James Temple lays out the debate surrounding "cloud brightening," a geoengineering strategy that may help combat rising global temperatures: 

It's clear that cloud brightening is possible. Satellites have observed "ship tracks," or whitened lines in marine clouds that large vessels have formed inadvertently by pumping out particles in their exhaust. Unknown is whether humans can do it purposely, on a large enough scale to matter, and without severely altering weather patterns elsewhere.

The World Economic Forum is pessimistic and included "rogue deployment of geoengineering" as an "emerging game changer" in its Global Risks 2013 report (pdf):

The problem is that incoming solar radiation drives the entire climate system, so reducing sunlight would fundamentally alter the way energy and water moves around the planet. Almost any change in weather and climate patterns is likely to create winners and losers, but determining causation and quantifying impacts on any given region or country would be a massive challenge.

They go on: