With thanks to Professor Paul Fennell.
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Whether you’re for it or against it, carbon capture and storage (CCS) is something worth talking about.
Carbon dioxide - CO₂ - is a greenhouse gas; after release, it builds up in our atmosphere, trapping heat and causing temperatures to rise. Carbon capture and storage (CCS) is a technique which can be used to stop the release of CO₂ into the atmosphere during certain industrial processes.
If this is a completely new concept to you - don’t worry, you’re not alone. It is discussed by academics, engineers and some politicians, but is not marketed enough to be known by the majority of the general public. That’s a problem. These ideas shouldn’t be limited to the experts: they should form part of everyone’s vocabulary.
This article exists for you to make up your own mind about CCS. It is not designed to support or condemn CCS. This is an article which puts technology at its heart. I am an engineer. I want you to walk away from this article knowing that carbon dioxide can be captured and it can be stored.
The truth is… I have spent four years of my life trying to understand the technology and the debate surrounding it. We only have ten minutes. You will not be an expert by the end of this article, but you will know enough about the basics to understand the complexities of this subject.
Let's dive into the details together.
Here is a very simple explanation of how CCS works:
Imagine a coal-fired power plant: the coal burns, releasing heat and gases. The heat is useful, producing electricity. The waste gases, mostly carbon dioxide and water vapour, must then be removed. The cheapest and most common option is to build a chimney - known as a 'stack' - to allow these gases to leave the plant.
What if you could separate those waste gases from the CO₂, keeping it away from atmosphere? That is carbon capture.
What if you take that separated CO₂and pump it underground? That is carbon capture and storage, or carbon capture and sequestration. Both terms are interchangeable, used in industry, and are often shortened to the acronym 'CCS'.
There are three types of commonly-discussed capture types: pre-combustion, post-combustion and oxyfuel combustion.
Pre-combustion capture works by exposing fossil fuels to high pressure steam.
Think back to our coal power plant: grinders crush up the coal, ready for reaction. Then, rather than burn it in air, the pipes pump out high-pressure steam instead. If we look at the chemistry for a moment, air contains oxygen (O₂) whereas steam is water (H₂O); oxygen (‘O’) is the key ingredient for burning fuel. Notice that oxygen has 2 Os and water has just one? Well, think of air ‘fully’ burning the coal, and steam ‘semi-burning’ it. When we semi-burn with water, we produce different products - carbon dioxide and hydrogen.
The CO₂ can be easily separated from the hydrogen. Pipes carry away the CO₂ for sequestration, and the hydrogen burns in a furnace, releasing energy for either heat or power.
This is the key benefit of pre-combustion capture: it can support the transition to hydrogen-based power.
Post-combustion capture is easier to visualise - in fact, it works like a vape.
Back to the coal power plant. This time, the target is after combustion. The fossil fuel burns in air, producing the waste gases carbon dioxide and water vapour. Rather than venting through a stack, the waste gases travel to a ‘separation station’. The aim is to separate the gases once again. However, this is a different mixture of gases to pre-combustion: nitrogen from the air, carbon dioxide and water.
These waste gases bubble through a special pool of liquid (known as a ‘solvent’). The CO₂ ‘likes’ the pool, clinging onto the liquid and staying in solution. The other gases are not as keen, passing through the mixture easily and to the top of the vessel.
CO₂ clings less when heaters warm up the pool, releasing the gas and allowing sequestration.
Post-combustion capture is useful for existing plants, as the capture technology is relatively easy to add to existing infrastructure, and works at the end of the process.
Oxyfuel combustion is the newest capture technology and is yet to be used in industry. It works in a similar way to post-combustion capture, except that the fossil fuel burns in pure oxygen rather than air. [1]
Why burn fuel in pure oxygen? It is a more efficient way to produce CO₂, as well as reducing the production of common pollutants. There is so much CO₂ that once all the water vapour is removed, it can be pumped away immediately.
Pumps compress the purified carbon dioxide to high pressures, transferring it from the plant to the storage site, before pressurising it to such high levels that it acts like both a liquid and gas (known as ‘supercriticality’). As it has properties of both liquid and gas, scientists call it a ‘fluid’.
It is injected underground in this fluid state using a wellhead, where it remains trapped. (The technology is virtually identical to oil and gas drilling).
However, CO₂ cannot just be injected anywhere underground. There needs to be enough capacity to store large amounts safely and for a long period of time. This means there are specific types of geological sites used to store carbon dioxide:
Deep saline aquifers: layers of rock storing saltwater deep underground
Old oil and gas fields: where oil and gas were trapped millions of years ago.
Source: Tsar et al.
The CO₂ initially remains trapped due to a layer of rock which sits above the fluid, stopping it from moving upwards towards the atmosphere. As time goes on, the CO₂ mixes with saltwater, dissolves, and eventually reacts with it to form rock. These processes can take millions, even billions, of years to occur.
Carbon capture and storage can be used in any industry which produces carbon dioxide.
At the moment, the major industry is natural gas processing. Natural gas contains methane - the flammable fuel burned in our boilers - and CO₂. Rather than transport all the CO₂ to the consumer, it is easier to separate it at source.
Carbon capture can also be applied to several other industries:
The Intergovernmental Panel on Climate Change says that CCS is a key asset in helping to prevent the worst effects of climate change.
Carbon dioxide emissions will not be lowered enough by simply decreasing fossil fuel consumption alone. While the world transitions to low-carbon power, CCS allows us to capture carbon dioxide at source, ensuring it cannot reach the atmosphere and greatly reducing its harmful effects.
The effectiveness of CCS is clear when examining a real-life example: Boundary Dam in Canada, which is a CCS plant attached to a coal power plant.
The plant was designed to take in one million tonnes of CO₂ each year, and this month it captured CO₂ at a rate equivalent to 900,000 tonnes per year.
Using figures published online, I was able to calculate that Boundary Dam would have released 59,000 tonnes of CO₂ emissions this month without CCS capabilities. However, with the help of carbon capture, this figure was reduced to 7,000 tonnes. In other words, 52,000 tonnes of CO₂ ‘avoided’ release into the atmosphere [2].
That is a lot of carbon dioxide which will not need to be dealt with further down the line, when its harmful effects are a lot harder to avoid. Importantly, it is not only in the energy sector that emissions can be reduced through CCS.
Perhaps the most useful aspect of CCS is that it can be applied to industries which cannot, at present, be decarbonised: notably, cement and steel.
Steel is made by heating iron oxide with carbon, and carbon dioxide is the waste product. Concrete and cement are central to our everyday lives, but their production releases CO₂ without any burning of fossil fuels. CCS allows the production of these fundamental materials - used in housing, dams (both hydroelectric and reservoirs), bridges, wind farm construction, and other large civil infrastructure projects-while greatly reducing their emissions rate.
CCS not only exists, but the number of sites is growing year on year. There are currently nineteen sites in operation, with thirty more under construction, proposed or waiting for approval.
Major universities such as Imperial College London and MIT, and oil companies like Exxon Mobil and Chevron are pushing forward development. Yes, Big Oil is interested...but more on that later.
CCS does offer some advantages. Fewer CO₂ emissions go into the atmosphere, reducing the impact of burning fossil fuels which, as we know, leads to global warming. Plus, it can do this incredibly efficiently when designed and put in place properly.
However, it would be wrong not to question CCS at all. Let’s run through some disadvantages of CCS technology, before you make up your mind.
Source: IPCC, Synthesis Report AR5, Fig 1.7
CCS is limited because it can’t be applied to all CO₂ emissions.
For example, forest fires and agricultural practices make up 25% of emissions. CCS cannot be applied here because combustion is unplanned.
CCS is also difficult to apply to the transport sector. Let’s take the automotive industry: there are approximately 1 billion cars worldwide, each releasing carbon dioxide.
In order to store this carbon dioxide on the individual level, each vehicle would require its own collection and storage unit. The carbon dioxide will accumulate, making the car heavier, meaning you need more fuel, meaning you produce more carbon dioxide. Plus, even if you were to make these changes to individual vehicles, then what? Everyone would have to have a carbon dioxide pipe in their homes; there would also have to be local and central hubs to dispose of this personal CO₂ collection, and so on...
In other words, it is far easier to capture carbon with a small number of large producers than with a large number of small producers.
(As a side note, this is another way in which electric cars help to reduce carbon dioxide emissions. Factories can easily capture the carbon dioxide when oil is burned in a power plant to produce electricity. It is practically impossible to capture tiny amounts of carbon dioxide when petrol is burned in your car.)
CCS is not a moneymaker. Not only that, it requires massive up-front investment for relatively little return. Companies typically do not implement CCS because they have little incentive to do so.
There is a world where CCS can exist, but it relies heavily on the world having a carbon tax. If countries and companies have to pay to release CO₂, they will seek out ways to stop releasing it into the atmosphere.
Some countries already have carbon taxes, and these are the countries in which CCS is being implemented - Norway being the primary example. However, it is also likely that these projects involve something called ‘Enhanced Oil Recovery’ (see below), as oil (usually) produces profit.
Also, there are issues with construction. Carbon dioxide needs to be transported somehow, and building the additional infrastructure to do this takes years. This could reduce its effectiveness, depending on how quickly we can move towards a future of low-carbon power. However, it is possible and some regions, such as Teesside in the UK and Rotterdam in the Netherlands, are planning to have completed construction within the next five years.
Back to Big Oil: they have a vested interest in CCS, due to something known as ‘Enhanced Oil Recovery’ (EOR). They can use carbon dioxide from pre-combustion capture, compress it, inject it again and force out more oil from an oil well. Companies can produce more oil per well, making wells more profitable. This increases the number of wells which are considered profitable for the company to exploit, therefore more oil will be produced and we continue the cycle of oil dependence.
It is important to note: there are still carbon emissions from EOR. EOR allows oil companies to harvest more oil profitably over a longer period of time, meaning more carbon dioxide could be released than if oil companies are limited by their current oil production. In other words, it may be more effective to kill fossil fuels quickly than let it die slowly.
However, there is some balance to this argument. Significantly more carbon dioxide is stored through EOR than is released by burning the crude oil that comes out. It is a much better option than crude oil production without EOR - providing that total oil demand decreases with time. Furthermore, EOR means companies want to fund carbon capture research and development which benefits everyone in the long run, and the implementation of EOR has also proven the safety of CCS on a large scale.
And while EOR currently generates the most profit for oil companies, if economies change, so will their approaches to carbon capture. In other words, they may choose to progress from EOR to ‘regular’ carbon capture and storage… with the introduction of subsidies or technological innovation.
This being said, there are sound arguments against this continued reliance on fossil fuels in a rapidly heating world.
CCS succeeds in decarbonisation models partly because it is the smallest possible change from the current infrastructure. There are other options for energy decarbonisation. However, it is ‘more secure’ to keep infrastructure as it is, and this desire is driven by everyone, whether they be politicians or members of the public.
The money that could be spent on these other options is put towards fossil fuel industries. $150 billion was spent by global governments subsidising oil in alone. Installing such complex energy decarbonisation systems may currently have high political and financial barriers to overcome, but countries will lose more money if they don’t change tactics as soon as possible.
Even ignoring the impact of climate change on national economies, there is still an economic case for renewable energy. The price of renewable energy is similar to fossil fuels (with some conditions), and CCS will actually make fossil fuels less competitive.
Should companies really be investing in expensive ways of reducing carbon emissions, when they could be investing in available green technologies and eliminate them completely?
There are some environmental risks associated with the storage of carbon dioxide.
Carbon dioxide is typically stored under oceanic rock. If the rock is placed under too much pressure, it may fracture, or earthquakes may cause rock layers to shift, leading to carbon dioxide leaks. If carbon dioxide leaks into the oceans it causes ocean acidification - a process which is already happening at alarming rates - and destroys marine ecosystems with devastating effects.
It is important to note that no sites have leaked in the short-term at present. In fact, one CCS site was shut down rather than risk putting the rock under too much pressure.
Right, that was a lot of information. Let it all sink in.
This view covers a range of opinions. Maybe CCS should be applied to every single industry it possibly can. Maybe it should be applied to essential industries that cannot otherwise be decarbonised. Maybe the lure of an entry route into hydrogen is too much to resist, and it is a good transition to a cleaner world.
If this is your view, the million-dollar question is: why aren’t all capable countries implementing CCS? In short, it comes down to an individual government's priorities. Ten countries have chosen to implement CCS. Hundreds have not.
Since CCS is an idea usually left to academics or engineers, there may not be enough public opinion on CCS to make it a priority in some countries. This should change, and is why CCS needs to be discussed by citizens in Citizens’ Assemblies.
Fair enough. Sometimes, governments need to take large strides to action rather than walking on their tiptoes. CCS is the equivalent of a half-step. There are different ways to implement decarbonisation - some of which I hope to discuss in future articles.
Again, there is no clear answer. These alternatives should also be part of the discussions by citizens within their Assemblies.
I would be surprised if ten minutes would convince you to feel strongly either way. Governments have not figured out their stances after several years! To pick just two examples, the Netherlands has flip-flopped on the issue, while the UK government has been indecisive, leading to estimated billion-pound losses.
The truth is that global governments are currently unlikely to spend large amounts of money on projects which have little public interest and aren’t economically profitable in the short-term. If, however, public opinion were to change, there is potential for CCS to be pursued more openly.
Regardless of your take on the CCS debate, carbon capture and storage should at the very least be part of the discussion.
Goto Chengde Energy Technology to know more.
It should form one of many urgent discussion topics for citizens’ assemblies: Extinction Rebellion’s third and final demand.
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Footnotes:
[1] With some recycled CO₂ to make it slightly less combustible.
[2] Boundary Dam has captured at the rate of 890kt/y this month. Capture efficiency is 90%. The efficiency penalty is 20%. (The efficiency penalty described how much extra carbon dioxide must be produced to capture the remaining emissions). Therefore: Originally 712 kt/y released; 801 kt/y can be captured; 89 kt/y is released now; carbon dioxide avoided: 623 kt/y, or over 85% of original emissions.
Further Reading
https://www.globalccsinstitute.com/resources/global-status-report/ - the current CCS picture
https://www.iea.org/reports/energy-technology-perspectives- - how carbon capture fits into the wider picture
https://www.iea.org/reports/ccus-in-clean-energy-transitions - the future for carbon capture
https://www.sciencedirect.com/science/article/pii/S#:~:text=CCS will not advance without significant public investment,CCS play a major role in this respect. - the politics of CCS, and ways to depoliticise it
https://www.edx.org/course/climate-change-carbon-capture-and-storage - more depth about the technology
https://www.catf.us//06/leveraging-enhanced-oil-recovery-for-large-scale-saline-storage-of-co2/ - more about EOR
In carbon capture and storage (CCS), CO2 is captured from an exhaust stream and then permanently stored. A fundamental distinction must be made here as to whether carbon dioxide is captured directly at the sites of large-scale plants or whether CO2 is filtered out of the air afterwards, so to speak, regardless of where it was previously generated (Erlach et al. ).
The classic CCS method consists of capturing emissions from fossil fuel power plants or large industrial facilities before they are released into the atmosphere. In this method, the CO2 is captured before, during or after the respective combustion or production processes via chemical processes. The carbon dioxide is then transported via pipelines, road or ships and then stored in long-term storage underground or under the sea, for example. Suitable geological formations for this include empty oil and gas reservoirs or salt aquifers, which are porous rock layers with salt water. In the USA and Canada in particular, compressed CO2 is also injected into nearly exhausted oil and gas fields to extract the remaining hydrocarbons, which is known as “enhanced oil recovery.”
In geological deposits in the earth's crust, carbon dioxide is trapped in various ways: sometimes it is dissolved in underground salt water, trapped in small or large cavities, or it forms solid compounds with certain minerals in the rock. The aim is always to keep CO2 out of the atmosphere as permanently as possible.
In specialist discussions on climate research and (international) climate policy, CCS technology falls under the umbrella term "carbon management" (see illustration). The different areas should be clearly distinguished because they have different fields of application and can play different roles in climate policy and climate protection.
There is another form of CCS known as bioenergy with capture and storage (BECCS). In this process, power plants do not capture carbon dioxide from the combustion of fossil fuels such as coal or natural gas, but rather from the combustion of biomass, such as wood chips. The CO2 released when burned was absorbed by plants from ambient air as they grew. By permanently storing that carbon dioxide, BECCS would result in a net removal of the gas from the atmosphere, which would not only slow down global warming (as with conventional CCS), but could even reverse it in the long term.
There is a consensus among researchers that a certain level of CO2 removal from the atmosphere is necessary to meet the two-degree and especially the 1.5-degree limit on global warming laid out in the Paris Climate Agreement. Even with strong climate protection, some emissions will be very difficult or impossible to reduce directly at source (for example in agriculture). BECCS or DACCS (see section 3) would be promising options for offsetting these residual emissions and ultimately achieving "net zero", a balance where the amount of greenhouse gas emissions released is equal to the amount that is removed from the atmosphere.
As an alternative to storage, captured CO2 can also be used directly in industrial processes, for example in the chemical industry to produce urea for fertilisers, plastics or for the production of synthetic fuels (otherwise known as ‘e-fuel’). This technology is called carbon capture and utilisation (CCU) (sometimes also referred to synonymously as carbon capture and usage). At present, the potential of this material utilisation is still low. In its Sixth Assessment Report (IPCC , AR6, Volume 3, Chapter 6.4.2.5), the IPCC gives an estimate of 1-2 billion tonnes per year; however, according to the IPCC, the potential could increase to 20 billion tonnes per year by the middle of the century, in other words: to a very considerable extent. However, dramatic technological developments would still be necessary to achieve this.
However, some CCU options require a lot of energy, which is likely to limit the number of possible applications. And in many cases, the products manufactured in this way do not store the CO2 permanently. In the case of synthetic fuels, for example, the CO2 is quickly released again and is usually released into the atmosphere after just a few days or months. In the case of processing in plastics, the binding is longer-term. However, if this plastic is burned during waste incineration, the carbon dioxide is re-released into the atmosphere. It should also be noted: for material use, CO2 is sometimes required in very high purity or at a very high pressure. For example, in urea production, which is needed for fertilisers, CO2 is required at 122 bar and 99.9 % purified: a very large, costly effort overall.
To date, very little carbon dioxide has been stored underground globally. According to the Massachusetts Institute of Technology’s (MIT) climate portal, this amounted to around 0.045 billion tonnes per year in , the equivalent annual emissions of around just ten million cars. For comparison: in , human activity produced 40.6 billion tonnes of CO2, according to the Global Carbon Budget report. Of this, 36.6 billion tonnes came from the combustion of fossil fuels.
This means that only around one thousandth of the carbon dioxide emitted every year is currently being stored via CCS. What is worse, a major proportion of this is currently attributable to enhanced oil recovery processes, which, on the one hand, result in additional emissions from the combustion of the extracted quantities of fossil fuels and, on the other hand, will no longer be required when oil and gas production is phased out.
CCS technology has been used so far at a small number of sites in some countries; the IPCC's Sixth Assessment Report cited a figure of 28 plants in commercial operation globally in (IPCC , AR6, WG3, Chapter 6.3). In Norway, CCS has been in operation on a smaller scale for more than 25 years and the CO2 is stored under the North Sea. Denmark has just commissioned its first plant and is planning to store larger quantities of CO2. In the USA, only plants that utilise CO2 to squeeze residual oil and gas from the fields have been operated to date. The world's only operating coal-fired power plant with CCS (Boundary Dam, Block 3) is located in the central Canadian province of Saskatchewan.
There are lists of CCS facilities from various sources, some industry-related, others, for example, from critical NGOs or the media. The number and assessment of the plants mentioned in these lists differ considerably in some cases:
CCS’s potential is considerable. However, according to the IPCC in its Sixth Assessment Report of /22, the deployment and development of the technology took much longer in the past than previously assumed (IPCC , AR6, WG3, Chapter 1.4.3). German science academies have come to a very similar conclusion in a joint paper:
"The individual process steps of CO2 capture, CO2 transport and underground CO2 storage (CCS) are in principle ready for use on an industrial scale. Nevertheless, the development and market launch of CCS technology has progressed much more slowly in recent years than had been expected five to ten years ago." (Erlach et al. )
In principle, the technology is costly and energy-intensive (see section 8), and the storage sites must be regularly checked and maintained, possibly for centuries. It must also be taken into account that plants with CCS are not completely CO2-free. Because the technology increases the total energy input, power plants in which carbon dioxide is captured, for example, initially produce more CO2; a special report on the subject by the IPCC in spoke of a ten to 40 percent increase in CO2 emissions (SRCCS, Summary for Policy Makers). With the current state of technology, around 90 percent of these emissions can be captured (Dods et al. ); in practice, according to media reports, often less. Even if only ten percent CO2 emissions from for example coal-fired power plants remain, these still are enormous quantities and climate neutrality cannot be achieved in this way. Research is currently working on further increasing effectiveness. But it would probably make the technology even more expensive. From a residual amount of two percent CO2, the costs increase sharply (Brandl et al. ).
As mentioned, only BECCS and DACCS offer the possibility of permanently removing carbon dioxide from the atmosphere that has already been emitted in the past or elsewhere, thereby reducing the CO2 composition of the atmosphere (and thus the earth's temperature). The State of Carbon Dioxide Removal report provides an overview of the status of carbon removal from the atmosphere; the four main authors have also contributed to IPCC reports. The report states (Chapter 6.2, Current CDR Deployment) that for BECCS, storage could increase from the current 0.02 billion tonnes of CO2 per year to between 0.03 and 0.2 billion tonnes by . In the case of direct air capture and carbon storage (DACCS), the total quantity could increase from currently less than 0. billion tonnes to up to 0.3 billion tonnes per year over the same period. Nevertheless, even these increased quantities are rather small in relation to the approximately 40 billion tonnes of CO2 currently emitted each year.
In its Sixth Assessment Report of /22 (IPCC , AR6, WG3, Technical Summary TS5.7), the IPCC cites significantly higher figures: in the long term, the potential of DACCS alone is five to 40 billion tonnes of CO2 per year, meaning a significant proportion of the (hopefully then lower) emissions could be removed from the atmosphere by CO2 removal in the long run. However, according to the IPCC, this potential is "limited mainly by requirements for low-carbon energy and by cost" (for the latter, see section 8).
According to the IPCC, approximately 10,000 billion tonnes of CO2 can theoretically be stored in geological structures globally (IPCC , AR6, WG3, Chapter 6.4.2.5), the equivalent of global emissions from around 250 years. The majority (80 percent) of the theoretical storage capacity lies in so-called "salt aquifers", porous rock layers containing salt. Exhausted oil and gas reservoirs are also suitable for storage in principle. Here, existing infrastructure used for the extraction of oil and gas could be used to store the CO2.
However, not all reservoirs where CO2 could be stored can be used in practice. For example, the pressure in a fundamentally suitable formation may be too high for the carbon dioxide to be injected. The potential storage locations might be too far away to be reachable from production sites, or can only be reached at very high additional costs. Nevertheless, the potential for storage is very high. The IPCC writes about this in the report of Working Group 3:
"Not all the storage capacity is usable because geologic and engineering factors limit the actual storage capacity to an order of magnitude below the theoretical potential, which is still more than the CO2 storage requirement through to limit temperature change to 1.5°C " (IPCC , AR6, WG3, Chapter 6.4.2.5)
Realistically, according to the IPCC, around 1,000 billion tonnes of CO2 could be stored globally. However, storage capacity varies between regions.
In Germany, depleted natural gas deposits and deep salt aquifers are particularly suitable for storage. A few years ago, two researchers from the Federal Institute for Geosciences and Natural Resources found that the country could in theory store around 20 to 115 billion tonnes for the German salt aquifers alone; this means that up to 109 billion tonnes of CO2 could be stored in northern Germany alone (Knopf/May ). By way of comparison, around 0.66 billion tonnes of CO2 were emitted in Germany in according to the German Federal Environment Agency. In the CDRmare project, several German marine research institutes are currently investigating the possibilities of storing carbon dioxide in geological formations under the North Sea. According to initial publications, the potential is several billion tonnes. By the end of the century, perhaps 30 million tonnes of CO2 per year could be stored there.
A study of Austria found that up to 0.12 billion tonnes of the gas could be stored (Welkenhuysen et al. ), compared with the country’s annual emissions of 0.08 billion tonnes in according to the Austrian Federal Environment Agency. In , a study for the Swiss Federal Office of Energy put the capacity for Switzerland at around 2.6 billion tonnes of CO2 (Diamond et al. ), with annual emissions of around 0.045 billion tonnes according to the Federal Office for the Environment.
However, there are major differences in the methods used to estimate capacity. The given values can therefore only be considered guidelines.
So far, every form of CCS has been very expensive. According to the IPCC, the capture of carbon dioxide at the site where it’s released alone currently costs more than 50 US dollars per tonne of CO2 (IPCC , AR6, WG3, Chapter 6.4.2.5). The investment costs for a coal or gas-fired power plant with CCS are almost twice as high as if CCS is not used, according to the IPCC. In addition, there are increased costs during operation and a lower efficiency of the plant because considerable amounts of energy have to be used just to capture the carbon dioxide.
If storage sites are far away from the emission sources, there are also considerable costs for transporting the gas to the storage site, not to mention expenses for the long-term maintenance and safety of the storage site. The German research consortium CDRmare speaks of a total of 150 to 250 euros per tonne of CO2 for injection in the North Sea.
DACCS, which not only reduces CO2 emissions, but also removes the greenhouse gas from the atmosphere, is even more expensive. The IPCC report puts the costs (for the middle of the century) at 100 to 300 dollars per tonne of CO2 (IPCC , AR6, WG3, Summary for Policy Makers C.11.1). The State of Carbon Dioxide Removal report quotes prices of 780 dollars in and 1,200 dollars for for existing pilot plants that are actually in operation (Chapter 3.1 Measuring growth in Carbon Dioxide Removal).
The German Academy of Sciences, a scholarly society, explains the reason for the high costs in clear terms:
"CO2 only makes up a very small proportion of the air (only 0.04 percent by volume). In order to produce one cubic metre of CO2 with 1.96 kg of CO2, at least cubic metres of air must be 'filtered'. For one tonne of CO2, this corresponds to around 1.27 million cubic metres of air, even if one hundred percent filter performance is achieved." (Erlach et al. )
Prices are likely to fall further as DAC technologies are developed and operationalised. However, whether the costs of generating electricity in coal or gas-fired power plants with CCS, for example, will be able to compete with those of generating electricity from photovoltaics or wind power in the medium or long term is unclear. These forms of energy generation are already significantly cheaper and their costs are also likely to fall further. In other words, the price difference that already exists between renewables, which tend to be cheaper, and fossil-fuelled power plants, which are more expensive on average, is likely to increase further as a result of CCS.
The German science academies write on the subject:
"Possible risks include minor localised earthquakes, the displacement of saline water [underground] and its infiltration into the groundwater, and the escape of CO2 through leaks. Leakages would release some of the CO2 back into the atmosphere, which would impair the effectiveness of CO2 removal. According to many experts, these risks are low in well-implemented projects with professional risk management at suitable locations." (Erlach et al. )
The IPCC assumes that less than 0.001 percent of the CO2 stored in suitable structures will escape each year (IPCC , AR6, WG3, Chapter 6.4.2.5). The risks of CCS are therefore, if implemented carefully, rather low.
One difficulty, however, is that the use of CCS requires a lot of water. Power plants that use CCS have a 25 to 200 percent higher water consumption than power plants without CCS technology (IPCC , AR6, WG3, Chapter 6.7.7). By contrast, photovoltaic and wind power plants consume practically no water during operation.
The fact that so much water is required when using CCS is due to the higher energy consumption and the fact that the plants need to be cooled. Building CCS facilities in very dry areas (such as the south-west of the USA or south-east Asia) or on rivers with an increasing risk of low water levels, could lead to power plants having to be throttled back or shut down completely in summer. However, the problem could be minimised if water were used more efficiently or recycled more effectively.
How and whether CCS can be used safely on a large scale is still being investigated in many research projects. However, it is clear that measures such as the underground storage of CO2 are not as easy to reverse if problems arise as, for example, reforestation, which is a nature-based solution of sequestering carbon dioxide (IPCC , AR6, WG3, Summary for Policymakers, C.11.3).
In this question, the different variants of the technology must be considered separately – namely CCS on the one hand and BECCS and DACCS on the other (see section 1 for a distinction). In principle, however, all three technologies are needed to mitigate climate change; all paths considered by the IPCC to limit the global temperature rise to below two degrees or 1.5 degrees Celsius include various forms of CCS (IPCC , AR6, WG3, Technical Summary 4.2).
Firstly, BECCS and DACCS, which can remove CO2 from the atmosphere. This could also be achieved through nature-based solutions, such as large-scale reforestation. However, new forests do not store carbon dioxide very reliably. Climate change increases the risk of forest fires sharply, throwing the potential of forests to reliably sequester carbon into question. In addition, forestry or agricultural measures require huge areas of land, so their potential is limited. Technological methods that act as carbon sinks, especially bioenergy with carbon capture and storage (BECCS) and direct air capture and carbon storage (DACCS), are therefore essential, according to the IPCC.
Due to the high costs and the great effort involved, the use of these forms of CCS is only possible to a limited extent and cannot replace the reduction of emissions by other means. Volume 3 of the Sixth IPCC Assessment Report generally refers to carbon dioxide removal (CDR):
"Carbon Dioxide Removal (CDR) is necessary to achieve net zero CO2 and GHG emissions both globally and nationally, counterbalancing ‘hard-to-abate’ residual emissions [...] As part of ambitious mitigation strategies at global or national levels, gross CDR can fulfil three different roles in complementing emissions abatement:
(i) lowering net CO2 or GHG emissions in the near term;
(ii) counterbalancing ‘hard-to-abate’ residual emissions such as CO2 from industrial activities and long-distance transport, or CH4 and nitrous oxide from agriculture, in order to help reach net zero CO2 or GHG emissions in the mid-term
(iii) achieving net negative CO2 or GHG emissions in the long term if deployed at levels exceeding annual residual emissions” (IPCC , AR6, WG3, Box TS.10, Technical Summary)
The variants of CCS that are also considered carbon sinks (BECCS and DACCS) should therefore definitely be expanded in the view of the IPCC.
There is also broad consensus among researchers that conventional CCS will also be necessary in certain industrial processes in the medium and long term in order to achieve climate mitigation targets, as these cannot be made climate-neutral in any other way or only with great difficulty. In cement production, for example, there is no alternative to the use of CCS in the foreseeable future if the necessary emission reductions are to be achieved, according to the IPCC (IPCC , AR6, Volume 3, Chapter 11). Particularly in the long term, CCS and the material use of CO2 (CCU) play a decisive role in the IPCC scenarios for the decarbonisation of industry, but only in conjunction with, for example, the switch to emission-free energy, greater energy efficiency and the transition to a circular economy.
However, research and development into CCS is currently still proceeding too slowly to meaningfully slow global warming to the necessary extent in time. In the summary of the report for political decision-making, the IPCC writes:
"Implementation of CCS currently faces technological, economic, institutional, ecological-environmental and socio-cultural barriers. Currently, global rates of CCS deployment are far below those in modelled pathways limiting global warming to 1.5°C or 2°C. Enabling conditions such as policy instruments, greater public support and technological innovation could reduce these barriers.” (IPCC , AR6, WG3, Summary for Policymakers, C.4.6)
For countries such as Germany, Austria and Switzerland, CCS plays virtually no role in scientific debates on the energy sector. Occasionally, the question is still raised around whether CO2 capture could be an option for gas-fired power plants or whether it could be used in the production of blue hydrogen from natural gas. For coal-fired power plants, on the other hand, CCS is no longer being seriously discussed in research (unlike in the s). This is mainly due to the high costs of the technology (see section 8) and the poorly developed infrastructure. The expansion of renewable energy is currently considerably cheaper and less complex. And the decision to phase out coal-fired power generation has rendered the topic obsolete.
In some countries, however, the IPCC believes that CCS can facilitate the transition to a more climate-friendly energy supply, especially in countries where renewable energy is not easily available (IPCC , AR6, WG3, Chapter 6, FAQ 6.1). At the same time, the storage options available could also make methods such as bioenergy with capture and storage (BECCS) more attractive and ultimately accelerate the phase-out of fossil fuels (IPCC , AR6, WG3, Chapter 6.7.4).
CCS is making a comeback in the EU as the bloc strives for climate neutrality. The European Commission has underscored the critical role of carbon capture and storage (CCS) in achieving the bloc's climate targets. In February , it unveiled its proposal for a European industrial carbon management strategy, outlining guidelines for capturing, transporting, trading, permanently storing, and utilizing carbon as a cornerstone of its path to climate neutrality by . The Commission is aiming to establish "a European single market for industrial carbon management," with the goal of scaling up over the coming decades to ensure that residual greenhouse gas emissions can be captured and stored or balanced through CO₂ removals by mid-century.
As part of its ambitious proposal to reduce greenhouse gas emissions by 90 percent by , the European Commission has advocated for large-scale CCS deployment, with a steadily rising carbon price in the Emissions Trading System (ETS) serving as a key incentive. The strategy envisions capturing 450 million tonnes of CO₂ annually by , with 250 million tonnes destined for underground storage.
The remaining captured CO₂ would be recycled into the production of synthetic fuels (e-fuels) for sectors like aviation, as well as chemicals and plastics, gradually replacing fossil fuel-based carbon and creating sustainable carbon cycles. The impact assessment says approximately 150 million tonnes of CO₂ is expected to be used for e-fuels and a further 60 million tonnes for synthetic materials by mid-century, although much of this carbon will eventually be released back into the atmosphere.
Transport: The lack of a dedicated pipeline infrastructure currently hinders large-scale CO2 transport in Germany, and requires the use of trains, lorries, and ships. The government acknowledges that outdated regulations and legal uncertainties have stalled the development of such infrastructure, and has promised reforms. CO2 transport is regulated under the storage law and additionally under hazardous goods legislation.
The government has already classified the technology as mature and safe. A draft carbon management strategy by the former government focusses on industries with hard-to-abate emissions, such as cement, lime, basic chemicals, and waste incineration, as well as applications where "electrification or switch to hydrogen is not possible in a cost-efficient manner in the foreseeable future." CCS/CCU on gas-fired power plants would also be allowed but will receive no state support. The former government also planned to enable CO2 storage on an industrial scale, both under the seabed or abroad, but not onshore.
The new government has said it aims to continue efforts to make CCS/CCU possible in Germany and is expected to largely base its work on the legislative drafts of the former German leadership, which must now be re-introduced in parliament.
Five CCS/CCU projects in Germany are poised to become operational before , provided supportive policies and financial frameworks are in place (as of March ), according to the CCS lobby organisation Zero Emissions Platform (ZEP). Two projects include CCS in industry, while another is researching and piloting a CO2 pipeline infrastructure.
The German economy ministry emphasised that the use of CCS/CCU must be in line with greenhouse gas reduction targets and climate neutrality. In a Q&A, it says that a ramp-up by seems realistic if legislative amendments come into force quickly.
For additional information on CCS in Germany and the EU, see this factsheet.
Scientists have accumulated a surprising amount of specific knowledge about how effective various technologies can be. Their findings can be found, for example, in the IPCC’s Sixth Assessment Report, which runs to more than pages.
To highlight that the selection of sources is central to this project, we have deviated from our usual editorial guidelines in this Q&A, and inserted sources in academic style - to remind readers that these texts represent the scientific consensus as accurately as possible.
With this aim in mind, we ranked sources in the following order, which values relevance much more than a very recent publication date:
1) Wherever possible, the texts rely on the IPCC, which provides highly reliable summaries and assessments of the state of research.
2) A second-best are thorough meta-studies (studies that evaluate many other studies), as well as synthesis reports from large research consortia or organisations, where a broad circle of participants and intensive review processes are common.
3) Only in third place, we used individual studies - limited to publications in recognised research journals that guarantee a peer review process, meaning each publication is checked by competent specialist colleagues.
This Q&A and others in this series are based on texts published by our German-language sister project Klimafakten, which were written by expert journalists, and double checked by relevant experts. Two foundations supported this editorial project, which was overseen by our colleague Toralf Staud: the Marga und Kurt Möllgaard-Stiftung and the Deutsche Bundesstiftung Umwelt.
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