The Convection and Evaporation Effects




We’ve all heard a lot about the Greenhouse Effect (GHE) over the last 30 years, but what about the Convection and Evaporation Effects?  No? That’s not surprising considering these two cooling properties of nature completely discredit the Anthropogenic Global Warming hypothesis by overwhelming the GHE’s warming properties.

The Convection Effect (CE) is a property of nature that describes what happens when air near the surface of the Earth is heated and becomes less dense than the air above it making it rise.  This phenomena occurs all the way up to a point called the Tropopause, on average about 10,000 meters, where convection ceases to operate due to temperatures starting to rise at the bottom of the Stratosphere. The Convection zone (troposphere) is on average about 14 C (57 F) at the surface and -56 C (-69 F) at the top for a 126 F difference.

Wind, wind chill, hurricanes, and tornadoes are all examples of the effects of Convection, but one can see the effects in mirages as well. While mirages are formed from extreme instances of convection they give a good picture of how effective convection is near the surface.

For example; the Earth’s atmosphere has a common vertical temperature gradient of about -1 C every 100 meters, but it takes a gradient of at least -2 C per meter to create the conditions for a mirage.  Highway mirages are commonly -5 C over 1 meter, and there are extreme cases of -10 C per meter in desert conditions.  This is an example of how much more effective convection is as the temperatures driving it increase, and why most mirages are close to the surface given the cooling effect quickly reduces the temperature gradient  to less than -2 C within a short distance from the surface.

Convection is very efficient close to the Earth’s surface.

Other tEiF posts on Global Warming

The Evaporation Effect is even greater than the Convection Effect.  For those who have taken physics, you may be familiar with a property of nature called the Latent Heat of Vaporization (LVH).  This property shows how much extra energy it takes to change matter from a liquid to a vapor, or the kinetic energy it takes to separate the molecules in a liquid state into a gas.  In the case of water, it takes about 2,300 joules per gram.  A Watt is a joule per second.  To get a picture, it takes 415 joules to raise the temperature of 1 gram of water from 1 to 99 degrees C, and an extra 2260 joules to go from 99 C to Water Vapor at 100 C.

There are about 13 Trillion metric tons (1 million grams per ton) of water vapor in the atmosphere at any given moment and it is recycled as rain and  evaporates again about every 10 days.  This means every 10 days right at 30 Sextillion (1 million trillion) joules are absorbed by water just to evaporate it.  The energy used to evaporate this massive amount of water cannot be used to heat the surface, but instead acts to cool the surface of the planet.  It takes 23,000,000 joules to evaporate just 10 liters of water (1 square meter, 1 centimeter deep) at sea level.

Water vapor must lose an equivalent amount of energy to condense to form rain high up in the atmosphere acting as a heat scrub of sorts.

Now back to the GHE.  The CO2 portion of the GHE traps 2 W/m^2 (joule per second per meter squared) at the surface of the planet.  We keep hearing that it is some powerful force of nature, but we must recognize that a greenhouse does not trap heat by trapping Radiation, but rather by preventing Convection.  Open the door on a greenhouse and it cools quickly.

Imagine a Greenhouse with a net as a roof and no walls.  That is the Greenhouse Effect.

When taking into account the Convection and Evaporation Effects, we see that the Greenhouse Effect is a very minor force of nature.

Posted in Environment, Global Warming

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