Nature Geoscience 9, 277–281 (2016); published online 14 March 2016; corrected after print 5 May 2016.

In the version of the Letter originally published, the following reference was mistakenly omitted:

27. Yang, Q., Bitz, C. M. & Doherty, S. J. Offsetting effects of aerosols on Arctic and global climate in the late 20th century. Atmos. Chem. Phys. 14, 3969–3975 (2014).

This should have been cited with ref. 25 at the end of the sentence beginning 'Over the past 100 years...'. The original refs 27–31 have been renumbered accordingly. This has been corrected in the online versions of the Letter.