Pictures of the Future    Spring 2007

The Sources of Greenhouse Gases

About one third of the approximately 40 billion tons of CO₂e that are emitted annually around the world as greenhouse gases comes from agriculture, forestry, land clearing measures and waste. "CO₂e" refers to CO₂ equivalents. Other greenhouse gases –including methane, laughing gas, fluorocarbons and industrial gases (e.g. sulfur hexafluoride) –are converted into these equivalents to show their global warming potential compared to carbon dioxide (CO₂). Methane’s global warming potential, for example, is 21 times that of CO₂, with one ton of methane corresponding to 21 tons of CO₂e. More than two-thirds of the greenhouse gas emissions (currently about 27 billion tons of CO₂e) are energy-related, meaning they are caused by people’s energy consumption. The emissions result from electricity generation in power plants, generation of heat, and fuel combustion by transport vehicles. In Germany, about 87 % of greenhouse gases result from energy use, while the remaining 13 % come from other sources, including agriculture and the chemicals industry.

Power plants are the source of nearly 25 % of the world’s greenhouse gas emissions. The largest share of CO₂ from these plants results from turning fossil fuels into usable energy such as electricity and district heating; a small share is also generated during the facilities’ construction and by the supply of fuels. The cumulative CO₂ emissions of lignite power plants, for example, are about 1,000 g/kWh of electricity; hard coal plants produce 780 g/kWh.

And the atmosphere even feels the effect of nuclear power plants, which give off small amounts (around 25 g/kWh) of CO₂ from uranium mining and enrichment. Photovoltaic facilities account for about 100 g/kWh of CO₂, due to the production of solar cells, modules and inverters. Wind plants (20 g/kWh) and hydroelectric facilities (4 g/kWh), by contrast, have very low CO₂ emissions.

A look at regional distribution of energy-related emissions shows the biggest shares are from the U.S. (over 21 %) and China (almost 18 %), followed by Russia (nearly 6 %), Japan (4.5 %), India (4 %), and Germany (3.2 %). According to the IEA, energy-related emissions will rise by almost 50 % to about 40 billion tons of CO₂ by 2030 if countermeasures aren’t taken. As the world’s largest coal consumer, China is expected to surpass the U.S. as the largest producer of CO₂ by 2010. But China’s emissions are still low, seen on a per capita basis: about four tons of CO₂ per year, compared to roughly ten tons in Germany and 20 tons in the U.S.
                                                                                                                    Sylvia Trage