This is going to get seriously nerdy. Like, not fantasy nerdy but science nerdy. You have been warned.
One of the fundamental laws of the real universe is that as time moves forward, the entropy of a system (such as the universe) will increase.
What exactly do we mean by entropy?
First off - a caveat. I have a major in dramatic writing, not physics, and this is based on my sort of general curiosity and having read Stephen Hawking's A Brief History of Time. So if I get some details wrong here, well... I might get details slightly wrong.
Entropy is a way of measuring disorder. An ordered thing has a relatively small number of states it can be in, but as disorder grows, the number of potential states increases. Think of a chess game - as the game begins, there are only 20 moves you can make on the first turn (each of your pawns up one step or two, or your Knights going up and to the right or up and to the left.) But as the moves go on, the number of possible games becomes absurdly huge to the point where having a computer "solve" chess by calculating every possible game still rests outside our technical capabilities.
It turns out that the universe works a lot like that too. Energy in disorder - meaning that it's not all moving in one direction but causing particles to bounce around like your late-game chess pieces - is what we call heat. Something that is hot is actually something in which there's a bunch of energy, but rather than moving the thing in one direction, all its parts are going in different directions, bouncing into each other.
People have proven mathematically that entropy will always increase over time. When you run an air conditioner, for example, you cool your room by actually making the outside a little hotter - we think of this as ok because the relative volume of your room is so small that the increase to the outdoor air temperature is pretty small. But the net effect of running an air conditioner is that electrical energy is converted into heat energy, and the universe gets a little hotter.
This is so fundamental an aspect of reality that some physicists have hypothesized that it isn't so much that entropy increases over time as much as it is that time is simply our human perception of an increase of entropy.
Let that sink in for a moment.
So what the hell does this have to do with a video game about wizards and monsters?
Well, the Warcraft universe has six primal forces that each have an opposite number, and each of these has an affiliated type of magic. You have Life and Death, Light and Shadow, and finally Order and Chaos.
The magic of Chaos is Fel magic - used by Demons and Warlocks (and of course Demon Hunters.) It is most commonly manifested in the form of green fire.
The magic of Order is Arcane.
If Chaos and Entropy are almost synonymous, that would make Order a kind of opposite to chaos.
As far as we know, our universe doesn't have an Arcane force that counters the progression of entropy, which is why physicists think that in a very, very long time (we're talking a number of years that I don't even know how to spell out without using scientific notation) eventually all the potential energy in the universe will have done what it had the potential to do, and the only thing that will remain will be a perfectly even, dull heat - called the Heat Death of the Universe.
But with this Arcane force, there could be a counter-balance, allowing the universe to be preserved.
If using or generating chaos causes heat - which it does in our universe and certainly seems to in the Warcraft universe as well - then shouldn't Arcane cause coldness?
Indeed, the fact that mages can manipulate time and generate coldness through Arcane magic might actually just be two sides of the same coin.
But what about Fire mages?
Well, even though our universe tends toward heat, we can still cool down individual portions of it at the expense of heating up other portions. It would stand to reason that using Arcane magic to heat something up could be done, at the expense of cooling other parts of the universe.
But we have to imagine that, like the way the air conditioner actually winds up generating more heat than it cools, a Fire Mage would be cooling things down more than they're heating things up.
An air conditioner in reverse is actually a highly efficient heater called a heat-pump. A Frost Mage is basically using the "waste" product of his or her magic as the product - allowing the Arcane to do its work, cooling things, and using that cold to attack his or her foes.
Thus, a Frost Mage has a minimal environmental impact, while a Fire Mage will put more of a drain on the universe's heat. And it might be for that reason that Frost is considered the more classic and respectable type of arcane magic, while Fire is considered reckless.
As to Arcane Mages... Get back to me on that.