Conditions on Earth may be moving outside humanity’s “safe operating space.”

An anonymous reader quotes a report from CNN: Human actions have pushed the world into the danger zone on several key indicators of the planet’s health, threatening to radically change conditions on Earth, according to a new analysis by 29 scientists in eight countries. The scientists analyzed nine interconnected “planetary boundaries”, which they identified as thresholds the world needs to stay within to ensure a stable, habitable planet. These include climate change, biodiversity, freshwater and land use, and the impact of synthetic chemicals and aerosols. Human activities have violated safe levels of six of these limits and are pushing the world outside humanity’s “safe operating space,” according to the report published Wednesday in the journal Science Advances.

The Nine Frontiers, first laid out in a 2009 paper, aim to set a set of specific “boundaries” on the changes humans make to the planet — from pumping out pollution from heating the planet to clearing forests for agriculture. The theory goes that beyond these limits, the risk of destabilizing conditions on Earth increases dramatically. Katherine Richardson, a professor of biological oceanography at the University of Copenhagen and co-author of the report, said the boundaries were designed to be conservative, to enable society to solve problems before reaching a “very high-risk area.” She pointed to the unprecedented summer of extreme weather that the world has just witnessed with global temperatures rising by 1.2 degrees Celsius. “We didn’t think it would be like this at one degree Celsius,” she said. She added: “No human being has experienced the conditions we are experiencing now.”

Of the three limits that scientists found are still within a safe space, two of them — ocean acidification and the amount of aerosols in the atmosphere — are moving in the wrong direction. There is some good news, however. Richardson said the ozone layer was on the wrong side of the border in the 1990s. But thanks to international cooperation to phase out ozone-depleting chemicals, it is on track to fully recover. Crossing planetary boundaries does not mean that the world has reached a catastrophic turning point. Hitting someone doesn’t mean “falling off a cliff,” Richardson said. But it is a clear warning sign. The importance of the planetary boundaries model is that it does not analyze climate and biodiversity separately, the report’s authors said. Instead, it looks at the interaction between the two, as well as a range of other ways in which humans impact the planet. Violation of one boundary is likely to have spillover effects on other boundaries.

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