Why your ice cubes disappear by Maki via sci-ence.org
I like cold beverages. I have a fire within that demands to be quenched by near-frozen liquids. As such, I go through a lot of ice—figurative tons of ice. I probably make and consume enough ice to warrant suspicion from climate scientists, asking “Where’s all our ice going?”* and when they talk about anthropogenic** global warming, they’re talking about me.
But lately, like in today’s comic, you might have asked, “Where is our ice going?” as your stare at the bottom of your ice cube tray, which is now only inhabited by contact lens-sized slivers of ice nuggets. If you’ve never seen this happen, I highly suggest you set a tray aside and check on it every week or so. Funnily, the mechanism responsible for making your ice cubes disappear is the same as the one keeping your freezer tidy and manageable. Relatively speaking.
Back in the day, freezers used to accumulate frost on the inside of them, which would build up over the years until you couldn’t fit anything in your freezer, in turn causing you to have to find a hammer and go Old Boy on the poor thing to knock the ice loose. Now most freezers are “frost free” and accomplish this by creating the perfect conditions for a thermodynamic marvel called sublimation.
In school we learn that water has three phases (solid, liquid, gas) that it proceeds through as its temperature changes from cold to hot. But like most things you find out as a grownup, we can skip a step and go right from solid to gas. In your freezer, the air that is being blown around is cold enough and the humidity is low enough, that water molecules on the surface of the ice can occasionally gain enough kinetic energy to just pop off into the air. No liquid phase required.
Sublimation is why dry ice creates spoooooky smoke and it’s the principal mechanism in freeze-drying. That’s right, astronaut food is made by freezing normal food and subjecting it to reduced pressure, causing the water to sublime. Then the dry chunks are eaten by sad astronauts. It’s science!
For most of us, we’ll only see the effects of sublimation in our freezers, where it cruelly takes our ice. Luckily for me, I go through cubes fast enough that it never gets a chance. But you can always tell who prefers hot beverages over cold ones by checking their ice cube trays.
*Note: This is not how climate change works at all. Keep enjoying ice.
…while you can.
**Not Anthropomorphic.
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