It's satellite microwave transmissions
What the science says...
According to UCS Active Satellite database, they know of 873 active satellites, for which those whose total power is known average around 3,200 Watts. The biggest was 18,000 Watts. To be generous, let us assume there are 1,000 satellites averaging 5,000 Watts. That yields 5 MegaWatts total. This is equivalent to about 5 big (but not biggest) windmills.
Suppose they were all orbiting about 6500km from the center of the Earth (i.e., Very Low Earth Orbits) and all the power was being radiated towards the Earth (it isn’t). The surface of a 6500km sphere is about 530 million square kilometres which means the incoming energy would be 5 Mega Watts / 530M km2 which is equivalent to ~ 1 Watts/km2 or 0.000001 Watts/m2.
In other words, the sum amount of energy being emitted towards the Earth from orbiting satellites is no more than 0.000001 Watt/m2. The IPCC AR4 (Figure SPM.2) gives total net anthropogenic forcing as 1.6 Watts/m2.
So, the energy required for satellites to cause global warming is off by a factor of around one million.
Last updated on 20 July 2010 by John Cook.