Climate researchers last week warned that, over the course of a few decades, humanity has exceeded four out of nine 'boundaries' that make our planet inhabitable.

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The researchers behind a major report and two scientific papers published last week have said that climate changing carbon emissions, massive biodiversity loss, serious alterations to chemical cycles (including those governing phosphorus and nitrogen) and the scale of land-use change have all crossed beyond "safe operating" levels.

That these four 'planetary boundaries' have already been exceeded should serve as a wake-up call to policymakers, according to Professor Steve Carpenter, who said, "We're running up to and beyond the biophysical boundaries that enable human civilization as we know it to exist." Prof Carpenter worked on a report detailing the damage, which will be discussed this week at the World Economic Forum in Davos, Switzerland.

Nutrient pollution

Prof Carpenter added that, for the 11,700 years leading up to the turn of the last century, the Earth had been in a "remarkably stable state." However, the professor, who looked at the changes in chemical cycling said, "We've changed nitrogen and phosphorus cycles vastly more than any other element. [The increase] is on the order of 200 to 300 percent. In contrast, carbon has only been increased 10 to 20 percent and look at all the uproar that has caused in the climate."

The University of Wisconsin Professor pointed to the rise of industrial agriculture, which has driven the massive increase in the use of the two chemicals. Since the middle of the Twentieth Century, fertiliser use has increased by 800 percent and the amount of nitrogen entering the oceans has quadrupled.

Run-off and leaching of the two chemicals has been especially damaging to aquatic life; overuse of both nutrients has created 'dead zones' in the planet's lakes, rivers and seas.

However, Prof Carpenter added that the use of these chemicals, and their negative side-effects, isn't evenly distributed. He said, "We've got certain parts of the world that are overpolluted with nitrogen and phosphorus, and others where people don't even have enough to grow the food they need."

In order to address this "distribution problem," Prof Carpenter said that those in areas where nitrogen and phosphorous are overused must find ways to vastly reduce the amount of inputs their agricultural systems require, whilst still maintaining production. He said that the Midwestern US, one of the main culprits in nutrient pollution, could vastly reduce its use of fertilisers and still support productive crops, which would also allow farmers in nutrient-poor regions to slightly increase their use.

Another of the 18 experts who contributed to the report, McGill University's Prof Elena Bennett, explained the threat from nutrient pollution in simple terms. Prof Bennett said, "People depend on food, and food production depends on clean water. This new data shows that our ability both to produce sufficient food in the future and to have clean water to drink and to swim in are at risk."

Biodiversity loss

On the subject of biodiversity loss, Professor Will Steffen, another of the report's authors who works at the Australian National University and the Stockholm Resilience Centre, warned, "We are starting to destabilise our own planetary life support system."

Prof Steffen said that, as a result of our activity, "Humans are having to spend more time and effort cleaning up what nature used to do. In some parts of the world humans have to pollinate fruit trees, because bees have gone extinct."

The Professor continued, "Planetary boundaries are reminding us that there are limits to how much of the biosphere [the totality of life on earth] we can erode before it comes back to bite us. That's what's happening now."

Commenting on the impacts of carbon emissions, Prof Steffen said, "For climate change, the risk to humans begins increases as carbon dioxide rises above 350 parts per million (ppm). We're now at nearly 400 ppm; we're coping so far, but we're seeing extreme weather events become worse, loss of polar ice and other worrying impacts."

The ANU professor blamed an unsustainable economic system and overconsumption (largely in the global north) for the precarious position in which humanity now finds itself. "We've now entered a new geological epoch, named the Anthropocene, in which the global economic system is the primary driver of change on Earth," he said. "We have become a planetary-scale force in a single lifetime."

Prof Steffen continued, "When experts look at [the current situation] from technology engineering, agronomy [viewpoints], they estimate that we can live, we can prosper with nine billion people, within these planetary boundaries. But we have to innovate, we have to change, we have to be clever."