What is carbon removal?

Carbon dioxide removal (CDR), or carbon removal, is the process of removing CO2 from the atmosphere and permanently sequestering it. Carbon has circulated for millennia from the atmosphere to forests, soils and the ocean as part of the natural carbon cycle. However, atmospheric (and oceanic) concentrations of CO2 and other greenhouse gases have increased rapidly since the Industrial Revolution, predominantly due to burning fossil fuels. Carbon removal seeks to accelerate and augment the natural carbon cycle to reduce the level of CO2 in the atmosphere or use technologies that directly extract CO2 from the air.

How Can Carbon Be Removed from the Atmosphere?

Carbon removal includes a range of approaches. Nature-based or “conventional” approaches include methods like growing trees and restoring coastal wetlands. More novel, technological approaches include direct air capture (DAC), carbon mineralization, and approaches that store the carbon found in biomass (bioenergy with carbon capture and storage is the most common approach here, but others have been proposed as well). A robust portfolio of natural and technological approaches will help reduce costs, increase flexibility, minimize risks and balance tradeoffs associated with any one solution.

Why Is Carbon Removal Needed?

Keeping long-term temperature rise to 1.5 degrees C, as outlined in the Paris Agreement, will require the world to reach net-zero CO2 emissions by midcentury and net zero emissions across all greenhouse gases soon after. Reaching this goal will require deep emissions reductions, first and foremost, from every sector of the economy.

However, some emissions will likely not be able to be reduced by midcentury. These include agricultural emissions (from activities like fertilizer use or livestock management), transportation emissions (such as from aviation or maritime shipping), and emissions from other “hard-to-abate" sectors. Carbon removal is therefore needed to balance residual GHG emissions that cannot, or would not, be reduced by midcentury if abatement technologies do not become available or cost effective at scale.

After the world reaches net zero, carbon removal can help reduce the excess CO2 that has built up in the atmosphere (sometimes called “legacy emissions”) to safer levels. Current concentrations of CO2 are already causing more frequent and intense extreme weather events and sea level rise that are disproportionately affecting countries least responsible for these emissions.

How Much Carbon Removal Does the World Need?

The Intergovernmental Panel on Climate Change (IPCC), the world’s most authoritative body on climate science, has stated that all pathways that limit long-term warming to 1.5 degrees C will require some degree of carbon removal. The IPCC’s climate modeling scenarios show that roughly 5-10 GtCO2/year of removal will be needed around midcentury across both conventional and novel approaches, and likely even more in subsequent years.

The amount of carbon removal ultimately required to reach this goal depends on the level of emissions reductions. Reducing emissions as much as possible in the near term will not only help avoid increasingly dangerous climate impacts, but will also minimize future reliance on carbon removal. In most cases, it will be more costly and difficult to pull emissions out of the atmosphere than to prevent them from being emitted in the first place.

Is Large-Scale Carbon Removal Possible?

Some carbon removal approaches, such as tree restoration, can be deployed at large scales today but require supportive policies to incentivize implementation. Other approaches that are at earlier stages of development, such as DAC, would benefit from continued research, development and demonstration; policy support to accelerate deployment of existing technologies; and adoption of best practices and protective measures to ensure responsible scale up.

These investments are necessary to develop approaches today so they will be ready to deploy more widely when they are needed in the coming decades. Complementary infrastructure will also be needed to support carbon removal build-out, including CO2 transport and geological sequestration sites to store captured CO2 for approaches like DAC, and renewable energy infrastructure to power carbon removal technologies.

What Are the Local Impacts of Carbon Removal?

The long-term objective of carbon removal is to reduce CO2 concentration in the atmosphere to safer levels. While the benefit of this is global, carbon removal projects may also have local impacts, which can be positive or negative.

For example, tree planting can not only increase carbon sequestration, but also improve air quality, water cycling and resilience to climate change. But changes to the way the land is currently being used may also impact the livelihoods of people who work in agriculture. Technological approaches like DAC can bring jobs and investment but need significant amounts of land, energy and water to operate.

These effects need to be considered in project planning and in partnership with potential host communities. Understanding the local impacts of proposed projects, communicating those with nearby communities and providing opportunities to negotiate how benefits are distributed will be critical to bolstering public understanding and acceptance of carbon removal technologies and ultimately scaling carbon removal responsibly.

What’s the Difference Between Carbon Capture and Carbon Removal?

Carbon capture, use and storage (CCUS) is a technology that captures carbon dioxide emissions at the emissions source, such as a cement plant, before they enter the atmosphere — making it a form of emissions reduction. CCUS is likely to be particularly critical in the industrial sector, where there are few or no alternatives to abate some types of emissions.

Carbon removal is distinct from CCUS because CDR removes excess carbon dioxide directly from the atmosphere, rather than at an emissions source. Further, CCUS — as a form of emissions reduction — and CDR play different roles in climate action portfolios and have different impacts on the ground.

Cover Image by: Cecilio Ricardo / USDA Forest Service