000 years. Global CO2 concentrations in the atmosphere increased from 2009 to 2011 at 2 ppm per year. Over the same period, nitrous oxide increased at nearly 1 part per billion (ppb) per year and the synthetic greenhouse gases (CFCs, HFCs and so on) increased at nearly ten parts per trillion per year. Methane has increased by about 6 ppb per year from 2009 to 2011 after a temporary pause in growth from 1998 to 2005. The temporary pause was due to an overall reduction in methane sources (likely to be a combination of natural gas, agricultural and wetland emissions). The cause(s) of the recent methane increase are at present unidentified, but again likely to be a combination of the above sources. The relative contributions to the enhanced greenhouse effect from pre-industrial times to 2011, due to the long-lived greenhouse gases, are: CO2 (64 per cent), CH4 (18 per cent), synthetics (12 per cent), and N2O (six per cent).

State of the Climate 2012 [pdf]