What is carbon dioxide (CO2)?
|Carbon dioxide (CO2) is an odorless, colorless trace gas in the atmosphere.
It makes up about 410 parts per million (ppm) by volume(0.041%) of the atmosphere as of 2019, and its concentration
is slowly rising primarily due to the burning of fossil fuels to meet global energy demand.
Carbon dioxide is necessary for life on Earth, being required for photosynthesis within plants
on land and plankton in the ocean, which represent the start of the food chain. Only about 50% of
the CO2 emissions of humanity shows up as an increase in atmospheric CO2, the other half presumably
being absorbed by plants, phytoplankton, and by being dissolved in the ocean.
The rising atmospheric concentration of CO2 has been implicated as the primary cause of recent
global warming due to its role as an infrared
absorbing "greenhouse gas" in the atmosphere.
The natural flows of CO2 in and out of the surface of the Earth are about 20 times the rate of
human emissions. Those flows are very nearly in balance on a global, year-to-year basis, although there
is a natural rise in atmospheric CO2 during warm El Niño years, and a fall during cool La Niña years.
(page last updated 12/13/2019)