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The "Simple Physics" Slogan

16 Apr 2019 | Fact Checks, Videos

The Simple Physics Slogan

Hey you dummy, don't you know climate change is the simplest thing ever? It's so simple a child could explain it with a crayon. That's why it's settled. It's simple you see. So simple it's settled and there's no debate or doubt or uncertainty. Really. Well, except for the core concepts. And the measurement problems. And the modeling problems. And the discrepancies between models and reality. And all the stuff that we just don't know, which happens to be a lot of important stuff. What happens when we talk to a real expert and look at textbooks rather than comic books? Press play to find out, then press share and help get the discussion going.



One of the most popular slogans in the climate debate says that the underlying science is not only settled, it’s simple.


I’m John Robson for the Climate Discussion Nexus, and this is a Fact Check video on the Simple Physics slogan.


Al Gore called it “high school physics.”

NASA shows cartoons of a greenhouse to explain how the process works.

The National Geographic Magazine explains it this way: "The more greenhouse gases concentrate in the atmosphere, the more heat gets locked up in the molecules."

And kids go on TV to explain it to Donald Trump.


Gosh. It looks so simple even a Twitter Troll could understand it. Greenhouse gases warm the atmosphere like the walls of a greenhouse, and the heat gets locked up into the molecules.

Wait, how does heat get “locked” in molecules?

And if it’s high school physics, why are climate models so complex? And why does it take thousands of scientists to study the subject?

The answer is, it’s not simple. That’s just another empty slogan.


At this point, in a traditional video about global warming, we’d start with our own cartoons. We’d show sunlight coming down and warming up the Earth, and then we’d show the heat going up into the air and a bunch of it getting back out through the blanket of greenhouse gases. And we’d show you cute pictures of snowmen waving or happy polar bears or something.

But we’re going to do something very different.


Instead of drawing a cartoon, I’m going to ask a physicist to explain what greenhouse gases do. And not to dumb it down. I’m going to ask what is actually going on at the molecular level, and how that affects the air temperature in the atmosphere. And I’m going to insist he use the proper scientific terminology, even if it means it’s hard to understand.

Let’s see what happens when we look at textbooks not comic books.


William van Wijngaarden is a professor of physics at York University in Canada. He’s an expert on all things to do with temperature. He’s made detailed studies of the physics of energy at the molecular level. He’s shown how to cool down atoms to near absolute zero using lasers. And he’s also an expert on the climate system at the macro level, having published many studies of temperature and precipitation changes around the world.

William van Wijngaarden

The Basic Mechanisms

So the first question we want to ask is suppose there was no CO2, no greenhouse gases in the Earth’s atmosphere. What would happen?

Well, you would have the surface that would absorb sunlight and that would radiate heat to space. And the heat that is emitted from the surface would just go unimpeded to space, so basically there’s no blanket. So then it would be a lot colder than it is with greenhouse gases.

Now if you have an atmosphere with gases like CO2 and it isn’t just CO2 but water vapour, that’s the big greenhouse gas that people should talk about more, it’s water vapour, CO2, ozone, N2O and methane, those are the five big naturally occurring greenhouse gases.

If you have, say, a photon, or some heat, it goes up, it gets absorbed by one of those molecules. Well if that molecule has absorbed that heat, it will re-radiate it, but it will re-radiate in general in any direction. So some of the heat will come back down and some will come back up.

So it’s a bit difficult for that infrared radiation to just go out into space. Its trip to space is going to be slowed down and in being slowed down it turns out that results in the heating of the Earth’s surface.

Computing the Radiative Forcing of Greenhouse Gas Molecules

First consider: We have to ask ourselves what are the transitions where you can absorb this infrared light or heat. And by considering these five molecules, water vapour or H2O, CO2, ozone, N2O and methane, we’ve considered several hundred thousand different transitions.

So that’s one, just getting that data. Now there are libraries available where people have measured the frequencies and how strongly each of those frequencies is absorbed. So that’s Step 1.

Step 2 you have to know what’s the concentration of each of those molecules with altitude. So there you also rely on observations.

Step 3 is we need to know what’s the temperature versus altitude. So there are these standard temperature profiles that are also based on observation.

And then you have to calculate for each of those frequencies how each of those say 200,000 transitions absorb your different frequencies of light and you have to do that at every altitude. So that’s pretty involved.

The Logarithmic Relation Between CO2and Temperature

If you look at the greenhouse effect, the amount of warming, that depends logarithmically on CO2 concentration. So if I increase the CO2 concentration from 400 to 800 parts per million and get, say, a temperature increase of, say, 1 degree C, to get an additional 1 degree C of warming on top of that I can’t go from 800 to 1200, I have to go from 800 to 1600 parts per million. So it goes logarithmically. And that’s accepted by everyone.

Estimating the Temperature Effect of Doubling CO2 and Other GHGs

Well, what we’ve done in our work is we just consider those five gases. We see what happens if we double CO2, double methane, double N2O and have about a 6% increase in water vapour which corresponds to about a 1 degree C increase.

We find then that the temperature increase due to all those doublings is about 1 to 1.5 degrees C. That’s far below what many of those Armageddon folks like to talk about.

The big uncertainty is water vapour and especially clouds. And people don’t know what clouds do. If you have clouds during the day they block the sunlight and things cool down. If you have clouds at night they’re going to trap heat hence the temperatures stay warmer.

So are we going to have more clouds? Fewer clouds? We just don’t know.

Lots We Don’t Know

First of all, there are a lot of things we don’t know. We don’t know how to model ocean currents very well. Convection is extremely difficult to model, you’re dealing with a turbulent process, the equations are very complicated and no one can model that very well. So that’s why we have focused on radiation.

Right now we are unable to make a prediction of how turbulence, those fluid equations, how that behaves. That’s just too hard for us to model. And even if we get much, much faster computers that’s going to remain a very, very tough problem.

The H2O Continuum

Some basic physics that even isn’t very well understood: For example, people like to talk about when you calculate the absorption of these different wavelengths, they say OK you have all these different lines for CO2, H2O etc. So then they make some predictions based on those lines of absorption and then they look at observations and then they look for the difference and they find that there’s a big difference and that they say is due to something called the H2O continuum. Well you ask “What is the H2O continuum due to?” and no one seems to know.

So when you ask, is this well understood, no it’s not. I think the problem in this field is people have not said, make some predictions, what are the observations, is there agreement between the model and the observations? And sometimes these models just have failed abysmally.

That doesn’t mean the modelers are dumb folks. But it’s just a very difficult thing sometimes to model. Climate is not simple to model.


Oh dear. That sounded disquietingly like real science. The kind you might study at college and fail. And there's no doubt we lay people need to try to keep up to speed on that and all kinds of other scientific subjects, partly to be informed citizens on important policy issues and partly just to be well-rounded. But part of understanding science is understanding where the complexities lie, and not getting browbeaten, especially by people who aren't scientists or won't admit science is complex, into believing it's so simple a child can explain it with a crayon.

That’s not true of economics. It's not true of foreign policy. It's not true of how our system of government works, or all sorts of other things we want to understand in order to make informed decisions. And it's not true of climate science.

For the Climate Discussion Nexus, I'm John Robson. Thanks for watching our Fact Check video on the Simple Physics slogan, and we’ll see you next time.

6 comments on “The "Simple Physics" Slogan”

  1. Greenhouses work by supressing convection, not IR emission. Carbon dioxide is a greenhouse gas because it is used in greenhouses to encourage tomatoes! So basically the term GHG needs quotation marks. Incidentally a very large number of our terms need quotations, eg. "Liberal", "Conservative", "Newspaper". You get the drift.
    PS. John your commentaries are extremely good. Facts and wit. I have come to a very Bristish conclusion that much of what troubles us needs to be laughed at, loudly.
    PPS. Christopher Monckton. He would love your stuff.

  2. This simple mind still has some simple questions:
    If there is global warming and ozone is a "geenhousegas", why did we have to "fight" to close the hole in the ozone layer?
    Whasn't that just an exhaust valve for excessive heat? Maybe a natural feedback from mother earth?
    Another question I have: How can geothermal technic be good for the climate, if it brings heat from the inner earth to the atmosphere?
    Just simple questions with probably no simple answer.

  3. Ozone in the stratosphere blocks ultraviolet light which is dangerous to plants and animals. Ozone in the troposphere acts as a greenhouse gas.

  4. Ozone is an unstable form of oxygen. It 'blocks' uv frequencies by absorbing the energy of the photons. It naturally decays back to O2 at a rate dependent on temperature. The ozone hole appears in the hemisphere that is in winter because the uv levels coming in are low.

  5. I am not a scientific person but I do know that humans ,plants and animals couldn't live without co2,that is basically high school science 👍🏻

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