Negative emissions

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Negative mission technologies or negative emissions technologies ( English negative-emission technologies , shortly NET or NETs ) - also known as Carbon Dioxide Removal (CDR) called - are technologies for the retrieval of carbon dioxide (CO 2 ) from the atmosphere . They are counted among the geoengineering technologies , but are also described as “unconventional climate protection”. The flow of carbon from the atmosphere into permanent carbon sinks caused by NETs is also known as negative emissions.

Their long-term effectiveness, their side effects and their marginal effects are scientifically controversial.

background

Climate scientists assume a CO 2 budget which, if exceeded, would have unpredictable consequences, such as the state of the greenhouse earth , which would lead to conditions hostile to human life. With average emissions of around 40 gigatons of CO 2 equivalent (Gt CO 2 eq) per year in 2017, humankind will have around 20 to 30 years from this year, depending on the assumed CO 2 budget, if there is no change in emissions until this budget is exhausted; thereafter, due to the very long-term absorption of greenhouse gases by the earth system, no greenhouse gases should be emitted for millennia. In order to keep the climate system for the human species within an appropriate framework in the long term, it is therefore necessary to quickly abandon greenhouse gases. In the context of the climate crisis, however, it can be assumed that very rapid decarbonisation and energy savings are not sufficient to stabilize global warming to 1.5 ° C ( 1.5 degree target ), as is aimed at in the Paris Agreement , but carbon dioxide must also be extracted from the atmosphere with negative emissions. This is not about avoiding future emissions, but rather "reversing" past emissions. In the meantime (2016), negative emissions and thus the large-scale use of NETs are also required in most scenarios for compliance with the two-degree target .

The climate scientist Glen Peters sums up the challenges that negative emissions pose for decision-makers as follows: “The media is teeming with images of wind turbines and solar panels. That is all well and good, but if we are to achieve the goals set in the Paris Agreement, what are known as negative emissions are required - so that we are removing CO 2 already released into the atmosphere and removing it on a large scale. But little is said about it, although politicians are beginning to understand the enormous task this represents. "

techniques

There are proposals for biological, chemical and physical methods of how the CO 2 could be removed from the atmosphere. Many of the processes proposed so far are slow; they would require large-scale use of probably more than 100 years in order to significantly reduce atmospheric CO 2 concentrations:

Under certain circumstances, negative emissions can also be achieved with power-to-gas technology. This is the case, for example, when the carbon dioxide for methanation is obtained from the air and the synthesized methane is later burned in a power plant with CO 2 separation and storage .

Leading climate scientists assume that in order to meet the two-degree target from 2030, all building constructions would have to be CO 2 -neutral or CO 2 -negative. For this, the construction industry would either have to use emission-free concrete or steel or replace these materials with emission-free or emission-negative substances such as wood (see timber construction ) or stone. It is also conceivable that the use of concrete could lead to negative emissions in the long term, as concrete absorbs carbon dioxide from the air over time. However, this is only possible if the energy supply for cement production is switched to emission-free sources and the carbon dioxide produced during the cement production process is separated and stored permanently.

Negative emissions only have an impact on the climate if the carbon bound in the process does not get back into the atmosphere as CO 2 . Deposition requires repositories for similar amounts of carbon as extracted from the earth, in any modification or chemical combination.

chances and risks

Currently, the oceans and the biosphere are rapidly absorbing around half of human CO 2 emissions from the atmosphere. On the one hand, this dampens the rise in atmospheric CO 2 concentrations; on the other hand, the oceans become acidic and have effects on plant growth. Negative emission technologies also counteract these two effects: If the CO 2 concentrations decrease, the oceans and the biosphere would release some of the stored CO 2 back into the atmosphere. Because of this rebound effect has with Carbon Dioxide Removal (CDR) but for a desired CO 2 -reduction in the atmosphere in about twice as much CO 2 are removed.

Depending on the technology, different reservoirs serve to store the carbon removed from the atmosphere. Reservoirs differ in their storage capacity and the length of time they store carbon. Reservoirs in which carbon has been trapped for at least tens of thousands of years are called permanent . The storage of carbon in non-permanent reservoirs has a retarding rather than a preventive effect on global warming. Geological reservoirs could permanently store the carbon, while land- or ocean-based reservoirs are not considered permanent. In the case of land-based reservoirs (soils, biosphere) in particular, there is also the risk that CO 2 will be released more quickly in the event of further climate change . Geological and oceanic reservoirs could hold several thousand gigatons (Gt) of carbon, land-based reservoirs roughly 200 Gt. For comparison: The energy-related CO 2 emissions - i.e. without cement production, land use changes and without other greenhouse gases - amounted to around 32.5 Gt in 2017, which corresponds to around 8.9 Gt of carbon.

A major problem with policy strategies that rely on large amounts of negative emissions in the future is the fact that such technologies have hardly been tested today and it is uncertain whether they will ever be available in any significant quantity. For today's politicians it is much more attractive to hope for negative emissions in the future than to initiate a fast and far-reaching decarbonisation policy at the moment. However, there is a great risk that negative emission technologies such as BECCS in particular will result in a variety of problems such as B. the enormous land consumption can not be used on a large scale and thus today's hesitant climate protection policy would send the world to a strong global warming in the range of 4 ° C. This would particularly affect societies that cause few emissions themselves, but are at the same time particularly susceptible to rapid climate change. Climate researchers like Kevin Anderson and Glen Peters therefore emphasize that negative emissions technologies are not an insurance strategy, but rather an unfair and high-risk game of chance that should not be the basis for a climate protection strategy.

A review study published in 2016, which systematically examined the potentials and risks of various negative emission technologies, states that it is very risky to strive for the use of negative emission technologies from the outset, as there are currently no such technologies with which the two -Grad goal can be achieved without significant negative effects on the consumption of land , energy , water , nutrients or on costs or by interfering with the albedo . Plan A must therefore always be the immediate and rapid reduction of today's greenhouse gas emissions by decarbonising the economy and not hoping for negative emissions in the future. Because if the hope for future negative emissions is plan A from the outset, then there is no longer a plan B in the event that negative emissions cannot be sufficiently achieved due to various ecological or economic limits.

If CO 2 removal technologies are actually to be used on the scale that can be seen in many climate protection scenarios, then greater progress must have been made in the areas of innovation, market launch and market penetration than has been the case so far. According to Jan Minx, however, this urgency is not reflected in the scientific literature or in political discourse.

costs

In a review published in Nature Climate Change in 2016 , the costs of various negative emission technologies were analyzed, with considerable bandwidths depending on the technology. The costs for the direct capture of carbon dioxide from the air ( DAC ) were given as 1,600–2,080 US dollars per ton of CO 2 eq, while for BECCS for the year 2100, with large fluctuations, an average value of 132 US dollars per ton of CO 2 eq was determined. The afforestation and reforestation of forests will also cause between 65 and 108 US dollars per ton of CO 2 eq for the year 2100 , with an average value of 87 US dollars, while the costs of artificial weathering will be around 88 to 2120 US dollars. Dollars per tonne of CO 2 eq. A study from 2018 came to the conclusion that the costs of negative emissions from artificial weathering of dunite were 60 US dollars per ton of CO 2 and in the case of basalt it was 200 US dollars per ton of CO 2 .

Researchers at Carbon Engineering calculated costs for the DACCS process in 2018 of 94–232 US dollars per ton of CO 2 absorbed . Prior to this calculation, according to reports from media such as Nature, among others, greater costs were assumed for the removal of CO 2 from normal air, namely 600 US dollars, calculated in 2011 by the American Physical Society . It is believed that as the technology becomes more advanced, the cost will decrease. Another company, Climeworks , claims their tech could get them under $ 100 in five to ten years; they are currently still at $ 600. However, the cost of 94 US dollars is above the current market price for CO 2 savings and is not profitable.

literature

Individual evidence

  1. ↑ Oliver Geden, Felix Schenuit, Stiftung Wissenschaft und Politik: Unconventional Climate Protection: Targeted CO2 Extraction from the Atmosphere as a New Approach in EU Climate Policy . In: SWP study . 2020, doi : 10.18449 / 2020S10 ( swp-berlin.org [accessed January 15, 2021]).
  2. ↑ Leon Clarke, Kejun Jiang et al .: Assessing Transformation Pathways . In: Otmar Edenhofer et al. (Ed.): Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 2014, p. 433, 485 .
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  6. ↑ Will Steffen , Johan Rockström , Katherine Richardson , Timothy M. Lenton , Carl Folke , Diana Liverman , Colin P. Summerhayes, Anthony D. Barnosky , Sarah E. Cornell, Michel Crucifix, Jonathan F. Donges, Ingo Fetzer, Steven J. Lade, Marten Scheffer, Ricarda Winkelmann, Hans Joachim Schellnhuber : Trajectories of the Earth System in the Anthropocene. In: Proceedings of the National Academy of Sciences . August 6, 2018 doi: 10.1073 / pnas.1810141115
  7. ↑ Joeri Rogelj u a. .: Scenarios towards limiting global mean temperature increase below 1.5 ° C . In: Nature Climate Change . tape 8 , 2018, p. 325-332 , doi : 10.1038 / s41558-018-0091-3 .
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  10. ↑ If he has imagined technologies that should be redde. VG, September 17, 2017, accessed February 2, 2019 (Norwegian).
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  12. ↑ a b c d e f CO2 removal from the atmosphere is unavoidable for a 1.5 degree target. Several recent MCC studies discover significant differences in the potential and risks of negative emissions. Mercator Research Institute on Global Commons and Climate Change (MCC) gGmbH, May 22, 2018, accessed on May 24, 2018 .
  13. ↑ Constanze Werner, Hans-Peter Schmidt, Dieter Gerten, Wolfgang Lucht , Claudia Kammann : Biogeochemical potential of biomass pyrolysis systems for limiting global warming to 1.5 ° C. In: Environmental Research Letters . Volume 13, No. 4, 2018. Article 044036. doi: 10.1088 / 1748-9326 / aabb0e
  14. ^ A b Hans-Peter Schmidt: Biochar and PyCCS included as negative emission technology by the IPCC. In: the Biochar Journal (tBJ), Arbaz, Switzerland. October 19, 2018, accessed June 16, 2019 . ISSN 2297-1114 .  
  15. ↑ Capturing CO2 directly from the air - that has a future. Retrieved March 6, 2019 .
  16. ↑ Michael Sterner , Ingo Stadler (Ed.): Energy storage. Need, technologies, integration. 2nd Edition. Berlin / Heidelberg 2017, p. 457.
  17. ^ Johan Rockström , Owen Gaffney, Joeri Rogelj , Malte Meinshausen, Nebojsa Nakicenovic, Hans Joachim Schellnhuber : A roadmap for rapid decarbonization . In: Science . tape 355 , no. 6331 , 2017, p. 1269-1271 , doi : 10.1126 / science.aah3443 .
  18. ↑ Stephen J. Davis et al .: Net-zero emissions energy systems . In: Science . tape 360 , no. 6396 , 2018, doi : 10.1126 / science.aas9793 .
  19. ^ A b c Leon Clarke, Kejun Jiang et al .: Assessing Transformation Pathways . In: Otmar Edenhofer et al. (Ed.): Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 2014, 6.9 Carbon and radiation management and other geo-engineering options including environmental risks, p. 484-489 .
  20. ↑ International Energy Agency (Ed.): Global Energy & CO 2 Status Report 2017 . March 2018 ( iea.org [PDF; 389 kB ]).
  21. ↑ Kevin Anderson , Glen Peters: The trouble with negative emissions . In: Science . tape 354 , no. 6309 , 2016, p. 182 f ., doi : 10.1126 / science.aah4567 .
  22. ↑ Jan Minx in conversation with Ralf Krauter : Negative emissions: There is no scientific work on CO2 extraction. Technologies that can fish CO2 out of the air do not appear enough in scientific and political discourse: "A lot more needs to be done here," said Jan Minx from the Mercator Institute for Climate Change Research in the Dlf. This also includes an open debate about the opportunities and risks of these technologies. www.deutschlandfunk.de, May 24, 2018, accessed May 25, 2018 .
  23. ↑ Strefler et al. (2018). (iopscience.iop.org)
  24. ^ Robinson Meyer: Climate Change Can Be Stopped by Turning Air Into Gasoline . In: The Atlantic . June 7, 2018 ( theatlantic.com [accessed June 8, 2018]).
  25. ↑ Jeff Tollefson: Sucking carbon dioxide from air is cheaper than scientists thought . In: Nature . June 7, 2018, ISSN  0028-0836 , doi : 10.1038 / d41586-018-05357-w ( nature.com [accessed June 8, 2018]).