Global warming melts the ice caps and the Maldives disappear. We all know the scenario, but how do we prevent it? Whilst governments are being realistic and trying to cut greenhouse gas emissions, I wondered how gigantic benevolent aliens would solve the problem.

Think about it: if some aliens, whose only technical superiority over us were interstellar travel, were to drop by, what would we ask them to do for us? The earth to them, in this scenario, is the size of a football is to us, so it'd be easy for them to rearrange huge amounts of material very quickly. The obvious idea would be simply to get an alien spoon, a pan hundreds of miles across to us, and scoop some water out of the oceans. But the shockwave that this would create, though a tiny ripple to the giants, might cause untold damage in the form of a tidal wave to us.

So the answer is pretty obvious really. You'd have to use a giant space straw that the aliens could suck through. At first glance you might think that in fact they wouldn't have to suck at all, because space is a vacuum and sucking is just the process of creating a vacuum at one end of the straw whilst the other end is in some medium that you want to suck. But there's an article about just this problem called Space Pipe which explains that this is a fallacy. Consider, instead, a straw that goes into the air rather than going into the water. It's pretty obvious then that all you're doing is putting a cover around the column of air, and that it's not going to be sucking anything. To make it even more clear, think in terms of a giant alien toilet roll tube.

So if the aliens wanted to suck part of the oceans up, does this mean that they couldn't do it? After all, if space is already a vacuum then surely there's no way that they can suck? Well I'm not sure but I think they could still do it if they had air in their mouths and then evacuated that air by breathing in, which is actually what we do when we suck a straw. So it's not the fact that there's a vacuum at one end of the tube, exactly, it's the fact that we're changing the pressure at that end. If you had a vacuum chamber it would be quite easy to test experimentally.

What this means is that we can't just get a free ride by creating a giant space straw ourselves, which is a bit of a shame. This is probably a similar class of problem to the question of whether you can harness the current induced in a plane flying across the lines of flux of the earth's magnetic field; you can't do it even though you'd think you might be able to, as my physics teacher proved to us once.

Once the giant hypothetical aliens had sucked the water up, I suggest that instead of just pooting it out of the solar system they might rather consider depositing it on the Sahara so as to give it the chance of being made fertile land. Whilst they're at it, they might as well put a huge dynamo on the moon, spin it and run a cable down; but then the sun already does that in effect anyway.