Updates are available Erratum dated 2016-07-29

Article History

Received: 9 April 2015

Accepted: 26 June 2015

First Online: 10 August 2015

Change Date: 23 June 2016

Change Type: Corrigendum

Change Details: In the version of the Letter originally published, in the last sentence of the Fig. 1 caption, the coordinates given for the dashed boxes in Fig. 1 and Fig. 3 were incorrect. The coordinates for eastern China should have been '108°–123° E, 20°–44° N' and not '105°–129° E, 18°–42° N', and the coordinates for western US should have been '130°–105° W, 30°–50° N' and not '130°–105° W, 20°–50° N'. This has been corrected in the online versions of the Letter.

Competing interests

: The authors declare no competing financial interests.