An Overview of Carbon Sequestration

Photo by Marcin Jozwiak on Unsplash

What is carbon sequestration?

Carbon sequestration, or carbon capture and storage (CCS) is the process of taking carbon dioxide out of the atmosphere and storing it. CCS is a critical part of the solution suite for limiting global warming to1.5°C above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) includes CCS in 3 out of its 4 pathways to 1.5°C. CCS can allow for a more gradual and therefore easier path to decarbonization.

In this article, we are focusing on CCS. A related process, carbon capture and utilization (CCU) refers to taking carbon dioxide out of the atmosphere and reusing it, for example in fizzy beverages, enhanced oil recovery to increase the productivity of oil wells, or biofuel. The CCU market presents a different set of opportunities and challenges from CCS in terms of its viability and scalability.

There are two general categories of CCS processes — biological and geological.

Biological CCS occurs in nature, such as storage of CO2 in the soil through photosynthesis. Oceans absorb ~25% of carbon dioxide emitted by human activity every year, and vegetation such as grasslands and forests also store CO2.

Geological CCS, the focus of this article, involves storing captured CO2 underground. CO2 is captured, compressed into a fluid, and then transported to a storage site, typically by pipeline or ship. These storage sites can be depleted natural gas or oil reservoirs, or deep saline formations.

Capturing CO2 can either occur at the source of the emissions, such as power plants or steel factories, or occur anywhere through direct air capture. The first method involves pulling CO2 out of the flue gases, or waste streams, produced during industrial processes. Given the greater concentration of CO2 in these waste streams, this method is much more efficient than direct air capture. However, direct air capture has the advantage of flexibility — it can be set up in any location, including close to a storage size, and it can scale to any size.

What does the future hold for carbon sequestration?

Today, there are only 26 operational commercial CCS sites in the world. These sites capture 40 million tons of CO2 a year — good progress, but far short of the 50 billion tons that we emit each year.

CCS faces an economic viability challenge. Without a price on carbon or other regulatory incentives, CCS is a pure cost for operators with no material revenue streams. Investment in CCS is no petty change either — carbon removal is estimated to cost $300 per metric tone per year. CCS requires building long-lived assets and infrastructure for transporting carbon dioxide, in addition to operational costs.

In September 2020, the DOE announced that it is awarding ~$72 million to support the development of CCS technologies. Biden’s climate change plan, targeting a 50–52% reduction in US greenhouse gas pollution from 2005 levels by 2030, speaks to the expansion of carbon capture. Biden’s website states that he will “double down on federal investments and enhance tax incentives for CCUS”. Billionaire Elon Musk recently announced a $100 million XPrize encouraging inventors to tackle CCS.

The increased spotlight on carbon sequestration will hopefully offer us a commercially viable solution in the near future. We will likely need not only more cost effective technology, but — perhaps more importantly — regulatory incentives for building and maintaining carbon sequestration infrastructure. The hope is that in a few years, when I am reading back on this article, we will have moved much further on the maturity curve for CCS.

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