How can such a small percentage of CO2 (390PPM--4/100's of 1%) alter heat retention for the entire atmosphere?

Answer 1

There are a couple of ways to approach this from a scientific basis. The most powerful way of looking at it is to look at the total energy flows.

Suppose that greenhouse gasses do cause only an effect proportional to their concentration in the atmosphere. CO2 makes up 0.038% of the atmosphere. Suppose it only affects 0.038% of the energy received from the sun.

Energy received from the sun every year is about 5.5 × 10^24J. 0.038% of that is 2.1 x 10^21J, which is a lot of energy. It is about 5 times the total amount of energy used by mankind every year!

So what can that much energy do? Lets see how much we could heat the oceans. The total mass of the oceans is about 1.4 × 10^21 kg. Since the entire ocean will not be heated for centuries because the deep ocean currents are very slow let us consider just the first 100 meters. The average ocean depth is 3,711 meters. The heat capacity of water is 4186 J/(kg·C).

The amount of heating per year then would be:

2.1 x 10^21 J/yr / ( 1.4 x 10^21 kg x (100 m / 3711 m) x 4186 J/(kg-C)) = 0.013 deg C / yr

So that means that just 0.038% of the sun's annual energy striking the earth can heat the oceans by 0.013 deg C per year. That is just about how fast the ocean is actually heating up. Records indicate the ocean is heating at a rate of about 0.13 deg C/ decade. That my numbers match the actual rate is just a coincidence based on the depth of the heating effect I guessed at of 100 meters. It is actually much more complicated but this calculation does give you an idea of why this can actually be happening.

The point should be very clear, that even very tiny changes in the atmosphere could have big changes on earth because there is such a tremendously large amount of energy hitting the earth from the sun.

Answer 2

The small percentage of CO2 is in equilibrium with liquid water from the planet, so practically the man can't change this value. Working with close mo dells, like a greenhouse, this value is changed up to 100 times more and the result is that the absorption of the heat is increasing quit 10 times. Working whiteout any criteria some politicians have discovered here a nice subject. Practically, entire atmosphere isn't homo-gene, so appear "hot" places with concentrations upper limit.
At atomic level, molecular weight for CO2 is 42, for N2 is 14 and O2 16.

Answer 3

It does not alter it much, but it does alter it some. The smallest change is still a change. It remains to be seen if the change from 250PPM to 390PPM will alter the heat balance enough to actually melt the polar ice caps. It also remains to be seen how high the CO2 concentration will go, since we are now adding more to the atmosphere than ever before.