CO ₂ budget

Emission budget and the necessary paths to reduce emissions in order to meet the two-degree target agreed in the Paris Agreement without negative emissions, depending on the emission peak

The CO ₂ marketing budget , even carbon budget , Carbon budget or emissions budget or -Credit called - in the context of climate policy and global climate protection measures - the amount of CO ₂ emissions from anthropogenic sources, since the beginning of industrialization was released or yet released in order to avoid global warming beyond a defined limit with a certain probability .

In the context of the climate science representation of the carbon cycle, a CO ₂ or carbon budget is understood to mean a carbon balance, i.e. a budgetary listing of the carbon flows from and to carbon stores such as the atmosphere (→ carbon cycle ).

The CO ₂ budget in the sense of a residual amount of greenhouse gases that can still be emitted - sometimes also illustrated as the "remaining atmospheric landfill space " - results from the fact that there is an approximately linear relationship between the total amount of greenhouse gases emitted and the resulting increase in temperature as long as one no tipping point ( Tipping Point ) is the climate system too close. Therefore, for effective climate protection, the cumulative amount of greenhouse gases emitted must be limited. To achieve this, the entire energy industry must be fully decarbonised . The decisive factor for the extent of climate change is not the current emission of greenhouse gases, as is often wrongly assumed, but the total amount of emissions that occur over time. It follows that postponing climate protection to a later point in time will lead to greater climate change. Conversely, with regard to climate protection, this means that for every year delay in the present, all the faster and more far-reaching climate protection measures must be taken.

The Intergovernmental Panel on Climate Change ( IPCC) specifies the remaining global CO ₂ budget in its 2018 special report as 420 gigatons if the 1.5 degree target (with regard to the mean global surface temperature ) is to be achieved with 66% probability. If output remained the same, this budget would be used up in nine to ten years. In 2018 around 42 gigatons of CO _{2 were} emitted worldwide , and the trend is rising.

In climate policy, national carbon budgets and the extent to which they are in line with a global budget are key issues. For Germany, which, as an industrialized country, produces higher per capita emissions than the world average, climate researcher Stefan Rahmstorf determined a remaining budget - based on these figures and a 67% probability of limiting global warming to a maximum of 1.75 degrees in accordance with the Paris Agreement of 9.7 gigatons. Of this remaining budget, which was available at the beginning of 2016, 2.4 gigatons had already been consumed by the beginning of 2019 (around 0.8 gigatons per year), so that at the beginning of 2019 there would still be 7.3 gigatons available. In order to comply with the Paris climate protection agreement, Germany would have to reduce its emissions linearly by 6% every year and achieve zero emissions by 2036. The Advisory Council for Environmental Issues comes to similar values ​​and cites a remaining budget of 6.6 billion tons for 2020 to limit global warming to 1.75 degrees under the same assumptions. With constant emissions at the current level, this budget would have been raised in 2028, with a linear reduction to zero emissions in 2037. In contrast, the climate protection plans drawn up by the federal government in 2019 provide that Germany will release around 7.5 billion tons of carbon dioxide by 2030. This would mean that Germany would exceed the budget mentioned above before 2030, although very advantageous assumptions were made for this budget calculation for Germany.

Starting position

CO ₂ budget, with uncertainties
(according to IPCC SR1.5 , 2018)

Further warming compared to 2006–2015 in ° C 1)	Resulting total warming 2) compared to 1850–1900 in ° C 1)	Remaining CO 2 budget 3) from Jan. 1, 2018, in Gt CO 2
		Percentile (TCR 4 )
		33%	50%	67%
0.3		290	160	80
0.4		530	350	230
0.5		770	530	380
0.53	~ 1.5 ° C	840	580	420
0.6		1010	710	530
0.63		1080	770	570
0.7		1240	900	680
0.78		1440	1040	800
0.8		1480	1080	830
0.9		1720	1260	980
1		1960	1450	1130
1.03	~ 2 ° C	2030	1500	1170
1.1		2200	1630	1280
1.13		2270	1690	1320
1.2		2440	1820	1430
The table should be read as follows: In order to limit further warming to 0.53 ° C with a 67% probability and thus to meet the 1.5 ° C target, a historical temperature increase of 0.97 ° C must not exceed 420 Gt CO 2 are emitted. (The light gray areas are the uncertainty area for the historical temperature rise: If it is not 0.97 ° C, but already 1.1 ° C, there would only be a further warming of 0.4 ° C and a budget of 230 Gt CO 2. ) Certain feedback mechanisms of the climate system were taken into account, others (even less well understood) not.
1) near-ground air temperatures 2) the warming 2006–2015 compared to 1850–1900 is approx. 0.97 ° C 3)without further feedback in the Earth System, which c. the budget by an additional ~ 100 Gt CO 2 decrease 4) transient climate response

In 2014 gave IPCC (English Intergovernmental Panel on Climate Change IPCC, for short) the entire budget with 2,900 gigatons of CO ₂ at when the heating with 66 percent probability to be kept below 2 ° C, which by 2011 already 1,900 Gigatons of CO _{2 were} emitted. If the two-degree target is to be achieved with a probability of more than 50%, between 2011 and 2050 a maximum of between 870 and 1,240 gigatons of carbon dioxide may be released. Converted to the reserves, this means that in the global context, for example, about one-third of the oil reserves , half of natural gas reserves and more than 80 percent of coal reserves should not be consumed.

At the end of 2016, the remaining budget with 66% probability that the two-degree target would be met was, according to various estimates, between 390 and 940 gigatons of CO ₂ (760 gigatons on average) when aiming for the 1.5 ° C target 50% probability between −48 and 167 gigatons (mean 59 gigatons).

Depending on the model, the remaining budget relates to a period up to the middle of the century, after which the IPCC scenarios compensate for the otherwise continuous rise in temperature with negative emission technologies .

CO ₂ versus CO ₂ equivalent

→ Main article : CO2 equivalent

The global warming potential of various greenhouse gases is usually given in CO ₂ equivalents. The IPCC climate model proceeds differently and assumes a certain reduction scenario for the other greenhouse gases such as methane and nitrous oxide . The reason for this is that CO _{2 is} both the most important greenhouse gas in terms of quantity and the fastest and easiest greenhouse gas to reduce. In contrast to many other greenhouse gases, it also remains in the atmosphere for a long time. However, the exact length of stay is difficult to determine: In contrast to the other greenhouse gases, the IPCC does not specify an average length of stay for CO ₂ , but states that a certain proportion (approx. 20%) of the emitted CO ₂ remains in the atmosphere for many thousands of years. According to the Federal Environment Agency, the mean time spent in the atmosphere is around 120 years.

In general, it is assumed in the climate models that emissions from energy generation and industry can be reduced more quickly than emissions from forestry and agriculture.

CO ₂ concentration in the atmosphere

The Keeling curve shows the increase in the carbon dioxide content in the atmosphere, measured on the Mauna Loa

→ Main articles : Carbon cycle  and Keeling curve

When looking at carbon dioxide levels, a distinction must be made between natural and human sources. A lot of carbon dioxide is released through natural processes, for example through the breakdown of biomass , but this is offset by a natural fixation by plants of practically the same size. The natural cycle of matter is thus closed. However, through the burning of fossil fuels and other human interventions such as slash and burn , additional carbon dioxide is released into the atmosphere, which increases its proportion in the atmosphere.

This additional CO ₂ emitted by humans is partially bound, but a good 40% of the previous man-made CO ₂ emissions remain in the atmosphere over the long term, which increases the CO ₂ concentration there and increases the greenhouse effect. The rest is stored in plants and soils as well as in the ocean and thus withdrawn from the atmosphere. The increase in carbon dioxide concentration in the earth's atmosphere only accounts for about 45% of total emissions; 27% each is taken up by oceans and terrestrial ecosystems. These act as carbon sinks . Without this effect, the carbon dioxide concentration of about 280 would ppm (millionths, more precisely, parts per million air particles, english parts per million , abbreviated ppm) before industrialization increased by about 250 ppm to about 530 ppm by 2015, with this effect they actually took but only to around 400 ppm.

In February 2015, it reached a value of 403 millionths, according to the National Oceanic and Atmospheric Administration (NOAA) - the US agency for weather and marine research. Up to a limit of 450 ppm, it is expected that global warming can be limited to two degrees compared to pre-industrial times. At the Mauna Loa measuring station in Hawaii, an annual increase of 3.05 millionths was recorded for the first time in 2015.

Due to the slow degradation processes, the concentration of atmospheric CO _{2 will} continue to increase in the long term, even if emissions are significantly reduced compared to today's level. Scientists from the University of East Anglia expect the climatic impact of CO ₂ to peak ten years after the emission and anticipate an impact of more than 100 years.

Time of zero emission

The United Nations Environment Program (UNEP) recommended in 2015 that a period between 2060 and 2075 should be set by which CO ₂ emissions should “bottom out” to zero. In order to be able to achieve the goal set at the UN climate conference in Paris in 2015 of limiting global warming to 1.5 ° C, the world must reduce net greenhouse gas emissions to zero between 2045 and 2060 and thus pursue very ambitious climate protection. The need for CCS measures , in particular the BEECS technology (biomass combustion with carbon dioxide capture) or increased CO ₂ uptake due to changed land management (e.g. planting forests) during the second half of the century was also pointed out. In addition, the window to achieve this goal closes quickly (as of 2015).

Many calculations do not yet take into account that the permafrost is melting faster than assumed and thereby releasing more greenhouse gases.

The NewClimate Institute, taking into account the decisions made in Paris, specifies the phase-out date as 2035, provided that the removal of carbon dioxide from the atmosphere is to be avoided. There are currently no scenarios that stay below 1.5 degrees and do not take negative emissions into account.

If the 1.5 degree target is to be achieved without using CCS technology , the burning of fossil fuels in Germany must be completely stopped by around 2040 and the energy supply - i.e. H. Completely in this period - electricity, heat and transport renewable energy converted are. A study by the NewClimate Institute mentions, in addition to the significant acceleration of the energy transition, an earlier phase-out of coal-fired power generation by 2025. In this scenario, the world would have to phase out fossil fuels completely by 2035.

According to calculations by the Mercator Research Institute on Global Commons and Climate Change , zero emissions must be implemented in 2035 so that the 2-degree target can still be achieved. In order to achieve the 1.5 ° C target, zero emissions would have to be implemented before 2020. In order to visualize this clearly, a 40-meter-long carbon clock was installed on the gasometer on the EUREF campus in Berlin on September 18, 2019 . It counts down the remaining time.

CO ₂ budget per year and per capita versus reduction path

It is often calculated in how many years the CO ₂ budget would be "used up" under certain assumptions. With unchanged emissions, for example, the carbon budget for the two-degree target would be reduced after 20 to 30 years, i.e. H. between 2035 and 2045. In addition, the global CO ₂ budget is often divided by the world population and the number of years remaining until zero emissions are reached, thus calculating a "permitted" per capita emission of, for example, 2.7 t CO ₂ per year.

The consulting firm PricewaterhouseCoopers ( PWC ) calculates that CO ₂ emissions would have to drop by six percent annually in order to achieve the climate targets. This is an order of magnitude as it was already made binding under international law for the industrialized nations by the Kyoto Protocol , with the difference that the Kyoto targets should be met within 4 years.

In addition, a climate expert from Switzerland suggests defining the budget itself as a path that specifies the extent to which emissions should be reduced over a period of time.

Reduction targets at certain points in time would also not do justice to the facts, said Manfred Sargl from the University of the Federal Armed Forces . The only decisive factor is the sum of the emissions in the years up to the complete CO ₂ phase-out.

Distribution of the remaining CO ₂ budget to countries

For the distribution of the remaining CO ₂ budget among states, as for the determination of national budgets, a large number of methods of burden-sharing or effort-sharing have been proposed.

In the so-called “Regensburg model”, the actual emissions of a country are initially assumed. After that, the system will gradually switch to an equal per capita distribution. The model thus tries to combine justice with political pragmatics, focuses on structural change and avoids structural breaks.

A similar process is described by the terms contraction and convergence , but developing countries are temporarily granted higher emissions until the time of convergence.

Further suggestions rely on other principles:

• Oriented towards the costs, the solution with the lowest costs is sought
• Oriented towards equity - taking into account previous emissions
• oriented towards equity - without taking into account the previous emissions

In July 2016, the European Commission launched a legislative initiative to distribute the common CO ₂ savings targets among the EU countries on the basis of per capita income .

The WBGU recommends setting up an independent, international global climate bank to review the decarbonization roadmaps.

See also : climate justice

Overshoot and negative emissions

→ Main articles : CO2 sink  and negative emission technologies

Most of the climate scenarios that investigate how the two-degree target can be met assume that so-called overshoots will occur during the 21st century. This means that initially more greenhouse gases are emitted than are allowed to achieve the climate targets, but then towards the end of the 21st century carbon dioxide will be removed from the earth's atmosphere again, so that the climate target can be met again by 2100. Therefore, ways are being sought worldwide to fix carbon and thus remove it from the atmosphere.

One of the concepts envisages (wooden) coal or organic waste materials derived biochar not burn, but to mix agricultural soils and so bind for several thousand years. This “coal fertilization” ( terra preta ) also has the advantage that the soil can better retain water and nutrients and that agricultural yields can be improved. The potential to reduce the CO ₂ pollution of the atmosphere through coal fertilization is estimated at almost two billion tons of CO ₂ per year.

Almost all of the IPCC scenarios assume that carbon capture and storage technologies ( CCS ) will be used in the second half of the century . In the 1.5 ° C scenarios, the need to use such technologies is even higher. Relying on negative emissions also harbors major risks. While there is a very good chance that such strategies will be successful. If failure is just as possible, however, there is a risk that future generations will be affected by significant climate impacts, high management costs and unacceptable (target) conflicts. In addition, tipping elements in the earth system can be triggered during the temporarily planned exceeding of the temperature target , which then has permanent consequences. Examples of this are the destabilization of ice sheets , which would lead to a strong and irreversible rise in sea levels, or the release of large amounts of greenhouse gas in the Arctic or the Amazon region, which in turn would increase global warming.

See also

• CO ₂ footprint
• CO ₂ balance
• Fifth assessment report by the IPCC
• Global Atmosphere Watch
• List of major carbon dioxide emitters
• Geoengineering

literature

• Bård Lahn1: A history of the global carbon budget . In: WIREs Climate Change . 2020, doi : 10.1002 / wcc.636 (open access).
• Joeri Rogelj, Piers M. Forster, Elmar Kriegler, Christopher J. Smith, Roland Séférian: Estimating and tracking the remaining carbon budget for stringent climate targets . In: Nature . July 17, 2019, doi : 10.1038 / s41586-019-1368-z (open access).

Individual evidence

1. ↑ Christiana Figueres et al. a .: Three years to safeguard our climate . In: Nature . tape 546 , 2017, p. 593-595 , doi : 10.1038 / 546593a .
2. ↑ ^{a b c} Climate Change 2014 Synthesis Report Summary for Policy Makers , German IPCC Coordination Office, Bonn, 2016
3. ^ Matthias Schaefer: Balance . In: Dictionary of Ecology . Spectrum Academic Publishing House, September 2011.
4. ↑ ^{a b} Valérie Masson-Delmotte u. a .: Annex I: Glossary . In: JBR Matthews et al. a. (Ed.): Global Warming of 1.5 ° C. An IPCC Special Report on the impacts of global warming of 1.5 ° C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty . Keyword “carbon budget” .
5. ↑ Ottmar Edenhofer , Brigitte Knopf and Gunnar Luderer: Global Climate Policy Beyond Harmless Utopias . In: Wirtschaftspolitische Blätter . No. 4 , 2009.
6. ↑ Joeri Rogelj et al .: Paris Agreement climate proposals need a boost to keep warming well below 2 ° C . In: Nature . tape 534 , 2016, p. 631–639 , doi : 10.1038 / nature18307 .
7. ↑ Ottmar Edenhofer , Susanne Kadner, Jan Minx: Is the two-degree target desirable and can it still be achieved? The contribution of science to a political debate. In: Jochem Marotzke , Martin Stratmann (Hrsg.): The future of the climate. New insights, new challenges. A report from the Max Planck Society. Beck, Munich 2015, pp. 69–92, here p. 85.
8. ↑ Peter U. Clark et al .: Consequences of twenty-first-century policy for multi-millennial climate and sea-level change . In: Nature Climate Change . tape 6 , 2016, p. 360-269 , doi : 10.1038 / NCLIMATE2923 .
9. ^ Gregor Hagedorn et al .: The concerns of the young protesters are justified. A statement by Scientists for Future concerning the protests for more climate protection . In: GAIA . tape 28 , no. 2 , 2019, p. 79-87 , doi : 10.14512 / gaia.28.2.3 .
10. ↑ United Nations Environment Program : Emissions Gap Report 2019, p. XV . Retrieved November 26, 2019.
11. ↑ ^{a b} That's how fast the CO2 clock is ticking. Mercator Research Institute on Global Commons and Climate Change , December 2018, accessed November 1, 2019 . 
12. ↑ ^{a b} J. Rogelj , D. Shindell , K. Jiang, S. Fifita, P. Forster, V. Ginzburg, C. Handa, H. Kheshgi, S. Kobayashi, E. Kriegler, L. Mundaca, R. Séférian , and MV Vilariño: 2018: Mitigation Pathways Compatible with 1.5 ° C in the Context of Sustainable Development . In: Valérie Masson-Delmotte u. a. (Ed.): Global Warming of 1.5 ° C. An IPCC Special Report on the impacts of global warming of 1.5 ° C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty . 2018, 2.2.2 The Remaining 1.5 ° C Carbon Budget, p. 108 .
13. ↑ How much carbon dioxide is there left in Germany? . In: Spektrum.de , April 2, 2019. Retrieved April 3, 2019.
14. ↑ For the implementation of ambitious climate policy and climate protection measures . Open letter from the Advisory Council on Environmental Issues . Retrieved September 16, 2019.
15. ↑ A billion tons too much . In: taz , November 20, 2019. Retrieved November 20, 2019.
16. ↑ Christophe McGlade, Paul Ekins: The geographical distribution of fossil fuels unused When limiting global warming to 2 ° C . In: Nature . tape 517 , 2015, p. 187–190 , doi : 10.1038 / nature14016 (English).
17. ↑ Vicki Duscha, Alexandra Denishchenkova, Jakob Wachsmuth: Achievability of the Paris Agreement targets in the EU: demand-side reduction potentials in a carbon budget perspective . In: Climate Policy . May 25, 2018, doi : 10.1080 / 14693062.2018.1471385 (English).
18. ↑ Estimates of the remaining CO2 budget hide the challenges in climate policy , among others by Wilfried Rickels, Kiel Institute for the World Economy , November 2018
19. ↑ ^{a b} The CO ₂ budget , klima-retten.info, undated
20. ↑ ^{a b c d} The CO ₂ budget , klima-retten.info, accessed on July 19, 2016
21. ↑ ^{a b} Question 10.3: If greenhouse gas emissions are reduced, how quickly do their concentrations in the atmosphere decrease? ( Memento of July 19, 2016 in the Internet Archive ), German IPCC Coordination Office, accessed on July 19, 2016
22. ^ The greenhouse gases , Federal Environment Agency (UBA), January 15, 2016
23. ↑ ^{a b c d e} What does the Paris Agreement mean for climate protection in Germany? , by Niklas Höhne, Takeshi Kuramochi, Sebastian Sterl and Lina Röschel, NewClimate Institute for Climate Policy and Global Sustainability, Ed .: Greenpeace, February 2016
24. ↑ Hermann-Josef Wagner , What are the energies of the 21st century? , Frankfurt am Main 2011, p. 180.
25. ↑ Markus Reichstein: Universally and Everywhere. The terrestrial carbon cycle in the climate system. In: Jochem Marotzke , Martin Stratmann (Hrsg.): The future of the climate. New insights, new challenges. A report from the Max Planck Society. Beck, Munich 2015, ISBN 978-3-406-66968-2 , pp. 123-136, especially p. 127.
26. ↑ ^{a b} 2015 brings record for CO ₂ -increase ( Memento of 29 March 2016 Internet Archive ), business daily, March 22, 2016
27. ↑ Annual Mean Growth Rate for Mauna Loa, Hawaii , Earth System Research Laboratory, July 2016
28. ↑ CO2 emissions could fall slightly for the first time in 2015 , scinexx.de, December 8, 2015
29. ↑ Emissions Gap Report 2015 - Executive Summary , UNEP, 2015
30. ↑ Launch of UNEP Emissions Gap Report Executive Summary , UNEP, November 6, 2015
31. ↑ Joeri Rogelj et al .: Energy system transformations for limiting end-of-century warming to below 1.5 ° C . In: Nature Climate Change . tape 5 , 2015, p. 519-527 , doi : 10.1038 / NCLIMATE2572 (English).
32. ↑ Christian Mihatsch: In 2050, climate neutrality will be two decades too late. In: Klimareporter. August 17, 2019, accessed on August 20, 2019 (German). 
33. ^ Robert McSweeney: Permafrost and wetland emissions could cut 1.5C carbon budget 'by five years'. In: CarbonBrief. July 9, 2018, accessed September 11, 2019 . 
34. ↑ Volker Quaschning : Sector coupling through the energy transition. Requirements for the expansion of renewable energies to achieve the Paris climate protection targets, taking into account sector coupling . Berlin University of Applied Sciences , June 20, 2016. Accessed July 21, 2016.
35. ↑ CO₂ budget may already have been used up , klimaretter.info , January 11, 2017
36. ↑ That's how fast the carbon clock is ticking , Mercator Research Institute on Global Commons and Climate Change
37. ↑ 40-meter CO2 clock high above Berlin. Retrieved September 24, 2019 (German). 
38. ↑ ^{a b c} The WBGU budget approach , Scientific Advisory Board of the Federal Government on Global Change (WBGU), 2009
39. ↑ Ottmar Edenhofer , Susanne Kadner, Jan Minx: Is the two-degree target desirable and can it still be achieved? The contribution of science to a political debate. In: Jochem Marotzke , Martin Stratmann (Hrsg.): The future of the climate. New insights, new challenges. A report from the Max Planck Society. Beck, Munich 2015, pp. 69–92, here p. 78.
40. ↑ ^{a b} Earth's CO ₂ budget soon to be exhausted , global °, Magazine for Sustainable Future, undated
41. ↑ Climate protection: CO ₂ budget for 2-degree target already exhausted in 2034 instead of 2100? , Institute of the Renewable Energy Industry (IWR), November 6, 2013
42. ↑ The electricity system of the future is renewable and flexible , Meteo Zurich, June 20, 2016
43. ^ The Regensburg Mode , climate calculator
44. ↑ Cf. Ottmar Edenhofer , Susanne Kadner, Jan Minx: Is the two-degree target desirable and can it still be achieved? The contribution of science to a political debate. In: Jochem Marotzke , Martin Stratmann (Hrsg.): The future of the climate. New insights, new challenges. A report from the Max Planck Society. Beck, Munich 2015, pp. 69-92, especially pp. 79f.
45. ↑ CO ₂ filter: A net for greenhouse gas , by Ralph Diermann, Spiegel-online, January 10, 2016
46. ↑ The two-degree goal is only "negative" , Klimaretter.info, November 21, 2015
47. ↑ "Negative CO2 emissions" are possible , Science-orf.at, February 19, 2013
48. ↑ What happens after the Paris Agreement? Opportunities and potential risks , by Barbara Unmüßig, Heinrich Böll Foundation, April 21, 2016
49. ^ Government: No concept for 1.5 degrees , by Benjamin von Brackel and Sandra Kirchner, Klimaretter.info, February 23, 2016
50. ↑ Christopher B. Field , Katharine J. Mach: Rightsizing carbon dioxide removal. Betting the future on planetary-scale carbon dioxide removal from the atmosphere is risky . In: Science . tape 356 , no. 6339 , 2017, p. 706 f ., doi : 10.1126 / science.aam9726 .