Categories
Climate Crisis

Greenhouse Gas Emissions

To help explain how greenhouse gases heat the planet, physicist John Tyndall used a dam as an analogy:1 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. In the same manner, the sun’s energy continually enters Earth’s atmosphere and because humanity has increased the concentration of greenhouse gases, the atmosphere now traps more heat. This warming will continue until the atmosphere again returns to space the same amount of energy arriving from the sun.

The quantity of energy trapped by greenhouse gases is known as radiative forcing, with units of Watts per square metre (W/m2). This is a measure of the contribution to global warming from each greenhouse gas, and radiative forcing due to anthropogenic emissions shown in chart 1. Two thirds of total radiative forcing in 2019, relative to year 1750, was due to carbon dioxide (CO2).2

Chart 1(a). Annual radiative forcing of anthropogenic greenhouse gases relative to year 1750. Data: NOAA ESRL.3 4 Chart 1(b). Stacked version of (a). The values shown in the charts exclude modelled climate feedbacks as explained by the IPCC: ‘Forcing can also be attributed to emissions rather than to the resulting concentration changes. Carbon dioxide is the largest single contributor to historical RF from either the perspective of changes in the atmospheric concentration of CO₂ or the impact of changes in net emissions of CO₂. The relative importance of other forcing agents can vary markedly with the perspective chosen, however. In particular, CH4 emissions have a much larger forcing (about 1.0 W/m² over the Industrial Era) than CH4 concentration increases (about 0.5W/m²) due to several indirect effects through atmospheric chemistry.'5

Radiative forcing of greenhouse gases is partially reduced by that from cooling aerosols, and global warming is caused by the net amount.6

Chart 2 shows the annual change of radiative forcing by each greenhouse gas.

Chart 2. Annual change of radiative forcing by greenhouse gas, 1980-2019. Data: NOAA ESRL3

Chart 3 shows the same data as chart 2, but by share. The share of annual change caused by civilisation’s CO2 has been greater than 70% for every year since 1993, and reached 90% or more in 2003, 2005 and 2013.

Chart 3. Annual change of radiative forcing by greenhouse gas, as share of total annual change, 1980-2019. Data: NOAA ESRL.3

Our long term warming commitment is almost solely determined by cumulative CO2 emissions (nitrous oxide (N2O)7 is also a long-lived greenhouse gas that contributes to our warming commitment, but as shown in chart 1(a) above, it’s contribution is much smaller than that from CO2).

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.8

Chart 4 shows the temperature response to a 1 year pulse of emissions, using 2008 emissions as an example. Chart 5 shows the temperature response to sustained emissions, using 2011 emissions as an example.

Chart 4. Temperature response to a 1 year pulse of our emissions from 2008.9
Chart 5. Temperature response to sustained 2011 emissions. Carbon dioxide (red), methane (blue), organic and black carbon (black), nitrous oxide (green) and HFC-152a (pink).10

Allen et al. (2016) explains below that to stabilise global temperatures, net emissions of the long lived greenhouse gases (GHGs or ‘climate pollutants’) must be reduced to zero. These GHGs determine our warming commitment because their impact is cumulative.

The warming impact of the cumulative pollutants, CO2 and nitrous oxide, increases steadily as long as these emissions persist, whereas sustained emissions of methane and organic and black carbon aerosols cause temperatures to warm rapidly at first, and then stabilize. A permanent reduction of 50–75% in these SLCPs (short lived climate pollutants) could reduce global temperatures by over 0.5˚C by mid-century, comparable to the impact on these timescales of similar-magnitude reductions of CO2 emissions and, it has been argued, at much lower cost. Stabilizing global temperatures, however, requires net emissions of cumulative pollutants, predominantly CO2, to be reduced to zero.

Allen, M., Fuglestvedt, J., Shine, K. et al. New use of global warming potentials to compare cumulative and short-lived climate pollutants.10

After 500 years, about a third of a CO2 emission pulse remains in the atmosphere.11

Half of cumulative CO2 (i.e all emitted from preindustrial year 1750 to the end of 2018) has been emitted in just the previous 37 years, as shown below. A third has been emitted in the past 22 years and a quarter in the last 15 years. In 2018 alone, 2% was emitted.12 13 14

Chart 6. Proportion of total CO2 historically emitted over the period 1750 – 2019.14 15

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: @neilrkaye16

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.”17

Consequently, the atmospheric concentration of CO2 has increased, as shown in chart 8(a). The steep change of growth began in 1955. Chart 8(b) shows that for every year since 2001, the atmospheric concentration of CO2 has increased by more than 1.5ppm, as indicated by the columns that exceed the black line. The largest annual increase was in 2015.

Chart 8(a). Annual global mean CO2 concentration in units of parts per million (ppm). Data: IPCC and NOAA ESRL.18 Chart 8(b). Annual global mean CO2 growth rate. Data: NOAA ESRL.19 For clarity, values shown are rounded to one decimal place.

Our emissions of CO2 originate from three sectors: energy (i.e. fossil fuel combustion), cement manufacture and land-use change. Charts 9 and 10 show that fossil fuel emissions obviously dominate.

Chart 9(a). 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 2018. Chart 9(b). As per (a) but showing seperate contributors. Data: Global Carbon Project (2019).20

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, 2016, Anthropogenic carbon release rate unprecedented during the past 66 million years.21
Chart 10. World CO2 emissions, 1959-2019 (1959-2018 for Land use Change). Data: Global Carbon Project (2019).20 Projected values shown for year 2019, shown in the Global Carbon Project’s Budget 2019 presentation.22

CO2 emissions in 2018 from all sources are shown below. In 2017 and 2018, 83% of CO2 emissions originated from fossil fuels and flaring (the burning of waste gases).20 23

Chart 11. CO2 emissions from all sectors in 2018. Data: Global Carbon Project (2019).20
Note that the share of CO2 emissions shown from cement is that from clinker production which is the main constituent of cement. This process requires a large amount of heat that’s currently generated using fossil fuels. The resulting CO2 emissions from heat generation are a similar quantity to that from clinker production, and therefore total global cement industry CO2 emissions are about an 8% share.

Global emissions from fossil fuels and cement are projected to reach a historic high in 2019 of 36.8 GtCO2,22 as shown in chart 12 below.

Chart 12. World fossil fuel and cement CO2 emissions, 1959 – 2019. Data: Global Carbon Project (2019).20 Projected values used for year 2019, shown in the Global Carbon Project’s Budget 2019 presentation.22

Global fossil CO₂ emissions have risen steadily over the last decades & show no sign of peaking.

Global Carbon Project (2019) Global Carbon Budget.22

Although the recent acceleration of global emissions from fossil fuels and cement has ceased (based on the projected 2019 value of CO₂ emissions), the annual change is still an increase of +0.5% relative to 2018, as shown below.

Chart 13. Annual change of world CO2 emissions from fossil fuel and cement, 2000-2019. Percentage values are current year emissions relative to those from previous year. Data: Global Carbon Project (2019).20 Projected values used for year 2019, shown in the Global Carbon Project’s Budget 2019 presentation.22

Summary

Our CO2 emissions: (i) are trapping two thirds of the energy causing global warming; (ii) are the only rapidly increasing contributor; (iii) almost solely determine our long term warming 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. The present anthropogenic carbon release rate is unprecedented during the past 66 million years. 

  1. p. 5, Hansen, 2018, Climate Change in a Nutshell http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf, accessed 18 December 2018()
  2. 2.076 W/m2 / 3.1410 W/m2, https://www.esrl.noaa.gov/gmd/aggi/aggi.html()
  3. https://www.esrl.noaa.gov/gmd/aggi/aggi.html()()()
  4. 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()
  5. p. 56, Technical Summary, IPCC AR5, WG1, Stocker, T.F., D. Qin, G.-K. Plattner, L.V. Alexander, S.K. Allen, N.L. Bindoff, F.-M. Bréon, J.A. Church, U. Cubasch, S. Emori, P. Forster, P. Friedlingstein, N. Gillett, J.M. Gregory, D.L. Hartmann, E. Jansen, B. Kirtman, R. Knutti, K. Krishna Kumar, P. Lemke, J. Marotzke, V. Masson-Delmotte, G.A. Meehl, I.I. Mokhov, S. Piao, V. Ramaswamy, D. Randall, M. Rhein, M. Rojas, C. Sabine, D. Shindell, L.D. Talley, D.G. Vaughan and S.-P. Xie, 2013: Technical Sum- mary. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assess- ment 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/()
  6. p. 13, Climate Change in a Nutshell: The Gathering Storm, 18 Dec 2018. http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf()
  7. https://en.wikipedia.org/wiki/Nitrous_oxide()
  8. 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.()
  9. 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/.()
  10. Allen, M., Fuglestvedt, J., Shine, K. et al. New use of global warming potentials to compare cumulative and short-lived climate pollutants. Nature Clim Change 6, 773–776 (2016), https://www.nature.com/articles/nclimate2998, http://sequoiaforestkeeper.org/pdfs/attachments/Allen_et_al_on_SLCP_GWP_2016.pdf()()
  11. 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.()
  12. Value for 2019: projection for fossil fuel and flaring emissions = 36.8GtCO2 from https://www.globalcarbonproject.org/carbonbudget/19/presentation.htm. 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%.()
  13. Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project. https://doi.org/10.18160/gcp-2019. Download available at https://www.icos-cp.eu/GCP/2019, labelled ‘2019 Global Budget v1.0’.()
  14. Value for 2019 is projection made in https://www.globalcarbonproject.org/carbonbudget/19/presentation.htm()()
  15. Emissions from fossil fuel combustion and cement production: Global Carbon Project. (2019). Supplemental data of Global Carbon Budget 2019 (Version 1.0) [Data set]. Global Carbon Project. https://doi.org/10.18160/gcp-2019. Download available at https://www.icos-cp.eu/GCP/2019, labelled ‘2019 Global Budget v1.0’.()
  16. What percentage of all global fossil fuel CO₂ emissions since 1751 have occurred in my lifetime? @neilrkaye,Climate data scientist at UK Met Office.()
  17. 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()
  18. Data from 1850 to 1980 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 1981 to 2019 inclusive: Ed Dlugokencky and Pieter Tans, NOAA/ESRL, https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_data.html()
  19. Ed Dlugokencky and Pieter Tans, NOAA/ESRL, https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_data.html()
  20. 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’.()()()()()()
  21. 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()
  22. https://www.globalcarbonproject.org/carbonbudget/19/files/GCP_CarbonBudget_2019.pdf()()()()()
  23. Calculations: (1) 2017: Total emissions = fossil and cement emissions + land-use change emissions = 35.84 + 5.39 = 41.23 GtCO₂. Fossil fuel plus flaring emissions = (14.49 + 12.28 + 7.11 + 0.34) / 41.23 = 83%. (2) 2018: Total emissions = fossil and cement emissions + land-use change emissions = 36.60 + 5.53 = 42.13 GtCO₂. Fossil fuel plus flaring emissions = (14.69 + 12.43 + 7.49 + 0.34)/42.13 = 83%.()
Categories
Climate Crisis

Summary

Our Greatest Threat

Sea-level rise figures prominently among the consequences of climate change. It impacts settlements and ecosystems both through permanent inundation of the lowest-lying areas and by increasing the frequency and/or severity of storm surge over a much larger region.

Kopp et al. Probabilistic 21st and 22nd century sea-level projections at a global network of tidegauge sites.1

The impacts of multi-metre sea level rise would be irreversible and may leave global civilisation ungovernable.2 The world’s coastal cities and ports would be permanently flooded, devastating high population areas, international trade and finance. Shown below is land area in 2050 projected to be below annual flood level, due to 26cm sea level rise relative to year 2000.

In the past, Earth’s climate has alternated between ice ages and warm periods. Civilisation developed during the most recent warm period, known as the Holocene, that lasted 11,700 years. The prior warm period, known as the Eemian, occurred between 130,000 to 115,000 years ago.7 The best estimate of the maximum temperature of the Eemian, relative to preindustrial time, is between +0.5℃ and +1.0℃.7 The global surface temperature averaged over 2014–2018 wrt 1850-1900 was +1.04℃ according to the WMO,8 and in 2019 wrt 1880-1920 was +1.2˚C according to NASA GISS (Goddard Institute for Space Studies) global temperature analysis (GISTEMP).9 Temperature data of the Holocene (smoothed over centennial time periods) does not exceed +0.5℃.

We conclude that the modern trend line of global temperature crossed the early Holocene (smoothed) temperature maximum (+0.5℃) in about 1985.

Hansen et al. (2017), Young people’s burden: requirement of negative CO2 emissions.10

Therefore we have warmed our climate beyond the temperature range of the Holocene, and are about to warm it beyond that of the Eemian.

During the Eemian, seas were 6 to 9 metres (20 to 30 feet) higher than today, indicating that multi-metre sea level rise will be a consequence of global warming beyond 1.0˚C. This would result from the collapse of Earth’s ice sheets, of which there are three – the Greenland, West Antarctic and East Antarctic ice sheets. Therefore the principal question is not how much sea level rise, but how fast?

The Holocene, over 11,700 years in duration, had relatively stable climate, prior to the remarkable warming in the past half century. The Eemian, which lasted from about 130,000 to 115,000 years ago, was moderately warmer than the Holocene and experienced sea level rise to heights 6–9 m (20–30 ft) greater than today.

Hansen et al. (2017), Young people’s burden: requirement of negative CO2 emissions.10

Our GHG Emissions

Cumulative quantities of long lived greenhouse gases (GHGs) solely determine our long-term warming commitment, simply because of their long lifetimes in the atmosphere11 and they can’t be removed and sequestered at necessary scale. Cumulative carbon dioxide (CO2) is almost the singular cause, and is increasing rapidly12 13 (nitrous oxide (N2O) is the only other significant contributor but only accountable for about one tenth that of CO2, and changing slowly).

Half of all anthropogenic CO2 emissions have been emitted in the last 40 years and almost all (83%) by the world’s energy system.14 The most rapid increase of CO2 was emitted during 2015, second fastest 2016, and 2018 tied with 1998 as the third fastest.14 15

The trend of global average atmospheric CO2 concentration now exceeds 410 ppm.16

In the mid-Pliocene, 3–5 million years ago, the last time that the Earth’s atmosphere contained 400 ppm of CO2, global mean surface temperature was 2–3℃ warmer than today, the Greenland and West Antarctic ice sheets melted and even some of the East Antarctic ice was lost, leading to sea levels that were 10–20m higher than they are today.

WMO, 2017, State of the Global Climate in 2017.17

The progress of international climate negotiations has been astonishingly slow, and the process ineffective. In 2020, 5 years since the Paris Agreement, 26 years since the UNFCCC came into force, 32 years since the formation of the IPCC, and 40 years since the first joint scientific meeting about atmospheric CO2, annual CO2 emissions from fossil fuels and industry have soared. Between the first joint scientific meeting in 1980, and 2019, CO2 emissions from fossil fuels and industry increased 90%, and increased 57% since COP1 in 1995.18 19 To make matters worse: (i) as explained above, limiting warming to 1.5℃ (the goal of the Paris Agreement) is not safe because when earth was last warmed 1.5℃, seas were 6 to 9m (20 to 30ft) higher; (ii) the scale of emission reductions prescribed are beyond any historic precedent;20 (iii) prescribed emission reductions depend on concurrent massive CO2 removal;21 (iv) the annual increase of CO2 emissions is near record rate;22 (v) 1.5℃ is imminent;23 and (vi) carbon offsetting is spurious.24

Charts 1 and 2 show we are still carbonising.

Chart 1. World fossil fuel and cement CO2 emissions, 1959 – 2019. Data: Global Carbon Project (2019).25 Projected values shown for year 2019, copied from the Global Carbon Project’s Budget 2019 presentation.26
Chart 2. World CO2 emissions, 1959-2019 (1959-2018 for Land use Change). Data: Global Carbon Project (2019).25 Projected values shown for year 2019, copied from the Global Carbon Project’s Budget 2019 presentation.26

Chart 3 shows that ‘every year energy use increases, & most of the increases come from fossil fuels.’27

Chart 3. Annual change of world energy supply, 2000 to 2018. Data: BP(2019).28 Note: (i) BP’s definition of Renewables is energy supplied by Solar, Wind, Geothermal, Solid Biofuels & ‘Other’; and (ii) BP does not fully account for biofuels; and (iii) Solid biofuels may not be carbon-neutral.29 From https://www.worldenergydata.org/world/.

What To Do?

Two prominent efforts have pursued solutions: the UN’s climate treaty relying on the science of the IPCC (explained in 1.5˚C) and the efforts of Dr James Hansen30 (explained in 350 ppm). The most important finding of both is that it’s too late for decarbonisaton alone, and now ‘negative emission technologies’ (NETs), also known as ‘carbon dioxide removal’ (CDR) methods, are also required (this includes measures to increase natural carbon sinks such as reforestation).

Negative emissions are a burden being imposed on young people.

Hansen, Young people’s burden: requirement of negative CO2 emissions.31

To stabilise temperature, CO2 emissions need to be made net-zero as shown below. This can only be achieved by rapidly reducing CO2 emissions (i.e. decarbonising) to the lowest level possible, and by using negative emissions. The faster emissions are reduced, the smaller the negative emissions burden.

Net zero emissions concept. IPCC(2018), ‘Understanding the IPCC Special Report on 1.5°C’.32

The scale of the decarbonisation challenge to meet the Paris Agreement is underplayed in the public arena. It will require precipitous emissions reductions within 40 years and a new carbon sink on the scale of the ocean sink. Even then, the world is extremely likely to overshoot. A catastrophic failure of policy, for example, waiting another decade for transformative policy and full commitments to fossil-free economies, will have irreversible and deleterious repercussions for humanity’s remaining time on Earth. Only a global zero carbon roadmap will put the world on a course to phase-out greenhouse gas emissions and create the essential carbon sinks for Earth-system stability, without which, world prosperity is not possible.

Rockström, J. et al. (2016), The world’s biggest gamble.33

The IPCC’s 1.5℃ pathways demand that CO2 emissions are roughly halved by 2030,34 and over the next 30 years negative emissions are ramped up so that by 2050, an amount of CO2 will have been removed from the atmosphere equivalent to that removed by the world’s ocean over a period of 15 years (about 150GtCO2). By this time, these negative emissions will need to be so vast that that the total annual removal of CO2 will be equivalent to that annually removed by the global ocean.21 These pathways have only a 50% to 66% chance of success35 and large uncertainties remain concerning the feasibility and impact of large-scale deployment of negative emission technologies.36

Dr James Hansen30 prescribes changes needed to reduce atmospheric CO2 to less than 350 ppm, in order to limit global temperature close to the Holocene range of +1℃ maximum. CO2 emissions must be reduced by one third by 2030 and the negative emissions burden is the same as that prescribed by the IPCC above.37 Despite decarbonisation being slower than in the IPCC’s 1.5˚C pathways, Hansen’s modelling results in warming being limited to less than +1°C, hopefully averting multi-metre sea level rise.

What Time Remains?

Cumulative CO2 solely determines our long-term warming commitment, and the less CO2 emitted, the smaller the future burden of negative emissions.

The remaining carbon budget from 2018 onwards is 580GtCO2 for a 50% chance of keeping warming below 1.5C. This is less than 15 years of global emissions at current rates.38

So, what does that mean?

This means that if we start reducing emissions steeply now and by the time we reach net-zero levels we have not emitted more than 580GtCO2, our best scientific understanding tells us have we expect a one-in-two chance that warming would be kept to 1.5C.

Moreover, if we want to be sure that this is also true until the end of the century, we’d have to aim to emit only 480GtCO2 until we reach net-zero instead. This is under 12 years of current emissions.

‘A new approach for understanding the remaining carbon budget’, Dr Joeri Rogelj, Prof Piers Forster, CarbonBrief 2019.39

The remaining carbon budgets from 2020 onwards are listed below in table 1, calculated by subtracting the annual emissions of years 2018 and 2019 (shown in the supporting information below), away from the IPCC’s budgets shown in table 3. Also shown are the same remaining budgets with 50% of total uncertainties applied in either direction (50% was chosen because it would be unlikely for all uncertainties to align at an extremity). Note that 50th percentile of climate sensitivity refers to the most likely value.

Table 1. Remaining carbon budgets from 2020 onwards.

Table 1 shows the IPCC’s remaining carbon budget for 1.5˚C may be spent in 12 years at the current rate of emissions, but if 50% of total uncertainties are applied in either direction, the same budget is spent sometime in the next 2 to 23 years. The usefulness of IPCC budgets is questionable because associated with each budget are very large uncertainties and warming that will trigger rapid and large sea level rise. The exceedance of any budget doesn’t herald the end of our chance to limit and reduce warming. Instead it should be a very loud alarm that reminds us our greenhouse gas emissions remain dangerously excessive and unmanaged.

Sadly, the world’s energy system remains intensively fossil fuelled,40 ‘every year energy use increases, & most of the increases come from fossil fuels’,27 emission offsets are spurious to avoid adequate action now, and there is no time left for half-measures; ‘winning slowly is the same as losing.'41

Supporting information –
Table 2. Supporting information for table 1.
Table 3. IPCC remaining carbon budgets from 2018 onwards.42
  1. Kopp, R. E., R. M. Horton, C. M. Little, J. X. Mitrovica, M. Oppenheimer, D. J. Rasmussen, B. H. Strauss, and C. Tebaldi (2014), Probabilistic 21st and 22nd century sea-level projections at a global network of tide-gauge sites, Earth’s Future, 2, 383–406, doi:10.1002/2014EF000239, https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014EF000239()()
  2. section titled ‘Sea Level Rise’, https://www.worldenergydata.org/existential-threat-pt1/()
  3. https://coastal.climatecentral.org()
  4. https://link.springer.com/article/10.1007/s10584-011-0151-4()
  5. table 2,1. p. 60, AR5 Synthesis Report – Climate Change 2014
    IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp., https://www.ipcc.ch/report/ar5/syr/()
  6. https://tntcat.iiasa.ac.at/RcpDb/dsd?Action=htmlpage&page=compare()
  7. Hansen, J., Sato, M., Kharecha, P., von Schuckmann, K., Beerling, D. J., Cao, J., Marcott, S., Masson-Delmotte, V., Prather, M. J., Rohling, E. J., Shakun, J., Smith, P., Lacis, A., Russell, G., and Ruedy, R.: Young people’s burden: requirement of negative CO2 emissions, Earth Syst. Dynam., 8, 577-616, https://doi.org/10.5194/esd-8-577-2017, 2017()()
  8. p6, https://library.wmo.int/doc_num.php?explnum_id=5789()
  9. Global Temperature in 2019, http://www.columbia.edu/~jeh1/mailings/2020/20200115_Temperature2019.pdf()
  10. p 581, Hansen, J., Sato, M., Kharecha, P., von Schuckmann, K., Beerling, D. J., Cao, J., Marcott, S., Masson-Delmotte, V., Prather, M. J., Rohling, E. J., Shakun, J., Smith, P., Lacis, A., Russell, G., and Ruedy, R.: Young people’s burden: requirement of negative CO2 emissions, Earth Syst. Dynam., 8, 577-616, https://doi.org/10.5194/esd-8-577-2017, 2017()()
  11. chart 4, https://www.worldenergydata.org/ghgs/()
  12. 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 proportionality of global warming.pdf()
  13. charts 1 and 3, https://www.worldenergydata.org/ghgs/()
  14. https://www.worldenergydata.org/ghgs/()()
  15. https://www.esrl.noaa.gov/gmd/ccgg/trends/gl_gr.html()
  16. Black trend line at https://www.esrl.noaa.gov/gmd/ccgg/trends/global.html, accessed 22 Jan 2020.()
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  18. CO2 emissions from fossil fuel combustion and cement: (i) in 1980 = 19.4GtCO2; (ii) in 1995 = 23.39GtCO2; and (iii) in 2019 = 36.8GtCO2. 2019 with respect to 1980 = 36.8/19.4 = +90%, and 2019 with respect to 1995 = 36.8/23.39 = +57%()
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  22. chart 7, https://www.worldenergydata.org/ghgs/()
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