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Six of nine planetary boundaries that make Earth habitable have been exceeded

Human activities are inching dangerously close to triggering dramatic changes in Earth’s environmental conditions. According to a new study published in the journal Science Advances, humans have now surpassed six of the nine planetary boundaries that make Earth habitable.

Planetary boundaries 

The planetary boundaries were introduced in 2009 to define the global environmental limits within which humans can safely live. 

Johan Rockström, former director of the Stockholm Resilience Centre, led a group of 28 renowned scientists to identify the nine processes that regulate the stability and resilience of the Earth system

Framework update

In a study led by Professor Katherine Richardson of the University of Copenhagen, experts analyzed the degree of breaching of the safe boundary levels caused by human-driven activities. 

The research, which represents the third update of the framework, was carried out by twenty-nine scientists from eight different countries.

“This planetary boundaries framework update finds that six of the nine boundaries are transgressed, suggesting that Earth is now well outside of the safe operating space for humanity,” wrote the study authors. 

Furthermore, the experts report that transgression is increasing for all boundaries except the degradation of the Earth’s ozone layer. 

Clear warning signal 

The trend of increasing transgression of the boundaries is worrying, said Professor Richardson. “Crossing six boundaries in itself does not necessarily imply a disaster will ensue but it is a clear warning signal.” 

“We can regard it as we do our own blood pressure. A BP over 120/80 is not a guarantee of a heart attack but it increases the risk of one. Therefore, we try to bring it down. For our own – and our children’s – sakes we need to reduce the pressure on these six planetary boundaries.”

Integrity of the biosphere 

Rockström, who is now the director of the Potsdam Institute for Climate Impact Research (PIK), said that focus on human-caused climate change is not enough if we want to protect the Earth system from irreversible harm.

“Next to climate change, integrity of the biosphere is the second pillar of stability of our planet. Our research shows that mitigating global warming and saving a functional biosphere for the future have to go hand in hand,” added co-author Wolfgang Lucht.

Biodiversity loss

According to Professor Richardson, the study shows that humans are appropriating the equivalent of ~30% of the energy that was available to support biodiversity before the Industrial Revolution.

“Surely, the removal of so much of the energy that otherwise would have been available to nature must be a driver of biodiversity loss. Therefore, we propose the adoption of Human Appropriation of Net Primary Production (HANPP), i.e., biomass use, as one of two metrics when assessing human impacts on biodiversity,” said Professor Richardson.

A guide for action

“A world that develops within science-defined boundaries is the only way to navigate our current situation with rising, potentially catastrophic risks, at the planetary scale. We already recognize this on climate, where the Paris agreement has adopted the climate planetary boundary of holding the 1.5°C limit,” said Rockström.

“Similarly, the world has accepted the planetary boundary on biodiversity, when decided at the 2022 Montreal-Kunming COP15, to halt and reverse biodiversity loss on land and in the ocean.”

“Our study shows, however, that this is by far not enough. The planetary boundaries science provides a ‘guide for action’ if we truly want to secure prosperity and equity for all on Earth, and this goes well beyond climate only, requiring novel Earth system modelling and analysis, and systematic efforts to protect, recover and rebuild planetary resilience.”

Katherine Richardson hopes the study will serve as a wake-up call and increase focus on the necessity of limiting our impacts on the planet in order to preserve and protect the Earth conditions that allow advanced human societies to flourish.

More about planetary boundaries

As our planet faces unprecedented environmental challenges, understanding and respecting planetary boundaries becomes critical. These boundaries highlight the limits within which humanity can operate sustainably, without causing irreversible damage to Earth’s systems.

Defining planetary boundaries

Planetary boundaries are thresholds of environmental indicators that, when crossed, risk destabilizing the planet’s equilibrium. As mentioned above, they were developed by a group of international scientists in 2009, outlining nine crucial systems that maintain Earth’s stability.

The nine boundaries

Climate Change: Greenhouse gas concentrations, primarily CO2, are the primary metric here. Exceeding the recommended levels risks amplifying global warming.

Ocean Acidification: Oceans absorb CO2, leading to decreased pH levels. This boundary measures the carbonate ion concentration, vital for marine life like corals.

Stratospheric Ozone Depletion: The ozone layer protects life from harmful ultraviolet radiation. This boundary emphasizes the ozone concentration in the stratosphere.

Nitrogen and Phosphorus Cycles: Excess nitrogen and phosphorus, often from fertilizers, can disrupt ecosystems. Here, the focus is on their flow into the environment.

Freshwater Use: Freshwater is vital for life. This boundary pinpoints the annual consumption of freshwater resources.

Land-System Change: As we modify landscapes, particularly through deforestation, we alter habitats and carbon storage capabilities. This threshold concerns the amount of forested land remaining.

Biodiversity Loss: Biodiversity underpins ecosystem resilience. This metric observes the extinction rate of species.

Atmospheric Aerosol Loading: Aerosols influence climate and human health. This boundary examines their density in the atmosphere.

Chemical Pollution: Synthetic chemicals can harm ecosystems and human health. This boundary reviews their concentration and spread.

Why they matter

Planetary boundaries serve as a warning system. Respecting them ensures Earth remains a safe operating space for humanity. Ignoring them can trigger feedback loops, leading to rapid environmental change and decreased resilience against disturbances.

They also offer a science-based approach to understanding Earth’s limits. By recognizing and respecting them, we pave the way for a sustainable future, ensuring that the planet remains habitable for generations to come.

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