Earth isn't the only planet in the Solar System with an atmosphere, but its atmosphere is the only one in which human beings would be able to survive. The main component of Earth's atmosphere, like that of Saturn's moon Titan, is nitrogen, and the other abundant element is oxygen. Forming approximately 1 percent of the atmosphere are a host of other compounds including carbon dioxide, which plays a significant role in warming the planet.
Atmospheric Composition of Carbon Dioxide
Carbon dioxide levels in the atmosphere are not constant -- they have risen by nearly 40 percent since the Industrial Revolution, according to climate scientist Todd Sanford. They are small compared to the main atmospheric components of nitrogen and oxygen. Scientists express them as parts per million, or ppm. In March 2011, carbon dioxide levels were at 391 ppm, which is 0.0391 percent of the atmosphere. This roughly corresponds to a mass of 3 trillion tons. After nitrogen, oxygen, water vapor and argon, carbon dioxide is the fifth most abundant gas in the atmosphere.
Measuring Carbon Dioxide Levels
Beginning in the 1950s and continuing through 2013, scientists have undertaken a program to measure carbon dioxide levels at Mauna Loa in Hawaii. The program, operated by the Scripps Institute of Oceanography, has produced a record that shows a steady year-by-year increase in carbon dioxide levels. The Keeling Curve, named after the scientist who originally directed the program, provides evidence for rising carbon dioxide levels. Besides showing a steady upward climb in carbon dioxide levels in the atmosphere, it demonstrates seasonal fluctuations in atmospheric carbon dioxide levels caused by growth and decay of plants in the Northern Hemisphere.
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A Greenhouse Gas
Carbon dioxide is a greenhouse gas; it absorbs sunlight reflected from the surface of the planet and warms the atmosphere. In its absence, the sunlight would radiate into space. Carbon dioxide isn't the only gas that does this -- methane and nitrous oxide are even more potent greenhouse gases. However, the higher concentrations of carbon dioxide and the fact that the concentrations are rising make carbon dioxide the most important greenhouse gas. Although much atmospheric carbon dioxide dissolves into seawater and soil and becomes raw material for photosynthesis, the Keeling Curve demonstrates that production of this gas exceeds its consumption.
Rising Carbon Dioxide Levels
Because of its ability to form complex molecules, carbon cycles ceaselessly through the ecosystem from the soil and oceans to the atmosphere. Carbon dioxide levels are related to this cycle; carbon dioxide gas produced by volcanoes dissolves in the oceans to make them more acidic, and it becomes the raw material for photosynthesis. This natural cycle becomes perturbed by the addition of extra carbon dioxide into the atmosphere, such as happens through the burning of fossil fuels. Effects can include rising temperatures and increased ocean acidity, which can put marine life in danger.