Point of no return

We are killing our planet, and thus our selves.

The Earth has nine biophysical thresholds beyond which it cannot be pushed without disastrous consequences, the authors of a new paper in the journal Nature report. Ominously, these scientists say, we have already moved past three of these tipping points.

BY Carl Zimmer, for Yale360

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 today’s issue of the journal Nature, Rockstrom and 27 of his fellow environmental scientists argue 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.

Read the entire article from Yale360 here.

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This article appears in Sep 22-29, 2009.