Stopping pollution is not enough to prevent global warming. At the same time, billions of tons of carbon that ended up in the atmosphere must be removed. But how? To keep global temperature rise well below 2 degrees Celsius and avoid the worst effects of climate change, the planet’s inhabitants must start removing billions of tons of CO2 from the atmosphere, while reducing greenhouse gas emissions deeply and rapidly.
“It’s not one or the other,” said Jan Minx of the Mercator Research Institute on Global Commons and Climate Change (MCC) in Berlin and one of the authors of a new global overview of carbon removal projects published this week.
Governments around the world must make full use of established and future carbon removal technologies to reach the goal of netzero by midcentury, Minx said. It will also require increased efforts in the coming decades to bring atmospheric CO2 back to a climatesafe level.
advances over the past decade
By 2100, carbon removal technology will need to extract between 450 billion and 1.1 trillion tons of CO2 depending on how fast we reduce emissions over the next few decades, the report said.
“Innovation takes time, scaling takes time, and unless we start building these facilities now and develop appropriate policy plans, we won’t make it,” Minx warned.
But few governments have included carbon sink projects in their plans to meet emissions targets, though progress in this area has accelerated over the past decade, says the report, which is the first to focus efforts on carbon sinks globally.
“The next decade is crucial”
Since 1990, we’ve emitted more than 924 billion tonnes of CO2equivalent into the planet’s atmosphere — a metric used to compare emissions of different greenhouse gases based on their global warming potential. In 2021 alone, it was more than 37 billion, mostly from burning fossil fuels that are destroying the climate. That’s more CO2 emitted in three decades than in all of human history before that time.
Almost all of the world’s current carbon removal estimated at about 2 billion tonnes of annual emissions is achieved using conventional methods on managed land. These include established methods such as wetland restoration such as peat bogs and swamps, reforestation, and carbon fixation in plantations and pastures.
A small 0.1% comes from new technologies such as biochar (short for biocharcoal charcoal used for soil correction, for example), capture and direct storage of carbon in the air, and bioenergy with carbon capture and storage.
According to the report, “the next decade is crucial” for the development of new carbon removal technologies, given the advances made in the renewable energy sector over the past 20 years.
Biochar can help in agriculture
One of these technologies under development is biochar, which captures the carbon absorbed by agricultural and forest residues bark, roots, branches and sawdust and other organic residues.
These residues are heated under pressure in an environment with no or very little oxygen and charred, turning them into a black powder of carbon and ash. This process binds and stores CO2 in a stable and solid way, preventing it from decomposing naturally and releasing that carbon back into the atmosphere.
When mixed with soil, charcoal can act as a fertilizer, helping to increase crop yields and improve water retention.
Biochar has been the focus of about half of all research on carbon removal methods in recent years, particularly in China. By 2050, global application of this technology could help remove between 0.3 and 6.6 billion tons of CO2 per year.
However, biochar production can contribute to particulate matter pollution and greenhouse gas emissions through the initial warming process.
The underground storage of CO2 could be the solution
Carbon dioxide can also be captured and stored in underground reservoirs, an expensive and limited process that has been used in Norwegian oil fields since the late 20th century.
Chemical methods are used to extract the gas from the surrounding air, known as Direct Air Carbon Capture and Storage, or DACCS. It is then compressed and stored in liquid form in vast underground reservoirs.
Swiss company Climeworks recently announced that it has successfully sequestered CO2 in basalt rock formations, where natural processes will turn it into solid rock in about two years.
Other DACCS pilot projects are also being developed in Canada and the United States.
Since the amount of CO2 that can be captured and stored is unlimited, DACCS is said to have great potential. However, the process is still controversial because storing CO2 underground can lead to earthquakes and longterm soil carbon losses.
Both methods are still far from being widely used. A major disadvantage is the cost, which the independent World Resources Institute (WRI) currently estimates is between $250 and $600 per tonne. The institute estimates that mass production of DACCS systems could reduce prices by $150 to $200 per ton over the next 10 years.
Use of carbon as bioenergy
Another way to remove carbon from the air is to collect biomass leftovers from crops and forests, organic waste or plants grown specifically for this purpose and burn it in a power plant to produce bioenergy. The CO2 is then extracted from the plant’s exhaust gas and stored underground. This method helps phase out fossil fuels while sequestering CO2.
The big problem with this technology, known as Bioenergy with Carbon Capture and Storage (BECCS), is the huge footprint. BECCS crops could end up competing with food crops for land and water and contributing to the loss of biodiversity and soil fertility, the carbon removal report points out.
Binding of CO2 to gravel
In this process, called advanced rock weathering, carbonate and silicate rocks are mined, ground up and scattered on farmland or on the sea surface. There they mimic the natural erosion process of rain, which absorbs CO2 on its way through the atmosphere and retains it as bicarbonate. Theoretically, adding ground rock to ocean water increases alkalinity and increases CO2 uptake.
Recent research suggests this technique could capture between 2 and 4 billion tons of CO2 every year by 2050. The main challenges are the destructive effects of mining facilities and the potential contamination of some rock types with heavy metals.
Transplanting trees helps the soil
Trees are a powerful natural solution for sequestering carbon and, if protected, can sequester carbon for decades or even centuries.
A 2019 study by the Swiss Federal Institute of Technology in Zurich found that if trees were planted on an additional 0.9 billion hectares worldwide, they would store around 205 billion tons of carbon when they reached maturity.
But is that the problem? It can take many years for a tree to be ready to absorb that much carbon. And the land area needed is about the size of the United States. Our forests’ ability to remove carbon could also decrease as the impacts of climate change increase, leading to more wildfires, diseases and pests.
Another natural solution is humus — the rich, dark organic matter in soil that results from the decay of plants and animals. It also contains a lot of carbon. By growing crops that sequester carbon and adapting farming practices to leave crop residues in the soil, we can also increase the amount of CO2 stored in the soil.
In an analysis of EU climate policy, the German Society for International Politics and Security found that between 2 and 5 billion tons of CO2 could be bound by the accumulation of humus from around the world.
Author: Martin Kübler, Gero Rueter