In cold biomes, the distribution of plant species and the composition of vegetation communities is strongly shaped by climatic conditions. Under more benign growing conditions due to climate change, restrictions on plant growth and species distributions are being alleviated, resulting in rapid shifts of alpine and Arctic ecosystem composition and functioning. In our research, we explore the consequences for alpine and Arctic plant communities with long-term observational and experimental studies in mountain and Arctic ecosystems around the world. In our talk we will highlight how European alpine summit and alpine-arctic tundra communities responded to decades of climate warming, talk about potential winners and losers, and compare the results to ongoing changes in other cold biomes of the world.