The world faces a serious challenge, indeed one that is unique to our age. Developing countries
rightly yearn to catch up with the living standards enjoyed in developed countries. If incomes in
middle- and low-income countries were to catch up with incomes in high-income countries
(roughly $41,000 per capita), there would be a roughly 3.4-fold increase in global income from
$87 trillion to $290 trillion, which would increase even further if high-income countries grow
further and as the world population grows. And therein lies the problem.

If the Earth’s natural resource base were infinite, catching up by developing countries, continued
growth in high-income countries, and further global population growth, would all be relatively
straightforward. To catch up with the rich countries, the developing countries would invest in
technology, infrastructure, and human capital (especially health and education), and step by step,
would narrow the income gap with today’s high-income countries. That, after all, is the current
trajectory of Brazil, China, and India. It is also the preceding path of Japan and Korea. It is the
hoped-for path of Africa as well.

Yet the Earth’s natural resource base is not infinite. There is a global “adding-up” constraint that
is not evident at the country level. Until recently, there were always under-utilized primary
resources on the planet: for example new lands, new fossil-fuel reserves, and newly mined
groundwater. Moreover, the world’s ecosystems could absorb the waste of human activity:
carbon dioxide from fossil fuels, nitrogen runoff from fertilizers, and even toxic pollutants
dissipated by the oceans and rivers. Humanity could improve the productivity of hunting,
fishing, mining, logging, and other “harvesting” activities without fear of ultimate depletion of
those resources.

Now, however, the planet is crowded with 7.2 billion of us demanding primary resources, and
the Earth’s seemingly vast limits are being hit and hit hard. As a result global sustainability has
become a prerequisite for human development at all scales, from the local community to nations
and the world economy.

Various concepts exist to describe global environmental constraints: “carrying capacity”,
“sustainable consumption and production”, “guardrails”, “tipping points”, “footprints”, “safe
operating space” or “planetary boundaries”. We will employ the concept of planetary boundaries
(Rockström et al 2009a), which provides a powerful description of the global “adding-up”
constraints across key dimensions.

The concept of planetary boundaries has been developed to outline a safe operating space for
humanity that carries a low likelihood of harming the life support systems on Earth to such an
extent that they no longer are able to support economic growth and human development. As this
paper explains, planetary boundaries do not place a cap on human development. Instead they
provide a safe space for innovation, growth and development in the pursuit of human prosperity
in an increasingly populated and wealthy world.