About two years ago, I discovered the concept of “dishpan climate models”, through Iain Stewart’s Climate Wars documentary. The experiment is pretty simple: a large bowl filled with water (representing one hemisphere of the Earth) with a block of ice in the middle (a polar region) rotates on a turntable with a Bunsen Burner (the Sun) heating it from one side. By injecting some dye into the water, you can see regular currents from heat transport and the Coriolis effect. Spencer Weart dug up some fascinating results from the days when dishpan climate models were the only sort available: researchers were able to simulate the Hadley circulation, Rossby waves, and the Gulf Stream.
I wanted to try this out for myself. Iain Stewart had made it look easy enough, and he got some really neat currents flowing. So one Saturday afternoon a friend and I got to work in my kitchen.
We started by figuring out how to rotate the bowl. My family doesn’t own a record player, so we couldn’t use that as a turntable. We tried to rig something up out of an old toy helicopter motor, but it wasn’t strong enough. Eventually we settled for a Lazy Susan which we spun by hand. It wasn’t a constant rotation, but it would have to do.
Then Antarctica, which consisted of a handful of ice cubes, kept floating away from the centre of the bowl. Soon the ice cubes melted and there were none left in the freezer. We filled a Ziploc bag with frozen corn, which wasn’t quite as buoyant, and used that for Antarctica instead.
Unsurprisingly, there was no Bunsen burner in my kitchen cupboard, so the Sun was represented by a paraffin candle that sort of smelled like cinnamon.
The only serious problem remaining was the dye. Every kind of dye we tried – food colouring, milk, food colouring mixed with milk – would completely homogenize with the water after just a few rotations, so all the currents were invisible.
The only liquid in my kitchen that wouldn’t mix with water was vegetable oil, so we dyed some of it blue and poured it in. This was a really really bad idea. The oil seemed to be attracted to the plastic bag keeping Antarctica together, so it all washed up onto the continent like some kind of awful petroleum spill in the Antarctic Ocean.
At that point, our climate model looked like this:
I would like to try this again some day, perhaps when I have access to a better laboratory than my kitchen. Any ideas for improvement (besides the obvious)? In particular, what kind of dye does work, and how does Antarctica stay together without being encased in plastic?