How Real are "Geo-Engineering" Approaches?

Science has proposed some imaginitive, massive-scale "fixes" for global warming. But how real are they?

PopSci.com reports:

One of the theories proposed for reducing global warming involves deflecting heat away from the Earth's surface with solar shields or satellites with movable reflectors. Computer models suggest that blocking eight percent of the sun's Earth-bound radiation would effectively counteract the warming effect of our CO2 pollution. The idea was inspired by the cooling effects of large volcanic eruptions -- such as Mt. Pinatubo in 1991....

Another technological fix involves "sequestration," the storage of CO2 either deep underground or deep in the ocean. Some of the nation's largest utilities, which are also "washing" coal to filter out impurities, are working on ways to capture the CO2 they emit and store it miles below the Earth's surface. Costs of such technologies have been prohibitive.

Another leading theory, "ocean fertilization," entails scattering iron powder throughout the world's seas, providing nutrients to boost the amount of phytoplankton that thrive in the water's upper layers...

Yet another take on altering the seas for the sake of the climate, "engineered weathering," entails replacing some of the oceans' carbonic acid with hydrochloric acid. This, the theory goes, accelerates the underwater storage of CO2 ...

While the cost of many of these so-called "geo-engineering" fixes would not necessarily be prohibitive in light of the cost of transforming our global energy economy, the risks of unintended consequences weigh heavily on even the researchers proposing them. See full article.