We studied the oxidation of Cu(410) during thermal O2 exposure using high-resolution electron energy-loss spectroscopy. Cu2O is identified by loss peaks at 19 and 79 meV. By monitoring the intensity of the latter, we find that Cu2O formation depends strongly on the surface temperature and on the O2 pressure and is kinetically limited by the impinging O2 flux. Thermally activated step roughening, leading to detachment of Cu adatoms from the step edge, acts as a source of mobile Cu atoms, allowing for subsequent nucleation of Cu2O patches.