Provocative New Study Warns of Irreversible Consequences of Crossing Planetary Boundaries
Provocative New Study Warns of Irreversible Consequences of Crossing Planetary Boundaries. By Carl Zimmer, YaleEnviro360, September 23, 2009. "Human civilization has had a stable childhood. Over the past 10,000 years, as our ancestors invented agriculture and built cities, the Earth remained relatively stable. The average global temperature fluttered slightly, never lurching towards a greenhouse climate or chilling enough to enter a new Ice Age. The pH of the oceans remained steady, providing the right chemical conditions for coral reefs to grow and invertebrates to build shells. Those species, in turn, helped support a stable food web that provided plenty of fish for us humans to catch. The overall stability of the past 10,000 years may have played a big part in humanity’s explosion. Now, ironically, civilization has become so powerful that it can reshape the planet itself. ‘We have become a force to contend with at the global level,’ as Johan Rockstrom of the Stockholm Resilience Center in Sweden, puts it. Humans have changed the chemistry of Earth’s oceans, lowering their pH and causing ocean acidification.
"We are shifting the composition of the atmosphere, raising levels of carbon dioxide higher than they’ve been in at least the past 800,000 years. A number of scientists have warned in recent years that if we keep pushing the planet this way, we will cause sudden, irreversible damage to the systems that made human civilization possible in the first place. Typically, they’ve just focused on one of these tipping points at a time. But in the September 24 issue of the journal Nature, Rockstrom and 27 of his fellow environmental scientists argue [in their new paper, PDF, 4 pp] that we have to conceive of many tipping points at once. They propose that humans must keep the planet in what they call a ‘safe operating space,’ inside of which we can thrive. If we push past the boundaries of that space — by wiping out biodiversity, for example, or diverting too much of the world’s freshwater — we risk catastrophe. Unfortunately, [they] maintain, we’ve already started pushing out beyond these boundaries without knowing where they actually are…In their new study, Foley and his colleagues put down stakes to mark where they believe seven of these boundaries lie. By their estimate, we have already pushed beyond three of these boundaries, and are moving quickly toward the other four. ‘We’re running out of time, says Rockstrom…They concluded that there was good evidence for nine kinds of thresholds: climate change, ocean acidity, the ozone layer, freshwater use, the movement of nitrogen and phosphorus, the amount of land used for crops, aerosols (haze and other particles), biodiversity, and chemical pollution."