244Global warming greater than 1 °C would possibly melt methane hydrates. Source: Hansen et al. (2007, p1942).

245Table 31.5. Inescapable cost of concentrating and compressing CO2 from thin air. The unavoidable energy requirement
to concentrate CO2 from 0.03% to 100% at atmospheric pressure is kT ln 100/0.03 per molecule, which is 0.13 kWh
per kg
. The ideal energy cost of compression of CO2 to 110 bar (a pressure mentioned for geological storage) is
0.067 kWh/kg. So the total ideal cost of CO2 capture and compression is 0.2 kWh/kg. According to the IPCC special
report on carbon capture and storage, the practical cost of the second step, compression of CO2 to 110 bar, is 0.11 kWh
per kg
. (0.4 GJ per t CO2; 18 kJ per mole CO2; 7 kT per molecule.)

245Shoving the CO2 down a hole in the ground or deep in the ocean. See Williams (2000) for discussion. “For a large
fraction of injected CO2 to remain in the ocean, injection must be at great depths. A consensus is developing that the
best near-term strategy would be to discharge CO2 at depths of 1000–1500 metres, which can be done with existing
See also the Special Report by the IPCC: www.ipcc.ch/ipccreports/srccs.htm.

In 2005, the best methods for carbon capture were quite inefficient: the energy cost was about 3.3 kWh per kg, with a
financial cost of about $140 per ton of CO2.
Sources: Keith et al. (2005), Lackner et al. (2001), Herzog (2003), Herzog
(2001), David and Herzog (2000).

Wallace Broecker, climate scientist. . . www.af-info.or.jp/eng/honor/hot/enrbro.html. His book promoting artificial
trees: Broecker and Kunzig (2008).

246The best plants in Europe capture carbon at a rate of roughly 10 tons of dry wood per hectare per year. Source: Select
Committee on Science and Technology.

Enhanced weathering of rocks. See Schuiling and Krijgsman (2006).

247Ocean nourishment. See Judd et al. (2008). See also Chisholm et al. (2001). The risks of ocean nourishment are
discussed in Jones (2008).