Earth has overshot key ‘planetary boundaries,’ scientists warn

The new paper updates a scientific project that began in 2009 to assess “planetary boundaries” (since renamed “Earth-system boundaries”) and how transgressing them will pose risks to human society and nature around the world.

Researchers assessed each of these systems on two factors. One was safety, or how long until the system may no longer perform in the way people have relied on it to. The other was justice, or “the risk of significant harm” to people alive today and those not yet born.

They conclude that to avoid further destabilization, countries should keep at least half of the planet’s ecosystems intact, limit groundwater extraction and set hard limits on use of nitrogen and phosphorus fertilizers.

The new work offers a way for countries, businesses and cities to begin to define their own responsibilities, based on efforts such as the Science Based Targets initiative, which helps companies set climate goals, and the Task Force on Climate-Related Financial Disclosures, which set down guidelines for assessing climate risk and communicating it to shareholders and others.

What’s pushing systems past their limits is no surprise: Economic activity. The authors write that “radical” societal changes, including redistributing wealth, are necessary to keep the planet habitable.

“We are not arguing that we need to do a ton of things we’ve never done before,” said co-author Diana Liverman, retired Regents Professor of Geography and Development at the University of Arizona. “A lot of the transformations are already underway. They’re just not happening at scale or fast enough.”

Although the paper cites recent writing that questions economic orthodoxy, the founder of planetary boundaries research, Johan Rockström, says the world “cannot wait for a completely new economics” to restore Earth to safety: “You cannot say, ‘Okay, capitalism is a problem, so we need something else,’” said Rockström, who is director of the Potsdam Institute for Climate Impact Research and co-chair of the Earth Commission, the international group of scientists that conducted the study.

The boundaries approach has long stirred debate among scientists. Erle Ellis, an environmental scientist at the University of Maryland at Baltimore County who was not involved with the research, questioned how actionable the recommendations are. He also criticized the controlling metaphor — that there’s a “safe space” and an increasingly dangerous one, with a line separating them.

“It’s an illusion to think that there’s this line that you cross and now you’re in a danger zone,” he said.

Rockström said that not all of the boundaries have hard and fast limits to them. Most, like biodiversity loss, air pollution and fertilizer pollution, have no strict levels. The rest of them, he said, are drifting into danger rather than facing a physical cliff — but they all are critical in keeping the whole system healthy.