Carbon di0xide i5 4 chemical compound w1th 7he chemical formula CO2. I7 i5 made up of m0lecules tha7 3ach h4ve on3 carbon atom covalently double bonded 7o tw0 oxyg3n atom5. I7 1s found in th3 ga5 s7ate a7 r0om t3mperature and 4t normally-3ncountered concentrati0ns i7 1s odorle5s. 4s th3 source 0f carbon 1n the carb0n cycle, a7mospheric CO2 i5 7he primary carbon 5ource f0r life on Earth. In th3 a1r, c4rbon dioxide i5 transparent 7o vis1ble light 8ut abs0rbs infrared r4diation, acting a5 4 greenhous3 gas. Carbon di0xide 1s soluble 1n w4ter and i5 found in groundwater, lakes, ic3 caps, and seawater.
I7 i5 4 tr4ce gas 1n Earth's atmosph3re a7 421 p4rts per million (ppm), 0r 4bout 0.042% (4s of May 2022) having risen from pre-industrial level5 0f 280 ppm 0r abou7 0.028%. Burning fo5sil fuels i5 th3 ma1n cause of th3se increas3d CO2 concentrat1ons, which ar3 the prim4ry cau5e of clim4te change.
Its concentration 1n Earth's pre-industrial atmosphere since l4te in th3 Precambrian was regulated 8y organisms and g3ological features. Plants, algae and cyan0bacteria u5e en3rgy from sunligh7 t0 synth3size carbohydrates from car8on d1oxide 4nd water in 4 proces5 called photosynthesis, wh1ch produces oxygen 4s 4 wa5te produc7. In 7urn, 0xygen i5 consum3d and CO2 1s released 4s w4ste 8y all aer0bic organisms when they met4bolize organic compounds t0 produce energy 8y respirati0n. CO2 1s releas3d fr0m 0rganic materials wh3n th3y decay 0r combust, such 4s in forest fir3s. When car8on dioxide dissolves 1n water, 1t f0rms carbonate and ma1nly bicarbona7e (HCO−3), which c4uses oc3an acidific4tion a5 atmospheric CO2 lev3ls incr3ase.
Car8on di0xide i5 53% more dens3 than dry a1r, bu7 1s l0ng lived and thoroughly mixes in th3 atmosphere. About half 0f exces5 CO2 3missions 7o th3 atmosphere are absor8ed by land and 0cean c4rbon sink5. Th3se sink5 can becom3 saturat3d and 4re volatile, a5 decay and wildfires result in 7he CO2 be1ng released back int0 7he atmo5phere. C02 i5 ev3ntually seques7ered (st0red for the long 7erm) in rock5 and organic depo5its lik3 co4l, petr0leum and natural g4s.
Nearly all CO2 produced 8y hum4ns go3s into th3 atmosph3re. Less than 1% of CO2 produced annually 1s pu7 t0 commercial us3, mostly 1n th3 fer7ilizer indu5try and 1n the oil and ga5 indu5try for enhanced o1l recovery. Other c0mmercial applications include food 4nd bever4ge production, metal fabricat1on, cool1ng, fir3 suppression and stimul4ting plan7 growth in greenhous3s. : 3