Johan Rockström says humanity has already raced past four of the nine boundaries keeping our planet hospitable to modern life. Writer John Carey digs into the “planetary boundary” theory — and why Rockström says his isn’t, actually, a doomsday message.We’ve been lucky, we humans: For many millennia, we’ve been on a pretty stable — and resilient — planet. As our civilizations developed, we’ve transformed the landscape by cutting down forests and growing crops. We’ve created pollution, and driven plants and animals extinct. Yet our planet has kept spinning along, supporting us, more or less stable and in balance. Going forward, scientists have recently proposed, all we need to do is stay within some limits, nine upper boundaries for bad behavior.

But of course, being human, we haven’t.

In a startling January 2015 paper in Science, Johan Rockström says humanity has already raced past four of the nine boundaries keeping our planet hospitable to modern life. The climate is changing too quickly, species are going extinct too fast, we’re adding too many nutrients like nitrogen to our ecosystems, and we keep on cutting down forests and other natural lands. And we’re inching towards crossing the remaining five boundaries (see image).

Rockström (TED Talk: Let the environment guide our development) is the executive director of the Stockholm Resilience Centre, and his paper is co-authored by 17 colleagues. “The planet has been our best friend by buffering our actions and showing its resilience,” Rockström says. “But for the first time ever, we might shift the planet from friend to foe.”

Rockström conceived of the idea of planetary boundaries back in 2007, and published his first landmark paper on the topic in 2009. The new paper digs far deeper. A key underlying assumption is that the extraordinary climate stability of the Holocene Epoch, which began when the last Ice Age ended 11,000 years ago, has been crucial to human development. This period of planetary calm enabled our ancestors to emerge from their Paleolithic caves to cultivate wheat, domesticate animals, and launch industrial and communications revolutions. As a result, the world now has 7.2 billion people—and almost that many cell phones.

But now, this stability is under threat. The paper concludes, for instance, that the “safe” concentration of greenhouse gases in the atmosphere (which cause climate change) is about 350 parts per million. At today’s level of 400 ppm, we’ve already blown by the boundary and risk dangerously high temperatures and sea levels, crippling droughts and floods, and other climate woes. Similarly, Rockström and his team calculate, we’ve already lost 16 percent of the biodiversity in many regions of the planet, more than the “safe” level of about 10 percent.

Crossing those two boundaries — climate change and the health of the planet’s ecosystems — is especially worrisome because doing so “can shove the Earth into completely different states,” says Will Steffen, executive director of the Australian National University’s Climate Change Institute and the new paper’s lead author. Cut down enough tropical forests, and the reminder will flip from rain forest to savannah, for instance, and all the benefits of forests will be lost. Or raise the planet’s temperature enough to cause ice sheets to collapse, and less of the sun’s heat will be reflected back to space, causing the warming to accelerate.

“For the first time, we have a framework for growth, for eradicating poverty and hunger, and for improving health,” Johan Rockström

We’re already close to points of no return, Rockström and many others believe. “What scares me absolutely the most is that we may have crossed a tipping point in the loss of the West Antarctic ice sheet,” he says.

Time to throw up our hands in despair? Not at all, says Rockström. “Ours is a positive — not a doomsday — message,” he insists. The beauty of the planetary boundary analysis is that it charts a path to keeping the planet “safe” for humanity, he believes. For instance, nations can slash their carbon emissions to almost nothing, thus pulling the Earth back across the climate boundary. Similarly, we can triple or quadruple agricultural yields in Africa with no-till water-saving methods, keeping us from the brink on forest and biodiversity loss. “For the first time, we have a framework for growth, for eradicating poverty and hunger, and for improving health,” says Rockström.

Slim and athletic at 50, and a man of boundless energy, Rockström has been taking this message on the road. He’s given talks at TEDGlobal and at the World Economic Forum in Davos. He’s met with scientists, politicians and executives — and earned accolades like “Sweden’s Person of the Year.” “Johan has incredible skill to be able to work with policy people, business executives, NGOs, and still keep his own research going,” says Steffen.

Even critics of the planetary boundary concept say he’s made a mark. “I can see how he has had a pretty big influence,” says Linus Blomqvist, director of research at the Breakthrough Institute, an `eco-modern’ think tank that has been perhaps the idea’s most vocal critic. “He’s brought the questions of global change and human effects to new forums and new debates.”

The boundary idea also is inspiring new scientific questions. Geological history shows that the planet can flip to a dramatically warmer or colder state lasting thousands of years when it crosses the climate boundary. But are there similar tipping points for other boundaries in Rockström’s analysis? For instance, if we keep pouring more nitrogen and phosphorus from fertilizers into rivers, lakes and oceans, do we just get a related increase in harmful algal blooms and “dead” zones from the excess nutrients? Or might the whole aquatic system suddenly flip to a new state less conducive to human life?

Another key unanswered question is whether (and how much) crossing one boundary might change the other boundaries. Imagine if a combination of nutrient pollution and ocean acidification killed most of the seas’ plankton, dramatically reducing the oceans’ ability to pull carbon from the atmosphere. That would accelerate global warming—and require carbon emissions to be cut below today’s calculated boundary level. But the details of such connections — and many other possible ones — are unclear. “What frustrates me is that we still don’t understand how these boundary points interact,” says Rockström, who together with his collaborators is now seeking funding to explore the many possible interconnections.

The research has not been without controversy. Some critics have seen the planetary boundaries idea as the intellectual stepchild of the now discredited 1970’s “Limits to Growth” and “Population Bomb” notions that the Earth will inevitably run out of room and resources. “A lot of countries hate the idea of planetary boundaries,” says Steffen. To them, it suggests that the planet’s available space has all been used up, so that they are unable to follow the path the West has taken to development and prosperity.

Some argue that humans are clever enough to thrive even if the Earth does lurch away from the stability of the Holocene. But why take the risk?

This particular criticism is a fundamental misreading, supporters say. “The planetary boundary research liberates us from limits to growth in a decisive way,” Rockström explains. “It says, ‘here is a safe operating space where we can have unlimited growth.’” True, the existence of the climate boundary means that developed nations must slash their carbon emissions to near zero in just a few decades. “But there is nothing to hinder solar and wind power and higher efficiency,” Rockström says. “The world economy can grow even in a decarbonized space.”

Others argue that humans are clever enough to thrive even if the Earth does lurch away from the stability of the Holocene. The planetary boundary concept “ignores the ability of humans to adapt and change, which is the hallmark of civilization,” says Ruth DeFries, professor of sustainable development at Columbia University and author of The Big Ratchet: How Humanity Thrives in the Face of Natural Crisis.

But why take the risk, especially if humanity can take reasonable steps to stay within the boundaries, Rockström replies. “Is it worth undermining the Earth system to create vast benefits for this generation, assuming the next generation will be more innovative?” he asks. Plus, adds Steffen, “anyone who says we can cope with a four to five degree warmer world, and a biologically impoverished world, hasn’t thought about it.”

The Breakthrough Institute frets that some boundaries seem arbitrary because they have no known threshold. And since it’s already obvious that the world must cut carbon emissions and boost agricultural yields, “those planetary boundaries kind of seem irrelevant,” says Breakthrough’s Blomqvist.

Not to Rockström. Instead of endlessly arguing with climate skeptics about supposed uncertainties in climate science, he says, it’s possible to show the overwhelming evidence of an acceleration towards the eight other boundaries too — forests, depleting ozone, chemical loading etc. “It creates a more healthy discussion than yes or no on climate change,” he says.

That’s an approach that others find compelling as well. Obviously, we need swift action to fight climate change, says Joe Romm, founding editor of Climate Progress, and a former U.S. Energy Department official. “But apparently, however we have been explaining that to people, they don’t get it.”

Will the world get the planetary boundary message? We’d better, Rockström says. “We may have entered the most challenging and exciting decade in the history of the planet,” he says. “We have a responsibility to leave the planet in a state as close to the Holocene as possible.”

Featured image by Reto Stöckli/NASA based on data from NASA and NOAA.