At the COP28 climate talks underway in Dubai, draft decisions thus far have referred to the abatement and removal of carbon emissions using carbon capture and storage (CCS) and carbon-dioxide removal (CDR) technologies. Considering the meaning of the word ‘abatement’ has become an important bone of contention, understanding the meaning and limitations of CCS is important – as also those of CDR.
What are CCS and CDR?
CCS refers to technologies that can capture carbon dioxide (CO₂) at a source of emissions before it is released into the atmosphere. These sources include the fossil fuel industry (where coal, oil and gas are combusted to generate power) and industrial processes like steel and cement production.
CDR takes the forms of both natural means like afforestation or reforestation and technologies like direct air capture, where machines mimic trees by absorbing CO₂ from their surroundings and storing it underground.
There are also more complex CDR technologies like enhanced rock weathering, where rocks are broken down chemically; the resulting rock particles can remove CO₂ from the atmosphere. Other technologies like bioenergy with carbon capture and storage (BECCS) capture and store CO₂ from burning biomass, like wood.
At COP28, the term “unabated fossil fuels” has come to mean the combustion of these fuels without using CCS technologies to capture their emissions. Draft decision texts point to a need to “phase out” such unabated fossil fuels. On the other hand, removal technologies have been referenced in the context of the need to scale zero and low-emission technologies and support forest restoration as a means to promote emission removals.
How well do CCS and CDR need to work?
While their technical details are clear, scientists have questions about the scale at which CCS and CDR are expected to succeed.
The Sixth Assessment Report (AR6), prepared by the United Nations Intergovernmental Panel on Climate Change (IPCC), deals with climate mitigation. It relies a lot on the use of CDR for its projections related to the world achieving the goal of limiting the world’s average surface temperature increase to 1.5 degrees C with no or limited overshoot. (Overshoot means the temperature limit is temporarily exceeded.)
The emission scenarios that the IPCC has assessed that have more than a 50% chance of limiting warming to 1.5 degrees C (with no or limited overshoot) assume the world can sequester 5 billion tonnes of CO₂ by 2040. This is more than India emits currently every year.
There is no pathway to 1.5 degrees C in AR6 that doesn’t use CDR.
“Without CDR, we would have to decrease emissions by more than during the COVID-19 pandemic annually,” David Ho, a climate scientist at the University of Hawaii, told this reporter.
“If CO₂ emissions continue at current levels, we will have a 50% chance of exceeding 1.5 degrees C compared to pre-industrial levels in seven years,” Dr. Ho added. “To achieve the decrease in CO₂ emissions we need by direct mitigation would be nearly impossible at this point, and would require a lot of CDR,” Dr. Ho explained.
Direct mitigation refers to reducing our reliance on fossil fuels with renewable energy sources like solar and wind power.
How well does CCS work?
The IPCC AR6 report states CDR ought to be used “to counterbalance hard-to-abate residual emissions.” The reason: “available CDR is to be used strategically to compensate hard to abate residual emissions, not to maintain a high level of fossil fuel use,” Alaa Al Khourdajie, a research fellow at Imperial College London and a contributing author to AR6, said.
For CCS, too, Dr. Al Khourdajie and other AR6 authors showed in a recent paper that the term “abated fossil fuels” should be used only in the context of highly effective CCS applications, with a capture rate of 90-95% or more, the captured emissions being stored permanently, and methane emissions leakage from upstream oil and gas production processes being kept under 0.5% (approaching 0.2%).
But in the real world, natural CDR has been tacked on to existing emissions. For example, the 2023 ‘Land Gap’ report estimated that various governments have proposed to remove CO₂ using around one billion hectares of land. Based on this, the report reflected: “Some pledges over-rely on land-based CDR to offset fossil fuel emissions. This raises serious concerns that these countries are shifting their mitigation burden away from reducing fossil fuel use.”
As for CCS developments, Henri Waisman, who leads a global initiative called ‘Deep Decarbonization Pathways’ and coauthored an IPCC Special Report, said, “CCS is still a technology under development without demonstrated feasibility at large scale despite decades of development.”
Aside from high cost, he pointed to creation of additional energy needs, and challenges in the transport and long-term storage of carbon.
How well does CDR work?
CDR methods like afforestation, reforestation, BECCS, and direct air capture are constrained by their need for land.
Land also invokes equity concerns. Land in the Global South is often considered to be ‘viable’ and/or ‘cost-effective’ for planting trees and deploying other large-scale CDR methods. As a result, such CDR projects can adversely affect land rights of indigenous communities and biodiversity and compete with other forms of land-use, like agriculture that is crucial for ensuring food security.
This is of particular concern vis-à-vis technological CDR at scale. “For example, what’s to prevent companies from using land in the global south for direct air capture and using land that would otherwise be used to generate renewable energy to power the economies of global south countries?” Dr. Ho asked.
He added that “the next decade will be pivotal in determining if there are viable and scalable CDR methods. But we also need to figure out who will pay for CDR at scale in the future.
“Imagine global north countries asking ‘why should we spend trillions of dollars on CDR when we can spend it on adaptation?’”
What are other pitfalls of CCS and CDR?
By removing CO₂ from their environs, there are concerns that CCS and CDR create more ‘room’ to emit the greenhouse gas. (In some cases, CCS has also been used to inject captured CO₂ is into oil fields to extract more oil.)
In future emissions scenarios that the IPCC has assessed, the world’s use of coal, oil, and gas in 2050 needs to decline by about 95%, 60%, and 45% respectively (all median values) from their use in 2019 to keep the planet from warming by less than 1.5 degrees C with no or limited overshoot. But without CCS, the expected reductions are 100%, 60%, and 70% for coal, oil, and gas by 2050.
In a recent paper, an international group of researchers wrote that higher use of CCS and CDR make way for emissions pathways with a higher contribution from gas.
Rishika Pardikar is a freelance environment reporter.
- CCS refers to technologies that can capture carbon dioxide (CO₂) at a source of emissions before it is released into the atmosphere.
- The IPCC AR6 report states CDR ought to be used “to counterbalance hard-to-abate residual emissions.
- CDR methods like afforestation, reforestation, BECCS, and direct air capture are constrained by their need for land.
