How do we know global warming is caused by us?

That has got to be a question you asked at some point. Isn't it strange to you, even now, that everybody seems to assume that we cause global warming?
Here's the answer to that question:
Human greenhouse gases cause global warming. It's as simple as that. All the fumes from cars, trucks, vans, lorries, factories, et cetera, et cetera, et cetera, contribute to global warming. So even if you take public transport, you contribute to global warming - though it wouldn't be as bad 'cos you're in the same vehicle as loads of other people who would otherwise be contributing fumes from each of their own cars. So that's why.

To add a funny note to this blog post, (though it's actually a rather serious problem) I'm going to talk about the danger from cows' bottoms.
Methane is increasing and it is eight times better at warming the Earth than carbon dioxide! Methane comes from rotting waste and wet paddy fields. It is also... uhh, released from both end - in huge quantities from grass-eating animals like cows. The more people there are on Earth eating meat, rice, and throwing out rubbish, the more methane is produced.
So all vegetarians, give yourselves a pat on the back for saving Earth - though the way in which you do it may be laughed at.