Albedo planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water — a so-called aquaplanet — the average temperature on the planet would rise to almost 27 °C. For land surfaces, it has been shown that the albedo at a particular solar zenith angle "θ" can be approximated by the proportionate sum of two terms: the directional-hemispherical reflectance at that solar zenith angle, formula_1, and the bi-hemispherical reflectance, formula_2, with formula_3 being the proportion of direct radiation from a given solar angle, and formula_4 being the proportion of diffuse illumination. Hence, the actual albedo
Incompressible surface compressing "S" along "D". A non-negative complexity measure on compact surfaces without 2-sphere components is "b"("S") − "χ"("S"), where "b"("S") is the zeroth Betti number (the number of connected components) and "χ"("S") is the Euler characteristic. When compressing a compressible surface, the Euler characteristic increases by two, while "b" might remain the same or increase by 1. Thus, every properly embedded compact surface without 2-sphere components is related to an incompressible surface through a sequence of compressions. Sometimes we drop the conditions that "S" be compressible or that "D" be anything more than a disk that intersects "S" only along