Human activity has pushed the planet across four out of nine environmental boundaries, according to a new study published in the journal Science. An international team of 18 researchers warns that the planetary boundaries that have been crossed are: climate change, loss of biosphere integrity, land-system change and altered biogeochemical flows (phosphorus and nitrogen cycles). Lead author, Will Steffen from the Stockholm Resilience Centre, said “transgressing a boundary increases the risk that human activities could inadvertently drive the Earth System into a much less hospitable state, damaging efforts to reduce poverty and leading to a deterioration of human wellbeing in many parts of the world, including wealthy countries”. Regarding climate change, the scientists argue that carbon dioxide levels should not exceed 350 parts per million (ppm) in the atmosphere. However, the current level is about 399 ppm, and this is growing by about 3 ppm per year. According to Johan Rockström, who is the director of the Stockholm Resilience Centre, “this boundary is consistent with a stabilisation of global temperatures at about 1.5 degrees above pre-industrial levels”. Biodiversity loss and species extinction are also reaching dangerous levels, with rates of extinctions of animals and plants being 10 to 100 times higher than safe levels. The study defines climate change and loss of species as two “core boundaries”, each of which “has the potential on its own to drive the Earth System into a new state should they be substantially and persistently transgressed”. The researchers also sounded the alarm about deforestation and pollution from nitrogen and phosphorus in fertilisers. On the regional scale, even more boundaries have been crossed, such as freshwater use in the western U.S. and in parts of southern Europe and the Middle East. “Implementing methods to use water more efficiently in agriculture can help sort out this dilemma and at the same time increase global food production”, says Dieter Gerten, another co-author. Although it may seem that the paper paints a gloomy picture, the authors wish to emphasise that the findings provide us with the chance to change course. “The world has a tremendous opportunity this year to address global risks, and do it more equitably. In September, nations will agree the UN’s Sustainable Development Goals. With the right ambition, this could create the conditions for long-term human prosperity within planetary boundaries,” said Rockström. (ab)