Human activities have already pushed the Earth beyond three of the planet’s biophysical thresholds, with consequences that are detrimental or even catastrophic for large parts of the world, conclude 29 European, Australian and U.S. scientists in an article in Nature. This force has given rise to a new era – Anthropocene – in which human actions have become the main driver of global environmental change.
The report started with a fairly simple question: How much pressure can the Earth system take before it begins to crash? “Until now, the scientific community has not attempted to determine the limits of the Earth system’s stability in so many dimensions and make a proposal such as this. We are sending these ideas out to be vetted by the scientific community at large,” explains van der Leeuw.
Nine boundaries were identified in the report, including climate change, stratospheric ozone, land use change, freshwater use, biological diversity, ocean acidification, nitrogen and phosphorus inputs to the biosphere and oceans, aerosol loading and chemical pollution. The study suggests that three of these boundaries -climate change, biological diversity and nitrogen input to the biosphere – may already have been transgressed.
Using an interdisciplinary approach, the researchers looked at the data for each of the nine vital processes in the Earth system and identified a critical control variable. Biodiversity loss, for example, is based on species extinction rate, which is expressed in extinctions per million species per year. They then explored how the boundaries interact. Here, loss of biodiversity impacts carbon storage (climate change), freshwater, nitrogen and phosphorous cycles, and land systems.
“Three of the boundaries we identify – 350 parts per million of atmospheric carbon dioxide, biodiversity extinction rates more than 10 times the background rate, and no more than 35 million tons of nitrogen pollution per year – have already been exceeded with fossil fuel use, land use change, and agricultural pollution, driving us to unsustainable levels that are producing real risks to our survival,” notes report co-author Diana Liverman, of the University of Arizona.
The report concludes that human pressure on the Earth system has reached a scale where abrupt global environmental change can no longer be excluded. To continue to live and operate safely, humanity has to stay away from critical ‘hard-wired’ thresholds in Earth’s environment, and respect the nature of planet’s climatic, geophysical, atmospheric and ecological processes, say the authors. “Transgressing planetary boundaries may be devastating for humanity, but if we respect them we have a bright future for centuries ahead,” warns lead author Professor Johan Rockström, of Stockholm University.
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