Anthropogenic CO₂ emissions

Published August 2021.

All statistics shown here rely on the most recently available data.

Cumulative long lived greenhouse gases (GHGs) solely determine our long-term warming commitment, simply because of their long lifetimes in the atmosphere1, and they can’t be removed and sequestered at necessary scale. Cumulative carbon dioxide (CO2) is almost the singular cause, and is increasing rapidly2 3 (nitrous oxide (N2O) is the only other significant contributor but accountable for about one tenth that of CO2, and is changing slowly4).

Prior to the Industrial Era, during the Holocene (beginning 11,700 years ago), 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) as a carbon sink. 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 zero5.

Anthropogenic CO₂ emissions rapidly altered this, creating an imbalance and causing CO₂ to accumulate in the atmosphere. The rate of our emissions dwarf that of natural CO₂ exchanges; in 2019 they were 7 times the preindustrial annual net land-atmosphere CO₂ exchange, and 17 times the preindustrial net annual ocean-atmosphere CO₂ exchange6.

Chart 1. Annual CO₂ exchanges, 1959 – 2019. Data: GCP(2020)7. Negative values represent an accumulation of CO₂. Atmospheric Growth refers to accumulation of CO₂ in the atmosphere, contributing to global warming. “Budget Imbalance is the sum of emissions (fossil fuel and industry + land-use change) minus (atmospheric growth + ocean sink + land sink); it is a measure of our imperfect data and understanding of the contemporary carbon cycle”7.

In response to our emissions, the net land-atmosphere CO₂ exchange roughly doubled in 2019 relative to preindustrial, and the net ocean-atmosphere CO₂ exchange reversed, causing the ocean to also function as a carbon sink, exchanging carbon at almost four times the preindustrial rate in the opposite direction8.

Despite these large alterations to Earth’s carbon cycle, anthropogenic CO₂ emissions have been so relatively rapid that CO₂ has accumulated in the atmosphere, to a quantity in April 2021 50% greater than preindustrial time9. 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 sight10. Half of all anthropogenic CO2 emitted during the Industrial Era has been emitted in the past 37 years, since 1983, as shown in chart 2.

Chart 2. Cumulative anthropogenic CO2 emissions from fossil fuels and land-use change in reverse chronological order. Data: Author’s own calculations using GCP(2020)11.

Chart 3 shows 81% of anthropogenic CO₂ emissions in 2019 was due to fossil fuel combustion and flaring (combustion of waste-gases). The trend of these emissions follows in chart 4.

Chart 3. The Global Carbon Budget: sources and sinks of CO₂, 2019. Data: GCP(2020)11. The share of CO₂ from cement is emitted by clinker production, the main constituent of cement. This share is often quoted as 8% but that refers to the cement industry, and therefore includes emissions from the industry’s energy consumption. Share of CO₂ emission from fossil fuels and flaring = 33.5% + 28.8% +17.7% + 1% = 81%. Share of land sink + ocean sink = 27.2% + 22.8% = 50%.
Chart 4. World annual fossil fuel and flaring CO2 emissions, 1965-2020. Data: bp Statistical Review of World Energy 202112.

In five of the years during the decade from 2001 to 2010, the annual growth of atmospheric CO2 exceeded +2ppm/yr. In the following decade, this occurred in nine years, as shown below.

Chart 5. Blue bars: Globally averaged annual mean CO₂ growth rate (ppmCO2/yr). Red line: 10 year running mean. Data: Ed Dlugokencky and Pieter Tans, NOAA Global Monitoring Laboratory, Earth System Research Laboratories, 202113.

Chart 6 shows anthropogenic CO₂ emissions from all individual sources.

Chart 6. World annual CO2 emissions, 1959-2021 (1959-2019 for Flaring and Land Use Change). Data: Global Carbon Project (2021)14. Values for 2021 are projected15.

Chart 7(a) shows that fossil fuel CO₂ emissions from countries emitting less than a 5% share account for nearly half of total emissions (46%, shown by the red outer segment).
Chart 7(b) shows 13 high emitting sectors across 6 countries also account for about half global fossil fuel CO₂ emissions (49%, numbered [1] to [13] , indicated by the dark blue outer segment).

Chart 7. World fossil fuel CO₂ emissions in 2018 by (a) country, and (b) economic sector, highlighting the 13 sectors with ≥1% share. Data: IEA(2020)16.

Anthropogenic CO₂ emissions are also discussed in Greenhouse Gas Emissions.

Footnotes
  1. Chart 4 of https://www.worldenergydata.org/ghgs/(↩)
  2. Matthews, H.D., Gillett, N.P., Stott, P.A. and Zickfeld, K., 2009. The proportionality of global warming to cumulative carbon emissions. Nature, 459(7248), p.829., http://indiaenvironmentportal.org.in/files/The proportionality of global warming.pdf(↩)
  3. Charts 1 and 3 of https://www.worldenergydata.org/ghgs/(↩)
  4. Chart 2 of https://www.worldenergydata.org/ghgs/(↩)
  5. Net rate of CO₂ exchange with the atmosphere prior to Industrial Era = -0.2GtC/yr (removal from the atmosphere.) from 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/.(↩)
  6. Anthropogenic CO₂ emissions in 2019 = fossil fuel emissions + land-use change emissions = 9.95GtC + 1.80GtC = 11.75GtC. Prior to the Industrial Era: Net-land-atmosphere flux = 1.7GtC/yr and net-ocean-atmosphere flux = 0.7GtC/yr. 11.75/1.7 = 6.9, and 11.75/0.7 = 16.8. Emission values obtained from Global Carbon Project. (2020), Supplemental data of Global Carbon Budget 2020 (Version 1.0) [Data set], Global Carbon Project, https://doi.org/10.18160/gcp-2020 , download labelled ‘2020 Global Budget v1.0’. Preindustrial net flux vales obtained from 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/.(↩)
  7. Global Carbon Project (2020). Supplemental data of Global Carbon Budget 2020 (Version 1.0) [Data set]. Global Carbon Project, https://www.icos-cp.eu/science-and-impact/global-carbon-budget/2020, download labelled ‘2020 Global Budget v1.0’.(↩)(↩)
  8. Prior to Industrial Era: land-atmosphere flux = 1.7GtC and ocean-atmosphere flux = 0.7GtC/yr. In 2019: land-atmosphere flux = 3.14GtC and ocean-atmosphere flux = 2.63GtC. Increase of rate of land exchange = 3.14/1.7 = 1.84. Increase of rate of ocean exchange = 2.6/0.7 = 3.75. Emission values obtained from Global Carbon Project. (2020), Supplemental data of Global Carbon Budget 2020 (Version 1.0) [Data set], Global Carbon Project, https://doi.org/10.18160/gcp-2020 , download labelled ‘2020 Global Budget v1.0’. Preindustrial net flux vales obtained from 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/.(↩)
  9. Atmospheric concentration of CO₂: April 2021 = 416.17ppm (after correction for the average seasonal cycle, https://gml.noaa.gov/ccgg/trends/global.html). Preindustrial = 589GtCO₂/(2.12GtC/ppm) = 277.8ppm. 416.17/277.8 = 1.498. Preindustrial value from 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/.(↩)
  10. https://www.worldenergydata.org/ghgs/(↩)
  11. Global Carbon Project (2020). Supplemental data of Global Carbon Budget 2020 (Version 1.0) [Data set]. Global Carbon Project, https://www.icos-cp.eu/science-and-impact/global-carbon-budget/2020, download labelled ‘2020 Global Budget v1.0’.(↩)(↩)
  12. https://www.bp.com/en/global/corporate/energy-economics/statistical-review-of-world-energy.html(↩)
  13. https://gml.noaa.gov/ccgg/trends/gl_data.html(↩)
  14. Global Carbon Project. (2021). Supplemental data of Global Carbon Budget 2021 (Version 1.0) [Data set]. Global Carbon Project. https://doi.org/10.18160/gcp-2021(↩)
  15. https://4c-carbon.eu/resources/carbon-outlooks(↩)
  16. https://www.iea.org/reports/co2-emissions-from-fuel-combustion-overview(↩)