The mid-20th century view that technology would enable unfettered population growth (for example, the development
of unlimited risk-free energy or mass space travel and the colonisation of other planets) proved a chimera for more
than 50 years. Yet some international agencies and many national governments still share a comprehensive vision of
global sustainable development and poverty alleviation that centres on unlimited consumption-based economic
expansion. There are still people who believe that Earth can support another 2.4 billion people, with all enjoying a
'sustainable' standard of living. Others believe an irreversible mass extinction is already under way. The uncomfortable
truth is that the impact on Earth's biosphere of more than 9 billion people living at a desired higher standard of living
in 2050 could be fatal for the planet in terms of greenhouse gas emissions alone. OPT's view is an optimistic one: that
an environmentally sustainable population can be achieved, if action is taken by governments, other policymakers, and
individuals immediately and worldwide.