Climate change vulnerability (or climate vulnerability or climate risk vulnerability) is defined as the "propensity or predisposition to be adversely affected" by climate change. It can apply to humans but also to natural systems (ecosystems). Human and ecosystem vulnerability are interdependent. Climate change vulnerability encompasses "a variety of concepts and elements, including sensitivity or susceptibility to harm and lack of capacity to cope and adapt". Vulnerability is a component of climate risk. Vulnerability differs within communities and across societies, regions and countries, and can change over time. Approximately 3.3 to 3.6 billion people live in contexts that are highly vulnerable to climate change in 2021.