In 2009, Johan Rockström, director of the Stockholm Environment Institute in Sweden, sat down with a team of 28 luminaries from environmental and earth-systems science to answer those questions. The team included Nobel laureate Paul Crutzen, NASA climate scientist James Hansen, Gaia researcher and “tipping point” specialist Tim Lenton, and the German chancellor’s chief climate adviser Hans Joachim Schellnhuber.
They identified nine “planetary life-support systems” that are vital for human survival. They then quantified how far we have pushed them already, and estimated how much further we can go without threatening our own survival. Beyond certain boundaries, they warned, we risk causing “irreversible and abrupt environmental change” that could make the Earth a much less hospitable place (Ecology and Society, vol 14, p 32).
The boundaries, Rockström stresses, are “rough, first estimates only, surrounded by large uncertainties and knowledge gaps”. They also interact with one another in complex and poorly understood ways. But he says the concept of boundaries is an advance on the usual approach taken by environmentalists, who simply aim to minimise all human impacts on the planet. Instead, he says, boundaries give us some breathing space. They define a “safe space for human development”. And here they are.
The nine boundaries involve 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.
These are planetary boundaries that we trespass at profound risk for ourselves and for our children.
Our life-support systems are not in good shape. Three of nine boundaries – climate change, biodiversity and nitrogen fixation – have been exceeded. We are fast approaching boundaries for the use of fresh water and land, and the ocean acidification boundary seems to be looming in some oceans. For two of the remaining three, we do not yet have the science to even guess where the boundaries are.
That leaves one piece of good news. Having come close to destroying the ozone layer, exposing both ourselves and ecosystems to dangerous ultraviolet radiation, we have successfully stepped back from the brink. The ozone hole is gradually healing. That lifeline has been grabbed. At least it shows action is possible – and can be successful.
During the 21st century, the entire circle would likely turn red unless there is a fundamental change of strategy. Put another way, humanity will exceed the safe operating limits unless the world adopts a strategy to achieve sustainable development.
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