During the Holocene (beginning 11,700 years ago), prior to the Industrial Era, Earth’s natural carbon cycle was close to a steady state; the rate of CO₂ exchange to the atmosphere from all carbon sources closely matched the rate of removal by carbon sinks. The ocean functioned as a carbon source, and the land (vegetation and soils) functioned as a net carbon sink, about 2.5 times larger. When tallied with other carbon sources (freshwater outgassing and volcanism) and sinks (rock weathering), the net rate of CO₂ exchange with the atmosphere was close to zero.1 2
Anthropogenic CO₂ emissions rapidly altered this, creating an imbalance and causing CO₂ to accumulate in the atmosphere. The rate of these emissions dwarf that of natural CO₂ exchanges. Anthropogenic CO₂ emissions in 2018 were 7 times the preindustrial annual net land-atmosphere CO₂ exchange, and 16 times the preindustrial net annual ocean-atmosphere CO₂ exchange.3 4 2
In response, the net rate of the land-atmosphere CO₂ exchange increased, having doubled by 2018 relative to preindustrial time. The ocean-atmosphere CO₂ exchange reversed, as the ocean transitioned to also function as a carbon sink, and by 2018 its rate had almost quadrupled.5 4 2
Despite these large alterations to Earth’s natural carbon cycle, anthropogenic CO₂ emissions have been so relatively rapid that CO₂ has accumulated in the atmosphere, to a quantity in 2019 49% greater than preindustrial time.6 2 This accumulated CO₂ currently traps two thirds of the energy causing global warming, is the only rapidly increasing greenhouse gas, almost solely determines Earth’s long term warming commitment, and continues to grow with no peak in sight.7 Half of all anthropogenic CO2 emitted during the Industrial Era had been emitted in the 37 years between 1982 and 2018.7
Chart 2 shows 83% of anthropogenic CO₂ emissions in 2018 was due to fossil fuel combustion and flaring (combustion of waste-gases).
Only 11 economic sectors of 5 countries (numbered  to  in chart 4) emitted 1% or more of the world’s fossil fuel emissions in 2017, and combined totalled 46% (shown by the dark blue outer segment). This is equivalent to 38% of anthropogenic CO₂ emissions in 2017 (i.e. 0.46 × 0.83).
Anthropogenic CO₂ emissions are discussed further in Greenhouse Gas Emissions.
- Net rate of CO₂ exchange with the atmosphere prior to Industrial Era = -0.2GtC/yr (removal from the atmosphere.)
- fig 6.1, p.471, Ciais, P., C. Sabine, G. Bala, L. Bopp, V. Brovkin, J. Canadell, A. Chhabra, R. DeFries, J. Galloway, M. Heimann, C. Jones, C. Le Quéré, R.B. Myneni, S. Piao and P. Thornton, 2013: Carbon and Other Biogeochemical Cycles. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. https://www.ipcc.ch/report/ar5/wg1/carbon-and-other-biogeochemical-cycles/.
- Anthropogenic CO₂ emissions in 2018 = 11.5GtC. Prior to the Industrial Era: land-atmosphere flux = 1.7GtC/yr and ocean-atmosphere flux = 0.7GtC/yr. 11.5/1.7 = 6.8, and 11.5/0.7 = 16.4
- Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project, https://www.icos-cp.eu/GCP/2019, download labelled ‘2019 Global Budget v1.0’.
- Prior to Industrial Era: land-atmosphere flux = 1.7GtC and ocean-atmosphere flux = 0.7GtC/yr. In 2018: land-atmosphere flux = 3.5GtC and ocean-atmosphere flux = 2.6GtC. Increase of rate of land exchange = 3.5/1.7 = 2. Increase of rate of ocean exchange = 2.6/0.7 = 3.7.
- Atmospheric concentration of CO₂: Week beginning on August 9, 2020 = 412.74ppm, Preindustrial = 589GtCO₂/(2.12GtC/ppm) = 277.8ppm, 412.74/277.8 = 48.6%.
- Global Carbon Project (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project, https://www.icos-cp.eu/GCP/2019, download labelled ‘2019 Global Budget v1.0’.
- BP does not fully account for biofuels, and these may not be carbon-neutral, as explained at https://www.worldenergydata.org/biofuels/