As the name of this blog indicates I'm more concerned about getting everything, even the little things, right than most people. There are a bunch of groups and pages on Facebook that portray themselves as being pro-science yet post material that is, in my opinion at least, rather poor quality. A Facebook friend posted something from one of these. I responded by saying that this was the kind of thing that H.L. Mencken had in mind. Referring to the maxim that for every question there is an answer that is clear, simple, and wrong. Pointing out the ways that the post was wrong in a comment didn't seem appropriate so I'm doing it here.
It starts out without obvious error but promising to "disregard all of the finer details" may not mean what the reader would think.
This is going to be quick and simple. I’m going to be disregarding all of the finer details and just focusing on the overall role CO2 plays in our climate.
Next, we read:
Sunlight reaches earth in 2 forms, longwave radiation, and shortwave.
This is somewhere between untrue and meaningless. If "Sunlight" refers to visible light it is, at best, meaningless. There is no sensible way to divide the visible spectrum in two. If it means any electromagnetic radiation it is even worse. There are more than two categories. After reading the rest of the post, the "best" interpretation is that infrared and visible light are longwave and shortwave respectively. For discussions of climate, those are the two kinds of light that matter. But infrared radiation from the Sun isn't the infrared that matters.
Of the shortwave radiation that hits the ground, less than half is absorbed by water, plants and everything else; the rest is bounced back towards space.
This is just plain wrong. The albedo of the Earth is about 0.3. This means that about 70% of the energy is absorbed, far more than the "less than half" in the post. This error is strange for two reasons. It is trivial to get right and it doesn't matter to the story at all.
When the radiation bounces off of a surface and heads back towards the atmosphere, it is converted from shortwave to longwave.
This is also just wrong. Visible light that "bounces" or reflects is not converted to infrared. Infrared radiation is emitted by everything at the temperatures we are accustomed to. This is a vitally important difference because it allows the radiation to come from both the day and night sides of the Earth. The post describes a nonexistent process that would only be active during the day. In reality, infrared radiation is given off by everything that is at the temperatures we are accustomed to.
It’s longwave radiation that reacts with molecules in our lower atmosphere. Molecules such as carbon-dioxide, nitrous-oxide, and methane. Of these gasses, CO2 currently makes up 76% of the total.
This seems to be a list of the greenhouse gasses in the atmosphere but it is missing the most powerful greenhouse gas: Water vapor. If you ignore Water vapor and all of the major gasses in the atmosphere then 76% is a reasonable estimate. I guess that the actual percentage of CO2, 400 ppm or 0.04% in the atmosphere, is too small to seem important.
When the outgoing radiation interacts with these molecules, they absorb it and give off infrared radiation in all directions.
The radiation leaving Earth has two main sources, reflected visible light and infrared, Only the infrared light is absorbed by greenhouse gasses. There is another subtlety at work here, the absorption of infrared light is far from uniform. This is needed to get any of the details right, but at this level of explanation, it can safely be ignored.
This is the first time that "infrared" is used. Introducing it now makes everything preceding this point at best unclear.
The fewer the molecules in the atmosphere, the more longwave radiation makes it back into space. The more molecules in the atmosphere, the more radiation gets absorbed. It’s basically simple maths.
This is way past oversimplified but could be almost correct if we continue to assume that by "molecules" they mean molecules of greenhouse gasses. The nitrogen and oxygen in our atmosphere make up about 99% of the total, aren't they made of molecules as well?
When climatologists say that the increase of CO2 in our atmosphere is warming the planet, this is why. This is the science and maths behind that train of thought.
Uhm ... NO! This is NOT the science behind CO2-induced global warming or any train of thought that shouldn't be derailed.
The worst thing about "explanations" like this, at least for me, is that it is possible to actually explain the basics, teach some actual science, and not be wrong. Here's my attempt to address these issues:
To understand how increased CO2 warms the Earth we need to understand a couple of things first. What most people think of as light is really just a tiny part of a larger phenomenon called electromagnetic (EM) waves. A good way to think of EM waves is as things that carry energy, even through empty space. Different kinds of EM carry different amounts of energy. We see visible light but there is a lot of light that is invisible. Another thing we need to know is that everything that isn't at absolute zero emits EM waves. the energy and amount of which increases with temperature.
Sunlight reaching the Earth warms it. That makes the temperature higher and causes the Earth to emit EM waves to carry away some of the energy coming from the Sun. When the average temperature of the Earth is steady the energy coming from the Sun and the energy leaving the Earth are balanced.
The Earth's atmosphere is transparent to visible light but it is somewhat opaque to the light it emits, infrared (IR) light. This makes the energy leaving the Earth less efficient, raising the temperature. Without this the Earth would be much colder than it is. Although CO2 makes up a tiny fraction (0.04%) of the atmosphere, it is one of the major ingredients that reduces its transparency to IR. When we add CO2 we change the balance and the Earth heats up.
The first paragraph should be stuff that everyone knows and therefore not important. But, as a pedant, I felt it was worth including.
