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Even if we completely stop emitting CO2 tomorrow, the CO2 already in the atmosphere will continue to affect the climate for centuries. Scientists agree that we need to not only reduce new emissions but also actively remove the excess CO2 already up there to avoid the worst effects of climate change.
Everyone has a part to play to have an impact
As a response to the growing urgency of climate change, carbon removal has emerged as a critical tool to limit global warming. But why exactly do we need it?
Climate Change and Excess CO2
Human activities, particularly the burning of fossil fuels like coal, oil, and gas, have pumped an enormous amount of CO2 into the atmosphere over the past two centuries. CO2 is a greenhouse gas that traps heat, and its excess buildup is causing out planet’s temperature to rise — a phenomenon known as global warming, which is causing climate change. This warming is already having disastrous consequences, including extreme weather events, rising sea levels, and disruptions to ecosystems.
Even if we completely stop emitting CO2 tomorrow, the CO2 already in the atmosphere will continue to affect the climate for centuries. Scientists agree that we need to not only reduce new emissions but also actively remove the excess CO2 already up there to avoid the worst effects of climate change.
Carbon Removal in Two Steps
The two main steps in carbon removal are capture and storage. CO2 must be captured from the atmosphere, and can be done via various methods, including tree planting, from geochemical reactions, or from ocean interactions.
After the CO2 is captured, it needs to be stored in place where it will not be re-released into the atmosphere on a time scale that is impactful for climate change mitigation. Ideal permanent storage can last from 1000s to millions of years.
Types of Carbon Removal
There are several methods of carbon removal, each with a different mechanism for capturing CO2 and storing it away, at different stages of development:
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Land-Based Biological: Uses biological CO2 capture mechanisms (i.e., photosynthesis) to remove CO2 from the atmosphere and store it away.Afforestation, Reforestation, and Improved Forest Management: Afforestation is planting trees in places there were not trees before. Reforestation is planting trees in places where trees used to grow. Improved Forest Management is improving the ways we care for our existing forests so they are able to capture more CO2 from the atmosphere. In each of these cases, the CO2 is stored in the body of the trees, where it can stay so long as the tree remains alive. This means that if trees die, whether it is from drought, disease, wildfires, or human activity, the CO2 they once stored is released back into the atmosphere. Peatland and Wetland Restoration: Restoring peatland and wetland areas increases the amount of plants and improves local ecosystems, which increases their ability to capture CO2 from the atmosphere. The CO2 is stored in the plants and in the ecosystems while they are alive. This means that if the plants or ecosystems start to deteriorate, the CO2 they once stored will be released back into the atmosphere. Soil Carbon Sequestration: CO2 from the atmosphere is captured and stored by the soil ecosystem, which can include a mixture of plants, microorganisms, minerals, and the interactions between these different components. When the soil remains in-place, the CO2 remains stored, but when the soil is heavily disturbed, like during tilling activities, there is a risk the CO2 will be released back into the atmosphere. Biochar: Biochar is the result of concentrating and securing carbon from plants in a solid, durable form. As plants grow, they capture CO2 from the atmosphere through photosynthesis. When they die, from drought, disease, or human activity, they can be collected and cooked in the absence of oxygen, producing a charcoal-like material, biochar. This biochar keeps the carbon from the plants concentrated in a secure form where it is not released back to the atmosphere. Biomass for Carbon Removal and Sequestration (BiCRS): BiCRS is a suite of pathways that process plants to concentrate and secure the CO2 they captured during their life to result in carbon removal. Some of these process pathways may result in bio-oil products, bioplastics products, or hydrogen production. These pathways must result in CO2 storage for long periods of time, whether that be in the solid form, or otherwise, to qualify as carbon removal.
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Ocean-Based Biological: Uses biological CO2 capture mechanisms (i.e., photosynthesis) to remove CO2 from the atmosphere and store it away.Coastal Blue Carbon: Restoring and improving coastal ecosystems can result in healthier plants and ecosystems, that contribute to increased CO2 capture from the atmosphere. The CO2 is stored in the plants and in the ecosystems while they are alive. This means that if the plants or ecosystems are continuously disturbed or start to deteriorate, the CO2 they once stored will be released back into the atmosphere. Ocean Fertilization: Similar to fertilizing soil, fertilizing the ocean with nutrients can increase the ocean-bound plants (i.e., algae, kelp, seaweed), that will capture CO2 from the atmosphere. The CO2 is stored in these plants as the remain alive. When these plants die, the fate of the CO2 often depends on where the plants end up. When the plants are washed ashore, the CO2 is released back into the atmosphere. When the plants sink to the bottom of the ocean, the CO2 may remain in the plants, or may be released into the deep ocean, where it wills stay stored for long periods of time.
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Geochemical: Uses geo- (earth) chemical CO2 capture strategies to remove CO2 from the atmosphere and store it away. These geochemical reactions usually involve Earth’s crust (rocks and salts), water, and CO2.Enhanced Rock Weathering: Some rocks naturally react with CO2 from the atmosphere. These reactions usually involve a combination of CO2, water, and silicate rocks. For millions of years, these rocks and their natural reactions acted as Earth’s thermostat. Enhanced Rock Weathering is focused on accelerating these slow geologic reactions so they can be used to capture CO2 from the atmosphere at a faster rate to have an impact on climate change mitigation. When these rocks capture CO2, the CO2 is mineralized, or turned into a stable, mineral form, indicating durable storage for long periods of time. These minerals can also be applied on croplands to enhance the nutrients in soil systems. Ocean Alkalinity Enhancement: Increasing the alkalinity in the ocean through alkaline additives, such as calcium oxide (CaO), has the potential to capture CO2 that was once in the atmosphere, and now resides in the ocean. As these additives capture CO2 from the ocean, they store the CO2 in mineral form and sink to the bottom of ocean, resulting in durable long-term storage.
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Chemical: Uses chemical CO2 capture methods to remove CO2 from the atmosphere and store it away. These differ from geochemical pathways because the chemistry used in chemical capture methods is often a mixture of organic and inorganic.Direct Air Capture (DAC): CO2 from the atmosphere is captured using chemical reactions. The chemistry used to perform direct air capture is often called a “sorbent.” When the sorbent is full of CO2, and can no longer capture any more, it is regenerated, which allows for the captured CO2 to be released in a controlled way, for storage. The sorbent material is then ready to capture additional CO2 from the atmosphere. Direct Air Capture requires a dedicated storage method because these machines can capture and concentrate large masses of CO2 from the atmosphere annually. One of the most secure methods for storing these massive amounts of CO2 is geologic storage.
Each of these different approaches are critical to achieve climate goals. Check out the Road to 10 Gigatons game to make your own carbon removal solution portfolio!
Why Do We Need Carbon Removal?
While reducing CO2 emissions through clean energy resources, more efficient transportation, and better agricultural practices is essential, it is not enough to solve the climate crisis on its own. We need carbon removal because
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Hard-to-eliminate emissions: Certain sectors, like aviation and heavy industry, are challenging to fully decarbonize. Carbon removal can be used to offset these unavoidable emissions.
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Overshoot scenarios: If we exceed the temperature targets set by the Paris Agreement, carbon removal will be necessary to bring global temperatures back down.
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Restoring balance: By removing excess CO2 we’ve already emitted, carbon removal helps restore the natural balance of greenhouse gases in the atmosphere
The graph below illustrates how carbon removal (in blue) complements traditional mitigation strategies (in gray) to achieve net-zero emissions goals. Even with aggressive reductions in CO2 emissions, carbon removal is necessary to capture and store the remaining CO2 that’s already in the atmosphere.
As shown, by mid-century, carbon removal becomes increasingly critical as emissions from harder-to-decarbonize sectors continue. Together, carbon removal and emissions reductions give us a chance to meet global climate goals and stabilize Earth’s climate.
In short, carbon removal is an essential part of the climate action toolkit. It won’t replace the need for reducing emissions, but alongside those efforts, it can help us achieve the climate stability we desperately need.
As shown, by mid-century, carbon removal becomes increasingly critical as emissions from harder-to-decarbonize sectors continue. Together, carbon removal and emissions reductions give us a chance to meet global climate goals and stabilize Earth’s climate.
In short, carbon removal is an essential part of the climate action toolkit. It won’t replace the need for reducing emissions, but alongside those efforts, it can help us achieve the climate stability we desperately need.
Everyone has a part to play to have an impact!