Carbon removal

Carbon removal, also known as carbon dioxide removal or CDR, is the process of removing carbon dioxide from the atmosphere and locking it away for decades, centuries, or millennia. This is envisioned as slowing, limiting, or even reversing current human impacts on the climate and climate change but is not often seen as a potential substitute for cutting greenhouse gas emissions. Rather, carbon removal is often envisioned as a complementary technology for an overall strategy toward reducing the impacts of climate change. Especially as most carbon removal methods or techniques are untested at scale, rely on expensive technology, or have long timelines for overall effectiveness.

Generally, the methods of carbon removal are seen as complementary to an overall strategy for reducing emissions and reaching net-zero emissions for a given country. Many of these methods can also be employed beside each other to allow for a more complete carbon removal strategy to help a state reach a net-zero strategy. The most widely discussed or used approaches to carbon removal include those below:

Carbon removal can be an important part of a climate strategy as between 15 to 40 percent of carbon dioxide emitted through human industry remains in the atmosphere for up to a thousand years, with an additional 10 to 25 percent persisting for tens of thousands of years. Carbon removal promises the potential for removing and sequestering carbon dioxide, leading to a slowing or potentially reversing of climate change.

For many states, the lack of carbon removal will make the chance of these states meeting their climate change mitigation goals difficult, if not impossible (especially given the ambition of certain goals). For example, in studies reviewed by the Intergovernmental Panel on Climate Change for their Fifth Assessment Report found most of the pathways to meet the targets laid out in the 2015 Paris Agreement would require at least some form of large-scale carbon removal alongside aggressive emissions reductions.

One of the most important concerns in the development of carbon removal methods and technologies is the ability to monitor, report, and verify that the methods are effective. Especially as long-term studies into the effectiveness of these methods and technologies have not, generally, been conducted. Monitoring, reporting, and verification offers a chance to quantify the amount of carbon dioxide these efforts can remove from the atmosphere and lead to a greater understanding of the overall effect of the technologies and the potential for the technologies to scale and lead to net-negative emissions.

Carbon removal has grown as an area of interest, particularly as global temperatures have continued to rise even as global efforts to forestall or reverse those temperatures and their impacts have moved forward. However, much of carbon removal remains unstudied, particularly in its potential side effects. This has led some to suggest that the technology and methods for carbon removal require immediate research before implementation, while others have emphasized implementation and placed their faith in largely untested technology.

Existing technologies and methods have been noted as too slow-acting, limited in scope, or expensive to offset the amount of carbon dioxide that would make a serious difference to any society's current carbon dioxide emissions. Carbon removal has been suggested as effective when paired with ambitious emissions reductions, in which carbon removal could be part of an effective net-zero strategy and could even, eventually, reach its potential and enable net-negative emissions or gradually lower atmospheric carbon dioxide concentrations.

Further, there is a general concern around the "moral hazard effect" of carbon removal, in which policymakers could view the removal of carbon as an excuse to avoid cutting carbon dioxide emissions. Especially, as noted above, the potential effectiveness of carbon removal remains largely theoretical, and basing a climate strategy on the hope for these technologies could actually worsen the climate and saddle future generations with a worse climate than is necessary. This is even worse if these methods and technologies prove infeasible for any reason.

The converse can be true as well. If carbon removal technologies and methods require further study, and in turn can take decades before they can make a significant difference on atmospheric carbon dioxide levels, then any delay in the research and development of the technology can make the later elimination of greenhouse gases more difficult and further worsen the climate than strictly necessary.

Carbon removal and carbon capture tend to be compared as they are rather similar in the description of their removal of carbon dioxide. However, where carbon removal is the process of removing atmospheric carbon, which is then often trapped in a carbon sink where it can remain for as long as possible, carbon capture tends to be described as the capturing of carbon dioxide at the point of emission, such as in a coal-fired power plant or cement mixer, where the carbon is captured throughout the process or in the smokestack through the use of scrubbers.

Often, carbon capture is associated with the use of carbon in commercial products, such as bioplastics, which can reuse carbon from emissions. Whereas carbon removal is more often associated with carbon sequestration or the trapping of carbon dioxide in a natural carbon sink, such as soil, a forest, or minerals.

These two approaches are often blurred due to their similarities, especially as some carbon removal techniques—particularly direct air capture—could reintroduce the carbon into commercial products. However, some argue that maintaining the distinction can be incredibly important as carbon capture does not do anything to address the carbon dioxide in the atmosphere and only reduces or eliminates the introduction of any further carbon dioxide from human industry. Both can be considered important to an overall climate policy and can complement each other in many ways.

Another commonly conflated approach to the use of carbon dioxide levels in the atmosphere is carbon removal and carbon sequestration. This makes sense, as both tend to be discussed similarly; however, they remain different methods to reduce global atmospheric carbon levels. Carbon removal works to remove or eliminate carbon dioxide in the atmosphere, whereas carbon sequestration is the storage of removed or captured carbon in various environmental reservoirs.

Carbon sequestration is best considered a downstream industry of carbon removal, as the carbon removed from the atmosphere by non-natural methods needs to be either used in a commercial application, such as bioplastics or stored in concrete, or else sequestered in a long-term carbon sink. In a natural removal method, such as afforestation or reforestation, the carbon is captured by the trees and is sequestered both in the plants and the soil.