The future technology of molecular manufacturing will enable long-term sequestration of atmospheric carbon in solid diamond products, along with sequestration of lesser masses of numerous air pollutants, yielding pristine air worldwide ~30 years after implementation. A global population of 143 x 10^9 20-kg “diamond trees” or tropostats, generating 28.6 TW of thermally non-polluting solar power and covering ~0.1% of the planetary surface, can create and actively maintain compositional atmospheric homeostasis as a key step toward achieving comprehensive human control of Earth’s climate.
Robert Freitas as usual provides a lot of specific data that describes the scope of the problem and solution. Therefore, his information can provide scaling information for more conventional approaches to achieve the same result. There are many systems that are in design, research and development that are based on more conventional chemistry and biology for removing CO2 from the atmosphere. The calculations provided by Robert Freitas provide a roadmap and scoping for any proposed system for atmospheric homeostasis of material with regular technology.
Previously J Storrs Hall had described using nanotechnology for a global climate control machine. Nanotechnology for Climate Control and Enabling a Kardashev Type 1 and 2 Civilization - J Storrs Hall has conceived of Utility Fog and a Space Pier.
Weather machine Mark I - many small aerostats (a hydrogen balloon) - at a guess an optimal size is somewhere between a millimeter and a centimeter in diameter that have a continuous layer in the stratosphere. Each aerostat contains a mirror, and also a control unit consisting of a radio receiver, computer, and GPS receiver. About 100 billion tonnes of material with regular technology and 10 million tons with more advanced nanotechnology. However, the Weather Machine does not address rising levels of atmospheric greenhouse gases and could risk rapid global warming if a systemic failure of the Machine occurs while gas concentrations are high, whereas Freitas' diamond trees are inherently "fail safe" and directly regulate the greenhouse effect by placing atmospheric gas concentrations under human control.
In the “tree” configuration (Section 4), tropostats are spheres attached to the end of a short stalk of fixed length. If further investigation reveals that vertical atmospheric mixing is too slow because the tropostat field can extract CO2 faster than fresh air can be imported (e.g., the system is convection-limited, contrary to estimates in Section 4.7), one solution may be to employ a “balloon” configuration in which individual spherical neutral-buoyancy tropostats are tethered to ground anchors via thin retractable or spoolable cables that allow the spheres to freely move continuously between ground level and ~1 km altitude, thus giving the filtration network direct access to a much larger volume of air. In this configuration, each tropostat is a hollow sphere of slightly larger radius R tropostat = 2 m with wall thickness twall = 63 microns and material density ρwall = 3510 kg/m3 (diamond) filled with hydrogen gas.
Once global CO2 concentration is reduced to 300 ppm, many of the carbon-processing components of the system can be furloughed and held in reserve to combat future unexpected atmospheric challenges such as those posed by major volcanoes or supervolcanoes, massive forest or peat fires, modest asteroid strikes, regional nuclear wars, and the like. For example, the June 1991 eruption of Mt. Pinatubo caused global average temperature to decrease by 0.4 oC in the first year after the stratospheric injection of ~20 x 10^9 kg of SO2, some of which remained aloft for up to 3 years. Such pollutant clouds might be cleared in ~10^6 sec (~2 weeks) using a population of free-floating diamondoid blimpstats having only ~1% the mass and capacity of the proposed ground-based global tropostat network.
The network reserve capacity also provides some initial defense against catastrophic carbon releases. One such event may have occurred 550 million years ago during a period of widespread glaciation extending close to the equator, believed to have ended suddenly when a colossal volcanic outgassing raised the CO2 concentration of the air to 12%, ~350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm/day. Another similar possible event might involve the future rapid release of gaseous methane from seabed methane clathrates into the atmosphere as the oceans warm, though this hypothesis currently lacks support. Alternatively, if someday the planet is threatened by an impending ice age, the tropostat network can be used to quickly ramp up the level of greenhouse gases present in Earth’s atmosphere under precise human control, providing an offsetting warming effect to oppose the global cooling trend.