Nature Climate Change 4, 806–810 (2014); published online 3 August 2014; corrected online 8 August 2014; corrected after print 4 September 2014.

In the version of this Letter previously published, the value given for net ecosystem productivity was incorrect, and should have read 99.2 Tg C yr−1; this has no impact on the reported results. These corrections have been made in the online versions of the Letter.