Anthropogenic cloud
The intermediate layers of the troposphere are the regions with less influence of human activity. This region is far enough from the surface for not being affected by the surface emissions. Additionally, commercial and military flights only cross this region during ascending or descending maneuvers. Moreover, in this region there exist two types of clouds with a large horizontal extension: "Nimbostratus" and "Altostratus", which cannot originate from human activity. Consequently, it is assumed that there are no anthropic clouds of these two "genera". However, what can occur is enhancing existing "Nimbostratus" or "Altostratus" due to the additional water vapor or condensation nuclei emitted by a thermal power plant, for instance.
Cloud
Tropospheric clouds form in any of three levels (formerly called étages) based on altitude range above the Earth's surface. The grouping of clouds into levels is commonly done for the purposes of cloud atlases, surface weather observations and weather maps. The base-height range for each level varies depending on the latitudinal geographical zone. Each altitude level comprises two or three genus types differentiated mainly by physical form.