Noble gas in the United States alone. For large-scale use, helium is extracted by fractional distillation from natural gas, which can contain up to 7% helium. Neon, argon, krypton, and xenon are obtained from air using the methods of liquefaction of gases, to convert elements to a liquid state, and fractional distillation, to separate mixtures into component parts. Helium is typically produced by separating it from natural gas, and radon is isolated from the radioactive decay of radium compounds. The prices of the noble gases are influenced by their natural abundance, with argon being the cheapest and xenon the most expensive. As
Regulation of greenhouse gases under the Clean Air Act in the climate system. Once emitted into the atmosphere, GHGs influence the Earth's energy balance for a period of decades to centuries. Consistent with their long-lasting impacts, the IPCC found that even if the concentrations of all GHGs had been kept constant at year 2000 levels, a further warming of approximately 0.1C per decade would be expected. The fact that GHGs are long-lived in the atmosphere also means that they become well mixed across the globe – hence the global nature of the problem. After considering the scientific evidence before her, Administrator Jackson found that greenhouse gases could be reasonably