The present invention relates to methods of increasing the activity of a polypeptide having cellulolytic enhancing activity, comprising: adding a soluble activating divalent metal cation to a composition comprising the polypeptide having cellulolytic enhancing activity, wherein the presence of the soluble activating divalent metal cation and the polypeptide having cellulolytic enhancing activity increases degradation or conversion of a cellulose-containing material by a cellulolytic enzyme composition compared to the polypeptide having cellulolytic enhancing activity without the soluble activating divalent metal cation. The present invention also relates to compositions, methods for degrading or converting a cellulose-containing material, and methods for producing a fermentation product.