BACKGROUND: Carbon, in the form of carbon dioxide, is a greenhouse gas released into the atmosphere as a direct result of human activities all the time. This in turn raises the temperature of the earth, leading to global climate change. The concentration of atmospheric CO2 has already increased by about 30% since the beginning of the industrial revolution in the late 1800's. Most of this increase comes from using fossil fuel -- coal, oil and natural gas -- for energy, but approximately 25 percent of the carbon came from changes in land use, such as the clearing of forests and the cultivation of soils for food production. Natural sources of atmospheric carbon include gases emitted by volcanoes, and respiration of living things. We breathe in oxygen, and breathe out carbon dioxide.
CAPTURING CARBON: It is possible to reduce the amount of CO2 released into the atmosphere by modern power plants by as much as 80-90% through carbon capture and storage technologies. The downside is that the fuel needs of a plant would increase by 10-40% in order to capture and store the carbon dioxide, thereby increasing operating costs by 30-60%. There are three basic ways to capture carbon. One is the remove it after burning fossil fuels, an approach that is already being used on a small scale by conventional power plants. Or the fossil fuel can be turned into a gas before the burning process and captured from the exhaust stream in a purer form of CO2 and water vapor. A third emerging option is called chemical looping combustion, in which metal particles interact with the fuel and produce solid metal particles and a mix of CO2 and water vapor than can be captured and transported to a storage site.
STORING CARBON: There are many alternatives for storing the captured CO2. The most promising is storing the CO2 deep in rocky formations in the earth, including oil and gas fields, and unminable coal seams, using various trapping mechanisms to ensure the CO2 doesnęt escape back to the surface. In fact, injecting CO2 into oil fields can increase oil recovery, thereby offsetting the extra cost of storage. Another option is ocean storage, in which CO2 in injected deep into the ocean, where it dissolves, or deposited onto the ocean floor, where it is denser than water and therefore forms a "lake" of CO2. The downside is that an excess of CO2 in ocean waters increases acidification and can kill marine organisms. A third option is trapping the carbon in stable minerals permanently by reacting the CO2 with metal oxides. But the reaction rate is slow. You need expensive pre-treatment to speed up the process, which would increase energy costs as much as 60-180%.