January 12, 2024
By Volker Sick

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

Capturing carbon dioxide from the air or industries and recycling it can sound like a win-win climate solution. The greenhouse gas stays out of the atmosphere where it can warm the planet, and it avoids the use of more fossil fuels.

But not all carbon-capture projects offer the same economic and environmental benefits. In fact, some can actually worsen climate change.

I lead the Global CO₂ Initiative at the University of Michigan, where my colleagues and I study how to put captured carbon dioxide (CO₂) to use in ways that help protect the climate. To help figure out which projects will pay off and make these choices easier, we mapped out the pros and cons of the most common carbon sources and uses.

Replacing fossil fuels with captured carbon
Carbon plays a crucial role in many parts of our lives. Materials such as fertilizer, aviation fuel, textiles, detergents and much more depend on it. But years of research and the climate changes the world is already experiencing have made abundantly clear that humanity needs to urgently end the use of fossil fuels and remove the excess CO₂ from the atmosphere and oceans that have resulted from their use.

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, carbon will be harder to replace. For these, 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, utilization and sequestration, or CCUS. Of all the options to handle captured CO₂, my colleagues and I favor using it to make products, but let’s examine all of them.

CCUS best and worst cases
With each method, the combination of the source of the CO₂ and its end use, or disposition, 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 using captured CO₂ to produce construction materials, such as concrete. It seals away the captured carbon and creates a product that has economic value.

Comparing CCUS by source and disposition
The value or risk of capturing and using or sequestering CO2 strongly depends on the source, whether fossil fuels, limestone, biomass, air or ocean, and how it is stored or used.

A few methods are carbon-neutral, meaning they add no new CO₂ to the environment. For example, when using CO₂ captured from the air or oceans and turning it 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 amount of excess CO₂ in the environment. One of the most common underground storage methods – enhanced oil recovery – is a prime example.

Underground carbon storage pros and cons
Projects for years have been capturing excess CO₂ 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, geologic storage can durably remove large amounts of CO₂ from the atmosphere.

When the CO₂ is captured from air, water or biomass, this creates a carbon-negative process – less carbon is in the air afterward. However, if the CO₂ instead comes from new fossil fuel emissions, such as from a coal- or gas-fired power plant, carbon neutrality isn’t possible. 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 become a costly service ultimately covered by taxes or fees, similar to paying for trash disposal.

Slow growth: Worldwide commercial CCS facilities
Globally, carbon capture and storage facilities have been slow to come online. In 2022, only 30 commercial facilities were operating, with a capacity of 42.6 million metric tons per year.