This chart seems to be sourced from a chart done in the UK with the data smoothed. Originally presentec by E.G. Beck with the green circles added by RC team. RC - "It originally is taken from the first IPCC report of 1990: a scan of the original is shown in Figure 3. At that time, no large-scale temperature reconstructions were available yet. To give an indication of past climate variability, the report showed Lamb’s Central England estimate. (Unfortunately this was not stated in the report". http://www.realclimate.org/index.php?p=450
When all the temperature reconstructions are considered you achieve a picture of the Global Mean Temperature (GMT) http://www.realclimate.org/index.php?p=450
Possibly this is the original graph that the IPCC used for their 1990 report. Possibly from a university in the UK.
This is the typical image used to show that it was warmer during the medieval warm period that today. The graph is apparently representative of real data but the data is regional and therefore does not represented the global mean temperature (GMT).