The Carbon Must Flow

Written by Ryan McGuine //

Most countries around the world, and increasingly many companies, have pledged to reach net-zero carbon emissions by or around 2050. Crucially, net-zero does not necessarily mean zero emissions. Rather, it means that a quantity of carbon emissions equivalent to those emitted have been either removed from the atmosphere, or prevented from having reached the atmosphere in the first place. Additionally, nearly every modeled pathway to meet the Paris Agreement’s goal of keeping the global temperature rise well below 2°C above pre-industrial levels, and preferably below 1.5°C, include assumptions for large amounts of carbon capture and sequestration. As such, even though carbon management is a nascent field today, it is poised to grow dramatically in the next few decades.

The earth has a natural carbon cycle, which constantly moves carbon between its major reservoirs like plant biomass, soil, and fossil carbon on land, as well as marine biomass, ocean water, and ocean sediment at sea. All carbon reservoirs are not created equal however: the length of time something has been absorbing carbon influences how much carbon it contains. This means that fossil fuels formed by hundreds of millions of years of heat and pressure contain more carbon than trees that are tens of years old, and that domestic animals contain more carbon than the grasses and cereals they were raised on. Humans affect earth’s natural carbon cycle in a number of ways, like burning fossil fuels, which releases stored carbon into the atmosphere, or converting forests to agriculture or grazing land, which reduces the land’s ability to store carbon. The good news is that human actions can disrupt the carbon cycle in the other direction too, using a suite of practices broadly referred to as carbon management, or carbon capture, utilization, and storage (CCUS).

There are numerous ways to categorize the available CCUS solutions. For example, one could do so based on the method of removal – “natural” methods bolster the earth’s ability to pull carbon dioxide from the air, while “engineered” methods utilize mechanical or chemical means that do the same. One could also sort based on the method of storage – carbon can be stored in “organic” sources like biomass, or in “inorganic” forms in a gaseous state or mineral formations. However, many techniques lie somewhere in between any plausible categories, so bucketing exercises are more helpful for clarifying the conversation than saying something meaningful. Each category comes with a range of trade-offs. Photosynthesis is a super efficient method of pulling carbon dioxide from the air, but biomass approaches take up huge amounts of land. Meanwhile engineered solutions can be installed nearly anywhere, but require lots of energy and ancillary equipment to operate. 

Carbon dioxide can be prevented from reaching the atmosphere by removing it from an exhaust stream or process waste stream at the facility where it is generated, a technique known as “point-source” carbon capture. This is done at a handful of sites today, but even if point-source capture systems were installed at every site that emits carbon dioxide, some amount of atmospheric carbon removal will also be necessary. One reason is that certain sectors like aviation or agriculture are relatively large emitters of greenhouse gases, but lack feasible ways to capture those emissions. Atmospheric carbon capture could help balance today’s emissions from these difficult sectors. Second, it is possible that carbon emissions will not reach net-zero by 2050. In that case, atmospheric capture could help prevent the worst effects of climate change by removing historical carbon emissions, which can remain in the atmosphere for hundreds of years.

The cost of capturing carbon varies greatly by technology. For some idea, Stripe has shared details about the companies it has funded (here and here), and the International Energy Agency has compiled a list of costs for various engineered solutions. Over time, costs should come down as companies gain experience building and operating systems. Costs for renewable energy systems fell rapidly over the last decades, while natural gas combined cycle power plants also declined from where they started, but have not declined as quickly or as dramatically. This has to do with the fact that they are complex facilities with many interacting systems, each moving different fluids at different temperatures and pressures. Since carbon capture systems are more similar to natural gas combined cycle plants than solar panels or wind turbines, their cost curves will probably look alike. Most actors working on carbon capture are targeting $100 per ton, a round number that reflects the fact that large American customers currently pay around $65-110 per ton of carbon dioxide.

Once carbon dioxide is captured, it can then be utilized for something as a means of preventing further emissions. For example, enhanced oil recovery is the largest use today. Enhanced oil recovery can reduce total emissions if it is used to displace higher-emitting oil resources like oil sands, but the business case for operating facilities depends on a relatively high price of oil. Oil prices are notoriously unpredictable, though, so researchers are currently working to find other novel ways to use carbon dioxide like synthetic fuels, concrete, and new plastics formulations. However, capturing carbon to re-emit it merely keeps the atmospheric concentration constant, but does not actually reduce the concentration of carbon dioxide in the atmosphere. Accordingly, carbon utilization is feasible during the next few decades, particularly if it drives the deployment of more carbon capture technologies, but humanity probably needs to move toward sequestering the stuff in the long term.

As with capture and utilization, there are a number of methods to sequester carbon dioxide, each with unique costs and benefits. For example, methods of sequestration vary in their “durability,” or the likelihood that they retain the carbon. Biomass storage is cheap and easy to scale quickly, but is effectively eliminated if a wildfire burns the plot. Meanwhile, storage in geological deposits is more technically challenging, but minimizes leakage rates. Sequestration methods also vary in terms of “additionality,” or the likelihood that they would have happened without any incentives. Preventing development of a piece of land to avoid the associated carbon emissions is only valid if that land was going to be developed in the first place, and if its conservation does not drive development elsewhere. Geological storage does not suffer the same problem, since the volume of potential storage is hundreds of years of current emissions rates.

As of 2021, there were a total of 27 operational (engineered) carbon capture projects around the world, and another 108 in various stages of development or construction. Once they are all operational, those 135 projects are projected to have a combined capture capacity of around 150 megatons (Mt, or 1m tons) per year. Most of these are point-source systems attached to power generation or industrial facilities, but there are a few direct air capture systems as well. For a sense of magnitude, limiting warming to 2°C will require scaling that number up to around 5,600 Mt per year by 2050, something that will take around $1,000 billion between now and then. Most currently-operating facilities use the captured carbon dioxide for enhanced oil recovery, since there is a business case for doing so, but some of the coming projects plan to sequester it in saline aquifers.

Rapidly scaling up the world’s CCUS would benefit all of humanity, but it is technologically challenging and expensive. This is exactly the kind of situation that national governments should spend money on. In fact, some already are in small ways, like the 45Q tax credit in America and Australia’s recent amendments to its pipeline transportation regulations. As things stand, more government incentives are needed to boost the industry, but in the meantime a whole host of private actors are stepping in to help. Digital payments firm Stripe, whose 2020 donation of $1m was the largest-ever at the time, has organized a collection of companies to kick-start a market for carbon removal. The group has pledged almost $1bn in advanced market commitments for startups working on different carbon management methods. In addition, the Musk Foundation instituted a $100m prize for carbon removal, and numerous business incubators and VC firms are directing their expertise toward the space. 

CCUS is sometimes criticized as a way to extend operating license to the status quo, pulling momentum from renewables deployment and fossil fuel reduction. However, this kind of “either-or thinking” in the context of climate change is faulty – the sheer scale and complexity of the problem requires “both-and thinking” instead. While humanity simply cannot continue burning fossil fuels at near its current rate, meeting climate targets will be nearly impossible without lots of CCUS. The adoption of an economy-wide price on carbon would speed up its development by internalizing the externality of carbon emissions. However, there is no time to wait for a carbon price, and many instruments are available to governments in the meantime. Policies like financing and zoning net-zero infrastructure hubs, adopting procurement standards or tax credits, and instituting green banks would all greatly accelerate the deployment of carbon management systems, while being flexible within different markets and political systems.