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.
Yes, it's fine, but you should be aware that the earlier period of the data is incapable of showing large variations within a century or so. They are all smoothed out, even if they happened. So you get the wrong impression if you assume that temps have been smooth with no centennial scale gyrations. The plain fact is our data is not good enough to show this level of granularity.
...no temperature variability is preserved in our reconstruction at cycles shorter than 300 years, 50% is preserved at 1,000-year time scales, and nearly all is preserved at 2,000-year periods and longer.
My personal Bayesian guess is that the recent temp rise is abnormal in historical perspective. But you are getting the wrong impression of the surety of that view from looking at the XKCD cartoon. Randall has a small caveat on this issue but does not go in depth to analyze it (and it is the key issue in extracting insight from the Marcott study).
