"Because electricity and heat account for 41 percent of global carbon dioxide emissions, curbing climate change will require satisfying much of that demand with renewables rather than fossil fuels. But solar and wind come with their own up-front carbon costs. Photovoltaics require much more aluminum—for panel frames and other uses—than other technologies do, according to a 2011 study at Leiden University in the Netherlands. Alloys for wind turbines demand lots of nickel. Those metals are carbon culprits because they are produced in large amounts by high-energy extracting and refining processes." (Quoted from article)