Scientific American Magazine
March 19, 2010
Boundaries for a Healthy Planet
Scientists have set thresholds for key environmental processes that, if crossed,
could threaten Earth's habitability. Ominously, three have already been exceeded
By Jonathan Foley, Gretchen C. Daily, Robert Howarth, David A. Vaccari, Adele C.
Morris, Eric F. Lambin, Scott C. Doney, Peter H. Gleick and David W. Fahey
For nearly 10,000 years—since the dawn of civilization and the Holocene era—our
world seemed unimaginably large. Vast frontiers of land and ocean offered infinite
resources. Humans could pollute freely, and they could avoid any local repercussions
simply by moving elsewhere. People built entire empires and economic systems on their
ability to exploit what seemed to be inexhaustible riches, never realizing that the
privilege would come to an end.
But thanks to advances in public health, the industrial revolution and later the green
revolution, population has surged from about one billion in 1800 to nearly seven billion
today. In the past 50 years alone, our numbers have more than doubled. Fueled by
affluence, our use of resources has also reached staggering levels; in 50 years the
global consumption of food and freshwater has more than tripled, and fossil-fuel use
has risen fourfold. We now co-opt between one third and one half of all the
photosynthesis on the planet.
This wanton growth has also expanded pollution from a local problem to a global
assault. Stratospheric ozone depletion and greenhouse gas concentrations are obvious
complications, but many other deleterious effects are rising.
The sudden acceleration of population growth, resource consumption and
environmental damage has changed the planet. We now live in a “full” world, with
limited resources and capacity to absorb waste. The rules for living on such a world are
different, too. Most fundamentally, we must take steps to ensure that we function within
the “safe operating space” of our environmental systems. If we do not revise our ways,
we will cause catastrophic changes that could have disastrous consequences for
What would cause these changes? And how can we avoid them? A worldwide team of
scientists—led by Johan Rockström of the Stockholm Resilience Center in Sweden,