EARTH'S NINE LIVES
This balmy springtime for humanity is known as the Holocene. But we are now in a new era, the Anthropocene, defined by human domination of the key systems that maintain the conditions of the planet. We have grabbed the controls of spaceship Earth, but in our reckless desire to "boldly go", we may have forgotten the importance of maintaining its life-support systems.
The demands of nearly 7 billion humans are stretching Earth to breaking point. We know about climate change, but what about other threats? To what extent do pollution, acidifying oceans, mass extinctions, dead zones in the sea and other environmental problems really matter? We can't keep stressing these systems indefinitely, but at what point will they bite back?
Last year, 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.
1.
Acid oceans
More carbon dioxide in the atmosphere means more is absorbed by the oceans, creating carbonic acid – bad news for animals with shells. Read more
2.
Ozone depletion
With most of the culprit chemicals now banned, the worst of the danger has passed – but it has not entirely vanished. Read more
3.
Fresh water
A quarter of the world's river systems no longer reach the ocean for at least part of the year. This is drying out swathes of the landscape. Read more
4.
Biodiversity
Individual species may not matter much on their own, but collectively they form ecosystems that provide a range of vital "ecosystem services". Read more
5.
Nitrogen and phosphorus cycles
We fix around 121 million tonnes of nitrogen a year, far more than nature does – and nature cannot cope. Read more
7.
Climate change
Every degree of warming caused directly by CO2 is amplified by feedback processes that could drive temperatures much higher. Read more
8.
Aerosol loading
We have more than doubled the global concentration of aerosols such as soot since pre-industrial times. Read more
9.
Chemical pollution
There are approaching 100,000 different human-made chemical compounds in use around the world today, and many of them harm humans and wildlife. Read more
CONCLUSION
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.
Fred Pearce is New Scientist's senior environment correspondent
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