If we remain on the current course, it's estimated that by 2050, the world's population may have increased by at least half and many parts of the world may be facing grave shortages of resources. The Southwest U.S. could face an extended drought, while pests threaten crops. As global sea levels rise, much of the world map could be redrawn. People will begin to migrate back to urban areas in search of better lives.
There would likely still be beacons of green living -- massive solar farms may produce enough power to light up entire regions of the country. Towns like Greenburg, Kan., decimated in 2007 by a tornado and rebuilt to be completely self-sustaining, may inspire communities around the globe do the same. But unless the rest of the world gets on board -- and fast -- some experts warn it may just not be enough.
"A few hundred years down the line, they'll look back and say the dark ages began with the twenty-first century," says E. O. Wilson, an award-winning evolutionary biologist and professor at Harvard University.
But just how bad could things get? In one scenario, scientists imagine that by the year 2100, immense storms irreparably damage major metropolises. Streets, subway tunnels, and buildings would flood and begin to rot. The stagnant water would breed filth and displace residents, forcing them into homelessness. Poverty levels and death rates could skyrocket. A new and virulent strain of disease might develop -- then mutate and spread around the globe, potentially claiming tens of thousands of lives.
In this scenario, as the crisis explodes, looting grows rampant, major world powers go to war over water, and millions of people die from famine. Civilization literally collapses under its own weight.