Terraforming the Earth

A recent report commissioned by the Royal Society acknowledged the possibility of counteracting the effects of climate change by means of geoengineering. The idea of terraforming in science fiction means the creation of environments capable of human habitation on otherwise humanly uninhabitable planets or other bodies beyond the earth. So if man has already dared to conceive of rendering extraterrestrial environments fit for human habitation, the business of making earth (re)habitable through the use of technology can't be that farfetched, can it?