The necessity of sustainability becomes clear when you pull on one thread of our current society and begin to realize how much begins to unravel as a result. For example, greenhouse gases are warming the planet, making ever growing amounts of land uninhabitable, which only lowers the number of people the earth can ultimately sustain.

In the U.S. the drought in the West could be worst in history.

The drought gripping the West could be the worst in 500 years, with effects in the Colorado River basin even worse than during the Dust Bowl years, scientists at the U.S. Geological Survey say.

“That we can now say with confidence,” said Robert Webb, lead author of the new fact sheet released Thursday. “Now I’m completely convinced.”

The drought has produced the lowest flow in the Colorado River on record, with an annual average flow of only 5.4 million acrefeet at Lees Ferry, Ariz., during the period 2001-2003 , adjusted for the effect of Glen Canyon Dam. By comparison, during the Dust Bowl years, between 1930 and 1937, the annual flow averaged about 10.2 million acre-feet , the report said.

In other parts of the world, climate change is turning land the size of Rhode Island into desert wasteland every year, threatening to send millions of people fleeing to greener countries.

One-third of the Earth's surface is at risk, driving people into cities and destroying agriculture in vast swaths of Africa. Thirty-one percent of Spain is threatened, while China has lost 36,000 square miles to desert -- an area the size of Indiana -- since the 1950s. ...

'It's a creeping catastrophe," said Michel Smitall, a spokesman for the UN secretariat that oversees the 1994 accord. ''Entire parts of the world might become uninhabitable."

Slash-and-burn agriculture, sloppy conservation, overtaxed water supplies, and soaring populations are mostly to blame. But global warming also takes a toll.

Each facet of the problem aggravates another facet, causing an ever growing snowball effect, that can only be solved by a drastically smaller population.