A recent analysis by a multinational team of 29 scientists reveals that human actions have propelled the world into the risk zone across several key indicators of Earth's health. The scientific study, involving participants from eight countries and published in Science Advances, outlines nine interconnected "planetary boundaries," representing the key areas that must be protected to preserve a stable, habitable world.
The list includes challenges like climate change, biodiversity loss, synthetic chemicals, aerosols, and changes to freshwater and land use. Alarmingly, human activities have surpassed safe levels on six of these indicators and are pushing Earth beyond the defined "safe operating space" for life.
The concept of the nine boundaries, first proposed in a paper in 2009, is to set a defined limit on the drastic alterations humans inflict upon the Earth. Bypassing these boundaries can significantly escalate the risk of the Earth witnessing destabilizing changes, according to the pioneering scientists in this field.
The limits are intentionally designed to be conservative in order to provide society ample time to address the problems, before reaching a "very high risk zone,” stressed Katherine Richardson, a professor in biological oceanography at the University of Copenhagen and a co-author of the report.
While there are still three boundaries that remain within a safe space, two of them – ocean acidification and atmospheric aerosol levels – are rapidly moving towards dangerous thresholds. However, there is a glimmer of hope. The ozone layer, which was in a critical condition in the 1990s, is on a recovery path, thanks to the global phasing out of ozone-depleting chemicals.
Crossing these boundaries does not imply immediate disaster or a tipping point, emphasizes Richardson. But, they serve as crucial warning signs, indicating that we are rapidly depleting Earth's finite resources. The analogy is akin to a bank balance decreasing, suggesting that while we might continue to thrive for now, we can't afford to ignore the long-term consequences.
A distinguishing feature of the planetary boundaries model is that it examines the climate and biodiversity as interlinked systems, rather than isolated issues, and takes into account the numerous ways humans impact the planet. A negative shift in one boundary is likely to trigger a cascading effect on the others. For instance, widespread deforestation can significantly escalate climate issues.
Simon Lewis, a professor of global change science at University College London, remarked that the report paints a "starkly gloomy update on an already alarming picture.” He warned that humanity is pushing the planet beyond its stable conditions, which could prove disastrous.
Andrew Fanning, a researcher at the University of Leeds, believes the planetary boundaries model provides strong evidence to policymakers about the urgent need to transform economies and societies in tackling the climate crisis.
However, the model also faced criticism. Raymond Pierrehumbert, a physics professor at Oxford University, believes that while the model serves as a useful guide in some cases, like carbon pollution, in issues like land-use changes, deciding the boundary and its breach could prove to be a distraction.
“The measures they use make no sense and they cannot estimate them,” declared Stuart Pimm, the chair of conservation ecology at Duke University, who previously criticized the model in a 2018 paper.
Richardson admitted more comprehensive data collection and monitoring are needed to access the impact of human activities on the ecosystem. She expressed concern over the fact that the breaches are increasing across the boundaries, a situation which has worsened since the previous report in 2015.
