My son has a fascination with ice. He loves it in drinks (something he gets from me, more than from his mother), and he loves to look at it. We play games with it, like the time I put an ice cube in a bowl for him so he could watch it melt. Or the time we left a cup of water outside to see it freeze. I think he likes the idea that water can turn into a solid, and the fact that it’s cold is just a bonus bit of entertainment.
So we’re driving to church one Sunday, and looking at the snow that’s covered everything – one of the few days this winter where we’ve actually had snow – and he asks me “what if the oceans froze?”
Well, that sounds like an apocalyptic scenario if I’ve ever heard one. “Froze solid?” I reply?
“Yes! So we could ice skate on them!”
Bear in mind that my son has never gone ice skating. So I have no idea where that came from. But the question is interesting. And, sadly, nowhere near as much fun as he’d hope.
When Does Salt Water Freeze?
To start with, ocean water has a much lower freezing point than freshwater. In “Can the ocean freeze?“, NOAA informs us that seawater freezes at 28.4 degrees Fahrenheit (which is -2 degrees Celsius), because of the salt. They also tell us that the average temperature of all ocean water is about 38.3 degrees Fahrenheit (3.5 degrees celsius). So, in theory, to freeze the oceans we’d simply need to reduce the average ocean temperature by 9.9 degrees Fahrenheit (5.5 degrees Celsius).
How cold would it have to get?
Interestingly, the simple truth is that all you’d have to do to freeze the ocean is get the air below the freezing point of the ocean. Then, eventually, you’d manage it. That would require bringing the average equatorial temperature down to that level, and the best figure I could find for that average temperature is 77 degrees f (25 degrees C). That’s a 38.7 degree F (21.5 degree C) difference. This would bring average global temperatures down to 22.3 degrees F (-5.5 degrees C), so things would be terribly cold. To put it in perspective, polar climates have an average temperature of 50 degrees F (10 degrees C).
A killing frost is a temperature that will kill a plant entirely – not just damage the extremities. Corn and soybeans will die below 28 degrees F. Wheat is a little hardier, depending on the growth stage, but will pretty much die at 24 degrees F (-4 degrees C). So if it got cold enough to freeze the oceans, we’d be living in a permanent killer frost. Which is another way of saying that we’d be in huge trouble.
Interestingly, this may have happened before. There is something called the Snowball Earth hypothesis, that says the Earth may have been frozen like this some 650 million years ago. Equatorial temperatures would have been around what present day Antarctic temperatures are like now – which means an average range of -67.18 degrees F (-55.1 degrees C) in Vostok to 22.46 degrees F (-5.3 degrees C) in the Antarctic Peninsula. There’s a whole lot of disagreement about this theory, though, so take it with a grain of salt until and unless more information comes along.