The fine climatic structure of the air space that extends from the very surface of the earth to a height where the effects of the immediate character of the underlying surface no longer can be distinguished from the general local climate (mesoclimate or macroclimate). The microclimate varies with and in turn is superimposed upon the larger-scale conditions. While some rigid limits have been placed on the thickness of the layer concerned, it is more realistic to consider variable thicknesses. (Observe the microclimate of a putting green versus that of a redwood forest. ) Generally, four times the height of surface growth or structures defines the level where microclimatic overtones disappear. Microclimate can be subdivided into as many different classes as there are types of underlying surface. With sufficient detail, this could be almost limitless. Currently, the most studied broad types are the “urban microclimate,” affected by pavement, buildings, air pollution, dense inhabitation, etc. , the “vegetation microclimate,” concerned with the complex nature of the air space occupied by vegetation, and its effects upon the vegetation (see phytoclimatology); and the microclimate of confined spaces (the cryptoclimate) of houses, greenhouses, caves, etc.