From Montserrat Filella and Juan Carlos Rodríguez-Murillo
The cover of your 9 January issue promises to tell us “what's muddying the world's waters”. But, as the article (p 34) in fact reports, this “global browning” effect has been demonstrated only for North America and northern Europe – as we reported in the journal Water in May 2014 (doi.org/bcgs). In most of the rest of the world there simply isn't enough data.
Geneva, Switzerland and Madrid, Spain
