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This is the short edition of Morales, first broadcast on the BBC World Service.

Hello and welcome to more or less on the BBC World Service, the programme which makes

sense of numbers in the news and in life. I'm Tim Harford.

This week we take a look at what problems climate migration might pose.

So if we get climate change wrong, there is a very real danger we shall see levels of mass migration as yet unparalleled.

That's Chris Bryant, Britain's shadow immigration minister.

Warning that millions of people around the world will be forced to flee their homes

and in their droves move to countries less affected by environmental problems.

Now some of this has already happened.

The United Nations estimates that in 2008 20 million people were displaced by climate change

compared to 4.6 million by virtue of internal conflict or violence.

But much more is to come.

You can imagine that the UN estimates of 200 million such refugees,

more than the total number of worldwide migrants today, may be about right.

Now in fairness to Mr Bryant, he didn't just make that claim up, it did indeed come from the United Nations.

But we still suspect that some kind of attraction may be necessary alas.

Here at more or less we have a climate migration correspondent Hannah Barnes.

Hannah, you've done this before. You've specialised in taking the heat out of these kinds of statistics.

That's right, but it's not just me.

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