Not all carbon capture projects pay off for the climate – we’ve mapped out the pros and cons of each project 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 applications, such as jet fuel or plastics, carbon will be more difficult to replace. To this end, technologies are being developed to capture and recycle carbon.

Capturing excess CO₂ – from the oceans, atmosphere or industry – and using it for new purposes is called carbon capture, use and sequestration or CCUS. Of all the options for dealing with captured CO₂, my colleagues and I prefer to turn it into products, but let’s explore them all.

CCUS best and worst cases

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

In the best case, the process leaves less CO₂ in the environment than before. A strong example of this is the use of captured CO₂ for the production of building materials, such as concrete. It locks in the captured carbon and creates a product that has economic value.

A number of methods are CO₂ neutral, meaning that they do not add new CO₂ to the environment. For example, if you use CO₂ from the air or oceans and turn it into fuel or food, the carbon returns to the atmosphere, but using captured carbon avoids the need for new carbon from fossil fuels.

However, other combinations are harmful because they increase the amount of excess CO₂ in the environment. One of the most common methods of underground storage – enhanced oil recovery – is a good example.

Advantages and disadvantages of underground carbon storage

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

When CO₂ is captured from the air, water or biomass, a carbon-negative process is created; there is less carbon in the air afterwards. However, if the CO₂ instead comes from new fossil fuel emissions, such as those from a coal- or gas-fired power plant, carbon neutrality is not possible. No carbon capture technology works with 100% efficiency, and some CO₂ will always escape into the air.

Capturing CO₂ is also expensive. Without a product to sell, underground storage can become a costly service that is ultimately covered by taxes or fees, similar to paying for waste disposal.

One way to reduce costs is to sell the captured CO₂ for better oil recovery – a common practice in which the captured CO₂ is pumped into oil fields to push more oil out of the ground. While most of the CO₂ is expected to remain underground, the result is more fossil fuels that will ultimately release more carbon dioxide into the atmosphere, negating the environmental benefit.

Using captured carbon for food and fuel

Short-lived materials made from CO₂ include aviation fuels, food, medicines and working fluids used in metalworking. These objects are not particularly durable and will quickly decompose, releasing CO₂. But the sale of the products provides economic value, which pays for the process.

This CO₂ can be captured back from the air and used to create a future generation of products, which would create a sustainable, essentially circular carbon economy. However, this only works if the CO₂ is captured from the air or oceans. If the CO₂ instead comes from fossil fuels, this is new CO₂ added to the environment as the products decompose. So even if it is caught again, it will worsen climate change.

Storing carbon in materials, such as concrete

Some minerals and wastes can convert CO₂ into limestone or other rock materials. The long-life materials made in this way can be very durable, with a lifespan of more than 100 years

A good example is concrete. CO₂ can react with particles in concrete, causing it to mineralize into a solid form. The result is a useful product that can be sold instead of being stored underground. Other sustainable products include aggregates used in road construction, carbon fibers used in automotive, aerospace and defense applications and some polymers.

These materials offer the best combination of environmental impact and economic benefit when they are made with CO₂ from the atmosphere instead of emissions from new fossil fuels.

Choose your carbon projects wisely

CCUS can be a useful solution, and governments have begun to pour billions of dollars into its development. Careful attention must be paid to ensure that carbon capture technologies will not delay the phasing out of fossil fuels. It is an all-hands-on-deck effort to use the best combinations of CO₂ sources and appetite to achieve rapid scale at an affordable cost to society.

Because climate change is such a complex issue that is harming people around the world, as well as future generations, I believe it is imperative that actions are not only swift, but also well thought out and evidence-based.

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, an independent nonprofit organization providing facts and analysis to help you understand our complex world.

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

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Volker Sick receives funding from the Grantham Foundation for the Preservation of the Environment.