Human activities are behind the fact that six of the nine planetary limits that regulate the stability and habitability of people on Earth have already been exceeded.
This is explained in a new study carried out by 29 scientists from eight different countries and published in the journal 'Science Advances'.
The planetary limits exceeded are climate change, the integrity of the biosphere, change in land use, freshwater use, biogeochemical flow and the introduction of new entities. On the other hand, ocean acidification, aerosol loading in the atmosphere and stratospheric ozone depletion have not yet been overcome.
For more than 3 billion years, the interaction between life (represented by the planetary boundary of the integrity of the biosphere) and climate has controlled the overall environmental conditions of the Earth.
Human activities influence these interactions, for example, replacing nature with other land uses, changing the amount of water in rivers and soil, introducing synthetic chemicals into the open environment. and the emission of greenhouse gases into the atmosphere.
Respecting and maintaining interactions in the Earth system to remain similar to those that have controlled planetary conditions for the past 12,000 years is critical to ensuring that human activities do not trigger dramatic changes in planetary conditions, which would likely diminish the ability of the Earth to sustain modern civilizations.
The nine planetary boundaries represent components of the global environment that regulate the stability and habitability of the planet for people. The degree of non-compliance with safety limit levels is due to human-driven activities that affect its components.
For the first time, metrics are presented for all limits. Six of them have been found to have been violated and this situation is increasing at all limits except the degradation of the Earth's ozone layer.
Katherine Richardson, professor at the Center for Sustainability Sciences at the University of Copenhagen (Denmark), considers this trend toward a growing transgression of planetary boundaries “worrying.”
Crossing six borders in itself does not necessarily spell disaster, but it is a clear warning sign. Just as a blood pressure higher than 120/80 is not a guarantee of a heart attack, it increases the risk of suffering one. “That's why we tried to lower it. For our own good – and that of our children – we need to reduce the pressure on these six planetary boundaries,” says Richardson.
On the other hand, the study indicates that it is necessary to pay more attention to the interactions between the limits. Focusing on human-caused climate change is not enough to protect the Earth system from irreversible damage, according to Johan Rockström, director of Germany's Potsdam Institute for Climate Impact Research (PIK).
After climate change, the integrity of the biosphere is the second pillar of the planet's stability. “Our research shows that mitigating global warming and saving a functional biosphere for the future have to go hand in hand,” emphasizes Wolfgang Lucht, head of the Earth System Analysis department at PIK.
The need to respect the limits of land use change draws attention to the growing global use of biomass as an alternative to coal, oil and gas. Biomass is the product of photosynthesis, the process in which plants convert energy from the sun into energy that can be used by other living organisms and, therefore, supplies the energy that sustains biodiversity.
“Humans are appropriating the equivalent of 30% of the energy that was available to sustain biodiversity before the Industrial Revolution,” says Richardson.
Rockström points out that a world that develops within limits defined by science is the only way to avoid “increasing and potentially catastrophic risks on a planetary scale.” It is already recognized in the climate, since the Paris Agreement has adopted the planetary climate limit of maintaining the limit of 1.5 degrees compared to the pre-industrial era.
Similarly, the world has accepted the planetary limit of biodiversity, when the Summit on this area agreed last December in Montreal, Canada, to halt and reverse the loss of biodiversity on land and in the ocean.
“This is not nearly enough. The science of planetary boundaries provides a 'guide to action' if we are serious about ensuring prosperity and equity for everyone on Earth, and this goes far beyond climate, and requires novel models and analysis of the Earth system, and efforts systematic efforts to protect, recover and rebuild planetary resilience,” concludes Richardson.
