World Energy Outlook 2007 : CO 2 Emissions Pathways Compared to Long - Term CO 2 Stabilization Scenarios in the Literature and IPCC AR 4

Stabilization of atmospheric concentrations of greenhouse gases (GHGs) is a declared objective of Article 2 of the United Nations Convention on Climate Change (UNFCCC, 1992). Carbon dioxide (CO2) is the most important of these gases followed by methane (CH4) and nitrous oxide (N2O). Current atmospheric concentrations of CO2 are about 380 ppmv (parts per million volume) CO2 only and are somewhere around 420 to perhaps 440 ppmv CO2 equivalent if other GHG concentrations are added, e.g. methane, nitrous oxide and cooling effects of aerosols subtracted. The pre-industrial concentrations of CO2 are estimated at about 280 ppmv for the end of the 17 century. This means that we have increased the atmospheric concentrations of CO2 by some 100 ppmv (and CO2 equivalent concentrations close to 140 ppmv) since the beginning of the Industrial era primarily by burning of fossil fuels and also by massive deforestation and land use changes. The corresponding global CO2 emissions have increased from about 1.1 GtCO2 (billion tons of CO2 or 0.3 GtC, billion tons of elemental carbon) to about 24.6 GtCO2 (6.7 GtC) in 2000. This translates into an average annual growth rate of about 1.5 % per year. IPCC (Intergovernmental Panel on Climate Change) in its Fourth Assessment Report (AR4 WGI and III, 2007) estimates that this increase in atmospheric concentrations of anthropogenic sources of GHGs have already resulted in an increase of global mean temperature by about 0.75 degrees Celsius, compared to the pre-industrial levels, or an increase of radiative forcing of about 1.6 W/m2 (Watts per meter square) and that just about equal additional increase will occur during the coming centuries even if concentrations are stabilized at current levels. This means that the humanity will have caused about a 1.5 degrees Celsius increase in mean global temperature through cumulative historical emissions since the beginning of industrialization.