Shane White, March 2019.
Humanity’s emissions of greenhouse gases originate from three sectors: energy, cement manufacture and land use. This page explains that carbon dioxide (CO2) is the greenhouse gas of greatest concern.
Physicist John Tyndall used an analogy to explain global warming by likening the addition of CO2 to the atmosphere, to increasing the height of a dam wall:1 If water continually flows into the dam, it holds more water than before, until it eventually overflows. In the same manner, increased greenhouse gases cause the atmosphere to hold more of the energy Earth receives from the sun, reducing the amount of energy returned to space. Consequently Earth warms until it again returns to space the same amount of energy arriving from the sun.
The measure of additional energy trapped by greenhouse gases is known as radiative forcing, with units Watts per square metre (W/m2). This causes Earth’s surface temperature to rise. A global radiative forcing of 1W/m2 is equivalent to stretching out a standard electric blanket (150W) to cover an area of 150 square metres (just over 12 metres by 12 metres, or 13 yards by 13 yards), repeating this to cover Earth’s entire surface, setting all the blankets to maximum and leaving them switched on continuously throughout every day and night.
Of the total amount of radiative forcing due to humanity’s emissions, two thirds is due to CO2.2 And –
Additional warming by non-CO2 greenhouse gases tends to be off-set by aerosol cooling; thus within the range of uncertainty CO2 provides a good approximation of the net human-made forcing.p. 13, Climate Change in a Nutshell: The Gathering Storm, 18 Dec 2018.3
Charts 1 and 2 below show that the contribution from CO2 is rapidly increasing (the greenhouse gases shown are those primarily responsible for global warming).
Chart 3 below shows the acceleration of the annual contribution from CO2, as well as the sharp decline from CFCs after 1992 due to the success of the Montreal Protocol.
Chart 4 shows that during the past two decades, the share of CO2 in the annual change of radiative forcing has frequently been greater than 80%, and in 2017 was 85%.
Furthermore, cumulative CO2 determines our long term warming commitment:
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 emissions5
The temperature response described above is shown in chart 5. After 500 years, about a third of a CO2 emission pulse remains in the atmosphere.6
Global CO2 emissions from fossil fuels are forecast to grow in 2018 by an astonishing +2.7% with respect to 2017. NYT reported that scientists likened this to a speeding freight train. 8
Global fossil CO2 emissions have risen steadily over the last decades. The peak in global emissions is not yet in sight.Global Carbon Project, 2018, Global Carbon Budget9
CO2 emissions since 1850 are shown below, displaying the acceleration of emissions from fossil fuels and cement after 1950 –
The largest annual increase of atmospheric CO2 concentration was during 2015, and for every year since 2001, it has increased by more than 1.5ppm (even including uncertainty).
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!13
Almost all our CO2 emissions originate from fossil fuels (energy, and flaring which is the burning of waste gases). In 2015, 82% of CO2 emissions originated from fossil fuels,14 rising to 84% in 2016.15
Humanity’s CO2 emissions: (i) are currently trapping two thirds of the energy causing global warming, (ii) are the only rapidly increasing contributor, (iii) solely determine our long term warming commitment, and (iv) continue to grow with no peak in sight. Half of all CO2 ever emitted has been emitted recently and almost all by the world’s energy system.
- p. 5, Hansen, 2018, Climate Change in a Nutshell http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf, accessed 18 December 2018
- Calculation is 2.013 W/m2 / 3.062 W/m2, values from NOAA ESRL
- 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.
- 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
- 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.
- Reprinted from the 2018 Global Carbon Budget
- 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. Data from 2011 to 2017 inclusive: Ed Dlugokencky and Pieter Tans, NOAA/ESRL, https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_data.html
- Fossil fuel combustion and cement production emissions: 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; available at: http://cdiac.ess-dive.lbl.gov/trends/emis/overview_2014.html.
- 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; available at: http://cdiac.ess-dive.lbl.gov/trends/emis/overview_2014.html. Value for 2018 is projection made in 2018 Global Carbon Budget
- Data for 2015 shown in the latest global budget Excel file. See pages named Fossil Emissions by Fuel Type and Land-Use Change Emissions. Calculations are: Total = (9,831 + 1,520) = 11,351 MtC. Fossil fuel plus flaring emissions = (4,006 + 3,346 + 1,899 + 68) / 11,351 = 82%, Cement emissions = 545 / 11,351 = 5%, Land Use Change emissions = 1,520 / 11,351 = 13%
- Data for 2016 shown in the link for the above endnote. Calculations are: Total = (9,875 + 1,270) = 11,145 MtC. Fossil fuel plus flaring emissions = (3,950 + 3,406 + 1,899 + 68) / 11,145 = 84%, Cement emissions = 552 / 11,145 = 5%, Land Use Change emissions = 1,270 / 11,145 = 11%