The important thing about CO2 levels is that they have doubled due to industrial emissions. As a proportion of the whole atmosphere greenhouse gases may not constitute much but the way the physics works means that they are an important constituent of the atmosphere.
A useful explanation of the history of the science can be found here
http://www.aip.org/history/climate/co2.htm
Thankyou very much for that link. It answers a lot of questions, and I was glad to see that the questions I have been asking have actually been asked by scientists, and answered. This stuff never gets as far as the papers, though, does it? I was quite the fence-sitter before, but now I see why people are so deeply worried by this.
I was looking at the Milankovitch cycles, too, to try and see where we are on them, but it is pretty difficult to figure out - not one page says "we are at x,y,z points on these cycles and therefore the globe should currently be cooling/warming. It looks as if we should broadly be at or approaching peak temperatures as a result of the Milankovitch cycles, and at some point in the next 10,000 ought to start to cool down again. That is quite a long time, though, and with the unknown effect of the high CO2 levels in terms of whether they might counter that cooling cycle, or whether we will still be around by then due to having boiled ourselves off the planet, it is rather difficult to say what will actually happen.
The problem is most people are pretty parochial at the end of the day, and simply can't worry about global effects, or effects in even 100 years, let alone 10,000, which is partly why it's so difficult to get this message across. There is also the question of whether we can actually make any difference now, or if it's too late. Quite a lot of people I know say things like, "this global warming business is highly debateable, and besides if those greenies are to be believed it's too late to change it now so what's the point?" So the one message that did reach the public consciousness is the one that leads to the most apathy, sadly.
Anyway, that's an extremely useful link you have there, very in depth, but really readable. Thankyou.