Nature Communications 4: Article number: 1748 (2013); Published: 23 April 2013; Updated: 7 November 2013.

The original version of this Article contained a chronological error concerning the counting of tree ring layers. During reanalysis of the data after publication, a missing layer was discovered around AD 956, which meant that all dates derived from annual layer counts beyond this datum needed to be increased by 1 year. For example, the date ranges quoted in the Abstract required revision from ‘AD 822 to 1020’ and ‘AD 992 to 993’ to ‘AD 822 to 1021’ and ‘AD 993 to 994’, respectively. These changes have now been applied throughout the PDF and HTML versions of the Article and accompanying Supplementary Information.