Geoengineering is the “deliberate large-scale intervention in the Earth’s natural systems to counteract climate change.” There are two broad types of geoengineering: Solar Radiation Management (SRM) and Carbon Dioxide Removal (CDR). The last post in this series dealt with SRM, which aims to reflect solar rays back into space.  This time we’ll address CDR, which aims to remove carbon dioxide from the atmosphere, thereby directly countering the greenhouse effect.

Here are some proposed CDR techniques, provided by the Oxford Geoengineering Programme:

Afforestation.  Engaging in a global-scale tree planting effort.

Biochar.  'Charring' biomass and burying it so that its carbon is locked up in the soil.

Bio-energy with carbon capture and sequestration.  Growing biomass, burning it to create energy and capturing and sequestering the carbon dioxide created in the process.

Ambient Air Capture.  Building large machines that can remove carbon dioxide directly from ambient air and store it elsewhere.

Ocean Fertilization.  Adding nutrients to the ocean in selected locations to increase primary production which draws down carbon dioxide from the atmosphere.

Enhanced Weathering.  Exposing large quantities of minerals that will react with carbon dioxide in the atmosphere and storing the resulting compound in the ocean or soil.

Ocean Alkalinity Enhancement.  Grinding up, dispersing, and dissolving rocks such as limestone, silicates, or calcium hydroxide in the ocean to increase its ability to store carbon and directly ameliorate ocean acidification.

Ambient air capture is especially promising. Air capture can remove far more CO2 per acre of land than trees. It also has the potential to pay for itself by producing a commercially viable product – low-carbon fuels – from the recycled CO2. Carbon Engineering, a Canadian company, has recognized the great promise of air capture and is building an air capture plant and piloting the technology for industrial use. Bill Gates is an investor.

There is hope yet.