In September Britain’s Royal Society, one of the world’s most sober-minded scientific bodies, released a study on "geoengineering." A few years ago such ideas would have been considered crazy. Geoengineering was the realm of whacked-out paranoids obsessed with "contrails" and propeller-head tech geeks with no grasp of politics or economics. But the changes associated with a warmer world–polar ice melt, desertification and ocean acidification–are happening faster than predicted. At the same time, political efforts at climate change mitigation–such as the Copenhagen talks–are making very little progress. So scientists are rethinking the unthinkable: technological schemes to reshape the earth’s climate, no matter how risky or expensive, are officially on the table.
Typically, geoengineering ideas range from deploying a massive fleet of sun-reflecting mirrors into orbit to filling the oceans with iron shavings that would trigger carbon-eating algae blooms. Scientists have even taken inspiration from the global cooling that followed a 1991 volcanic eruption in which 20 million tons of sun-diffusing ash entered the atmosphere. They are now exploring whether injecting sulfur into the atmosphere could lower the planet’s thermostat.
But of all the ideas that are being considered, carbon capture and sequestration stands out because it might, just might, not be totally nuts. CCS involves a complicated process through which carbon dioxide is removed from fuels like coal and oil–or even from the air–and is then forced into spent oil wells, porous rock formations or under the ocean floor for long-term storage. Already there are a smattering of small CCS projects around the world. Most of them involve oil companies that pump CO2 into active oil wells to help force up more petroleum in a practice known as enhanced oil recovery. A few companies use the CO2 for industrial purposes, like carbonation of drinks.
A combination of available technologies are used to capture CO2 before it escapes into the atmosphere. Postcombustion scrubs CO2 from coal, gas or oil smoke after the fuel is burned; then, through the manipulation of temperature and pressure, the CO2 is absorbed with solvents and recovered for storage. The technology is extremely expensive, but it has proven effective in retrofitted and new facilities. Precombustion capture, also called Integrated Gasification Combined Cycle technology, involves essentially cooking coal into a gas from which the CO2 is easily stripped away and captured. In either case, the capture of CO2 requires huge amounts of additional energy. Coal can also be burned in a process called oxy-fuel combustion, which captures more CO2 than the other options mentioned here but is not compatible with older facilities and can be used efficiently only on new plants.