<Tr> <Td_colspan="2"> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Carbon dioxide (CO) is an important trace gas in Earth's atmosphere . It is an integral part of the carbon cycle, a biogeochemical cycle in which carbon is exchanged between the Earth's oceans, soil, rocks and the biosphere . Plants and other photoautotrophs use solar energy to produce carbohydrate from atmospheric carbon dioxide and water by photosynthesis . Almost all other organisms depend on carbohydrate derived from photosynthesis as their primary source of energy and carbon compounds . CO absorbs and emits infrared radiation at wavelengths of 4.26 μm (asymmetric stretching vibrational mode) and 14.99 μm (bending vibrational mode) and consequently is a greenhouse gas that plays a vital role in regulating Earth's surface temperature through the greenhouse effect . </P> <P> Reconstructions show that concentrations of CO in the atmosphere have varied from as high as 7,000 parts per million (ppm) during the Cambrian period about 500 million years ago to as low as 180 ppm during the Quaternary glaciation of the last two million years . Global annual mean CO concentration has increased by more than 45% since the start of the Industrial Revolution, from 280 ppm during the 10,000 years up to the mid-18th century to 410 ppm as of mid-2018 . The present concentration is the highest in the last 800,000 and possibly even the last 20 million years . The increase has been caused by human activities, particularly the burning of fossil fuels and deforestation . This increase of CO and other long - lived greenhouse gases in Earth's atmosphere has produced the current episode of global warming . About 30--40% of the CO released by humans into the atmosphere dissolves into oceans, rivers and lakes, which has produced ocean acidification . </P>

What function does carbon dioxide play in earth's atmosphere
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