What Is Geoengineering?
Evaluation of the effectiveness, affordability, safety, and timeliness of various proposed geoengineering techniques (Royal Society, 2009)
Simple schematic of various proposed SRM and CDR techniques (Lenton & Vaughn, 2009)
Visual representation of proposed geoengineering techniques (New Scientist, 2009)
The stages of geoengineering research (Blackstock, 2010)
Geoengineering is the deliberate large-scale intervention in the Earth’s natural systems to counteract climate change.
There is wide range of proposed geoengineering techniques. Generally, these can be grouped into two categories:
Solar Radiation Management (SRM) or Solar Geoengineering
SRM techniques aim to reflect a small proportion of the Sun’s energy back into space, counteracting the temperature rise caused by increased levels of greenhouse gases in the atmosphere which absorb energy and raise temperatures. Some proposed techniques include:
- Albedo enhancement. Increasing the reflectiveness of clouds or the land surface so that more of the Sun’s heat is reflected back into space.
- Space reflectors. Blocking a small proportion of sunlight before it reaches the Earth.
- Stratospheric aerosols. Introducing small, reflective particles into the upper atmosphere to reflect some sunlight before it reaches the surface of the Earth.
Carbon Dioxide Removal (CDR) or Carbon Geoengineering
CDR techniques aim to remove carbon dioxide from the atmosphere, directly countering the increased greenhouse effect and ocean acidification. These techniques would have to be implemented on a global scale to have a significant impact on carbon dioxide levels in the atmosphere. Some proposed techniques include:
- 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 Fertilisation. 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.