The reconstructions used, in order from oldest (bluest) to youngest (reddest) are:
(black): Instrumental data was jointly compiled by the Climate Research Unit and the UK Meteorological Office Hadley Center. Global Annual Average data set TaveGL2v (http://www.cru.uea.ac.uk/cru/data/temperature/) was used.
- (dark blue): P.D. Jones, K.R. Briffa, T.P. Barnett, and S.F.B. Tett, 1998, "High-resolution Palaeoclimatic Records for the last Millennium: Interpretation, Integration and Comparison with General Circulation Model Control-run Temperatures", The Holocene 8, 1998, 455-471.
- (blue): Michael E. Mann, Raymond S. Bradley, and Malcolm K. Hughes, 1999, Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations, Geophysical Research Letters Vol. 26 , No. 6 , p. 759, March 15, 1999.
- (light blue): Crowley and Lowery 2000 (Ambio 29, 51), "Northern Hemisphere Temperature Reconstruction", Modified as published in Crowley 2000 (Science v289 p.270, 14 July 2000).
- (lightest blue, somewhat green): Briffa et al. (2001) J Geophys Res 106, 2929-2941.
- (light green): Esper, J., E.R. Cook, and F.H. Schweingruber, 2002, Low-Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability, Science, Volume 295, Number 5563, 22 March 2002.
- (yellow): Mann, M.E. and P.D. Jones, 2003, Global Surface Temperatures over the Past Two Millennia, Geophysical Research Letters, Vol. 30, No. 15, 1820, August 2003. doi: 10.1029/2003GL017814.
- (orange): Jones, P.D. and M.E. Mann. 2004. Climate Over Past Millennia. Reviews of Geophysics 42, RG2002, 6 May 2004.
- (red-orange): Huang, S.. 2004. Merging Information from Different Resources for New Insights into Climate Change in the Past and Future. Geophys. Res, Lett. 31, L13205, doi:10.1029/2004GL019781.
- (red): Moberg, Anders et al., 2005, Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data. Nature 443, 613-617.
Documentation for the most recent update of the CRU/Hadley instrumental data set appears in: Jones, P.D. and Moberg, A., 2003: "Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001". Journal of Climate, 16, 206-223.
The original picture is at:
http://en.wikipedia.org/wiki/Image:1000_Year_Temperature_Comparison.png and is used here under GFDL.