Clearing the Air: How Do We Capture and Store CO2?

By California Institute of Technology (Caltech)April 24, 2023

Carbon dioxide (CO2) emissions, which account for 81% of all greenhouse gases, pose a significant challenge to Earth's climate. As natural methods are unable to fully counteract the rising levels of human-produced emissions, scientists and policymakers are exploring carbon capture, utilization, and storage (CCUS) techniques to reduce atmospheric CO2. These methods include ocean alkalinity enhancement, direct air capture, carbon offsets, carbon farming, reforestation, and afforestation. Newer strategies, such as accelerated limestone weathering, geological sequestration, and solar fuels, are also being researched. The global push for carbon reduction is partly driven by the Paris Climate Agreement, which aims to limit the increase in Earth's average global surface temperatures to no more than 2 degrees Celsius by 2050. Credit: Caltech

Scientists and policymakers are pursuing carbon capture techniques like CCUS, direct air capture, and reforestation to mitigate the harmful effects of CO2 emissions, driven by the Paris Climate Agreement's goal to limit global temperature increases to no more than 2 degrees CelsiusThe Celsius scale, also known as the centigrade scale, is a temperature scale named after the Swedish astronomer Anders Celsius. In the Celsius scale, 0 °C is the freezing point of water and 100 °C is the boiling point of water at 1 atm pressure." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">Celsius by 2050.

Carbon dioxide (CO2) is a greenhouse gas that traps heat and warms the planet. Because of the burning of fossil fuels, the amount of CO2 in the earth's atmosphere is higher than it has been in at least one million years.

Other gases contribute to climate change, but CO2 poses the greatest challenge: It accounts for 81 percent of all greenhouse gas emissions and can linger in the atmosphere for thousands of years. Methane, in comparison, has a lifetime of a decade.

Nature mitigates carbon and reduces some of the effects of climate change: Plants, trees, and algae in the ocean turn CO2 into oxygen through photosynthesisPhotosynthesis is how plants and some microorganisms use sunlight to synthesize carbohydrates from carbon dioxide and water." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">photosynthesis, and the ocean absorbs and stores CO2 in ocean sinks. However, nature cannot withstand the rising levels of human-produced emissions. Consequently, Earth and the people on it have experienced the effects of climate change, such as more frequent and intense weather events.

That is why, in addition to efforts that reduce emissions through decreased fossil fuel use, scientists, engineers, and policymakers are pursuing techniques to decrease the CO2 that reaches and stays in the atmosphere and oceans.

Currently, 40 million tons of CO2 are captured from power and industrial facilities each year. But the International Energy Association estimates that number needs increase by more than 100 times to meet the United Nations’ energy-related sustainable development goals. Some scientists believe implementing these techniques may be more feasible than decarbonizing certain industries, such as long-distance transportation and the airline industry.

Carbon capture, utilization, and storage (CCUS) involves collecting CO2 from emission sources such as coal-burning power plants and converting it to other products, storing it, or burying it. Ocean-based solutions, such as ocean alkalinity enhancement, increase the ocean's natural ability to remove and store CO2. Direct air capture physically and chemically pulls existing CO2 from the atmosphere and returns it to the ecosystem in less harmful forms, such as oxygen or low-carbon synthetic fuel.

Policy makers attempt to reduce CO2 emissions by promoting carbon offsets, which allow companies to compensate for the CO2 they emit by paying another entity to remove carbon elsewhere.

Methods to capture, sequester, and pull CO2 are gaining traction today partly because of the Paris Climate Agreement, which calls for limiting the jump in Earth's average global surface temperatures to no more than 2 degrees Celsius by 2050.