In the current leading technology, steam-methane reforming, for producing hydrogen in large quantities extracts hydrogen from methane. However, this reaction releases fossil carbon dioxide and carbon monoxide into the atmosphere which are greenhouse gases exogenous to the natural carbon cycle, and thus contribute to climate change. In electrolysis, electricity is run through water to separate the hydrogen and oxygen atoms. This method can use wind, solar, geothermal, hydro, fossil fuels, biomass, nuclear, and many other energy sources. Obtaining hydrogen from this process is being studied as a viable way to produce it domestically at a low cost.