Vulnerability is the degree to which human and environmental systems are likely to experience harm due to a perturbation or a stress. In the last years, it has become a central focus of the global change (including climate change). The climate change literature contains many explanations of vulnerability, stemming from the notion of sensitivity to more complex ideas, yet taking into account the exposure history of the system up to residual impacts of climate change after adaptation. This work addresses the issue of ecosystems vulnerability assessment by presenting a conceptual framework, as an attempt to generalize previous approaches. We present a model of concepts linked to climate change vulnerability, based on literature review, in which we detail the key concepts of adaptation and mitigation measures (and their respective capacity), ecosystem stability (sensitivity, ecological resilience and elasticity), exposure and impacts. An exemplary case-study is given to address the issue of vulnerability assessment for grassland ecosystems with the help of an impact model (ModVege). This paper emphasizes on the interest of using a design of experiment (DOE) accounting for different levels of uncertainties. It also demonstrates that a set of vulnerability indices, accounting for exposure, may be necessary to capture (if not all) most of the information.