Atmosphere of Earth However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft. The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about , although this altitude varies from about at the geographic poles to at the Equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e. a layer of
Ozone depletion and climate change the IPCC findings, that even extreme weather is not climate. While the greenhouse effect, "per se", is essential for life on earth, the case was quite different with the ozone hole and other metaphors about ozone depletion. The scientific assessment of the ozone problem also had large uncertainties; both the ozone content of the upper atmosphere and its depletion are complicated to measure and the link between ozone depletion and rates of enhanced skin cancer is rather weak. But the metaphors used in the discussion (ozone shield, ozone hole) resonated better with lay people and their concerns. The CFC regulation