Six carbon removal methods

Humans have emitted a large amount of carbon dioxide since the Industrial Revolution (more than 2,000 gigatons) , so we have reached a point where we need to make significant changes to combat climate change. It's crucial to reduce emissions quickly, but we also need to remove and store carbon that's already in the atmosphere to keep global temperature rise below 1.5 degrees C and prevent the worst impacts of climate change.

Carbon dioxide removal, also known as carbon removal, aims to reduce the amount of carbon dioxide in the atmosphere to mitigate climate change. Estimates for the amount of carbon removal needed to mitigate climate change range from 5 to 16 billion metric tons per year globally by 2050. To put this into perspective, the United States emitted just over 6 billion metric tons of greenhouse gases in 2021. The amount of carbon being removed today is much lower than what is needed to address climate change, highlighting the need for increased investment in both the public and private sectors to scale up carbon removal efforts in the coming decades.

Here are six options for removing carbon from the atmosphere:

1. Trees and forests. Trees naturally remove carbon dioxide from the air through photosynthesis, making reforestation effective ways to store carbon. Other management approaches such as restocking, silvopasture, cropland agroforestry, and urban reforestation can also increase carbon removal by trees and forests. The theoretical carbon-removal potential from forests and trees outside forests in the United States alone is more than half a gigaton per year. Carbon removal through forests can be relatively inexpensive (less than $50 per metric ton of CO2) and yield cleaner air and water.

2. Farms and soils. Several practices can increase the amount of carbon stored in soils, including planting cover crops, using compost, and developing crops with deeper roots. The amount and duration of carbon sequestered depend on regional climate and soil type, among other factors.

3. Biomass Carbon Removal and Storage. Biomass carbon removal and storage (BiCRS) is a range of processes that use biomass from plants or algae to remove carbon dioxide from the atmosphere and store it for long periods of time. The methods include creating biochar, bio-oil, permanent storage of carbon-rich biomass, and bioenergy carbon capture and storage (BECCS). BECCS generates energy from biomass, captures the resulting CO2 emissions, and sequesters them. One type of BECCS involves converting biomass to hydrogen, which could result in carbon-negative fuel.

4. Direct air capture. Direct air capture is a technology that chemically removes carbon dioxide from the air and stores it underground or in long-lived products like concrete. Unlike carbon capture and storage, which reduces emissions from industrial facilities and power plants, direct air capture removes excess carbon that has already been emitted into the atmosphere. However, this method is still relatively expensive and energy-intensive compared to other carbon removal options.

5. Carbon mineralization. Carbon mineralization is a process where some minerals react with CO2 and turn the gas into a solid. This process occurs naturally, over hundreds of years, but scientists are working to accelerate it by increasing the surface area of the minerals and exposing them to CO2, both in the air and ocean.

6. Ocean based approaches. The goal is to speed up natural carbon cycles in the ocean to reduce CO2 levels. Solutions include using coastal plants, seaweed, or phytoplankton for photosynthesis, adding minerals to seawater that react with CO2, or using electric currents to extract CO2. However, almost all these ideas are still in the early stages of development and require further research.

It's unlikely that there will be a single "silver bullet" solution for removing carbon. Instead, a combination of approaches may be needed to effectively and efficiently increase carbon removal capacity.