It is a well-provisioned ship, this on which we sail through space. If the bread and beef above decks seem to grow scarce, we but open a hatch and there is a new supply, of which before we never dreamed.

That, from Henry George’s Progress and Poverty, is how humanity viewed the planet for most of modern history: a vessel stocked with virtually endless provisions. In the 20th century, however, our view of Spaceship Earth became more sober and more complicated. We realize now that our vessel’s provisions are finite, we are consuming at rates beyond what can be sustained, and we do not know with any precision how close we are to our limits or what happens if we cross them. “There is one outstanding important fact regarding Spaceship Earth,” said Buckminster Fuller, “and that is that no instruction book came with it.”

Now scientists have taken a first step toward creating just such a manual. In the latest issue of Nature is a groundbreaking new paper called “Planetary Boundaries: A Safe Operating Space for Humanity.” In it, a team of 28 scientists has identified 10 separate biophysical systems crucial to humanity’s flourishing; for each system they have identified a “safe operating boundary” within which humanity must remain if it wishes to maintain the basic environmental conditions in which it evolved.

human history and the holocene era
The last glacial cycle of 18O (an indicator of temperature) and selected events in human history. The Holocene is the last 10,000 years. Adapted from Young and Steffen (2009).
Nature

“Human activities,” the scientists warn, “have now reached a magnitude that may trigger irreversible and in a some cases abrupt environmental change by damaging the regulatory capacity of the systems on Earth that keep the planet in the desired Holocene state.”

Here’s the bad news about those boundaries, beyond which we risk nonlinear and irreversible consequences: we’ve already transgressed three of them. Here’s the tally:

Nature - tipping points
Click to embiggen.

We travel together, passengers on a little spaceship, dependent on its vulnerable reserves of air and soil; all committed for our safety to its security and peace; preserved from annihilation only by the care, the work, and, I will say, the love we give our fragile craft. — Adlai Stevenson

The numbers more or less speak for themselves. If you’re interested in the details, read the full paper in Nature. I’d just make one follow-on point.