My Dishpan Climate Model

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?


Moments of Revelation

Dr Iain Stewart holding a rock

Dr Iain Stewart holding a rock

Over the past few days I’ve worked my way through the three-part BBC series, Climate Wars, hosted by Dr Iain Stewart, a geology professor with a very cool Scottish accent. An excerpt from this series was featured in one of Peter Sinclair’s videos, which looked quite fascinating, and anything Peter refers to as “brilliant” is probably worth watching.

Worth watching indeed. I’d recommend anyone and everyone to watch this series. It’s basic enough for someone with little to no knowledge of this issue, yet presented in such a compelling way that the most experienced climate scientist wouldn’t get bored.

One of the film’s major strong points was simply the way it was organized. Dr Stewart traced the history of both the science and the politics around climate change, splitting it into three parts:

Part one: Scientists had known for decades that anthropogenic greenhouse gases could cause warming of the Earth, but now, following thirty years of aerosol-induced cooling, global warming was starting to show; almost every year was record-breaking. James Hansen was the first to “stick his neck out” – testifying to Congress that he believed anthropogenic climate change was underway. He later claimed that he had weighed the risks of being wrong and looking stupid, versus doing nothing and not telling the world about such a huge potential threat. Sort of like an early Greg Craven, I suppose. I found this part to be the least interesting of the three. It also began strangely – Stewart mentioned a letter to the US president, signed by top scientists, which warned of an impending ice age. I’d never heard about this before. Does anyone else know more about this letter?

Part two: The skeptics fought back as strongly as they could, questioning absolutely every scientific claim regarding global warming. I found this to be absolutely fascinating; it solidifed a lot of issues in my mind and helped to unify my knowledge on the topic. Stewart went through the research which showed that the Earth was warming as a result of human activities – and showed how all the yelling from skeptics helped to make the theory even stronger. He also “infiltrated the walls” of the Heartland Institute’s International Conference on Climate Change, which I found to be absolutely hilarious. They had a comedian making bad jokes about how New York could handle some global warming, Monckton and Singer making their usual accusations of fraud (Stewart remarked that “when these become the talking points, then I know that the scientific debate is really over”), and Patrick Michaels publicly admitting “Yes, the second half of the century did show some warming, and it was the result of human activities…..and now you all hate me for saying that…….” Dr Iain Stewart explained that, even though the controversy doesn’t really exist anymore in the scientific literature, the claims of skeptics still live on in the popular media and on the Internet. Instead of fighting a scientific battle, they’re now doing public relations.

Part three: Scientists knew that humans were causing global warming, but how bad would it be? After the brilliance of the second part, I wasn’t expecting to enjoy the last segment quite as much…….but I was proven very, very wrong. It both terrified and fascinated me. Terrified because it discussed the Younger Dryas, something I hadn’t really heard of before, where it warmed about 5 C in just a few years. So far beyond anything I thought was possible. When this research was released, the idea that the climate was steady and slow-moving could no longer be embraced.

And then it fascinated me because it was the first time that climate models seemed really, really cool.

The idea of modelling something – anything – on the computer is somewhat unremarkable to me. I am of the generation that literally grew up using computers; I vaguely remember playing astronaut addition games on Windows 3.1 when I was four. I have seen so many things digitalized; the prospect of modelling climate is obviously immense, but it doesn’t amaze me.

But then Dr Stewart made a “dishpan climate model” with a spinning bowl, water with some dye, an ice-cube Antarctica, and a Bunsen-burner Sun. He set it all up and before long… could actually see regular patterns in the water’s movements that looked like the prevailing winds. It was so, so amazing. Even more amazing than a complex model on the computer because it was real and tangible and you could touch it. Like a little Earth on the countertop. All of the complex processes of our climate eventually come back to these simple factors. (I want to make one myself. But I don’t have one of those spinny things.)

And then I started wondering what computer modelling would be like, and remembering how much I loved physics last year, how I liked to put four or five algebraic equations together and solve it all in one complicated step to reduce error. Manipulating variables and shifting things around. Like a little puzzle. I was remembering how much I love hard math problems, because you actually have to use your brain, try everything you can think of, stretch the limits of your logic…..and you feel such a sense of accomplishment when you finish that all the work is worth it.

Is a climate model just a really large and complex collection of equations and puzzles that have to fit together in the right way? It would be pretty cool if it was. I knew that studying climate change required a lot of math, but this is the first time that I can see a clear path showing how an issue I care deeply about could coincide with aptitudes I enjoy.