A single bloom of the alpine wildflower Dryas octopetala in a high valley in the Orjen Mountains of Montenegro. This tundra flower gave its name to the Younger Dryas, a cold period that briefly interrupted the long-term warming that had begun following the peak of the last ice age glaciation around 20 thousand years ago. Climate scientists think the episode was triggered by changes in the great system of currents in the Atlantic Ocean as a result of meltwater from Northern Hemisphere ice sheets. Image by P. Cikovac, used under a Creative Common license.