Combining classical molecular dynamics simulations with high level, multiconfigurational ab initio calculations, we demonstrate that even relatively mild collisions between ground state oxygen molecules can readily lead to the formation of highly reactive singlet oxygen molecules via a novel "ladder climbing" mechanism. We employ our findings to shed some light on two recent experiments that have remained poorly understood until now. The first one concerns the highly efficient cluster-catalyzed etching of silicon surfaces, whereas the second one involves a yet to be explained "dark channel" observed for the ozone photolysis in the stratosphere.