The relatively simple question posed by this title turns out to be complicated in its implementation, for a number of reasons: First, ecosystems have changed in response to changing climate throughout history - however this has not normally been qualified as “vulnerability”. Second, most changes in 26 ecosystems have multiple forcings, climate change being only one of them. Third, whether changes in ecosystem functioning qualify as “vulnerability” depends largely on the human point of view. Resolving the issue is very urgent today, because it is indisputable that rapid changes are taking place and that some of these are considered “negative impacts of climate change”. Given the complexity of European landscapes, simple extrapolation of observations will not provide the answer in time and with sufficient reliability - instead an integrated experimental and modelling approach has been developed in cooperation with stakeholders. I will present this approach and its latest stages of development which forms the conceptual core of past, present and (hopefully) future integrated projects within the EU framework programmes.