By Willis Eschenbach – Re-Blogged From http://www.WattsUpWithThat.com
I got to thinking again about the thunderstorms, and how much heat they remove from the surface by means of evaporation. We have good data on this from the Tropical Rainfall Measuring Mission (TRMM) satellites. Here is the distribution and strength of rainfall, and thus evaporation, around the middle of the planet.
Figure 1. Evaporation in W/m2 as shown by rainfall data from the TRMM. It takes about 80 watt-years of energy to evaporate a cubic metre of water, so a metre of rainfall per year is equivalent to an average surface cooling of 80 watts per square metre. The TRMM satellite only covers from 40° North to 40° South.
I have held for some time that the global surface temperature is restricted to a fairly narrow region (e.g. ± 0.3°C over the 20th century) by the action of emergent phenomena (see references at the end of the post). Chief among these emergent phenomena are tropical thunderstorms. My hypothesis says that when the tropical surface temperature goes over a certain threshold, that thunderstorms emerge to put a firm cap on the temperature by cooling the surface.
Thunderstorms cool the surface in a number of ways, but the main cooling method uses the exact same mechanism used by the refrigerators that keep our food cold. Thunderstorms use a standard evaporation/condensation cycle. In one part of the cycle the working fluid evaporates, cooling the surroundings. In another part of the cycle in another location, the working fluid condenses. For a refrigerator, the working fluid used to be some form of Freon, nowadays it’s some other fluid. For thunderstorms, the working fluid is water. When it evaporates at the surface, it cools the local area, and the heat is moved from the surface to the clouds and on upwards.