Not all carbon capture projects pay off for the climate – we mapped the pros and cons of each and found clear winners and losers.

Some carbon materials can be replaced with carbon-free alternatives, such as using renewable energy to produce electricity. However, for other uses, such as aviation fuel or plastics, replacing carbon will be more difficult. To that end, technologies are being developed to capture and recycle carbon.

Carbon capture, use and sequestration Carbon capture, use and sequestration, or CCUS, is the capture of excess CO₂ – from the oceans, the atmosphere or industry – and using it for new purposes. Of all the options for handling captured CO₂, my colleagues and I favor using it to make products, but let’s examine them all.

CCUS best and worst case scenarios

With each method, the combination of the source of the CO₂ and its final use, or disposal, determines its environmental and economic consequences.

In the best cases, the process will leave less CO₂ in the environment than before. A strong example of this is the use of captured CO₂ to produce building materials, such as concrete. It seals the captured carbon and creates a product with economic value.

Some methods are carbon neutral, meaning they do not add new CO₂ to the environment. For example, when CO₂ captured from the air or oceans is used and turned into fuel or food, the carbon returns to the atmosphere, but the use of captured carbon avoids the need for new carbon from fossil fuels.

Other combinations, however, are harmful because they increase the additional amount of CO₂ in the environment. A great example is one of the most common underground storage methods – enhanced oil recovery.

Advantages and disadvantages of underground carbon storage

Projects have for many years captured the excess CO₂ and stored it underground in natural porous rock structures, such as deep saline reservoirs, basalt or depleted oil or gas wells. This is called carbon capture and sequestration (CCS). If done correctly, geological storage can permanently remove large amounts of CO₂ from the atmosphere.

When the CO₂ is captured from air, water or biomass, this creates a carbon-negative process – there is less carbon in the air afterwards. However, if the CO₂ instead comes from new fossil fuel emissions, for example from a coal or gas power plant, carbon neutrality cannot exist. No carbon capture technology works at 100% efficiency, and some CO₂ will always escape into the air.

Capturing CO₂ is also expensive. If there is no product to sell, underground storage can be an expensive service that is eventually covered by taxes or fees, like paying for trash disposal.

One way to lower the cost is to sell the captured CO₂ for better oil recovery – a common practice that pumps captured CO₂ into oil fields to push more oil out of the ground. Although most of the CO₂ is expected to remain underground, the result is more fossil fuels that will ultimately put more carbon dioxide into the atmosphere, eliminating the environmental benefit.

Using captured carbon for food and fuel

Short-lived materials made from CO₂ include aviation fuels, food, drugs and working fluids used in metal machining. These items are not particularly durable and will soon decompose, releasing CO₂ again. But selling the products has economic value, which helps pay for the process.

This CO₂ can be recaptured from the air and used to make a future generation of products, creating an essentially circular, sustainable carbon economy. However, this only works if the CO₂ is captured from the air or oceans. If the CO₂ comes from fossil fuel sources instead, this is new CO₂ that will be added to the environment when the products decompose. So, even if it is caught again, it will worsen the climate change.

Carbon storage in materials, such as concrete

Some minerals and waste materials can convert CO₂ into limestone or other rock material. The long-life materials created in this way can be very durable, with a lifespan of over 100 years

A good example is concrete. CO₂ can react with particles in concrete, causing mineralization in its solid form. The result is a useful product that can be sold instead of stored underground. Other durable products include aggregates used in road construction, carbon fiber used in automotive, aerospace and defense applications ]and some polymers.

These materials provide the best combination of environmental impact and economic benefit when they are made with CO₂ captured from the atmosphere rather than new fossil fuel emissions.

Choose your carbon projects wisely

CCUS can be a useful solution, and governments have started pouring billions of dollars into its development. It needs to be closely monitored to ensure that carbon capture technologies do not delay fossil fuel phasing out. It is an all-hands effort to adopt the best combinations of CO₂ sources and disposal to achieve rapid scaling at an affordable cost to society.

Because climate change is such a complex problem that is harming people around the world, and for generations to come, I believe it is vital that actions are not only quick, but well thought out. and that they are based on evidence.

Fred Mason, Gerry Stokes, Susan Fancy and Stephen McCord of the Global CO₂ Initiative contributed to this article.

This article is republished from The Conversation, a non-profit, independent news organization that brings you facts and analysis to help you make sense of our complex world.

It was written by: Volker Sick, University of Michigan.

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Volker Sick receives funding from the Grantham Foundation for Environmental Conservation.