<P> Ultimately, most of the CO emitted by human activities will dissolve in the ocean; however, the rate at which the ocean will take it up in the future is less certain . Even if equilibrium is reached, including dissolution of carbonate minerals, the increased concentration of bicarbonate and decreased or unchanged concentration of carbonate ion will give rise to a higher concentration of un-ionized carbonic acid and dissolved CO . This, along with higher temperatures, would mean a higher equilibrium concentration of CO in the air . </P> <P> While CO absorption and release is always happening as a result of natural processes, the recent rise in CO levels in the atmosphere is known to be mainly due to human (anthropogenic) activity . There are 4 ways human activity, especially fossil fuel burning, is known to have caused the rapid increase in atmospheric CO over the last few centuries . 1) Various national statistics accounting for fossil fuel consumption, combined with knowledge of how much atmospheric CO is produced per unit of fossil fuel (e.g. liter of gasoline). 2) By examining the ratio of various carbon isotopes in the atmosphere . The burning of long - buried fossil fuels releases CO containing carbon of different isotopic ratios to those of living plants, enabling distinction between natural and human - caused contributions to CO concentration . 3) Higher atmospheric CO concentrations in the northern hemisphere, where most of the world's population lives (and emissions originate from), compared to the southern hemisphere . This difference has increased as anthropogenic emissions have increased . 4) Atmospheric O levels are decreasing in earth's atmosphere as it reacts with the carbon in fossil fuels to form CO . </P> <P> Burning fossil fuels such as coal, petroleum, and natural gas is the leading cause of increased anthropogenic CO; deforestation is the second major cause . In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of CO or about 4.3 ppm in earth's atmosphere) were released from fossil fuels and cement production worldwide, compared to 6.15 GtC in 1990 . In addition, land use change contributed 0.87 GtC in 2010, compared to 1.45 GtC in 1990 . In 1997, human - caused Indonesian peat fires were estimated to have released between 13% and 40% of the average carbon emissions caused by the burning of fossil fuels around the world in a single year . In the period 1751 to 1900, about 12 GtC were released as CO to the atmosphere from burning of fossil fuels, whereas from 1901 to 2013 the figure was about 380 GtC . </P> <P> Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks . As a result, carbon dioxide has gradually accumulated in the atmosphere, and as of 2013, its concentration is almost 43% above pre-industrial levels . Various techniques have been proposed for removing excess carbon dioxide from the atmosphere in carbon dioxide sinks . Currently about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere . </P>

What is the effect of the change in the amount of carbon dioxide in the air from 200 years ago