In my last post, I was telling you that you should question everything. I’m telling you now to accept that climate change is real. How shall I reconcile these contradictory statements? By explaining here how greenhouse gases work, and how we know that these gases are mostly from anthropogenic (human) sources. I promise to make it understandable.
First, let’s look at the greenhouse gas effect. It is the phenomenon in which gas particles in the atmosphere trap heat near the earth’s surface. This is, in limited amounts, a good thing. The atmosphere of Mars is approximately 1% the thickness of Earth’s, and the average temperature there is only -80° F (-60° C). However, too many “greenhouse gases” results in trapping too much heat, as we see on Venus: its atmosphere is approximately 872° F (467° C), much higher than would be caused by its proximity to the sun. For comparison, Earth’s average temperature is 58.3° F (14.6° C)
This raises two questions: what are greenhouse gases, and how do they trap heat? There are four gases that play a major role in Earth’s greenhouse effect: carbon dioxide, methane, nitrous oxide, and fluorinated gases. These molecules are particularly effective at trapping heat. But how? Well, let’s see if I can illustrate it for you.
You may know that light can be both particles and waves. For this explanation, we’re going to talk about it in terms of particles – packets of light called photons. When they leave the sun, they have very small wavelengths, so the photons are really small, and they slip between the gas molecules easily. When they hit the ground, however, their wavelengths increase and the photons grow. Now the gas molecules catch them, and absorb their energy. Then new photons are released, but not necessarily in the same direction. Instead of going off into space, it might be reflected down towards the earth, or be caught by another molecule. These photons are full of energy, which we detect as heat, and that is how they get reflected back down to the earth.
So what’s the problem? Levels of greenhouse gases are increasing due to the burning of fossil fuels. We know that it comes from fossil fuels, and not natural sources like volcanoes, because of different ratios of carbon isotopes – carbon atoms with different atomic weights. Some isotopes are more common in fossil fuels than they are today, so we can deduce that increasing levels of these isotopes come from burning coal, oil, and gas.
How do we know it’s increasing levels of carbon dioxide in the atmosphere that’s causing the warming, and not the sun? Solar output is actually decreasing, while the earth’s average temperature has been increasing. In addition, we can link carbon dioxide and temperatures using ice core data.
Still don’t believe climate change is real? I’m interested to hear what you have to say – just don’t be surprised if I debunk it in a future post.