While  absorption and release is always happening as a result of natural processes, the recent rise in  levels in the atmosphere is known to be mainly due to human (anthropogenic) activity. Anthropogenic carbon emissions exceed the amount that can be taken up or balanced out by natural sinks. Thus carbon dioxide has gradually accumulated in the atmosphere and, as of May 2022, its concentration is 50% above pre-industrial levels.
The extraction and burning of fossil fuels, releasing carbon that has been underground for many millions of years, has increased the atmospheric concentration of . As of year 2019 the extraction and burning of geologic fossil carbon by humans releases over 30 gigatonnes of  (9 billion tonnes carbon) each year. This larger disruption to the natural balance is responsible for recent growth in the atmospheric  concentration.  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.
Burning fossil fuels such as coal, petroleum, and natural gas is the leading cause of increased anthropogenic ; deforestation is the second major cause. In 2010, 9.14 gigatonnes of carbon (GtC, equivalent to 33.5 gigatonnes of  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 the period 1751 to 1900, about 12 GtC were released as  to the atmosphere from burning of fossil fuels, whereas from 1901 to 2013 the figure was about 380 GtC.
The International Energy Agency estimates that the top 1% of emitters globally each had carbon footprints of over 50 tonnes of  in 2021, more than 1,000 times greater than those of the bottom 1% of emitters. The global average energy-related carbon footprint is around 4.7 tonnes of  per person.