Two Simple Proofs of Global Warming

The simple, observable proof that human-caused CO2 is warming our planet.

The best way to talk about global warming is to take all the models, predictions, beliefs, and estimates out of the picture, and focus only upon actual direct measurements that we can make today, upon which there is no disagreement. Here are two of those direct measurements that prove humans burning fossil fuels are responsible for global warming, and not any natural cause.

First, the way the Earth stays in equilibrium with the heat coming in from the sun is to radiate it back out into space. Heat is transmitted as infrared radiation. The Earth radiates its heat in this window in the spectrum, electromagnetic centered around about the 10 micrometer band.

Now you know how different chemicals have different spectra? It's how we can look at a distant star and tell what gases are in it, by the absorption bands in its spectrum. Similarly, the gases in Earth's atmosphere absorb radiated energy in certain bands also. When heat energy is absorbed by our atmosphere, it no longer escapes into space, and stays here to heat us up.

The most important greenhouse gas is water vapor, and here is its absorption spectrum. Everywhere this is black, heat is absorbed, and stays here. Water vapor is so prevalent that it defines the basic shape of the window through which heat escapes the Earth. Methane is also important. Oxygen absorbs this little band. Carbon dioxide, CO 2 , is here where the water vapor band slopes. And this picture is the basic shape of the heat energy that Earth has always radiated safely out into space.

It's the variability of this longer-wavelength end of the spectrum that makes all the difference. At natural CO 2 levels of about .03%, enough heat still escapes through the window, and the planet stays in equilibrium. But as CO 2 increases — as it has by about 50% since the start of the industrial revolution — that end of the window is blocked, and it's like a curtain closing it off. The Earth is now absorbing more heat than it's radiating. Almost all of that excess is stored in the ocean, and that's the warming trend you see on all the historical temperature charts.

We DO directly observe that atmospheric CO 2 is responsible for the excess heat retained by the Earth since the beginning of the industrial revolution. That is not a model, a prediction, a belief, or an estimate; and no part of that is in reasonable dispute.

Second, how do we know that humans burning fossil fuels is THE source of this new CO 2 ? That's easy. We can carbon date it. Natural carbon in the atmosphere contains a known percentage of carbon14, caused by interaction with cosmic rays. But the carbon in oil has been sequestered underground for millions of years, and has no carbon14 left. When a forest fire burns, the carbon in that smoke has carbon14; but when fossil fuel is burned in an engine, there is no carbon14. By measuring the amount of carbon14 in our atmosphere, it's very easy for us to tell exactly how much of that CO 2 comes from burning of fossil fuels. The answer is ALL of the growth in CO 2 is human caused, and ALL of the closing of that atmospheric window is caused by fossil fuel burning.

Those are the direct observations, and they are NOT in dispute.

— Brian Dunning