Greenhouse Gas Emissions

Carbon dioxide (CO2) emissions from our combustion of fossil fuels are shown separately below, for years 1959 to 2017.

Chart 1. CO2 emissions from the combustion of fossil fuels (the energy sector), 1959-2017. Data: Global Carbon Project.1

The sun’s energy continually enters Earth’s atmosphere, and because humanity has increased the concentration of greenhouse gases, Earth’s atmosphere now holds more heat, causing global heating. This heating will continue until the atmosphere again returns to space the same amount of energy arriving from the sun. To help explain this, physicist John Tyndall used a dam as an analogy:2 If water continually flows into a dam and the dam’s wall is made higher, the dam holds more water than before until it again overflows.

The measure of energy trapped by greenhouse gases is known as radiative forcing, with units of Watts per square metre (W/m2). Two thirds of total radiative forcing is due to carbon dioxide (CO2).3 Chart 2 shows the contribution from each gas.

Chart 2(a). Annual radiative forcing of greenhouse gases. Data: NOAA ESRL.4 Chart 2(b). Stacked version of (a).

Radiative forcing due to greenhouse gases is partially reduced by that from cooling aerosols, and global heating is therefore caused by the net amount.5

Chart 3 shows the annual change of radiative forcing by each greenhouse gas.

Chart 3. Annual change of radiative forcing by greenhouse gas, 1980-2018. Data: NOAA ESRL4

Chart 4 shows the same data as chart 3, but by share. The share caused by CO2 has been greater than 70% for every year since 1993, and reached 90% or more in 2003, 2005 and 2013.

Chart 4. Annual change of radiative forcing by greenhouse gas, as share of total annual change, 1980-2018. Data: NOAA ESRL.4

Our long term warming commitment, and therefore sea level rise is determined solely by cumulative CO2 emissions –

Climate–carbon modelling experiments have shown that: (1) the warming per unit CO2 emitted does not depend on the background CO2 concentration; (2) the total allowable emissions for climate stabilisation do not depend on the timing of those emissions; and (3) the temperature response to a pulse of CO2 is approximately constant on timescales of decades to centuries.

Matthews, 2009, The proportionality of global warming to cumulative carbon emissions.6

The temperature response described above is shown in chart 5.

Chart 5. Temperature response to a 1 year pulse of our emissions from 2008.7

After 500 years, about a third of a CO2 emission pulse remains in the atmosphere.8

As shown below, half of all CO2 emitted by humanity, from preindustrial year 1750 to the end of 2018, has been emitted in just the previous 37 years. A third has been emitted in the past 22 years and a quarter in the last 15 years. In 2018 alone, 2% was emitted (assuming land-use change emissions in 2018 equalled that in 2017).9 10 11

Chart 6. Proportion of total CO2 historically emitted over the period 1750 – 2018.1 11

Another way to represent cumulative emission is shown below.

Chart 7. What percentage of all global fossil fuel CO₂ emissions since 1751 have occurred in my lifetime? Credit: @neilrkaye12

It has taken society nearly 220 years (from 1750 to 1970) to emit the first trillion tons of CO2 and only another 40 years (1970–2010) to emit the next trillion tons. The third trillion tons, under current emission trends, would be emitted by 2030 and the fourth trillion tons before 2050.

Xu, Yangyang, and Veerabhadran Ramanathan, “Well below 2 C: Mitigation strategies for avoiding dangerous to catastrophic climate changes.”13

Consequently, for every year since 2001, the atmospheric concentration of CO2 has increased by more than +1.5ppm, as indicated below by the blue columns above the black line. The largest annual increase was in 2015.

Chart 8. Annual mean global CO2 growth rate. Data: NOAA ESRL.14

We conclude that, given currently available records, the present anthropogenic carbon release rate is unprecedented during the past 66 million years. 

Zeebe, Ridgwell and Zachos, “Anthropogenic carbon release rate unprecedented during the past 66 million years.”15

Our CO2 emissions originate from three sectors: energy (i.e. fossil fuel combustion), cement manufacture and land-use change. In 2016 and 2017, 84% of CO2 emissions originated from fossil fuels (this includes flaring, which is the burning of waste gases).10 16 17 CO2 emissions from all sectors since 1850 are shown below.

Chart 9(a). Black line is annual global mean CO2 concentration in units of parts per million (ppm), from 1850 to 2018 (lefthand axis). Data: IPCC and NOAA ESRL.18 Solid area is annual global CO2 emissions from all sources (fossil fuels, cement and land use) in units of billions of tons of carbon dioxide (GtCO2), from 1850 to 2017 (righthand axis). Data: Global Carbon Project.1 Chart 9(b). Contributors of annual global CO2 emissions, showing that emissions from fossil fuels and cement manufacture dominate and continue to increase. Data: Global Carbon Project.1 19

By using only data since 1959, cement emissions can be displayed separately to show the obvious dominance of fossil fuel emissions.

Chart 10. CO2 emissions from all sectors. Data: Global Carbon Project.1

CO2 emissions from fossil fuels continued to grow in 2018 according to the IEA, increasing by +1.7% to reach a record high of 33 GtCO2.20

The peak in global emissions is not yet in sight.

Global Carbon Project, 2018, Global Carbon Budget.21

Summary

Our CO2 emissions: (i) are trapping two thirds of the energy causing global heating; (ii) are the only rapidly increasing contributor; (iii) solely determine our long term heating commitment; and (iv) continue to grow with no peak in sight. Half of all CO2 emitted since preindustrial times has been emitted in the past 37 years, and almost all by the world’s energy sector.

  1. Data available at https://www.icos-cp.eu/GCP/2018, download labelled ‘2018 Global Budget v1.0’. Emissions from fossil fuel combustion and cement production: Boden, T. A., Marland, G., and Andres, R. J.: Global, Regional, and National Fossil-Fuel CO2 Emissions, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A., doi 10.3334/CDIAC/00001_V2017, 2017.()()()()()
  2. p. 5, Hansen, 2018, Climate Change in a Nutshell http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf, accessed 18 December 2018()
  3. 2.013 W/m2 / 3.062 W/m2, https://www.esrl.noaa.gov/gmd/aggi/aggi.html()
  4. https://www.esrl.noaa.gov/gmd/aggi/aggi.html()()()
  5. p. 13, Climate Change in a Nutshell: The Gathering Storm, 18 Dec 2018. http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf()
  6. Matthews, H.D., Gillett, N.P., Stott, P.A. and Zickfeld, K., 2009. The proportionality of global warming to cumulative carbon emissions. Nature459(7248), p.829. http://indiaenvironmentportal.org.in/files/The%20proportionality%20of%20global%20warming.pdf.()
  7. Reprinted from Figure 8.33, page 719, IPCC, 2013: 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, 1535 pp. https://www.ipcc.ch/report/ar5/wg1/.()
  8. Fig. 1 of Aamaas, B., Peters, G. P., and Fuglestvedt, J. S.: Simple emission metrics for climate impacts, Earth Syst. Dynam., 4, 145-170, 2013. https://doi.org/10.5194/esd-4-145-2013.()
  9. 2018 projection for fossil fuel and flaring emissions = 37.1GtCO2. Land-use change emissions in 2017 = 1.39GtC = 1.39 * 44 / 12 GtCO2 = 5.1GtCO2. Total = 37.1 + 5.1 = 42.2 GtCO2. Cumulative CO2 from 1750 to 2018 = 2,355.75 GtCO2. Proportion emitted in 2018 = 42.2 / 2,355.75 = 1.8%.()
  10. Data available at https://www.icos-cp.eu/GCP/2018, download labelled ‘2018 Global Budget v1.0’. Emissions from fossil fuel combustion and cement production: Boden, T. A., Marland, G., and Andres, R. J.: Global, Regional, and National Fossil-Fuel CO2 Emissions, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A., doi 10.3334/CDIAC/00001_V2017, 2017.()()
  11. Value for 2018 is projection made in http://www.globalcarbonproject.org/carbonbudget/18/presentation.htm()()
  12. What percentage of all global fossil fuel CO₂ emissions since 1751 have occurred in my lifetime? @neilrkaye, Climate data scientist at UK Met Office.()
  13. Xu, Yangyang, and Veerabhadran Ramanathan. “Well below 2 C: Mitigation strategies for avoiding dangerous to catastrophic climate changes.” Proceedings of the National Academy of Sciences 114, no. 39 (2017): 10315-10323. https://www.pnas.org/content/pnas/114/39/10315.full.pdf()
  14. https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_gr.html()
  15. Zeebe, Richard E., Andy Ridgwell, and James C. Zachos. “Anthropogenic carbon release rate unprecedented during the past 66 million years.” Nature Geoscience 9, no. 4 (2016): 325. https://www.nature.com/articles/ngeo2681()
  16. Emissions from land-use change average of two bookkeeping models: Houghton, R. A. and Nassikas, A. A.: Global and regional fluxes of carbon from land use and land cover change 1850-2015, Global Biogeochemical Cycles, 31, 456-472, 2017;  Hansis, E., Davis, S. J., and Pongratz, J.: Relevance of methodological choices for accounting of land use change carbon fluxes, Global Biogeochemical Cycles, 29, 1230-1246, 2015.()
  17. Calculations: (1) 2016: Total emissions = (9.74 + 1.3) = 11.04 GtC. Fossil fuel plus flaring emissions = (3.95 + 3.4 + 1.92 + .068) / 11.04 = 84.6%. (2) 2017: Total emissions = (9.87 + 1.39) = 11.26 GtC. Fossil fuel plus flaring emissions = (3.98 + 3.45 + 1.97 + .068) / 11.26 = 84.1%.()
  18. Data from 1850 to 2010 inclusive: p. 1404, Table AII.1.2 IPCC, 2013: Annex II: Climate System Scenario Tables [Prather, M., G. Flato, P. Friedlingstein, C. Jones, J.-F. Lamarque, H. Liao and P. Rasch (eds.)]. 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/site/assets/uploads/2017/09/WG1AR5_AnnexII_FINAL.pdf.
    Data from 2011 to 2018 inclusive: Ed Dlugokencky and Pieter Tans, NOAA/ESRL, https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_data.html()
  19. Emissions from land-use change average of two bookkeeping models: Houghton, R. A. and Nassikas, A. A.: Global and regional fluxes of carbon from land use and land cover change 1850-2015, Global Biogeochemical Cycles, 31, 456-472, 2017;  Hansis, E., Davis, S. J., and Pongratz, J.: Relevance of methodological choices for accounting of land use change carbon fluxes, Global Biogeochemical Cycles, 29, 1230-1246, 2015.()
  20. https://www.iea.org/geco/emissions/()
  21. http://www.globalcarbonproject.org/carbonbudget/18/presentation.htm()