Noble gas to be retained. Neon, argon, krypton, and xenon also form clathrate hydrates, where the noble gas is trapped in ice. Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that when , a spherical molecule consisting of 60 carbon atoms, is exposed to noble gases at high pressure, complexes such as can be formed (the "@" notation indicates He is contained inside but not covalently bound to it). As of 2008, endohedral complexes with helium, neon, argon, krypton, and xenon have been obtained. These compounds
Regulation of greenhouse gases under the Clean Air Act time, whether due to natural variability or as a result of human activity." In its latest assessment on climate change, the IPCC found that "warming of the climate system is unequivocal" and that the anthropogenic component of this warming over the last thirty years has likely had a discernible influence on observed changes in many physical and biological systems. The properties of greenhouse gases are such that they retain heat in the atmosphere, which would otherwise escape to space. GHGs accumulate in the atmosphere when they are emitted faster than they can be naturally removed, and that accumulation prompts changes