Carbon dioxide (CO2) makes up the largest share of greenhouse gases. The addition of man-made greenhouse gases to the atmosphere disturbs the earth's radiative balance (i.e. the balance between the solar energy that the earth absorbs and radiates back into space). This is leading to an increase in the earth's surface temperature and to related effects on climate, sea level and world agriculture.
The table refers to emissions of CO2 from burning oil, coal and gas for energy use. Carbon dioxide also enters the atmosphere from burning wood and waste materials and from some industrial processes such as cement production. However, emissions of CO2 from these other sources are a relatively small part of global emissions, and are not included in the statistics shown here. The Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (see below) provide a fuller, technical definition of how CO2 emissions have been estimated for this table. The forecasts provided in the table refer to the Reference Scenario of the World Energy Outlook.
These emissions estimates are affected by the quality of the underlying energy data. For example, some countries, both OECD and non-OECD, have trouble reporting information on bunker fuels and incorrectly define bunkers as fuel used abroad by their own ships and planes. Since emissions from bunkers are excluded from the national totals, this affects the comparability of the estimates across countries. On the other hand, since these estimates have been made using the same method and emission factors for all countries, in general, the comparability across countries is quite good.
Global emissions of carbon dioxide have risen by 105%, or on average 2.0% per year, since 1971. They are projected to rise by another 39% by 2030, or by 1.4% per year. In 1971, the current OECD countries were responsible for 66% of the world CO2 emissions. As a consequence of rapidly rising emissions in the developing world, the OECD contribution to the total fell to 45% in 2007, and is expected to fall further to 31% by 2030. By far, the largest increases in non-OECD countries occurred in Asia, where China's emissions of CO2 from fuel combustion have risen by 5.8% per annum between 1971 and 2007. The use of coal in China increased the levels of CO2 emissions by 5.2 billion tonnes over the 36 years to 2007.
Two significant downturns in OECD CO2 emissions occurred following the oil shocks of the mid-1970s and early 1980s. Emissions from the economies in transition declined over the last decade, helping to offset the OECD increases between 1990 and the present. However, this decline did not stabilise global emissions as emissions in developing countries continued to grow. With the current economic crisis, early indicators suggest that growth in CO2 emissions from fuel combustion slowed in 2008 and may have declined in 2009.
Disaggregating the emissions estimates shows substantial variations within individual sectors. Between 1971 and 2007, the combined share of electricity and heat generation and transport shifted from one-half to two-thirds of the total. The share of fossil fuels in overall emissions changed slightly during the period. The weight of coal in global emissions has remained at approximately 40% since the early 1970s, while the share of natural gas increased from 15% in 1971 to 20% in 2007. The share of oil decreased from 49% to 38%. Fuel switching and the increasing use of non-fossil energy sources reduced the CO2/total primary energy supply (TPES) ratio by 5% over the past 36 years.