Tuesday, July 11, 2017

Cooling the Earth

Energy from a body can go in many different directions, but some of the energy heading in the right direction can escape directly to space (see atmospheric window).  Carbon dioxide is a very strong absorber of radiation trying to leave Earth in the about 12 to 13 micron and above range. This is closing the 8 to 14 micron atmospheric window that is allowing energy to escape from Earth on the 14 micron side. Using Planck's law I calculate that with an 8 to 13 micron window only 32% of the energy from a 25 deg C Earth can escape (using a blackbody approximation - the oceans, pavements, vegetation, etc have high emissivities close to that of a blackbody). With an 8 to 14 micron atmospheric window 37.4% of the energy could escape. Now if we had mirrors shading the ocean, that reflected sunlight onto black surfaces, the temperature of the ocean would change very little and we could heat up the black surfaces to high temperatures of 91 deg C. I say 91 deg C because at 91 deg C the highest percentage of energy radiated by the black surface can pass through the atmospheric window to space. At different temperatures only a smaller percentage can leave Earth. At 91 deg C the percentage of energy leaving to outer space is 34.5% of the energy radiated by the black surface. If the black surface were at 25 deg C only 32% of the energy it radiated could escape through an 8 to 13 micron atmospheric window.
With an 8 to 14 micron atmospheric window a temperature of 79 deg C allows the maximum proportion (39.3%) of radiation to escape to space.
Of course if we have higher temperatures more energy is radiated by a black body, but from an "efficiency" point of view, the highest ratios of energy can exit at the temperatures mentioned. Black surfaces heating seawater dripping onto them can also bring more rain, because of evaporation and convection. Clouds formed could cool Earth by reflection and radiation to space.

With increasing global warming it is expected that winters will warm faster than summers, ( see https://skepticalscience.com/The-human-fingerprint-in-the-seasons.html  ) so a question that might arise is this: Will winter rainfall regions have less rain?

No comments:

Post a Comment