Geoengineering to avoid climate change - science fiction or fantasy?

With ongoing debate on the ramifications of climate change on the planet or, in some quarters, continuing doubt as to the validity of the science itself, one aspect which has escaped wider consideration are some of the proposed solutions. While many focus on alternative energy production methods or ways to avoid carbon emissions, a few actually propose further intervention in the earth's climate. One of these is geoengineering or in simple terms using engineering solutions to affect climate change. In science fiction, this is often referred to as terra forming but whether it is science or science fiction, such a direction is fraught with high level risk particularly considering the basis for such proposals are untested and often commercial or 'market-based' approaches seeking a quick fix. The most unusual is injecting sulphur dioxide into the stratosphere to counteract carbon emissions. How sensible is such a proposal? Would this approach only add one more problem to the already existing ones?