What is Carbon Removal?

Greenhouse gases trap heat in the atmosphere. As their concentration climbs, the global average temperature climbs with it. The result is a feedback loop of environmental, climate, and health impacts that affect ecosystems and communities around the world. This accelerated pace of warming—and the far-reaching consequences—is climate change.

In an effort to slow warming, scientists and policymakers have pushed for measures to limit the behaviors driving climate change. "Carbon removal" (sometimes called carbon dioxide removal or negative emissions) is an umbrella category for a handful of these solutions.

As new as it might sound, the basic principle at work is actually an old idea.


The Carbon Cycle

Carbon is a fundamental component of our bodies and our lives. Over many hundreds of years, it travels between the atmosphere, oceans and rivers, rocks and sediments, and living things in a natural exchange. Through a number of processes—photosynthesis, decomposition, respiration, and fuel combustion, to name a few—carbon is recycled and reused. It happens all the time and everywhere.

[For a more in-depth look at the carbon cycle(s), check out this resource.]

In the last few hundred years, human activity has tipped the scales. Previously, carbon sinks—organisms and landscapes where carbon is absorbed—have removed enough atmospheric CO2 to maintain the balance of gases.

But deforestation and other major changes to the environment have limited the ability of forests and other sinks to regulate global emissions. With the huge volume of gas being released from human activities, the carbon cycle faces serious disruptions.

Some mitigation strategies tackle this problem by slashing the first half of the equation: total emissions. These approaches include stopping deforestation, adopting renewable energy, and improving energy efficiency.

These techniques are critical, but in order to succeed at a large scale, they would require massive upheavals to the global economy in a very short period of time. The window to act, however, is closing quickly: without immediate action, the pace of climate change will quicken and the feedback loop of consequences will become harder to redress.

Carbon removal targets the other half of the equation, the emissions that have already been released. It makes the most of natural processes that recycle and reuse carbon, like photosynthesis and carbon mineralization, to reset the balance. It also finds ways to integrate these time-tested processes with newer, innovative solutions for storing carbon.

In other words, carbon removal embraces the whole system. It takes advantage of the enormous scope of multi-disciplinary research that has been conducted to explore all of the most promising options we have for pulling heat-trapping carbon out of the atmosphere.


What are the Leading Carbon Removal Solutions?

The list of proposed and ongoing technologies and processes for capturing and storing carbon dioxide is extensive. Broadly speaking, these solutions can be divided into two categories: natural and technological (or engineered).

Natural solutions use photosynthesis to capture carbon dioxide from the atmosphere. Photosynthesis draws in carbon dioxide, storing it within sugars, plant fibers, tree wood, and soils. It has successfully stored carbon for billions of years! Carbon farming, forest management, and restoring forests all maximize carbon storage.

Engineered solutions employ technology to capture CO2 both from "point sources," like coal-fired power plants, and from the atmosphere. This captured CO2 is then permanently stored in rocks, building materials (like cement), and underground reservoirs. Direct air capture, carbon capture and storage (CCS), and enhanced carbon mineralization are all examples of technological solutions that can reliably and efficiently drawdown carbon.

How much do carbon removal approaches cost, and what is their scale potential?

Today, cost and supply estimates for carbon removal approaches are highly uncertain, as most carbon removal technologies have not entered large-scale commercial deployment. At the same time, more systems-level analysis of carbon removal approaches is needed to assess global scale potential. A handful of academic estimates of carbon removal potential have been published, which have been compiled in the supply curve graphic below.

  Above: Curve uses midpoint estimates from Working Group 3's contribution to the IPCC's AR5, as well as from analysis conducted by the Virgin Earth Challenge.

Above: Curve uses midpoint estimates from Working Group 3's contribution to the IPCC's AR5, as well as from analysis conducted by the Virgin Earth Challenge.

Why pursue carbon removal?

Carbon removal techniques provide a critical option for mitigating climate change—they provide a complement to other GHG abatement techniques, not an alternative:

  Image adapted from The Climate Institute report titled   Below Zero: Carbon Removal and the Climate Challenge

Image adapted from The Climate Institute report titled Below Zero: Carbon Removal and the Climate Challenge

Without carbon removal, we cannot overshoot our carbon budget and still prevent significant climate change, defined by scientists as a 2 degrees Celsius rise in average global temperatures.

  Image adapted from  UNEP Emissions Gap Report 2014

Image adapted from UNEP Emissions Gap Report 2014

The scientific consensus on the need for carbon removal as an option in the fight against climate change has grown increasingly strong:

The large majority of scenarios produced in the literature that reach roughly 450 ppm CO2eq by 2100 are characterized by concentration overshoot facilitated by the deployment of carbon dioxide removal (CDR) technologies.
— IPCC, Fifth Assessment Report on Climate Change, Chapter 6 from Working Group 3

Increasingly, carbon removal approaches are not only critical for keeping global temperatures below 2°C but also deployed heavily in modeling scenarios that involve 3+ °C climate change. Major uncertainties exist as to the viability and scalability of the carbon removal techniques assumed in these scenarios. Because existing technologies cannot generate negative emissions, it is critical to resolve these key uncertainties surrounding carbon removal approaches that have such great impact on our ability to prevent climate change.

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Why should we invest in developing carbon removal solutions today?

Carbon removal technologies may not deliver the greatest short-term carbon impact per dollar spent on GHG abatement today, but there still remains a large imperative to invest in these technologies today for several reasons:

1. The carbon removal field today is much more nascent than other GHG abatement fields, and investments in R&D in the field today could increase the competitiveness of carbon removal approaches in the future considerably. In many ways, the carbon removal field is reminiscent of the solar energy field in the 1970s:

Many energy and environmental technologies follow "learning curves" which require considerable investment in deploying technologies before they can be produced at economically-viable costs:

2. Only carbon removal approaches are capable of generating negative emissions. If we find that we need large scale negative emissions sooner than expected, it will be critical to have viable, scalable carbon removal developed, as more mature GHG abatement techniques cannot provide negative emissions.

3. Carbon removal offers more opportunities for companies and countries to fight climate change. The greater the opportunities we have for fighting climate change in economically and politically viable manners, the greater the likelihood that multilateral cooperative action to prevent climate change will materialize.

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What are the largest challenges facing the carbon removal field?

Many different approaches to achieve carbon removal have been proposed, but considerable research and development is needed to understand which approaches can be scalable, cost-effective, and sustainable:

Which carbon removal approaches are best suited for private-sector investment today?

There are good business cases to make for a number of potential carbon removal strategies today, including:

  • Conservation and restorative agriculture and forestry
  • Biochar

While the true carbon removal potential of some of the above approaches is uncertain, these investments can be profitable and have positive environmental/social impact regardless of carbon sequestration potential.

There are also profitable investments in carbon negative "pathway" technologies (i.e. projects that are not carbon negative but can de-risk and develop critical elements necessary for carbon removal solutions), including:

  • Fossil CCS / Bio-CCS for enhanced oil recovery
  • Low carbon cements/plastics
  • Fuel synthesis using direct air capture

What is critical for investments in these technologies is ensuring that learning from "pathway" approaches is translated into fully carbon-negative systems in the near future.

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By "carbon removal," do you mean "carbon capture and storage?"

No. A wide range of approaches can achieve carbon removal. Bio-CCS is one of those many carbon removal approaches, and fossil-CCS can provide a pathway to negative emissions, but the two terms are distinct.

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By "carbon removal," do you mean "geo-" or "climate-engineering?"

No. Most carbon removal approaches fit the popular conception of "mitigation" much better than the popular conception of geoengineering. Here at Center for Carbon Removal, we focus only on carbon removal mitigation approaches. Check out this blog post for more info. 

 At the Center for Carbon Removal, we only focus on carbon removal solutions that fall outside the popular conception of geoengineering.

At the Center for Carbon Removal, we only focus on carbon removal solutions that fall outside the popular conception of geoengineering.