NOVELTY - Increasing (M1) activity and stability of a glycoside hydrolase 61 (GH61) polypeptide having cellulolytic enhancing activity involves adding a divalent copper cation to a composition (C1) comprising the GH61 polypeptide, where the divalent copper cation is present at a concentration of 0.0001-20 mM.    USE - For increasing activity and stability of a glycoside hydrolase 61 (GH61) polypeptide having cellulolytic enhancing activity for producing a fermentation product (claimed) e.g. fuel, potable ethanol, and/or platform chemicals (e.g. acids, alcohols, ketones, gases).    ADVANTAGE - The divalent copper cation increases the activity and stability of a glycoside hydrolase 61 (GH61) polypeptide having cellulolytic enhancing activity. The presence of the divalent copper cation and the GH61 polypeptide having cellulolytic enhancing activity increases degradation or conversion of a cellulosic material by an enzyme composition compared to the GH61 polypeptide having cellulolytic enhancing activity without the divalent copper cation.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a method (M2) for degrading or converting a cellulosic material involving treating the cellulosic material with an enzyme composition comprising a GH61 polypeptide having cellulolytic enhancing activity and a divalent copper cation, where the divalent copper cation is present at a concentration of 0.0001-20 mM;    (2) producing (M3) a fermentation product involving a) saccharifying a cellulosic material with an enzyme composition comprising a GH61 polypeptide having cellulolytic enhancing activity and a divalent copper cation, where the divalent copper cation is present at a concentration of 0.0001-20 mM, b) fermenting the saccharified cellulosic material with at least one (e.g. several) fermenting microorganism to produce the fermentation product, and c) recovering the fermentation product from the fermentation;    (3) fermenting (M4) a cellulosic material involving fermenting the cellulosic material with at least one (e.g. several) fermenting microorganism, where the cellulosic material is saccharified with an enzyme composition comprising a GH61 polypeptide having cellulolytic enhancing activity and a divalent copper cation, where the divalent copper cation is present at a concentration of 0.0001-20 mM;    (4) a composition comprising a GH61 polypeptide having cellulolytic enhancing activity and a divalent copper cation, where the divalent copper cation is present at a concentration of 0.0001-20 mM during degradation or saccharification of a cellulosic material and the presence of the divalent copper cation and the GH61 polypeptide increases the degradation or conversion of the cellulosic material by an enzyme composition compared to the GH61 polypeptide without the divalent copper cation; and    (5) a whole broth formulation or cell culture composition comprising a GH61 polypeptide having cellulolytic enhancing activity and a divalent copper cation, where the divalent copper cation is present at a concentration of 0.0001-20 mM during degradation or saccharification of a cellulosic material and the presence of the divalent copper cation and the GH61 polypeptide increases the degradation or conversion of the cellulosic material by an enzyme composition compared to the GH61 polypeptide without the divalent copper cation.