Earth Has Overshot Key ‘Planetary Boundaries,’ Scientists Warn

Human activities are endangering eight of Earth's vital life-sustaining mechanisms, with seven already entering a perilous zone, according to an extensive Earth science review conducted collaboratively by over 60 researchers and released Wednesday in The Lancet Planetary Health.

Examining essentials for a habitable Earth — including climate, freshwater systems, biodiversity and soil nutrients — the researchers discover nearly all have surpassed crucial thresholds. The sole global system yet to exceed safe limits is aerosols, despite fine-particle air pollution contributing to 8 million fatalities annually.

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This new study updates a scientific initiative that commenced in 2009 to evaluate "planetary boundaries" (since renamed "Earth-system boundaries") and how breaching them will threaten human society and nature worldwide.

Investigators assessed each of these systems on two criteria. One was safety, or how soon until the system may cease to function as people have depended on it to. The other was justice, or "the risk of significant harm" to current and future generations.

They deduce that to prevent further destabilization, nations should preserve at least half of the planet's ecosystems intact, restrict groundwater extraction and establish firm limits on nitrogen and phosphorus fertilizer usage.

The novel work presents a method for countries, corporations and cities to begin defining their own responsibilities, based on endeavors such as the Science Based Targets initiative, which assists companies in setting climate objectives, and the Task Force on Climate-Related Financial Disclosures, which established guidelines for assessing climate risk and communicating it to shareholders and others.

The force pushing systems beyond their limits is unsurprising: Economic activity. The authors assert that "radical" societal transformations, including wealth redistribution, are necessary to maintain the planet's habitability.

"We are not suggesting that we need to undertake numerous unprecedented actions," stated co-author Diana Liverman, retired Regents Professor of Geography and Development at the University of Arizona. "Many of the transformations are already in progress. They're simply not occurring at the required scale or speed."

Although the paper references recent literature questioning economic orthodoxy, the founder of planetary boundaries research, Johan Rockström, contends that the world "cannot await a completely new economics" to restore Earth to safety: "One cannot say, 'Well, capitalism is problematic, so we require an alternative,'" 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 sparked debate among scientists. Erle Ellis, an environmental scientist at the University of Maryland at Baltimore County who was not involved with the research, questioned the actionability of the recommendations. 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 believe that there's this line you cross and suddenly you're in a danger zone," he stated.

Rockström explained that not all of the boundaries have rigid and absolute limits. Most, like biodiversity loss, air pollution and fertilizer pollution, lack strict levels. The remainder, he said, are drifting into danger rather than facing a physical precipice — but they all are crucial in maintaining the overall system's health.