Explainer: Taking Greenhouse Gases from the Sky: 7 Things to Know About Carbon Removal 

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With greenhouse gas emissions climbing and climate impacts becoming increasingly severe, the urgency to address climate change has never been greater. Many of the solutions to date have focused on mitigation—ways to slash emissions as quickly as possible, such as by adopting renewable energy, promoting energy efficiency and stopping deforestation. These efforts remain critically important, and we need to accelerate them. Yet the science shows they will not be enough on their own to have a good chance of meeting the goals of the Paris Agreement on climate change.

To prevent the worst impacts of climate change, the world will need to reach net-negative emissions, a point at which we’re actually removing and storing more carbon from the air than we’re putting into the atmosphere. This will involve deploying techniques that remove carbon from the atmosphere and permanently store it.

Here, we take a look at the latest science on negative emissions and carbon-removal approaches:

Why do we need to achieve negative emissions?

The latest climate science shows that in addition to climate mitigation, the world will need to remove carbon from the air and store it if we are to have a good chance of achieving the global goals of limiting temperature rise to 1.5-2 degrees C (2.7-3.6 degrees F), the temperature limit countries agreed to as part of the international Paris Agreement on climate change. Most scientific estimates show that to keep those goals within reach, the global emissions trajectory needs to not only reach net-zero by the second half of this century, but continue downward into net-negative emissions. Negative emissions are necessary to offset the last remaining greenhouse gas-emitting activities that are too challenging or expensive to eliminate, and to compensate for any temporary overshoot of the temperature goals.

How can we achieve negative emissions?

Carbon-removal strategies, as the name implies, remove carbon dioxide from the atmosphere and store it through various means, such as in soils, trees, underground reservoirs, rocks, the ocean and even products like concrete and carbon fiber. The most obvious example of this is photosynthesis, where trees absorb carbon dioxide from the surrounding air and use it to grow.

Carbon-removal strategies fall into two categories:

  1. Natural approaches, which use biological processes to improve carbon removal and storage in forests, soils or wetlands; and
  2. Technological approaches, which remove carbon directly from the air or manipulate natural carbon-removal processes to accelerate carbon storage.

Is carbon removal like solar radiation management?

No. While solar radiation management aims to reduce the severity of climate impacts, unlike carbon removal, it does not address the source of the problem: increasing concentrations of greenhouse gases in the atmosphere. Rather, solar radiation management seeks to reduce the amount of radiation that reaches Earth, such as by brightening clouds, injecting reflective particles into the atmosphere or even installing mirrors in space.

Carbon removal and solar radiation management come with very different risks, potential impacts, research needs and costs, but neither is exempt from controversy. Solar radiation management has sparked debate around potential unintended consequences for the hydrological cycle and plant life, among other issues. Some forms of carbon removal are also subject to significant debate, such as whether bioenergy with carbon capture and storage (BECCS)—which involves burning biomass like crop wastes for energy and capturing and storing the carbon emissions underground in geological formations—can be truly sustainable at a large scale given competing needs for land, among other concerns.

How much carbon removal do we need?

The UNEP Emissions Gap Report compiled the latest science related to emissions trajectories and temperature rise. Researchers found that:

  • Temperature rise cannot be limited to 1.5°C by 2100 without carbon removal, according to the models studied. By 2050, the world would need to sequester and store 8 gigatonnes of carbon dioxide (GtCO2) annually on average—removing more emissions than the total U.S. GHG emissions in 2015 (6.6 GtCO2e). Between 2010 and 2100, the world would need to store about 810 GtCO2 cumulatively, the equivalent of about 20 years’ of global emissions given current rates.
  • A few scenarios can meet the 2°C target without carbon removal, but the large majority require it, even when factoring in countries’ current climate action commitments. Even if countries ramp up their climate action immediately, most models show we’ll still need to remove about 670 GtCO2 cumulatively between 2010 and 2100, the equivalent of about 16 years’ of global emissions given current rates.

Is any of this actually possible?

Natural approaches for carbon removal can play a significant role in the near-term. Recent research found that natural solutions like improved management of forests, wetlands, grasslands and agricultural lands can remove about 5.6 GtCO2e of carbon per year by 2030—a figure equivalent to total global emissions from agriculture in 2014—at a cost of less than $100 per tonne of carbon. Natural approaches also carry numerous co-benefits, from improving soil and water quality to protecting biodiversity.

Yet they are not without risk. For example, carbon may not be removed permanently, eventually reverting to the atmosphere, such as when a major fire destroys restored forestland or when a farmer plows up a field previously restricted from tilling. Carbon-removal activities can also trigger emissions elsewhere, such as if planting trees on agricultural land leads to trees being cut down elsewhere to meet growing food demands.

Several technological approaches also offer promise, but most are not ready for deployment and others remain costly and risky. Most of the climate models rely significantly upon BECCS to achieve negative emissions, but this approach also poses challenges, such as displacing forests and crop lands to make way for bioenergy production.

Even when combined with ambitious mitigation, no single carbon-removal approach or category can keep warming well below 2°C over the course of this century. Therefore, the best strategy for achieving negative emissions at the scale needed is to build a portfolio of carbon-removal approaches.

Where is carbon removal already happening?

Efforts to manage soils and forests more effectively to store carbon—like through reforestation and restoring degraded landscapes into productivity—are ongoing, but have not occurred close to their estimated need or potential. For example, while countries around the world have set an ambitious goal to restore 350 million hectares of degraded lands by 2030, one study found carbon removal potential through restoration and several other measures across several billion hectares. But it is critical to note that whether and how the world can mobilize action at this scale is a subject of ongoing debate. Optimism needs to be tempered by what is realistic given competing demands for land and other resources.

Technological approaches are in their infancy, but gaining traction. For example, there are now a handful of commercial direct air capture and storage systems in CanadaEurope and the United States, as well as some academic research efforts. BECCS is also entering a demonstration phase, with half a dozen or so operational projects and more than a dozen planned.

A new power system called the Allam Cycle is also something to watch. The technology makes carbon capture part of the core electricity-generation process. NET Power is using the technology in the first-ever zero-emissions natural gas demonstration plant in La Porte, Texas, which is expected to begin supplying power to the grid in 2018. If it works, the Allam Cycle facility will capture all the carbon dioxide it produces, and is projected to be cost-competitive with conventional natural gas power systems once the technology matures. This demonstration plant could therefore have a transformative effect on the power system, and incentivize investments in critical infrastructure like geological storage, which will ultimately help bring down the cost of carbon removal.

How can the world limit warming to 1.5-2°C?

It will need to pursue all efforts to reduce emissions. We can’t take our foot off the pedal for any mitigation efforts, and at the same time, we need to explore options for investing in carbon removal—in a way that complements and even supports mitigation efforts, to the extent possible. This means rapidly deploying natural carbon-removal approaches while continuing to research, develop and demonstrate technological approaches that have the potential to scale.

Encouragingly, pathways for many carbon-removal approaches can go hand-in-hand with mitigation. For example, direct air capture technology requires low-cost, carbon-neutral energy, underscoring the need to scale up wind, solar and other renewables. And natural carbon-removal approaches can help cut emissions while providing a suite of benefits like improved food yields and resilience.

WRI is pursuing a new body of research to explore the challenges and opportunities to scale carbon-removal strategies in combination with advancing efforts to curb emissions.

At the UN Climate Conference in Paris, known as COP21, 196 countries joined together in the Paris Agreement, a universal pact that sets the world on a course to a zero-carbon, resilient, prosperous and fair future. While the Agreement is not enough by itself to solve the problem, it places us clearly on the path to a truly global solution.

Building on the foundation of national climate plans from 187 countries, the Paris Agreement is a reflection of the remarkable momentum from cities, companies, civil society groups and others that complement the global will to act that has grown over the years since the first international conference on climate change in 1992.

The Paris Agreement will maintain and accelerate that momentum. It offers clear direction with:

  • long-term goals and signals,
  • a commitment to return regularly to make climate action stronger,
  • a response to the impact of extreme climate events on the most vulnerable,
  • the transparency needed to ensure action takes place and
  • finance, capacity building and technology to enable real change.

But the Agreement does even more: it marks a new type of international cooperation where developed and developing countries are united in a common framework, and all are involved, engaged contributors. It reflects the growing recognition that climate action offers tremendous opportunities and benefits, and that climate impacts can be tackled effectively, with the unity of purpose that has brought us to this moment.

The moment in Paris extended far beyond the Agreement itself. Cities and forests, business and finance – all these were part of the many initiatives and commitments that were launched or strengthened over the past two weeks. And they will be key to the solution as action moves forward with the energy generated by Paris.

Key Provisions

Long-Term Mitigation Goals

The Paris Agreement sets landmark goals for taking action on climate change, aiming to keep temperature rise to well below 2 degrees C (3.6 degrees F) and to pursue efforts to keep it to limit temperature increase to 1.5 degrees C (2.7 degrees F). To achieve this, countries will aim to peak global emissions as soon as possible and – remarkably – countries agreed to reduce emissions rapidly to reach net-zero greenhouse gas (GHG) emissions in the second half of the century. They will do that taking equity, sustainable development and poverty into account.

Five-Year Cycles of Action

To build on the momentum from countries’ national climate plans put forward for Paris, countries have agreed to a process to ramp up action on emissions every five years. By 2020, countries have agreed to come back and either submit new or updated national climate plans (known as nationally determined contributions). Every five years after that, countries will submit new contributions. Countries have also agreed that their mitigation plans will represent a progression beyond their previous efforts.

Five-Year Comprehensive Global Stocktake

The Agreement establishes a strong process for countries to regularly assess implementation and take stock of climate action every five years, called the Global Stocktake. This will assess implementation of action on mitigation, adaptation and support, including finance, and inform implementation of countries’ climate plans. Assessment will start in 2023, but countries have agreed to return in 2018 to review implementation of mitigation measures to inform their 2020 mitigation contributions.


Adaptation to climate change is a central issue for global climate action in this Agreement, where it is on par with mitigation. It establishes a global goal of enhancing adaptive capacity, strengthening resilience and reducing vulnerability, including an adequate adaptation response given the Agreement’s temperature goal. The Agreement creates a cycle of action for strengthening adaptation efforts regularly, similar to the mitigation cycle. Countries will have flexibility on the timing and methods for communicating information about their adaptation activities or efforts. Support will be provided to developing countries for planning, implementation and communication of adaptation activities.

Loss and Damage

The Agreement addresses the important issue of loss and damage, referring to the serious impacts of climate change when mitigation and adaptation fail. Those people who are affected by climate change may face damage to their property or health, or in worse cases, permanent loss of land or livelihoods, or even loss of life. The Agreement acknowledges the issue of loss and damage as separate from adaptation, and makes permanent the Warsaw International Mechanism (WIM) on Loss and Damage, established two years ago to find ways to address these issues. The outcome also establishes a task force on climate change-related displacement within the WIM, and makes clear that the loss and damage provision does not create new legal liability for emitting countries.


Finance will provide the needed power to turn the world toward a zero-carbon, climate-resilient future, and the purpose of the Agreement states that all financial flows – both public and private – need to be shifted from high to low emissions activities and risky to resilient investments. The Agreement makes clear that developed countries will continue to provide and mobilize finance to support developing countries, and developed countries agreed to continue their 2020 commitment of mobilizing $100 billion a year until 2025. For the period after that, governments will adopt a new, higher, collective goal, though the extent to which finance will increase, and who will mobilize it, is a significant outstanding question. The Agreement opens the door for developing countries to provide support to their peers, recognizing that some developing countries are already doing so.

In addition, governments agreed to balance public funding between adaptation and mitigation, and agreed to significantly increase support for adaptation before 2020, which is of vital importance for the most vulnerable countries dealing with the impacts of a warmer world. Countries also committed to improve reporting on finance, with everyone providing information about finance provided or received, as appropriate.


The Agreement establishes a common system for transparency for all countries. Through an enhanced transparency framework all countries will be required to report on their emissions and track progress on achieving their nationally determined contributions regularly. The information provided by all parties will be subject to an expert review and facilitative multilateral consideration of progress. The framework provides flexibility and support that takes account of different countries’ capacities. Developed countries will report on the finance and support they provide, and developing countries will report on the finance and support needed and received.

Capacity Building

For the new international climate agreement to be universal, countries acknowledged that effective capacity building is vital to enable developing countries to take strong climate action. To elevate this issue, countries established the new Paris Committee on Capacity Building to oversee a work plan to enhance capacity building. The Committee will identify capacity gaps and needs, foster international cooperation and identify opportunities to strengthen capacity for climate action.

Legal Form

The Paris Agreement is a universal, legal agreement under the UNFCCC, with the participation of all countries. It will be open for signature next April, and will come into force in January 2020. Notably, the Agreement contains a strong, legally binding framework for reporting, transparency and review of implementation capable of driving greater ambition to tackle climate change. The establishment of a mechanism to facilitate implementation and promote compliance will provide further assurance of Parties’ actions.

Climate Conference Highlights

COP21’s outcome fulfilled the promise of its opening day, when more than 150 heads of state and government converged in Paris to express their commitment to climate action and a viable agreement. On the same day, 20 countries and 27 representatives from the private sector announced a multi-billion dollar clean energy fund and commitment to increase R&D investments, a major boost to the talks. This set the stage for more progress on climate action across a wide spectrum of areas.

Forests and Restoration

Opening day, November 30, also saw significant government commitments to protect forests, including $5 billion in funding from Germany, Norway and the United Kingdom. Global Forest Watch Climate, launched during the conference, offers the potential to shift the debate on monitoring forest-based emissions. The African Forest and Landscapes Restoration Initiative (AFR100) seeks to restore 100 million hectares (nearly 250 million acres) of degraded and deforested land in Africa by 2030.Initiative 20×20 is landscape restoration effort in Latin America and the Caribbean that has now reached nearly 28 million hectares (nearly 70 million acres) and $730 million in investment.


Building efficiency, sustainable mobility and interactive tools were among the city-level solutions advanced to prevent carbon-intensive congestion, sprawl and inefficiencies from locking in for decades to come. WRI announced 25 new partners to the Building Efficiency Accelerator as part of the UN SE4All initiativeand presented the New Climate Economy message of better transport, better climate. A coalition including WRI advanced the Paris Process on Mobility and Climate to position mitigation and adaptation contributions from transport sector. Along with UK DECC, WRI demonstrated the 2050 Global Calculator, an interactive model – WRI contributed the transport section – that allows users to explore 2 degrees C pathways. Looking ahead, the UN announced the Climate Action 2016 conference to deepen and expand action in six focus areas—with cities and transport being key.


More than 114 companies committed to set emissions reduction targets in line with Science Based Targets, using what scientists say is necessary to keep global warming below 2 degrees C. Participating companies have combined annual carbon dioxide emissions equivalent to what125 coal-fired power plants emit in a year. Goldman Sachs announced plans to invest $150 billion in clean energy projects and technology.The investment bank previously had a target to invest $40 billion in clean energy technologies by 2012, and will now almost quadruple that by 2025. Google added 842 megawatts of renewable energy capacity around the world, nearly doubling the amount of renewables it has purchased to 2 gigawatts, equivalent to taking nearly 1 million cars off the road.


Institutional investors and banks signaled their plans to build climate change considerations into their decisions. Allianz and ABP officially joined the Portfolio Carbon Initiative, bringing the value of the Coalition’s assets under management to $600 billion. Five Principles for Mainstreaming Climate Action within Financial Institutions also launched, with more than two dozen financial institutions indicating their intent to incorporate climate change into strategies and operations. An alliance of global investors, development banks, financial sector associations and NGOs launched the Green Infrastructure Investment Coalition to support the accelerated financing of green infrastructure through investor-government global and regional dialogues, and 27 global investors issued the Paris Green Bonds Statement to support policies that drive the development of long term, sustainable global markets in green bonds.