The Government Accountability Office has released a new report, Climate Engineering [PDF]. The GAO evaluated various proposals for engineering the climate to counteract any warming caused by loading up the atmosphere with greenhouse gases, chiefly carbon dioxide produced by burning fossil fuels. Two broad categories of engineering solutions were considered: carbon dioxide removal and solar radiation management.
The GAO convened a panel of experts to help evaluate the proposals. Each technology was …
…rated for its maturity on a scale of 1 to 9, using technology readiness levels (TRL)—a standard tool for assessing the readiness of emerging technologies before full-fledged production or incorporation into an existing technology or system. … [rating] a technology with a TRL score lower than 6 as immature.
With regard to carbon dioxide removal, the agency evaluated:
(1) Direct air capture of CO2 with geologic sequestration – using machines to chemically scrub CO2 from the air and pumping it underground for storage.
(2) Bioenergy with CO2 capture and sequestration—harvesting biofuel crops and sequestering the CO2 they emit when burned.
(3) Biochar and biomass methods – turning crops in fields into charcoal and burying it in the soil.
(4) Land-use management (reforestation, afforestation, or reductions in deforestation) – planting more trees to capture CO2 as they grow.
(5) Enhanced weathering – chemically reacting silicate or carbonate rocks with seawater to produce carbonic acid that could be spread in the ocean.
6) Ocean fertilization—releasing iron to certain areas of the ocean surface to increase phytoplankton growth and promote CO2 fixation.
With regard to solar radiation management, the agency evaluated:
(1) Stratospheric aerosols – injecting aerosols smaller than 1 micrometer in diameter (1 millionth of a meter) would cool Earth primarily by scattering a fraction of the solar radiation.
(2) Marine cloud brightening—a fleet of 1500 ships lofting droplets of seawater into the air where they brighten clouds which reflect sunlight.
(3) Scatterers or reflectors in space – a Saturn-like ring of reflective dust or 5 million parasol spacecraft to shade the earth from sunlight.
(4) Terrestrial reflectivity – cover 12 million square meters of desert with white polyethylene, plant more reflective crops, or paint roofs and roads white.
With regard to technical maturity, only direct air capture of CO2 with geologic sequestration garnered a rating of 3. All of the others were rated 2 or 1. Remember technologies that score above 6 are rated as mature.
The GAO report also analyzed the various costs and possible side effects of deploying each of the proposed technologies. Although some researchers and activists have urged that climate engineering be banned outright, the GAO reported
…the majority of the experts we consulted supported starting significant climate engineering research now. … They further envisioned a future federal research effort that would emphasize risk management, have an international focus, engage the public and national leaders, and anticipate new trends and developments.
Just in case man-made global warming turns out to be worse than many expect, it makes sense to do research to figure out how to deploy some form of climate engineering as a backup emergency measure.
For more background see my column, SuperFreaking Out Over Climate Engineering.