Many of the world’s biggest economies have committed to achieving net-zero emissions by 2050 or 2060, including the EU, UK, China, South Korea and Japan. But not one of them is suggesting that they will stop emitting greenhouse gases by that date.
Inherent to the term “net-zero” is an acceptance that no matter what nations do in terms of renewable energy, clean hydrogen, electric vehicles, carbon capture and storage (CCS) or anything else, they will not be able to eliminate all carbon emissions by those dates.
It is, however, a promise that any remaining emissions will be offset by carbon-negative solutions. In other words, for every tonne of carbon dioxide emitted, a tonne of CO2 will be removed from the atmosphere.
Yet while countries are rightfully focusing hard on reducing emissions, little thought seems to have gone into how millions of tonnes of carbon dioxide will be sucked out of the air within a few decades, whether it can be done at a sufficient scale, how much it might cost and who would pay for it?
The good news is that, yes, permanent carbon removal is possible and several innovative methods are now being put into practice. The bad news is that none of them have been used at scale and the cost of CO2 extraction is still extremely expensive.
After all, the world is still pumping more than 30 billion tonnes of CO2 into the atmosphere each year, so why should money be spent on removing a tiny part of those emissions?
But according to International Energy Agency (IEA) energy analyst Sara Budinis, investment in carbon-negative technology needs to happen now.
“[Carbon-removal] technologies are definitely not an excuse for delayed action [on reducing carbon emissions],” she tells Recharge. “We don’t know exactly how the climate cycle is going to respond to an overshoot of emissions — ie, emitting more now and then removing this carbon dioxide from the atmosphere later on.
“It also takes a very long time — 30 to 40 years — to bring those new technologies to the market. So those things [ie, cutting emissions and developing carbon-negative solutions] should happen in parallel. So there should be a reduction of emissions... and at the same time there should be a push to understand which of the carbon-removal technologies are the most promising.”
Recharge has identified the five most promising carbon-removal methods that could be achieved at scale and, ultimately, at a low cost within the next 20 years — a fascinating blend of nature working in tandem with new technologies.
Bioenergy with carbon capture and storage (BECCS)
The primary way of removing CO2 from the atmosphere will be bioenergy with carbon capture and storage (BECCS), according to the IEA.
This means converting plant matter (biomass), which naturally absorbs CO2 from the air as it grows, into electricity, heat, or biofuels, with the carbon emissions being captured and stored in subsea or underground geological formations, or perhaps embedded in long-lasting products such as carbon-enriched concrete or CO2-based plastics.
According to the UK government advisory body, the Committee on Climate Change, the UK needs to capture and store 50 million tonnes of CO2 annually through BECCS to reach net-zero by 2050.
And for the EU to hit net-zero by mid-century, the bloc would need to capture 25 million tonnes of CO2 a year via BECCS, according to the IEA — a lower figure than the UK due to the bloc’s plan to shut almost all fossil-fuel power plants by that date, aside from gas peaker plants that would help balance the grid.
If the planet were to reach net-zero by 2050 — an unlikely event, but one mapped out in the new Net-Zero Emissions scenario in the IEA’s new World Energy Outlook report — the world would need to capture 35 million tonnes of CO2 through BECCS in 2030 to stay on track.
In the IEA’s less bullish Sustainable Development Scenario, which sets out the path to a net-zero world by 2070, BECCS would remove 250 million tonnes of CO2 in 2050, but about 2.6 billion tonnes in the electricity and wider energy sectors in 2070. To hit this target an average of 7GW of BECCS power plants will need to be installed each year between 2025 and 2070.
In other words, the planet will not be able to decarbonise without vast amounts of BECCS.
BECCS: Current status
So where does BECCS technology stand today?
At the moment, there are only five commercial BECCS facilities up and running — all at ethanol and fertiliser plants in the US — with two pilot BECCS power plants in Japan and the UK, according to the Australia-based Global CCS Institute.
The pilot project at the 50MW Mikawa biomass power plant in Fukuoka, Japan, does not appear to be a prelude to a carbon-negative facility.
But the BECCS trial at the 4GW Drax power plant in northern England, which has been running since October 2018, capturing its first carbon in early 2019, is the first step to something much bigger.
The facility’s operator, Drax Group, plans to become a carbon-negative company by 2030, with its first commercial-scale BECCS unit going into operation in 2027, and a second in 2030. All four of the plant’s biomass power-generating units would use carbon capture and storage by 2035, it says.
The cost of commercial-scale BECCS is hard to predict, with variables including the cost of biomass and the storage and transportation of captured CO2, future power and carbon prices, along with potential income from capacity and ancillary markets and possible government grants and subsidies.
The Intergovernmental Panel on Climate Change (IPCC) puts the cost of carbon removal via BECCS at $60-250 per tonne.
BECCS: carbon-negative or not?
All the CO2 captured from the four US commercial BECCS facilities is currently used for enhanced oil recovery (EOR)— that is, injecting it into depleting oil wells to allow more of the fossil-fuel to be recovered and eventually burned — so it would be hard to argue that these plants are carbon-negative facilities.
To qualify as carbon-negative, not only must the captured CO2 be permanently removed, but the entire process — from the supply chain to storing the carbon — must emit less CO2 than the amount ultimately captured and stored. This includes everything from producing and transporting the biomass’ fertiliser (often derived from ammonia produced from unabated grey hydrogen), to the planting, harvesting, processing and transporting the biomass itself to the transportation and storage of the CO2. For instance, in Equinor’s Northern Lights project, CO2 would be trucked to a port and then shipped out to sea before being injecting into a depleted oil reservoir.
“That could really make a difference between a plant that is actually carbon negative and one that is not because if you source your biomass from a non-sustainable source, or if you are importing it and transporting it across the ocean, it could be that the emissions that you’re creating are larger than the amount that you’re storing,” says Budinis.
For instance, the biomass used by the Drax power plant is compressed wood pellets currently imported from the US, Canada, Brazil and mainland Europe via fossil-fuel-powered trains, trucks and ships.
Drax does not quantify its supply-chain emissions, other than to say that “the power generated [at the plant] has a carbon emissions profile that is more than 80% lower than coal”.
BECCS: Sourcing biomass
Another potential issue is the origin of the biomass needed to be burned at the tens of gigawatts of BECCS plants.
According to a US National Academy of Sciences report in 2018, every billion tonnes of CO2 removed from the atmosphere by BECCS requires approximately 30-40 million hectares of feedstock.
The 2.6 billion tonnes of carbon dioxide that needs to be extracted via BECCS in 2070 — according to the IEA’s SDS — would therefore require 78-104 million hectares of land.
That equates to 5.2-7.0% of the world’s arable land today.
And let’s not forget that land and crops are needed to feed an ever-expanding global population, at the same time as climate change reduces the amount of land suitable for agricultural purposes.
So it will be important to use low-maintenance energy crops — plants that cannot be eaten, but provide a lot of energy when burned, such as miscanthus and elephant grass — and leftover biomatter from food crops such as sugar-cane bagasse, palm kernel shells and corn stover.
Land use will also play a role. For instance, clearing woodland to plant energy crops would actually result in higher net carbon emissions after BECCS than if the forest was left alone, according to a recent Exeter University study (see trees/soil section below).
Direct air capture (DAC)
An alternative to burning biomass in large power plants is to use machines powered by renewable energy to suck carbon dioxide out of the air directly.
Direct air capture (DAC) technology has been commercially available for several years, with 15 pilot plants around the world currently drawing more than 9,000 tonnes of CO2 from the atmosphere annually — the equivalent of the emissions from about 2,000 cars.
Climeworks draws in air using fans and captures the carbon dioxide “on the surface of a highly selective filter material”. Once the filter is saturated, it is heated to 80-100°C, which releases the CO2 for storage.
Carbon Engineering also uses giant fans to suck in air, but uses thin plastic surfaces with a potassium hydroxide solution flowing over them. This liquid binds with CO2 molecules and traps them as a carbonate salt. The resulting carbonate solution is then concentrated, purified and compressed and later heated to release the CO2 gas for storage.
Global Thermostat says it uses “amine-based chemical ‘sorbents’ that are bonded to porous, honeycomb ceramic ‘monoliths’ which act together as carbon sponges”. The CO2 is then extracted from the sponges using low-temperature steam (85-100°C), ideally utilising residual or process heat from nearby industrial facilities.
As the technology has yet to be demonstrated at scale, the future cost of DAC is hard to ascertain. A study in the Nature Communications journal, published in July last year, said that capture cost estimates range from $100-1,000 per tonne of CO2 — and this does not include the cost of long-term storage.
Climeworks’ carbon dioxide currently costs about $600-1,000 per tonne, depending on the amount purchased, but the company expects this to fall to $200 within four years and to $100 in the next decade.
And Carbon Engineering recently stated that capture costs of $94-232 were “achievable”, depending on energy and financing costs and plant configuration.
Storage costs would be extra, so even a carbon price of $100 per tonne — far higher than the €25-30 ($29-35) currently being seen in Europe — might not make DAC profitable from a pure CCS market perspective.
However, DAC’s advantage is that it can be used anywhere.
“The fundamental advantage of direct air capture, in my mind, is it effectively allows you to eliminate any kind of emission from any location and from any time – you’re clearing up CO2 from the atmosphere that could have come from yesterday, or today, or 100 years ago,” says Carbon Engineering chief executive Steve Oldham. “It provides you with a flexibility that other carbon capture methods don’t have.”
DAC: next level
In August, a deal was announced by Carbon Engineering that promises to be a giant leap forward for DAC.
The British Columbia-based company agreed to licence its technology to a joint venture led by oil company Occidental Petroleum, which plans to build a DAC plant in Texas that will capture one million tonnes of CO2 a year, with operation beginning in 2023.
The JV between Occidental subsidiary Oxy Low Carbon Ventures and sustainability-focused private equity firm Rusheen Capital Management, known as 1PointFive, will use the captured carbon for EOR.
Budinis explains the project’s significance.
“The latest estimate we have is for 10 million tonnes [of CO2] to be captured by 2030 [under the SDS in the IEA’s recent Energy Technologies Perspective report],” she says. “And if this plant from Carbon Engineering goes ahead, that’s one million tonnes, which means we have ten years to build ten plants, which for us is quite realistic.”
Like the BECCS plants, in order for the technology to be carbon-negative, DAC facilities would have to ensure that their supply chains and operations result in lower CO2 emissions than the amount captured.
And this obviously requires the captured carbon dioxide to be stored indefinitely.
Yet most of the 15 pilot DAC projects sell the captured CO2 for use — such as for EOR or synthetic-fuel production.
While EOR generally involves the CO2 being stored long-term — the gas is usually separated from the recovered oil and reinjected to form a closed loop — the CO2 emissions from the extracted oil far outweigh the carbon dioxide stored in the process. According to the Boston-based non-governmental organisation Clean Air Task Force, the lifecycle emissions of EOR oil is 0.32 tonnes of CO2 per barrel, compared to 0.51 tonnes for a standard barrel of oil.
Climeworks sells some of its CO2 to Coca-Cola’s Swiss arm to carbonate mineral water, while Global Thermostat’s business model seems to revolve around selling captured carbon dioxide for profit.
If DAC companies are to make their projects carbon-negative, they will therefore need to find alternative sources of income.
DAC: online sales
Climeworks has begun such a journey by asking consumers and businesses to pay for permanent carbon removal in their name — a kind of charitable contribution for the good of the planet that the Swiss company calls “easy and direct climate action”.
For this scheme, CO2 will be captured at the Carbfix project in Iceland, where water containing dissolved carbon dioxide — a kind of soda water — is injected underground into porous rock. The CO2 slowly reacts with elements in the rock and turns into solid carbonate minerals in less than two years.
Anyone can visit Climeworks’ website and become a “subscriber” and pay however much they see fit, from €12 to €24,000 a year. For instance, an annual subscription of €960 ($1,140) would cover the cost of removing one tonne of CO2— equivalent to driving an average petrol car for about 1,400km. Or €12 will pay for 12kg.
Companies can also pay Climeworks for carbon removal to offset or reduce their total CO2 emissions. Audi, for instance, is now paying Climeworks an undisclosed sum to remove 1,000 tonnes of CO2 per year.
And Stripe, a US-based online payment services company, is paying Climeworks for the capture and storage of 322.5 tonnes of CO2 at the Carbfix project at a cost of $775 per tonne.
If this sounds expensive, that’s because it is. Even now, there are far cheaper carbon-removal methods.
A Finnish company called Puro.earth offers a similar voluntary online service — removing carbon via wood-based building products and biochar (see below) — with prices starting at €20.60 for the removal of one tonne of CO2.
Capturing and storing carbon dioxide — a gas — is a complex process involving tanks, compression equipment, pumps, pipelines and vast airtight underground or subsea caverns.
But what if the carbon was captured and stored in its pure state, as solid carbon — a useful product that can be stored anywhere?
The reason that carbon dioxide is produced when burning organic matter — or fossil fuels — is because the carbon in the raw material reacts with oxygen in the air to produce CO2.
But biomass can be burned in the absence of oxygen inside pyrolysis ovens, resulting in a charcoal-like form of solid carbon called biochar.
Biochar has a variety of useful properties — it can purify water, improve the water retention of soil and be used as an additive in animal feed that helps reduce livestock’s digestive greenhouse gas emissions — making it a potentially sought-after material.
According to Finnish company Carbofex, which produces pyrolysis technology and biochar, 3,500 tonnes of wood chip feedstock will produce 1,000 tonnes of biochar, along with 1GWh of clean energy and the removal of 3,000 tonnes of CO2.
Carbofex says its equipment could use a variety of biomass materials, including straw, coconut shells, palm kernels, nut hulls and olive and date pits.
On the Puro.earth exchange, Carbofex’s biochar is a more expensive option for carbon removal than wood products — at €61.80 per tonne of CO2. But it is far longer-lasting, storing the carbon for more than 1,000 years, rather than the 50 years minimum promised for the wooden building materials.
The pyrolysis process also offers a further green incentive as it produces syngas (a mixture of carbon monoxide and hydrogen) and bio-oil as by-products, which can be combined with green hydrogen to produce methanol — a versatile chemical that can be further refined into carbon-neutral jet fuel.
Pyrolysis technology is being scaled up rapidly and costs are expected to fall due to economies of scale in the coming years, according to Puro.earth.
Trees and soil
Almost a quarter of the world’s greenhouse gas emissions come from agriculture, forestry and “other land use”, according to the IPCC — just one percentage point behind electricity and heat production.
The IPCC says that deforestation, wood burning and soil cultivation (which releases CO2 absorbed in the soil) together cause about 20 billion tonnes of CO2 emissions annually. At the same time, global tree and plant growth removes about 14 billion tonnes of CO2 per year, giving a net value of six billion tonnes.
If this balance can be reversed — through preventing deforestation and planting more trees, which absorb CO2 as they grow — then that would create a carbon-negative environment.
A recent study by Swiss university ETH Zurich, published in the journal Science, showed that a worldwide tree-planting programme could remove two thirds of all the carbon ever emitted from human activity. Researchers found that 900 million hectares of unused land could be turned into forest, potentially absorbing 205 billion tonnes of CO2.
However, the world is on course to lose 223 million hectares of forest canopy around the world by 2050, they added. Forest fires are increasing due to climate change, with all the stored carbon in the trees, soil and nearby vegetation literally going up in smoke.
In January, the World Economic Forum in Davos unveiled its Trilion Tree Campaign (also known as 1t.org) — an initiative to “grow, restore and conserve” one trillion trees around the world by 2030.
Even climate change denialist President Donald Trump signed up to the initiative, and last month signed an executive order establishing his country’s One Trillion Trees Interagency Council, “which will be responsible for coordinating the Federal Government’s interactions with this important global initiative”.
While planting seeds seems like a cheap and easy carbon-negative solution — which it undoubtedly is — trees are clearly impermanent, and it is difficult to accurately measure how much CO2 they and their soil absorb as they grow. Which is a little problematic in a society that puts a price on carbon.
This raises questions as to whether tree-planting programmes could receive carbon credits, or have their removed carbon sold on Puro.earth-style exchanges — and whether countries could declare themselves to be net-zero if they rely on forestation.
“Soil, forest and ocean are living things; they breathe,” says Marianne Tikkanen, chief executive of Puro.earth. “So there are always emissions sinking in and going out. And in which portion is it this year, a sink or an emitter? And if it is a sink, how much is it absorbing? What if something happens and the dynamics and the ecosystem change?”
For these reasons, Puro.earth does not include trees among its carbon-negative solutions, but it does, however, include building materials made from wood, which are a more permanent and measurable form of CO2 removal.
“We currently have the guarantee of a minimum 50 years of storage — and that is impossible to guarantee so firmly with soil, forest or ocean,” she tells Recharge.
Yet she adds: “It’s still worth doing because the potential is there and we need to do things that are more uncertain, it’s just that the quantification is harder.”
However, this problem may soon be resolved. The European Space Agency is due to launch a satellite named Biomass in 2022 that will use P-band radar to measure how much carbon is being stored in each of the world’s forests (including in the soil), and how that is changing over time.
And, of course, the cost of planting seeds is negligible — and is a task often performed by volunteers, or even dogs.
Increasing the amount of CO2 stored in soil is another possibility for carbon removal, but how this could be done is still a subject of ongoing scientific debate. Different farming methods, aridity and make-up of the soil and its geographical location all have impacts on carbon retention, suggesting that there would need to be bespoke solutions for each plot of land.
There are soil microbes called mycorrhizal fungi, which are symbiotic with plant roots, that can convert CO2 into a solid carbon-based material called humus that enriches soil. But it is not clear if this process has a positive or negative impact on overall soil emissions, as humus formation might increase subsoil organic matter decomposition more generally.
Back in the early 2010s, a geoengineering concept called ocean fertilisation attracted a lot of attention. This was a proposal to dump large amounts of iron filings into the world’s oceans to speed up the growth of CO2-devouring algae, with the carbon sinking to the ocean floor as the individual algae died.
The idea was later discredited after studies showed that pooling the iron that certain algae need to grow in limited areas would negatively impact the growth of algae elsewhere, making any potential climate benefits negligible.
In recent years, however, a similar concept known as “enhanced weathering” has been gaining momentum, with the potential for low-cost large-scale carbon removal.
Enhanced weathering involves spreading sand-like grains of olivine — a common green mineral with the chemical symbol Mg2SiO4 — on beaches.
The idea is that the motion of waves and a slow chemical reaction with water will gradually break down the olivine into magnesium, silicate (H4SiO4) and hydroxide (OH-).
The hydroxide would react with CO2 in the air to form bicarbonate (HCO3), which is gradually captured and stored indefinitely by limestone rocks on the seabed. The alkaline bicarbonate would also help de-acidify the ocean, enabling it to absorb even more CO2 from the air. And the silicate would encourage the growth of microalgae called diatoms that convert CO2 into organic carbon in the form of sugar, and oxygen — and when they die, that carbon will also sink to the sea bed.
A San Francisco-based non-profit organisation called Project Vesta is now planning an open-source enhanced-weathering pilot project at an undisclosed location in the Caribbean. The group says the process will capture 20 times more CO2 than emitted during extraction, milling and transportation of the olivine — and if deployed on 2% of “global shelf seas” it could capture 100% of annual human emissions.
The online payment company Stripe is one of the project’s high-profile backers, committing to paying for the removal of 3,333 tonnes of CO2 at a cost of $75 per tonne — less than a tenth of what it is paying Climeworks. Project Vesta says costs would fall to $10 per tonne when performed at scale.
Studies will continue for several years under the auspices of Project Vesta, with scientists hoping that artificial green-sand olivine beaches will eventually be seen around the world, with olivine also being spread across seabeds with fast-moving currents, absorbing billions of tonnes of CO2.