This might sound like a crazy idea, but bear with me. I mean, why not? We’ve got some pretty general computer models of the climate, all we have to do is change the sign of a couple of numbers.

There are some legitimate scientific questions about how different aspects of our climate depend on their interaction with the Earth’s surface that we could use as “serious” motivation, but, if we’re honest, it’s mostly for fun. Because we can. Because we don’t know. It’s just a somewhat arbitrary sign on a parameter value, but it ought to make a big difference. What if…?

So we did it*. As it happens, the meridional overturning circulation in the Atlantic ocean that helps keep Europe warm shut down, and the UK and Scandinavia cooled by about 10 degrees on the annual average. The ‘Gulf Stream’ no longer exists – there is now an eastern boundary current instead (see figure). North African rainfall went up, and the Mediterranean received so much river input it became almost fresh. The reorganisation of the world’s hydrological cycle that we initiated might have frozen Europe, but it started up a big, heat-transporting overturning in the Pacific instead, something that doesn’t exist in our world. Of course, that was just my model**. Someone else had the same idea, and got a different answer*** – different climate models don’t always agree, especially if you push them too far.

So what’s the point? I find that these cartoon experiments generally elicit polarised opinions: some people think they’re fantastic, and launch into a stream of questions and speculations about what happens to their favourite bit of the climate. Others clearly think they’re a waste of time and effort. I think there’s real value in experiments like this though, however unrealistic the scenario and however wacky the results. You start thinking about the familiar mechanics of the climate system in a very different way from normal, and questions start occurring to you that you wouldn’t normally think to ask. They remind you that your model is just a model, and that maybe you should be thinking harder about what it’s telling you the rest of the time too, when you’re using it for more “serious” work. They’re fun, but also a great way of firing up your scientific instincts, of making you re-evaluate what you assume you know already about the world. What if…?

* EGU General Assembly Poster, EGU2008-A-06893, 2008

** www.famous.ac.uk

*** Kamphuis et al, Clim. Past 7, 2011

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