When Superstorm Sandy slammed into the U.S. East Coast last October, it was the latest in a series of “teachable moments” about our growing vulnerability to climate change.

The future is urban – but is it sustainable?

For decades – centuries, really – warnings have been issued: The burgeoning human population will outgrow the planet’s capacity to sustain us. The formula seems simple. More people equals fewer resources and greater environmental damage.

June’s Rio + 20 Conference on Sustainable Development left environmentalists little to cheer about. Kumi Naidoo, executive director of Greenpeace International, called the meeting “a failure of epic proportions.” And Washington Post reporter Juliet Eilperin said the conference “may produce one lasting legacy: convincing people it’s not worth holding global summits.”

Ethiopia has been deemed a population-climate “hotspot” – a place where rapid growth and a changing climate pose grave threats to food security and human well-being.

Change is a constant in human (and natural) history. But today, we have entered an era in which the pace, scale, and impact of change may surpass anything our species has previously confronted.

“For if one link in nature’s chain might be lost, another and another might be lost, till this whole system of things should vanish by piece-meal.”

This much is clear: As human numbers have grown, the number of species with whom we share the planet has declined dramatically. While it took about 200,000 years for humanity to reach one billion people around 1800, world population has grown sevenfold since then, surpassing seven billion last year.

Water – essential, finite, and increasingly scarce – has been dubbed “the new oil.” Experts debate whether human societies are approaching “peak water,” beyond which lies a bleak future of diminishing supplies and soaring demand. Others observe that, for many, the water crisis has already arrived.