Two degree goal

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Necessary emission paths to meet the two-degree target agreed in the Paris Agreement without negative emissions , depending on the emission peak
Development of temperatures on land and at sea 1880–2017 relative to the mean value from 1951–1980

The two-degree target describes the aim of the international climate policy that global warming to less than two degrees Celsius by the year 2100 compared to the level before the beginning of industrialization limit. The goal is a political determination based on scientific knowledge about the likely consequences of global warming . In many cases it is suggested to speak of a “two-degree limit”, which should not be exceeded. At the same time, the two-degree target is criticized for being insufficient, since even two degrees of global warming will have serious consequences for people and the environment, such as a. fromIPCC special report on 1.5 ° C global warming was documented.

background

history

Drill core data from the last 5 million years show that the global mean temperatures fluctuated strongly during this time; During this time, however, they were never more than two degrees higher than at the reference point in 1950
The burning embers graphic, here based on the IPCC report from 2014, is an illustration of the increasing risks with rising temperatures, often shown in connection with the two-degree target.

The two-degree target was first formulated by the economist William D. Nordhaus in 1975 and 1977. He argued that limiting global warming should be based on the amplitude of natural climate fluctuations. A temperature increase of 2 or 3 ° C compared to the current, already comparatively high level would bring the climate into a range that would not have existed for several hundred thousand years. However, Nordhaus did not introduce the two-degree limit as a value-based goal of a future climate policy, but used it as a conceptual basis for cost-benefit analyzes based on it.

In its report published in 1990 , an advisory group called the Advisory Group on Greenhouse Gases (AGGG), set up in July 1988 by the World Meteorological Organization , the International Council of Science and the United Nations Environment Program , recommended that global surface temperature be used as an indicator for climate policy. She saw a temperature rise of 1 ° C as hardly avoidable, beyond 2 ° C (at 400-560 ppm CO 2 ) she feared a rapid increase in serious risks for ecosystems and non-linear reactions.

The United Nations Framework Convention on Climate Change , adopted in 1992, contained the goal of avoiding “dangerous” climate change without, however, defining a specific limit. The submitted since 1990 scientific reports of the IPCC IPCC went from 2001 to five "reasons for concern" ( Reasons for concern ) one by which, readers themselves should make a judgment what changes were assessed as dangerous. You illustrated these reasons for concern with the graphic burning embers (German for example: Brennende Glut ) in the third assessment reportwhich was re-published in 2009 and 2014 in a revised form. The reports, however, avoided expressly defining the “dangerous” boundary.

The German Advisory Council on Global Change (WBGU) made a major contribution to bringing the two-degree limit into the political process. The WBGU endorsed the limit in an expert opinion in 1995, whereupon it was adopted by politicians and made the goal of European climate protection policy. Basis of the WBGU was also the assumption that when exceeding the two-degree limit tipping points ( tipping points ) would be achieved, would intentionally involve the other, non-linear, irreversible and hardly predictable consequences in their consequences.

Initially, the German federal government and later the European Union and, in December 2010, the 194 member states of the United Nations Framework Convention on Climate Change (UNFCCC) for the first time committed themselves to this goal. Indigenous peoples and especially island states consider the two-degree target to be insufficiently ambitious and pleaded in international negotiations for lowering the limit to a maximum of 1.5 degrees; In 2015, the UNFCCC states agreed in the Paris Agreement to make “efforts” to comply with this limit.

In October 2018, the United Nations Intergovernmental Panel on Climate Change (IPCC) published a special report on the implementation of the 1.5 degree target on the occasion of its 48th meeting, which took place in Incheon (South Korea) . Scientists are pushing for quick changes in it to limit warming. To achieve the 1.5-degree target, "rapid, far-reaching and unprecedented changes in all areas of society" are required. According to the report, these include changes in energy systems, agriculture and transport routes. The climate protection goals currently being pursued by the individual states up to 2030 would lead to a warming of 3 degrees by 2100, which would then increase further.

Consequences of global warming of two degrees or more

The graphic shows that there is no sharp line between “tolerable” and “dangerous” climate change . Hans Joachim Schellnhuber , emeritus director of the Potsdam Institute for Climate Impact Research , said in an interview in August 2010: "And of course the end of the world does not come at 2.01 degrees, especially not suddenly." Instead, it should be seen more as a landmark, beyond which the uncertainties and thus the risks associated with climate change increase significantly and the consequences of climate change threaten to become uncontrollable for some or even many societies. If the two-degree target could be met, the consequences of global warming would be numerousat best mitigated, but not averted. The melting of the glaciers would not be stopped, as would the rise in sea ​​levels . This would continue to run for hundreds of years even after a complete emission freeze.

With global warming of 2 ° C, significantly higher average temperatures are expected over the Arctic , with corresponding consequences for the region . Against this background, some climate researchers point out that 2 ° C is more the boundary between “dangerous” and “very dangerous” climate change than between “tolerable” and “dangerous”. Limiting warming to 1.5 ° C instead of 2 ° C would reduce the probability of the Arctic being free of ice in summer from 100% to 30% by 2100.

A study published in Nature in 2018 came to the conclusion that a global warming of 2 degrees the economic damage would be probably more than 20 trillion US dollars higher than a global warming of 1.5 degrees. According to this, the additional costs to achieve the 1.5 degree target are put at around 300 billion dollars, so that the benefit-cost ratio in limiting global warming to 1.5 degrees instead of 2 degrees is around 70. Significantly greater economic damage would result without stringent climate protection measures. Global warming of 2.5–3 degrees by 2100 could lead to additional economic damage amounting to 15–25% of the per capita gross world product , or more than 30% at 4 degrees.

Political fixing

The two-degree target is the political definition of the principle laid down in Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC), according to which "dangerous anthropogenic disturbance of the climate system" is to be prevented. The Framework Convention on Climate Change, adopted in 1992, does not contain any precise information on when climate change should be classified as "dangerous". The international community has made up for this with the two-degree target, which was officially recognized for the first time at the UN climate conference in Cancún in December 2010. The goal was already mentioned in the Copenhagen Accord , the final document of the UN Climate Change Conference in Copenhagen in 2009, but at that time the diplomats only “took note” of it.

The two-degree target was also mentioned outside of UN climate diplomacy and before the Cancún conference. The heads of state and government unanimously recognized it at the G8 summit in L'Aquila in July 2009 .

Individual states and regions had already committed themselves to the two-degree target for some time. In Germany, the German Advisory Council on Global Change (WBGU) has been recommending limiting average warming to a maximum of 2 ° C since 1994. The member states of the European Union decided in 1996 and again in 2005 to make the two-degree target a guideline for their climate policy. However, it is controversial whether the EU's self-imposed goals are sufficient for compatibility with the Paris Agreement.

Many developing countries consider the two-degree target to be too weak because the associated climate change endangers their very existence. In international climate negotiations, especially the 44 in the pleading Alliance of Small Iceland States federated island states for a tightening of the target to at least 1.5 ° C. Some climate researchers, including James E. Hansen from the Goddard Institute for Space Studies at NASA , also advocate stricter goals and call a carbon dioxide concentration of at most 350 ppm tolerable. In 2013 the value already reached 400 ppm.

Achievement of the two-degree target

Some projections of the temperature development up to 2100 show that the two-degree target will be very difficult to meet. Please note that the year 2000 was chosen as the zero line. This was already about 0.7 ° C warmer than the level from 1880 to 1920. A warming of +2 ° C above the year 2000 corresponds to a warming of 2.7 ° C above the pre-industrial level.

The two-degree target can only be met if greenhouse gas emissions are significantly reduced in the long term. How fast and comprehensive the reduction has to be depends on several variables and cannot be finally decided.

Limited emissions budget

CO 2 has, in comparison to most other climate-related materials, a long residence time in the atmosphere: about half of the CO 2 emissions is absorbed by the biosphere and oceans (and leads to ocean acidification ), the other half accumulates over many hundred years in the atmosphere and exacerbate global warming. The further global warming in the 21st century and beyond will therefore largely depend on the cumulative CO 2Emissions determined. These must not exceed a total amount depending on various boundary conditions - such as the emissions of other, short-lived greenhouse gases - in order to limit the warming to well below 2 ° C with some certainty. The difference between a total amount in line with the two-degree target and the amount already emitted is called the CO 2 budget .

The global warming since the beginning of industrialization (1850) is about 1.0 degrees Celsius (as of 2018). According to the WBGU budget from 2009, global greenhouse gas emissions would have to be avoided in order to avoid an increase of another degree Celsiusby at least 50% by 2050, and by 80–95% in industrialized countries (compared to 1990). The emission reduction should therefore have started in the course of the 2010s, otherwise there would no longer be a realistic prospect of meeting the two-degree target. In the second half of the 21st century, global greenhouse gas emissions must then be reduced to zero, as this is the only way to prevent the total amount of greenhouse gases in the atmosphere from increasing and thus avoid ever increasing temperatures.

Realistic accessibility

Technically, the 2-degree target can be achieved with currently known technologies. The longer climate protection is delayed, the greater the costs of climate protection; In addition, more high-risk technologies must be used than with rapid climate protection measures. In view of the uncertain further development of global climate protection , the increasing demand for energy and the slow implementation of the reduction commitments that have been made so far, some observers express serious doubts as to whether the goal can also be achieved politically. This is what Fatih Birol , chief economist of the International Energy Agency, called(IEA), in 2011, it was “practically impossible” to cope with the emissions reductions associated with the two-degree target. With a consistent climate protection policy, however, the limitation to 1.5 ° C warming is still possible, as in 2015 in the Paris Agreementagreed by the international community. To do this, however, the world has to reduce net greenhouse gas emissions to zero between 2045 and 2060, which is why the window for achieving this goal is quickly closing. In addition, in the second half of the 21st century, some of the previously too much carbon dioxide emitted must be artificially removed from the earth's atmosphere. It is scientifically controversial whether this amount of negative emissions can be achieved, so climate policy should not be based on the assumption that this technology will be available on a large scale in the long term.

Climatological uncertainties and probabilities of occurrence

A decisive factor in the question of which measures can be used to meet the two-degree target is the selected probability of occurrence or the willingness to take risks, if necessary, to exceed the target. Depending on whether you want to achieve the goal with a probability of 10%, 50% or 90%, there are seriously different requirements for climate protection.

In addition, there are existing uncertainties in climate research , above all the question of climate sensitivity . This describes the warming that is ultimately associated with a certain greenhouse gas concentration. Climate research currently assumes that doubling the concentration of the most important greenhouse gas in this context, carbon dioxide , compared to the pre-industrial level of 280 ppm, would cause a warming of 2 to 4.5 ° C.

Together, this leads to very different target values ​​for the permissible concentration of carbon dioxide in the earth's atmosphere , which range from 330 ppm to 700 ppm. Because of this range, among other things, the two-degree target has been criticized as a normatively perhaps justified, but technically unsuitable specification.

Amount of the necessary reductions

If the two-degree target is to be achieved, the carbon bubble on the international financial markets could burst

In order to meet the two-degree target with a probability of 50%, the carbon dioxide equivalent of the concentration of the most important greenhouse gases should not have exceeded 450 ppm. In order to meet it with a probability of 70%, this concentration should not have risen above 400 ppm. In 2015 it was 485ppm. According to the United Nations Environment Program (UNEP), the likelihood of meeting the two-degree target would be over 50% if:

  • global emissions start to decline between 2015 and 2021.
  • global emissions in 2020 will be between 40 and 48.3 billion tons.
  • by 2050 global emissions will decrease by 48% to 72% compared to 2000 or reduced by at least 90% compared to 2005.

Since carbon, which comes from the use of fossil fuels, only disappears naturally from the aforementioned compartments from the reservoirs of air, water, soil and vegetation through the very slow weathering of rock, man-made climate change ultimately depends on the total amount in addition generated carbon dioxide. Around 36 billion tons of CO 2 are currently emitted every year . The combustion of all known reserves of fossil raw materials (today technically and economically recoverable) would produce CO 2-Cause emissions of around 2,800 billion tons. In order to meet the two-degree target with a probability of 75%, emissions should not exceed 1,000 billion tons in the period from 2000 to 2050. Since 234 billion tons were emitted from 2000 to 2006 alone, the remaining emissions budget is already below 766 billion tons. If emissions remained high, the existing budget would be exhausted in 2027. If the risk of warming over 2 ° C is only 20%, this would occur three years earlier; if one is ready to increase the risk to 50%, the budget would last until 2039.

The German Advisory Council on Global Change has calculated that an immediate turnaround in greenhouse gas emissions must be brought about if global warming is actually to remain limited to 2 ° C.

“Even a slightly delayed turnaround in 2015 would require annual global emissions reductions of up to 5% (based on 2008) [...]. The world would then have to achieve annual reductions on a scale for which the Kyoto Protocol for the industrialized countries provides for over two decades. Delaying the trend reversal by 2020 could hardly require realizable global reduction rates of up to 9% per year. It is therefore necessary to stop the observed global increase in CO 2 emissions as quickly as possible and to switch to globally falling emissions. "

IPCC author Thomas Stocker from the University of Bern explains the situation in a model calculation . He assumes that global greenhouse gas emissions will continue to increase up to a certain date and then decrease by a constant percentage of around 3% per year. It turns out that if the point in time at which emissions begin to decrease is delayed by a decade, this delay will ultimately lead to warming that is three to eight times the global warming observed during this period. While the earth is currently warming by approx. 0.1 ° C per decade, a delay in the start of far-reaching climate protection measures in the same period leads to an increase in the warming ultimately achieved by around 0.5 ° C.

In another study by Valentin Crastan , a stabilization and slight reduction in CO 2 emissions from fossil fuels to 28 to 32 Gt / a by 2030 and their reduction to 16 Gt / a by 2050 is required in order to comply with the two-degree limit . The necessary and appropriate distribution across the world regions and all G-20 countries will be determined on a trial basis based on their economic performance, taking into account the GDP forecasts of the World Bank and IMF. The study was updated in 2016.

Reaching the two-degree goal is increasingly considered difficult or can only be achieved with great effort. Most models today assume that after 2050 bioenergy with CO 2 capture and storage (BECCS) will have to be used, with which carbon dioxide is actively filtered out of the atmosphere through the combustion of biomass , deposited with CCS technology and then stored in the Soil is grouted. It is controversial whether such measures can be implemented politically and technically.

Rule of thumb for accessibility

A group of scientists led by the Swedish resilience researcher Johan Rockström has developed a simple rule of thumb how the 2-degree target can be achieved. Accordingly, global CO 2 emissions must be halved every 10 years. The annual reduction would be around 7%. At the same time, the share of renewable energies in total energy demand should be doubled every 5 to 7 years. In addition, CO 2 must be removed from the atmosphere .

reception

Uncertainty about the consequences: Experts have revised the risks estimated in the 2001 IPCC report - with the same temperature increase, they saw mostly greater risks in 2009 and 2014.

Many researchers, including the IPCC, do not consider the two-degree target to be sufficient to prevent the serious consequences of global warming on humans and the environment. A warming of two degrees for indigenous peoples means a destruction of their culture and way of life, be it in arctic regions, in small island states or in forest or dry areas, as well as the almost complete loss of all coral reefs worldwide. According to a study published in 2012, the limit for the melting of the Greenland ice masses is between 0.8 and 3.2 degrees. Some climate researchers therefore consider the two-degree target to be too high and advocate a 1.5-degree target . Stefan Rahmstorfdescribes the concept of the two-degree “target” as misleading, since nobody who is “in their senses” would want to cause a temperature rise of two degrees. Rather, it is a matter of preventing this under all circumstances.

As early as December 1985 and again in 1987, the German Physical Society , together with the German Meteorological Society , pleaded for compliance with a one-degree target.

A study published in 2013 examined the growth of speleothems in Siberian caves over the past 500,000 years. According to this, a global warming of 1.5 degrees compared to the pre-industrial global average temperatures is sufficient to trigger a strong thawing of Siberian permafrost up to the 60th parallel. Since the permafrost of the northern hemisphere stores an amount of carbon that is twice the pre-industrial content of the atmosphere, this means that even with a warming of 1.5 degrees there is a great risk of a strong release of methane and carbon dioxide from this source, which is to would lead to further warming.

In December 2011, the climatologist James E. Hansen called the two-degree target a “recipe for a disaster” (original English: “a prescription for disaster”). Together with 15 other authors, he published a scientific paper in 2015 in which, among other things, he pointed out the dangers of an exponentially accelerating sea level rise and extreme storms that would result from a temperature rise of two degrees. Hans-Joachim Schellnhuber called the two-degree limit a “compromise between what is scientifically required and what is economically favorable”. However, even with regard to two degrees it must be clear that generally every tenth of a degree more global warming increases the risk of tipping elements in the earth system trigger which could lead to a "hot time".

See also

literature

  • Ottmar Edenhofer among others: The Economics of Low Stabilization: Model Comparison of Mitigation Strategies and Costs. In: Energy Journal. 31, 2010, pp. 11-48.
  • Michel den Elzen, Niklas Höhne: Sharing the reduction effort to limit global warming to 2ºC. In: Climate Policy . 10, 2010, pp. 247-260.
  • Oliver Geden , Silke Beck: Renegotiating the global climate stabilization target . In: Nature Climate Change . 4, 2014, pp. 747-748.
  • Oliver Geden : The modification of the two-degree goal. Climate policy targets in the field of tension between scientific advice, political preferences and rising emissions . SWP Study 12/2012, Science and Politics Foundation, Berlin (PDF; 454 kB)
  • Bill Hare, Malte Meinshausen: How much warming are we committed to and how much can be avoided? In: Climatic Change . 75 (1), 2006, pp. 111-149.
  • Carlo C. Jaeger, Julia Jaeger: Why two degrees? In: From Politics and Contemporary History . 32–33, 2010, pp. 7–15 (PDF; 792 kB)
  • Samuel Randalls: History of the 2 ° C climate target. In: WIREs Climate Change, Vol. 1 Issue 4, 2010 doi: 10.1002 / wcc.62
  • UNEP: The Emissions Gap Report 2014. (PDF)
  • WBGU: Kassensturz for the global climate agreement - the budget approach. Special report, Berlin 2009 (PDF)
  • WBGU: Climate Change: Why 2 ° C? Factsheet No. 2/2009 (PDF)

Individual evidence

  1. ^ Jaeger & Jaeger (2010): Three views of two degrees (PDF) , p. 516, "A first intuition".
  2. ↑ a b Samuel Randalls: History of the 2 ° C climate target. In: WIREs Climate Change. Vol. 1 Issue 4, 2010 doi : 10.1002 / wcc.62
  3. ↑ FR Rijsberman and RJ Swart (ed.): Targets and Indicators of Climatic Change . ISBN 91-88116-21-2 , pp. viii – ix ( sei-international.org [PDF; 10.7 MB ]).
  4. ↑ Smith et al .: Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) '' reasons for concern ''. In: Proceedings of the National Academy of Sciences . 106 (11), (2009), pp. 4133-4137, doi: 10.1073 / pnas.0812355106
  5. ^ Jaeger & Jaeger: Three views of two degrees (PDF) 2010.
  6. ↑ IPCC (2018) Global Warming of 1.5 ° C , Summary for Policymakers , page 25
  7. ↑ Kick in the buttocks. Interview with Hans Joachim Schellnhuber, In: Der Spiegel. August 16, 2010.
  8. ↑ a b Kevin Anderson , Alice Bows : Beyond 'dangerous' climate change: emission scenarios for a new world. In: Philosophical Transactions of the Royal Society A, 369, 2011, pp. 20–44, doi: 10.1098 / rsta.2010.0290 (PDF)
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  10. ^ Marshall Burke et al .: Large potential reduction in economic damages under UN mitigation targets . In: Nature . tape 557 , 2018, p. 549-553 , doi : 10.1038 / s41586-018-0071-9 .
  11. ↑ Bernhard Pötter: Study on EU climate targets: "Ambitious is not enough". “The EU energy ministers will decide on targets for CO2 emissions on Monday. A study shows: Even the most radical proposal is not enough. ”Www.taz.de, December 17, 2017, accessed on December 18, 2017 .
  12. ^ Website of the Alliance of Small Island States
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  14. ↑ Justin Gillis: Heat-Trapping Gas Passes Milestone, Raising Fears. In: The New York Times. May 10, 2013, accessed May 12, 2013 .
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  20. ↑ Peter C. Glover: “Kiss goodbye” to Cancun CO2 goals, says IEA chief economist. In: Energy Tribune. January 24, 2011.
  21. ↑ A little less drastically than Glover Birol formulated it shortly afterwards in other contexts, see Joel Kirkland: Scenario to Cap World Emissions by 2020 Is Fading Fast, Warns IEA Economist , in: New York Times, January 24, 2011.
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  25. ↑ NOAA's Annual Greenhouse Gas Index of 2015
  26. ↑ UNEP: How Close Are We to the Two Degree Limit? Information Note, 2010 (PDF; 184 kB)
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  29. ↑ Antropocene: The closing doors of climate targets excerpt from a lecture by Thomas Stocker at Imperial College London
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  35. ↑ UNFCCC COP13 Statement by Indigenous Peoples: Two degrees is too high. Our many strong voices must be heard (PDF; 114 kB)
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