The latest issue of Scientific American says "yes." An article in the November issue by Mark Z. Jacobson and Mark A Delucchi, "Sustainable Energy," argues that by 2030 100% of all global energy demand could be supplied by wind, water, and solar. This would even involve a reduction in power demand globally from 12.5 terawatts to 11.5 tw, as we would replace inefficient internal combustion engine autos and fossil fuel using airplanes with hydrogen technologies, the hydrogen obtained from electrolysis of water, using clean electricity sources to do so. 51% would come from wind, with 3.8 million wind turbines, 40% from solar, and the rest from water, including most tidal and waves, with some geothermal thrown in as well. While admitting that costs are still a bit too high for the solar components, they argue that the wind and water parts are already competitive economically with existing tech, with only some further improvements in transmission capability needed to really do it.
They do admit some caveats. In particular some rarer metals will be pushed to the limit unless there are some further tech breakthroughs: silver for solar cells, neodymium for gear boxes on wind turbines (mostly located in China), tellurium and indium for thin film solar cells, lithium for electric car batteries (half of world supplies in Bolivia and Chile), and platinum for hydrogen fuel cells. They note that nuclear has high carbon output in building the plants, but agree it does not once they are built (although other problems). I think there are other problems, with listening to local environmentalists here going on again over the weekend against wind turbines, reminding me that there will be lots of opposition to much of this, even if it is cost effective (and if it is not cost effective, just forget China or India signing on at all). But, it certainly makes for a nice vision just prior to the Copenhagen conference on global warming.