Often applied to global warming, "tipping point" is an apt metaphor that describes the hypothetical condition we will have reached when the earth can no longer recover from the warming influence of greenhouse gases, a sort of environmental point of no return.

I’m not enough of a scientist to say whether such a tipping point actually exists, but it seems possible. Consider these two Associated Press reports, both by Seth Borenstein, which were printed in my local newspaper within a few days of each other.

The first, headlined "Methane bubbling under permafrost," appeared on Sept. 7. Borenstein describes a study published recently in the respected journal Nature that says that methane is being released from melting permafrost at a rate five times greater than previously thought. Permafrost describes the vast swaths of soil in Siberia and elsewhere that have been frozen for millennia but which are now melting. As it warms, permafrost releases methane and carbon dioxide, both of which contribute to further global warming and, therefore, to yet more melted permafrost. Some researchers refer to this vicious cycle as a climate "time bomb."

A few days later, Borenstein reported on another study, this one from NASA, that says that during the past two years the melting of winter sea ice in the Arctic has occurred at rates 10 to 15 times greater than previously thought. In fact, the article’s headline says it all: "Pace of Arctic melt unprecedented, scientists observe." This condition is particularly crucial, says one of the NASA researchers, because winter sea ice is involved in the cycle that produces plankton, which is at the bottom of the food chain that leads up to marine mammals.

Although this seems serious, these two articles weren’t exactly front-page news. Still, they make one wonder if we’re approaching, or have already passed, a point when we may actually tip over into a downward spiral that makes the earth uninhabitable.

It’s hard to imagine, but it’s happened before, on a smaller scale. In his book "Collapse: How Societies Choose to Fail or Succeed," geographer Jared Diamond examines the factors that led to the extinction of a number of ancient societies, including Easter Island, the Anasazi, the Maya, and Norwegian colonies in Greenland. All of these societies survived and thrived for hundreds of years, then eventually declined and collapsed, in some cases leaving behind dramatic evidence of their sophistication in the form of elaborate temples and tombs, as well as vestiges of their advanced science and technology.

No two societies collapse in exactly the same way. Diamond describes a number of factors that are associated with declining societies, as well as the complicated relationships between the factors. Unsurprisingly, a society’s relationship with its local environment is crucial to its survival, and in all of Diamond’s examples environmental degradation, particularly deforestation, is an extremely important factor.

Some societies simply cut down all of their trees for fuel and construction materials, cashing in their environmental capital to prosper in the short term, but ensuring their eventual decline and collapse. Interestingly, in some cases, small-scale tipping points developed into downward spirals: deforestation modified local weather patterns, disrupting rainfall and leading to increased topsoil erosion, which made both agriculture and reforestation impossible. Eventually, collapse is inevitable.

But Diamond provides ample counter-examples, as well. Other societies learned to cope with the factors that lead to collapse and managed to prosper for millennia. His point is that societal collapse is highly possible, but not inevitable It’s hard to compare our society to the ancient Mayans or Anasazi, but the biggest difference between them and us is that we’re operating on a grander, globalized scale. When ancient societies ran out of resources they could _ and sometimes did _ move to richer territory and thereby prolonged their existence. We no longer have that option.

On the other hand, we have one thing that ancient societies didn’t: knowledge of how and why some societies collapsed and others survived.

If we’ve already passed the tipping point, which is entirely possible, we might as well enjoy whatever time the planet has left.

If not, we have the technology and knowledge that will permit us to prevent the ultimate societal collapse. But will we have the wisdom?

(John M. Crisp teaches in the English Department at Del Mar College in Corpus Christi, Texas. E-mail jcrisp(at)

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