Is this XKCD comic an accurate timeline of the earth's average temperature? Apologies for the length of the image, which I found at http://xkcd.com/1732/.
I'm mostly interested in the temperature line itself, both the historical data and the forward projections.
The reason I ask is that I'd like to (in a classroom context) hold this image up as a good example of the visualisation of data, that could be emulated in the area of science relevant to that classroom (zoology). However, I'd first like to check that the data itself is correct.

(click to enlarge)
Yes, it's accurate, see e.g. this picture taken from the Wikipedia Geologic temperature record page:



You could dig up the source if you wanted from the wikipedia article (or the graph description page), but any graph will be generally the same. Since there was an ice age, you'd expect global temperature to be low ~20k years ago and so on.