What does the idea of absorbing CO2 from the air to combat climate change entail?
Humanity is treading on dangerous ground. Only a rapid reduction in fossil fuel use, increased efficiency, and deep cuts in greenhouse gas emissions across all sectors could avoid the worst of climate change, according to a new report published by the United Nations Intergovernmental Panel on Climate Change (IPCC).
The new report should serve as a “survival guide for humanity,” according to United Nations (UN) Secretary-General Antonio Guterres, who recommended an “everything, everywhere, all at once” approach to climate action.
Alongside measures to reduce the amount of carbon emitted into the atmosphere, this approach will likely need to include another action that scientists, though frustratingly, consider increasingly necessary: the removal of carbon dioxide (CO2).
The term refers to a variety of mechanisms and technologies that would remove CO2 from the air and trap it so that it does not contribute to the greenhouse effect that is warming our planet.
The techniques being discussed include everything from direct air capture or bioenergy with carbon capture and storage (BECCS) to biochar or enhanced rock weathering.
Because for decades the world has failed to curb the rise in greenhouse gas emissions, many scientists now consider some form of CO2 removal essential to limit dangerous climate change.
Rob Bellamy, a professor of Climate and Society at the University of Manchester, says the IPCC report makes it clear that removing CO2 from the air “is not just an option but a necessity.”
However, he warns that carbon removal methods also carry significant risks for both people and the environment.
“We now need a wide-ranging conversation in society about which methods to pursue, how to incentivize them, and ultimately, how to govern them. Make no mistake, we need to remove carbon, but we must do so responsibly.”
In particular, the new IPCC report points out that CO2 removal will be necessary to offset “hard-to-abate residual greenhouse gas emissions” in order to achieve net-zero CO2 or greenhouse gas emissions.
Sectors with these hard-to-abate emissions include agriculture, aviation, shipping, and industrial processes, the report notes (these sectors are considered hard-to-abate due to a lack of technology or the high cost of decarbonization).
But not all scientists agree. Some are concerned about the feasibility of large-scale CO2 removal and say it would be a mistake to rely too heavily on it.
They also warn that it could provide an unjustified and risky excuse for governments to avoid the deep emission cuts needed to address climate change.
“IPCC reports show that we can prevent irreversible harm to people and the planet if we scale up the proven solutions available now: replacing fossil fuels with renewable energy, increasing energy efficiency, and reducing energy and resource use are the safest way to limit global warming to 1.5°C,” says Lili Fuhr, deputy director of the climate and energy program at the Center for International Environmental Law (CIEL), a non-profit environmental law firm based in Geneva, Switzerland.
“Building our mitigation strategies on models that instead sustain unequal growth and conveniently assume the risks of technological solutions like carbon capture and storage and CO2 removal ignores that clear message and increases the likelihood of overshoot,” adds Fuhr.
How much do we need?
Earlier this year, a report led by researchers from the University of Oxford provided the first comprehensive assessment of the current state of human CO2 removal worldwide.
It estimated this number at around 2 billion tonnes (Gt) of CO2 per year.
This is roughly equivalent to 5% of the 36.6 GtCO2 emitted into the atmosphere from fossil fuel use and cement production in 2022.
But currently, there are few plans by countries to increase CO2 removal above current levels, according to the report.
In its own assessments, the IPCC analyzes different pathways to achieve emission reductions that correspond to various degrees of ambition.
Most of these pathways now require some level of CO2 removal techniques, and virtually all scenarios consistent with the Paris Agreement’s goals of limiting warming to 1.5°C or well below 2°C include at least some CO2 removal.
Currently, the world is on track for a 2.4°C increase by 2100 if all UN countries’ climate commitments are fully implemented, or 2.8°C by 2100 if only existing climate policies are taken into account.
However, the exact amount of removal needed to reach this level depends greatly on the emission cuts made, making it difficult to pinpoint an exact figure.
Scenarios that show sharp and rapid emission cuts require the least amount of CO2 removal.
Some of the IPCC scenarios also allow for “climate overshoot,” a period where global temperature targets are temporarily exceeded before being brought back down to the set value.
Lowering temperatures in this way would require some form of CO2 removal, says the IPCC.
What are the options?
There are a wide variety of different ways we could remove CO2 from the air. However, it is worth noting that technological methods have not been tested at scale.
Bioenergy with carbon capture and storage (BECCS) is the most prominent technological method in the IPCC report.
Here, trees are grown to capture CO2 before being burned in a plant for energy.
The plant’s emissions are captured and permanently stored underground, a practice known as BECCS.
Another highly discussed technological method for removing CO2 from the atmosphere is direct air capture (DAC).
The technique uses machines to extract CO2 directly from the air. If this CO2 is permanently stored underground using BECCS, the total emissions are negative.
The vast majority of investment between 2020 and 2022 focused on this form of CO2 removal.
Meanwhile, using biochar for CO2 removal would involve using biomass, such as trees or plant matter, which has captured carbon while growing, being pyrolyzed (heated in the absence of oxygen) to produce a coal-like black substance that consists mainly of elemental carbon.
This biochar can be added to soils, theoretically locking in the carbon.
Enhanced rock weathering has also been proposed as a way to remove CO2 from the atmosphere. This would involve spreading large amounts of finely ground silicate rock, such as basalt, on the land in an effort to mimic the natural weathering of rock, which would eventually lead to CO2 being trapped in the ocean as bicarbonate or locked up in the seafloor.
Finally, ocean alkalinization is another proposed process that would involve adding alkaline materials to the ocean, such as silicate or carbonate rocks, to increase the amount of CO2 it absorbs.
Similarly, ocean fertilization would involve stimulating the growth of phytoplankton in the ocean to enhance carbon sequestration.
Despite being highly touted, these “novel” methods of CO2 are also actually in their infancy.
Steve Smith, executive director of Oxford Net Zero and CO2RE at the University of Oxford and lead author of the CO2 removal assessment, points out that even the combination of all the above methods removes only two million tonnes of CO2 per year (Mt CO2/year). That is an amount equivalent to 0.005% of global cement and fossil fuel emissions in 2022.
According to the CO2 removal assessment, capture through these methods needs to grow by four to six orders of magnitude by mid-century to meet the temperature goals of the Paris Agreement.
Source: www.bbc.com
