Imagine, if you will, that we can peer deep into a solid object, and looking very, very closely, smaller than the eye can actually see, we can begin to make out the internal structure of that object, and zooming even closer in, we find what appear to be the smallest things that make up this object.
Let’s call these things ATOMS.
That’s a bit of Ancient Greek (or Jain) philosophy, the theory of the atomisation of matter, the idea that there are small things that make up large things, and that these small things cannot be made any smaller. This is a fantastic theory, as it explains a lot of things that happen around us. In several thousand years, nobody has seriously been able to challenge this theory; however, it has undergone continuous refinement.
Besides ordinary solid objects there are also things that you can’t hold in your hands; things like light and heat and the little electric shocks you get when you comb really dry hair.
Heat appears to be what happens to ordinary solid objects when the tiny atomic parts are moving wider or further or faster. Most things expand but stay holding together when they get hotter, which confirms this idea. There are special cases, like water, which expands as it freezes, but that can be explained by thinking about how atoms move in relation to each other…
Anyway, back to light.
Light is a different matter altogether. It appears to be able to pass through some objects without changing radically. It travels very long distances without being stopped. It seems to cause ordinary matter to heat up. It doesn’t rest anywhere.
In English we use “radiation” to describe light, and things like light that we cannot see but behave in roughly the same way. There is some confusion, as there are other things that are also called “radiation” which are actually just parts of split atoms looking for a new home, but we won’t go into that just now.
Light radiation is ELECTROMAGNETIC RADIATION (or EMR), and it’s absolutely fascinating. The whole range of EMR includes not only the light that we can see, but also radiation that we call radio, microwaves, X-Rays, ultraviolet and infrared.
Just a point here : some people confuse infrared radiation with heat, but they’re not actually the same. It’s just that hot things often give out infrared radiation.
How EMR plays with atoms is fundamental Science, and is the basis of the Science of Global Warming.
Imagine further, if you will, a large orange with a thickish skin. This is our basic model of the atom.
If you were to place an orange on your breakfast table and then roll a coin towards it, the thickish, pulpy skin of the orange would bounce the coin back to you.
This is the main way that EMR plays with atoms. It bounces off.
If you were to place the same orange on the same breakfast table and throw a dart with a long enough point, it could quite possibly pass right through the orange, skin and all, and poke out the other side.
This is another main way that EMR plays with atoms. It passes right through without saying hello or goodbye. It might change direction slightly, on its way through, but it doesn’t stick around or cause any mayhem.
And again, sticking with the same orange on the same breakfast table and this time holding a pea shooter, you could fire a pea at the orange and it could lodge in the skin or even flesh of the orange.
This is almost the same as the third main way that EMR plays with atoms. Except there is this subtle difference. The green pea penetrates the skin of the orange and stays there. If EMR gets stuck in atoms, eventually the atoms spit out EMR again. It may have a different colour than when it went it, but it’s still EMR.
This is what is happening on the surface of the Earth and in the Earth’s Atmosphere, high above our heads.
The Sun’s rays, which are EMR, come in and a lot bounces off the atoms of the Atmosphere (air), but some passes right through and hits the Earth’s surface. Some will interact with the atoms of the Earth’s surface, but a lot of it will just bounce straight off the Earth and be radiated back out towards Space.
The key point here is that some of the radiation that comes out from the Earth will have a different “colour” than the original sunlight.
Part of the radiation that is coming off the Earth will hit the grouped atoms (molecules) of Carbon Dioxide in the Atmosphere (air). Because some of it is now a different “colour”, a lot will be “absorbed”, like the pea in the orange rind, and then EMR will be radiated out again, in all directions.
It’s this “in all directions” bit that’s the most important. Some of the EMR that gets absorbed by the Carbon Dioxide will be radiated out to Space, but some will get radiated back to the Earth where it just came from.
This is the Greenhouse Effect : Carbon Dioxide effectively “traps” some of the radiation that would have gone back out to Space.
We then need to know a little about how EMR changes atoms – the simple rule of thumb is this – if EMR plays with atoms, they tend to heat up a bit. So you have some of the radiation coming from the Sun directly heating up the Earth’s surface, and you have some of the radiation trapped by the Carbon Dioxide coming back to heat up the Earth’s surface.
More Carbon Dioxide in the Atmosphere will mean more trapping of the radiation which will mean more heating up of the Earth’s surface, which means Global Warming, an increase in the normal temperature of the Earth.
Next time : how we know that Carbon Dioxide absorbs EMR; how we know that Carbon Dioxide is accumulating in the Atmosphere; and how we know that the Carbon Dioxide accumulating in the Atmosphere is mostly caused by burning Fossil Fuels and taking down trees.