Nature 433, 613–617 (2005)

The authorship of this Letter is amended to include Stein-Erik Lauritzen. Details of the Søylegrotta Cave record (series 8), which should have been accredited to S.-E.L., were not supplied in the paper but are available from the corresponding author (A.M., anders.moberg@natgeo.su.se) on request.

 In addition, the tree-ring-width data from the Indigirka river region (series G) were inadvertently used without the proper permissions: although the series has been discussed in the literature1, they are unpublished data that have not been made publicly available; they may, however, be obtained through A.M.