The fact of irreversible effects, the second law of thermodynamics, is associated with the
concept of strong sustainability. Sustainability is the ability of an activity to continue
indefinitely without upsetting the balance between the resources used by the activity and
the wastes it creates. Sustainable development was defined in the Brundtland Report
(WCED,1987) as "Sustainable development is development that meets the needs of the
present without compromising the ability of future generations to meet their own needs.
It contains within it two key concepts: the concept of needs, in particular the essential
needs of the world's poor, to which overriding priority should be given; and the idea of
limitations imposed by the state of technology and social organization on the
environment's ability to meet present and future needs.