Another excerpt from Environmental Economics by Turner, Pearce & Bateman.
"Ecological economists would argue that once one adopts the 'systems perspective' then the requirements of the system (the economy and its supporting ecosystems) can take precedence over those of the individual. This argument has important ethical implications for the role and rights of present individual humans compared with the system's survival and therefore the welfare of future generations. The constant capital rule for sustainable economic development requires us to adopt an explicit position in equity (justice) and asset transfers across people and through time. The ethical argument is that future generations have a right to expect an inheritance ( in the form of natural capital / physical capital / human capital bequests) sufficient to allow them the capacity to generate for themselves a level of welfare (well being) no less than that enjoyed by the current generation. In more formal language, the requirement is for an intergenerational social contract that guarantees the future the same 'opportunities' that were open to the past ('justice as opportunity').