Due to anthropogenic (human-caused) emissions, atmospheric CO 2 is now significantly higher than at any time in the last 800,000 years and probably in the last 20 million. On the other hand, until human beings began to burn large amounts of fossil fuel in the late eighteenth century, CO 2 had been stable for about 20 million years. In the deep geological past, atmospheric CO 2 has sometimes been much higher than today for example, about 500 million years ago there was over 15 times as much atmospheric CO 2 as there is now. Historical Background and Scientific FoundationsĮmissions of CO 2 predate the human race by billions of years and are essential to life on Earth, since the natural greenhouse effect keeps Earth’s average surface temperature above freezing. Atmospheric concentrations of several other gases, including methane (CH 4) and nitrous oxide (N 2O), have also been increased recently by human activities and are contributing to greenhouse warming of the planet. In more recent times, this source of CO 2 emissions has increased rapidly, while destruction of forests has also become a major source of CO 2. The amount of CO 2 in the atmosphere has increased greatly since human beings began burning large amounts of coal and petroleum in the nineteenth century. Although other gases are also causing Earth’s climate to warm, CO 2 alone is responsible for about three-fourths of global warming. It is removed from the atmosphere mostly by plants, which extract carbon from CO 2 to build their tissues, and by the oceans, in which CO 2 dissolves.īecause CO 2 is opaque to infrared radiation (the electromagnetic waves emitted by warm objects) in the atmosphere, it acts as a blanket to slow the loss of heat from Earth into space. Under all conditions found naturally on Earth, CO 2 is an invisible, odorless gas. Carbon Dioxide (CO 2) Emissions IntroductionĬarbon dioxide (CO 2) is released into Earth’s atmosphere mostly by the burning of carbon-containing fuels and the decay of wood and other plant matter.
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