Talk abstract: Global climate change has been identified as a serious threat with profound impacts on terrestrial Arctic systems. Recent evidence indicates that widespread expansion of canopy-forming shrubs around the tundra biome is likely to be a response to recent climate warming. Climate change in tundra ecosystems is projected to continue to be rapid, with 2 to 10°C warming over the next 100 years. A significant unknown however, is whether and at what rate vegetation change will continue to respond to the warming climate and to what extent factors such as water availability, nutrient limitation, herbivory, pathogen outbreaks or fire will limit future shrub expansion. I will present the different lines of evidence including experiments, ecological monitoring and dendroecology that test the climate sensitivity of increases in shrub cover. I will illustrate how biogeographic patterns in plant functional traits help us to understand the implications of this shrub increase for climate feedbacks in the Arctic. And finally, I will discuss how we can move away from case-study approaches towards actually quantifying the attribution of tundra vegetation to climate versus other ecological factors across the tundra biome.