An analogy is a powerful tool in science communication. Here are two of my favourites to do with climate change.
The first is of my own creation (although it isn’t too original) and came about after I had presented to high school students a few times. As anyone taking high school physics learns pretty quickly, when using the formula F=ma, to find the net acceleration (the actual, observable result) you must always use the net force. If three people are pushing a box three different directions, you can’t just take one person into account. You have to look at all of them to see which way the box will move, and how fast.
Similarly, to analyze observed climate change, you can’t just take one forcing into account. You can’t only look at greenhouse gases and expect that they will track perfectly with the global temperature. You have to look at what the sun is doing, what aerosol levels are doing, where the ENSO cycle is. Climate is influenced by a combination of factors, and it will never track perfectly with any one. But if only one is changing significantly, and the others are staying pretty much steady, it’s obvious which way the box is going to move.
I found the second analogy in David Archer’s book Global Warming: Understanding the Forecast. I’m only two pages in and already I found something that I want to share here!
[The energy budget/climate equilibrium] is analogous to a sink with water flowing in from a faucet. The faucet fills the sink at some constant rate, while outflow down the drain depends on the water level in the sink. The sink fills up until water drains out as fast as it comes in.
It is possible to change the average temperature of the Earth by altering the energy flow either coming in or going out. In our sink, one way to raise the water level is to turn up the faucet and wait a few minutes. The water will rise until it finds a new equilibrium water depth. We can also alter the water level by partly constricting the drain. Egg shells and orange peels work well for this purpose. If the drain is partly obstructed, the equilibrium water level will rise.”
Brilliant, no? I think that Greg Craven had a similar analogy (the “bathtub”) in his book.
What are your favourite analogies – of your own creation or that you heard elsewhere? Share them in the comments below.
ClimateSight 
Check out John Sterman’s MIT page for much more on the bathtub analogy (in the context of the difficulty many people have in grasping stocks and flows, which unfortunately includes principles necessary for understanding climate change). IIRC there’s even an online test module.
Most striking is a study he did a few yeatrs back using MIT grad students, wherein it was demonstrated that the majority of them aren’t equipped to undertstand the problem! It was an eye-opener for me since it helps explain why lots of otherwise quite intelligent people don’t get it.
Michael Tobis’bathtub version is similar but adds a missing dimension (but read the comment thread).
I would go a step further and add a webcam to the mix. The issue is you don’t actually watch the cam (too lazy), but others (including the bane of the internet, Anonymous) do watch it, and you’re following their discussion about it on Twitter (between blocks, of couse; gotta focus on Important Things). Imagine how that changes as the tub overflows.
…What? It misses false balance and Overton windows (somewhat) but gets the signal:noise and audience apathy just about right.
My favourite ones, not sure if I made these up or stole them, all relate to people being confused by Monckton-like attacks based on climate and chaos – “it’s all to complex to predict”, as well as “it’s been cooling”. So, some nice intuitive examples to understand the basic statistics ideas. Realclimate mocked this in an April fool –
http://www.realclimate.org/index.php/archives/2005/04/doubts-about-the-advent-of-spring/
Genius quote: “This is not merely fiction: Crikey underpins his thesis with numerous scientific diagrams. He presents measurements from over a dozen weather stations in the Northern Hemisphere where temperatures show a cooling trend in March.”
Less sarcastically, it’s actually a really useful, intuitive response to anyone who says “but they can’t even predict the weather in two weeks!” Yes, but do you think you know if the temperature will be hotter or colder in six months time? Yes? Why? What’s the difference?
The underlying point: systems can exhibit chaos (can’t predict weather in two weeks) but have predictability at different timescales (can predict, within bounds, the temperature in six months.) It’s also a nice illustration of the idea of climate forcing (I think! Is it?) – in the case of the seasons, the forcing is due to the angle of the earth to the sun. Same with the bath example: the fact you can’t predict the exact turbulence of the water in no way impedes your ability to predict what will happen when you pull the plug!
[That RC post is hilarious – I love it! -Kate]
My other recent favourite, following the Daily Mail’s travesty of twisting Phil Jones’ ‘not statistically significant’ into ‘climate u turn’ is from potholer54: an example to illustrate that the more samples you take over time, the more likely you can detect a trend. He has a nice bit of video of a beach: stick flags where the waves get to. How many flags do you need to stick in before you can with any certainty that the tide is coming in or out? That sort of mental picture, everyone can get instantly, don’t have to bring p values into it…
The same applies to the first example, of course – as the realclimate spoof notes, a week of colder weather in March doesn’t mean summer isn’t coming. cf. one higher wave doesn’t mean the tide’s coming in – you need more samples! Everyone understands that – it’s not rocket science. And that’s why I conclude that stories like the Daily Mail u-turn ones are deliberate obfuscation, because no-one could be that stupid. I don’t think.
I blogged about this kind of metaphors a few weeks ago here: http://catenary.wordpress.com/2010/02/19/bathtubs-waistlines-and-credit-cards/
As you can see I’m less taken by the bathtub metaphor, but I’m not sure I’ve found something better.