The industrial revolution, based on the use of fossil fuels, has given humanity many useful technologies. In the meantime, the burning of coal, oil and gas has increased the concentration of CO2 in the atmosphere, thereby worsening the greenhouse effect and has already warmed the earth’s climate by more than 1o C in the last decade compared to the second half of the 19th century. There is, however, a view that technology will solve this problem, meaning technologies (as well as practices, methods and approaches) of Carbon Dioxide Removal (CDR) and its subsequent sequestration, burial or utilisation.
It is possible that CDR methods will solve the climate change problem completely sooner or later. However, while they are necessary to move towards net negative emissions (i.e. to a state where anthropogenic removal of CO2 from the atmosphere exceeds anthropogenic emissions), due to their limitations they cannot replace measures to reduce the carbon intensity of the current economy (primarily energy and transport). Rather, CDRs will contribute to balancing those emissions that cannot be eliminated completely (Figure 1). For example, the Sustainable Development Scenario (SSP1), which assumes keeping warming at the levels recorded in the Paris Agreement, assumes the removal of about 10 Gt CO2/yr in 2050 and about 20 Gt CO2/yr in 2100 (NegEmiss, 2019).
Figure 1. The role of CDRs on different time horizons
Source: IPCC, 2022
Overall, the role will increase, with a greater proportion being given to CDR methods to be carried out on unmanaged land
In fact, CDR technologies, while contributing to sustainable development, do not solve the problem as a whole.
Neither will CCUS (Carbon Capture, Utilisation and Storage) methods, which do not involve extracting carbon from the atmosphere at all. It could be capturing CO2 during the combustion of fossil fuels in a stack and then dumping it here — into the oil reservoirs — to increase the pressure on the oil. This method of enhanced oil recovery was used back in the 1950s, but has now taken on a certain ‘environmental’ connotation. It does indeed reduce the overall carbon footprint of the energy sector and at least partially prevents additional CO2 from burning fossil fuels from entering the atmosphere. But it does not remove excess carbon dioxide from the atmosphere from previous anthropogenic activities. Consequently, this is not part of the CDR technologies.
The only exceptions are two varieties of CCUS — Bioenergy with carbon capture and storage (BECCS) and Direct Air Capture with Carbon Storage (DACS). These approaches intend to capture and use/store carbon extracted directly from the atmosphere, either through photosynthesis (in the case of BECCS) or chemical reactions (in the case of DACCS).
However, the current BECCS and DACCS capacities are insufficient. According to an IEA report, as of September 2022, 18 small direct atmospheric carbon capture plants have been commissioned, capturing around 10,000 tonnes of CO2 per year. Several dozen more direct atmospheric CO2 capture projects are in the pipeline, including large-scale plants that can capture up to 1 million tonnes of CO2 per year. If all the planned projects are implemented, this would allow about 5.5 million tonnes of carbon dioxide to be captured from the atmosphere by 2030, 700 times the current level, but 10 times less than the level assumed in the ‘net zero’ scenario. And of course, this is not comparable to the amount of emissions: humanity emits about 37 billion tonnes of CO2 into the atmosphere every year.
The situation is slightly better with BECCS: according to an IEA report, the BECCS currently captures around 2 million tonnes of CO2 from the atmosphere, and if all the plans announced to date for the technology are fulfilled, this will rise to 40 million tonnes of CO2 by 2030 (with a “net zero” scenario of 250 million tonnes of CO2 being captured by BECCS in 2030).
In addition to the limited potential and so far high price (per 1 tonne of carbon captured), both BECCS and DACCS have other significant disadvantages. For example, bioenergy can reduce biodiversity, degrade ecosystems, and compete with agriculture for monoculture areas. Direct carbon capture requires large amounts of water and is extremely energy-intensive — 7–10 gigajoules are required to capture one tonne of CO2.
This is why scientists are talking about the need to develop different technologies for capturing carbon from the atmosphere. Thus, in addition to BECCS and DACCS, it is proposed to enhance the natural processes (cycles) of carbon removal from the atmosphere, which include chemical weathering of minerals and absorption of carbon dioxide by the ocean. This requires increasing the extraction of a number of rocks (primarily ultramafic igneous rocks such as olivinite, basalt, etc.), crushing them into a fine dust and dispersing it over land or the ocean. In addition, various agricultural practices are also proposed that will retain carbon in the soil. Enhancing photosynthesis — not only by planting forests but also, for example, by managing ecosystems in coastal wetlands — is also worth considering.
The technologies that have been proposed so far have different potentials and implementation costs and are at different stages of development (Figure 2). However, no single technology is the ultimate solution to climate change.
Figure 2: Comparison of different atmospheric carbon removal technologies for climate change mitigation potential and cost. The colour shows technology readiness: from basic principles and conceptual approaches to create technologies (red), to full readiness for application and use (green).
Author’s figure, based on IPCC, 2022.
CDR technologies: A/R — Afforestation/Reforestation (planting/reforestation to conserve carbon in forest ecosystems), Af — Agroforestry (agroforestry to conserve carbon in soil), BC — Blue Carbon management in coastal wetlands (management of coastal wetlands and marsh forests to sequester carbon), Bc — Biochar (biochar, charcoal and its addition as fertilizer), BECCS — Bioenergy and Carbon Capture and Storage, DACCS — Direct Air Carbon Capture and Storage, ERW — Enhanced Rock Weathering, IFM — Improved Forest Management, OAE — Ocean Alkalinity Enhancement, OF — Ocean Fertilisation (ocean fertilisation (primarily with iron) to enhance bioplankton), PCWR — Peatland and Coastal Wetland Restoration, SCS — Coil Carbon Sequestration (various agricultural practices to sequester carbon in the soil).
Cover photo: Soeren Stache / DPA
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