OK its time I chimed in, I've had this theory for years (since high school). Now seeing that scientists in general don't all agree on this, I feel that my theory is just as valid as any others.
Global warming is caused by people, more specifically their mere presence on this planet. Over population is causeing temperature to rise globally. I will argue this point indisputable. The body temerature of a person is 98.6 degrees, with over 5 billion people on earth, its getting warmer just from all of us standing around heating the place up. Eventually the temperature of the earth will hit an equilibrium temerature of 98.6 degrees. For proof of this look at these facts:
Okay no problem, here we go:
1) There were no people during the last ice age.
The were humans during the last ice age. You premises are incorrect, your proof is useless.
2) Its hotter in places where people wear less clothing, thereby releasing more of their heat.
Correct.
3) Its cold in places where people insulate the environment from their extreme heat.
Observation is correct.
4) The same can be said for times of the year when its hottest and coldest. Summer is hot because of people wearing little clothing. This also has the potential of raising the body temperature of those nearby, further increasing global warming trends. You can perform an experiment to prove this. Fill up a small room with many people and see how hot (temperature wise) it gets.
Observation is correct.
5) Its always coldest when and where there are fewer people outside.
Observation is correct.
6) When you have a fever you feel cold because you are losing more body heat to heating the planet.
So I have 1 incorrect premise, 5 correct observations, but any actual proof is missing.....
I'll show you how to do a more serious proof:
Step 1:
We will calculate the power of that the Sun does radiate in watts. The law of Stefan-Boltzman reads:
P(sun) = 4*pi*R(sun)^2*sigma*T(sun)^2
... where:
P(sun) = Amount of power the sun radiates
R(sun) = Radius of the sun = 700000 km
sigma = constant of Stefan Boltzman = 5.67*10^-8 W/m^2/K^-4
T(sun) = Temperature of the Sun = 5760 Kelvin
Doing the calculation you will find P(sun) = 3.84 * 10^26W
Step 2:
We will now calculate how much of this energy is received by earth orthogonally for each square meter
Q(earth_from_sun) = P(sun)/(4*pi*distance(earth_sun))
... where:
Q(earth_from_sun) = The energy the earth receives orthogonally per square meter
P(sun) = Amount of power the sun radiates
distance(earth_sun) = The distance between the earth and the Sun, about 150000000 km
Doing the calculation you will find that the earth will receive on each square meter 1.36 kW/m^2
Step 3:
The surface of the earth in quare meters is pi*R(earth)^2. About half of the earth is lit by the Sun, so we need to divide by two.
The formula for receiving the amount of power the earth receives from the Sun is:
P(earth_from_sun) = Q(earth_from_sun) *pi * R(earth)^2/2
You will find that P(earth_from_sun) is 8.5 * 10^16
On a yearly basis this amounts to 1.9 * 10^24 J.
Because of the albedo of the earth is 39% we need to multiply by 0.61, we get 1.2 * 10^24 J
Step 4:
For the world-wide energy production we use Wikipedia:
http://en.wikipedia.org/wiki/World_energy_resources_and_consumption
It's 5 * 10^20 J
5 * 10 ^20 / 1.2 * 10 ^ 24 = 0.00043
Moral of the story: The amount of heat humans produce is nothing compared to the amount of energy the earth receives from the sun. We do not need to worry about how many heat we produce, we need only to worry about not disrupting the amount of energy the earth receives and radiates back.
Actually, my calculation doesn't take all factors into account, but this calculation has been done and refined so often that, anno 2009, we can be totally confident that the amount heat we produce does not contribute to global warming. We need to focus on the amount of heat earth radiates into space, and the amount of CO2 in the atmosphere is one factor that affects that.