Question: what is a healthy amount of co2 in the earth atmosphere

title: Carbon dioxide in Earth's atmosphere
text: Most sources of CO emissions are natural , and are balanced to various degrees by natural CO sinks . For example , the natural decay of organic material in forests and grasslands and the action of forest fires results in the release of about 439 gigatonnes of carbon dioxide every year , while new growth entirely counteracts this effect , absorbing 450 gigatonnes per year . Although the initial carbon dioxide in the atmosphere of the young Earth was produced by volcanic activity , modern volcanic activity releases only 130 to 230 megatonnes of carbon dioxide each year . These natural sources are nearly balanced by natural sinks , physical and biological processes which remove carbon dioxide from the atmosphere . For example , some is directly removed from the atmosphere by land plants for photosynthesis and it is soluble in water forming carbonic acid . There is a large natural flux of CO into and out of the biosphere and oceans . In the pre-industrial era these fluxes were largely in balance . Currently about 57 % of human - emitted CO is removed by the biosphere and oceans . From pre-industrial era to 2010 , the terrestrial biosphere represented a net source of atmospheric CO prior to 1940 , switching subsequently to a net sink . The ratio of the increase in atmospheric CO to emitted CO is known as the airborne fraction ( Keeling et al. , 1995 ) ; this varies for short - term averages and is typically about 45 % over longer ( 5 year ) periods . Estimated carbon in global terrestrial vegetation increased from approximately 740 billion tons in 1910 to 780 billion tons in 1990 .