Geoengineering Basics

Human Intervention and Climate Change

The final installment of the IPCC Fifth Assessment Report (AR5) focuses on solutions and strategies for mitigating climate change. Some coverage of the report (called Working Group III or WGIII) has drawn attention to strategies to pull carbon out of the atmosphere through human intervention. For example, BBC coverage of an early draft warned that if governments overshoot carbon emissions targets severely enough, they will need to actively remove CO2 from the atmosphere in the latter part of the century.

The WGIII report strongly emphasizes that it would be both safer and cheaper to cut emissions before 2030 and avoid “overshoot” that would necessitate this type of action. According to delegates critiquing the WGIII draft, even the most practical possible technologies to accomplish this are unproven, risky, and unrealistic (BBCReuters).

Some commentators (the GuardianCBS) have referred to these carbon removal efforts as “geoengineering.” But the definition of the term geoengineering is imprecise. It has been used to mean any type of “intervention via technology in the climate system.” Under this definition, the burning of fossil fuels could be seen as geoengineering, as could the switch to renewable energy. In popular news coverage the term seems to frequently evoke the mention of untested, extreme measures such as seeding the atmosphere with silica dioxide or the ocean with iron ore.

Judging from advance media coverage, the IPCC is not advocating or even seriously considering these extreme measures in WGIII.

Because these technologies differ widely in their function and practicality, it is more accurate to discuss specific technologies by name — rather than use the catchall term “geoengineering.”

Glossary of useful terms:

Geoengineering: A catchall term for any type of human intervention via technology in the climate system. Unscientific in that it includes a wide range of possibilities of greatly varying relevance to current climate discussions.

Carbon Capture and Sequestration (CCS): A technological process that removes CO2 from the exhaust of emissions sources, including power plants and other industrial sources. Pilot projects have proved its functionality, and there are 19 large-scale CCS projects in operation or development in the United States. However, hurdles remain to CCS adoption, including its price tag, which has deterred emitters from installing the technology. The question of what to do with the captured CO2 also presents an issue, with various solutions proposed. For example, some projects havesuccessfully stored CO2 through injection into porous rock formations and others are investigating the potential for re-use of CO2 in industrial processes. Finally, CCS reduces the emissions of a specific source but doesn’t actually reduce total atmospheric CO2, which would be required in an “overshoot” scenario.

Carbon Dioxide Removal (CDR): A broad category of interventions that take carbon dioxide out of the atmosphere. This encompasses a range of options of varying practicality, from reforestation (quite practical) to bioenergy carbon capture and storage (BECCS) to direct air capture (DAC) to ocean fertilization (extremely impractical).

  • Bioenergy Carbon Capture and Storage (BECCS): Besides reforestation, this is likely the most practical form of carbon dioxide removal. BECCS consists of burning biomass such as wood, and then capturing the emitted carbon through readily available CCS technology. This has the advantage of being both carbon negative and technologically feasible. As of 2010, 16 BECCS projects were planned or implemented worldwide. But countriesand watchdog groups have also raised concerns about drawbacks such as the amount of land and water needed to grow plants for bioenergy.
  • Direct Air Capture (DAC): This technology removes carbon dioxide from the open air through chemical reactions. DAC modules, sometimes called “artificial trees” can remove more carbon than real trees —without the drawback of releasing the CO2 again when the tree dies. However, they have not been deployed at scale, and they cost more than similar BECCS carbon reductions (becoming profitable at a carbon price of about $600 per ton, vs.$100 per ton for BECCS).
  • Ocean fertilization: This strategy involves increasing the CO2 uptake of ocean organisms by “fertilizing” them with iron. It is extremely controversial, though, and scientists discourage the idea. Little is known about what effect such a project would have on ocean life, and the impacts of the strategy would be extremely difficult to reverse.

Solar Radiation Management (SRM): This broad category includes all efforts to cool the planet through reducing solar radiation. No SRM method is currently practical or advocated by scientists. Even if successful, SRM methods would not address ocean acidification, as excess CO2 would remain in the atmosphere.

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