Carbon dioxide is an acidic, colorless, water-soluble gas whose molecules consist of one carbon atom and two oxygen atoms. It occurs naturally in the earth's atmosphere as a trace gas, as well as in water bodies, and glaciers, as a result of volcanic eruptions, forest fires, hot springs, geysers, and the dissolution of carbonate rocks by water and acids.
The concentration of carbon dioxide in the atmosphere has been increasing rapidly during the past several hundred years as a result of human activity and is now generally recognized as the dominant cause of climate change. The current concentration in dry air is about 415 parts per million (0.04%) by volume, which is about 50 percent higher than the pre-industrial (c. 1750) level, estimated at 280ppm. This increase has occurred despite the absorption of more than half of the carbon dioxide emissions by various natural carbon sinks in the carbon cycle. The last time the concentration of carbon dioxide in the atmosphere was this high was more than three million years ago. Although 415 parts per million is tiny in comparison to the share of nitrogen (780,840ppm or 78.08%), oxygen (209,460ppm or 20.946%) and even argon (9,340ppm or 0.9340%), it has a disproportionately large effect.
Currently, attempts are beginning to be made to slow the rate of increase in carbon dioxide and eventually completely stop the increase within a few decades. However, this has been subject to much criticism both because it is too slow and because the final concentration of carbon dioxide would be too high, resulting in an acceleration of adverse effects on the earth's climate and environment. Thus, some environmental advocates are calling for not only a much faster slowing but also for an eventual reversal toward pre-industrial levels.
There are two basic ways in which the increase in atmospheric carbon dioxide can be slowed, stopped and reversed. One is to reduce emissions and the other is to increase capture and sequestration. By far the largest way that carbon dioxide emissions can be cut is by decreasing the burning of fossil fuels, which accounts for more than 85 percent of man-made carbon dioxide emissions. Other man-made sources of emissions include the effects on the soil from deforestation and some industrial processes.
Much progress has been made recently on developing techniques for capturing some of the carbon dioxide that is already in the atmosphere, with several small-scale pilot plants already in operation and others are being constructed. However, it could be many years until such facilities are sufficiently large and numerous to make much difference. Perhaps the most immediate and effective way to capture and sequester carbon is the implementing of vast reforestation and afforestation programs. However, it is important to do this in an ecologically sensitive manner, including by the planting of native species in each region.