Carbon dioxide removal (CDR), sometimes referred to as "negative emissions technologies" (NETs), encompasses a variety of techniques and methods aimed at extracting carbon dioxide (CO2) directly from the atmosphere or preventing its release, and then securely storing it. The overarching goal of CDR is to mitigate the impacts of climate change by reducing the levels of atmospheric CO2, which is a major greenhouse gas responsible for global warming.
Here are some of the main methods and technologies related to CDR:
- Afforestation and Reforestation: Planting trees or restoring forests can capture and store CO2 as the trees grow. Trees naturally absorb CO2 during photosynthesis.
- Bioenergy with Carbon Capture and Storage (BECCS): This process involves growing biomass, burning it to produce energy, and then capturing and storing the CO2 emitted during combustion.
- Direct Air Capture (DAC): DAC systems use chemicals to bind to and capture CO2 directly from the ambient air. The captured CO2 can then be stored underground or used for other purposes.
- Enhanced Weathering: This method involves spreading certain minerals (like olivine or basalt) on land or in oceans. These minerals react with CO2, forming stable carbonates.
- Ocean Fertilization: By adding nutrients, like iron, to the ocean, phytoplankton growth can be stimulated. These tiny organisms absorb CO2 as they grow.
- Carbon Mineralization: In this process, CO2 is chemically reacted with calcium or magnesium to form stable carbonates, which can then be stored.
- Soil Carbon Sequestration: This involves changes in land use, farming practices, or pasture management to increase the amount of carbon stored in soils.
- Blue Carbon: Coastal and marine ecosystems, including mangroves, seagrass meadows, and salt marshes, can sequester large amounts of carbon.
- Carbon Capture and Storage (CCS): While not removing CO2 from the atmosphere directly, CCS captures CO2 emissions at the source (e.g., power plants) and then stores it underground.
- Ocean Alkalinity Enhancement: By adding alkaline materials, such as crushed limestone, to the ocean, the ocean's capacity to absorb and store CO2 can be increased.
- Scale: To make a significant impact on global CO2 levels, these methods need to be deployed at a massive scale, which presents logistical, financial, and sometimes technological challenges.
- Safety and Environmental Concerns: Some methods, like ocean fertilization, might have unintended ecological consequences.
- Cost: Technologies like DAC are currently expensive, although costs may come down with technological advancements and economies of scale.
- Permanence: Some storage methods, especially biological ones, might not be permanent. For example, trees can release CO2 if they die and decay or if they burn in a wildfire.
Given the current trajectory of global greenhouse gas emissions and the ambitious targets set in international agreements, it's likely that a combination of emissions reductions and CDR methods will be necessary to stabilize global temperatures.