When we spent a little time on Thales a couple of posts ago, we touched on the importance of water to our survival (or even being here in the first place). Water is a remarkable substance, regardless of which planet or moon it might call home. It is, as you’ve probably heard, the universal solvent, meaning it can take a whole range of different substances and break them down into their individual atoms, so that they can interact and recombine in all kinds of different ways.
What makes water even more remarkable for us is that we live on a planet whose temperature is in just the right range that water can exist in all three basic states: gas, liquid, and solid. In the same post that referenced Thales, I noted that water vapor – the gaseous form of water – is extremely variable in our atmosphere, and also a fairly potent “greenhouse gas”. The liquid form of water is the main source of life for us, not just because we need to take it in on a daily basis, but also because we are literally made of water – 90 percent by weight. Water is likely the medium in which life on Earth first formed, so it’s not too surprising that it still forms most of what we are today. Water in solid form is a bit more fleeting for most of us. The average temperature across most of the Earth is simply too high for water to remain frozen – and so we either have to wait for a winter storm, expend significant energy keeping water frozen, or trek to some other location on the planet – generally either very high or very far north or south.
Wherever you may find it, ice has a different kind of relationship to photons, compared to the liquid and gaseous forms of water. The latter two generally like to absorb photons, but the crystalline structure of ice tends more to scatter and reflect them. That is why liquid water, especially on a grander scale, appears dark blue to us, while ice appears more white. Liquid water absorbs most of the Sun’s light (and therefore heats up in the process), and ice reflects most of the Sun’s light (and therefore remains relatively cool).
In addition to being at just the right distance from the Sun to support water in all its glorious forms, the Earth is also tilted at just the right angle to give us a well-defined set of seasons. Winter in a given hemisphere begins when that hemisphere is tilted away from the Sun the most, and summer is of course the opposite. Whichever hemisphere you’re in, for all of the history our species has known, winter has lasted long enough that the polar region facing away from the Sun gets cold enough that its water has turned to ice. Meanwhile, summer has not lasted long enough for that ice to melt away entirely, which is why we have come to expect the Arctic and the Antarctic to be substantially covered by ice year-round. The reflectance (brightness) of ice is a big reason for that. Even when the Sun’s photons are beating down on Antarctica, the continent stays relatively cool by rejecting said photons back into the atmosphere.
Let’s move our minds back to warmer climes for a moment, where it’s a very hot day, and your thirsty, and so you pour yourself a glass of ice water. Have you ever noticed that ice water feels incredibly colder than just cold water with no ice in it? That’s because the water is donating vast amounts of energy (heat) to the ice so that it can melt, which is a process that demands some amount of energy (ice is stubborn). Water is very much up to the task, and the more heat there is in the water, the faster it happens. Well, the sheets of ice in the Arctic are nothing more than a big ice cube, and the Arctic Ocean is nothing more than a big glass of water. So if the Arctic Ocean gets warmer, the Arctic ice sheets will melt faster. And then – and here is the geophysical bitch of it all – what was once bright, highly reflective ice has been replaced with dark, highly absorptive water. So now the water absorbs more photons from the Sun, and gets even hotter, which causes the ice to melt even faster. This is what they call a feedback loop. Who are they? I have no idea. But it doesn’t matter, the physics is ridiculously simple. Your respect for my PhD should rightfully be declining at an alarming rate. Much like the amount of ice in the polar regions. Whoops, I got ahead of myself there. Pretend you didn’t read that.
Antarctica is a little different from the Arctic because there’s an actual landmass there (i.e., a continent). But the edges of Antarctica are directly exposed to the Southern Ocean, and so if, hypothetically, the water around Antarctica were to get warmer, we’d see more icebergs fall off of Antarctica as it melts. I stopped just short of getting ahead of myself there.
Let’s just say this. In the year 2100 and beyond, If you want to hear Vanilla Ice’s “Ice Ice Baby”, even though it will have long since vanished from the Top 40, you will be able to download it in any number of ways. If you want to see ice sheets and glaciers in the polar regions, you may need a time machine. Dammit, got ahead of myself again.