It's an idea that most of us would rather not face -- that within the next century, life as we know it could come to an end. Our civilization could crumble, leaving only traces of modern human existence behind.
It seems outlandish, extreme -- even impossible. But according to cutting edge scientific research, it is a very real possibility. And unless we make drastic changes now, it could very well happen.
Experts have a stark warning: that unless we change course, the "perfect storm" of population growth, dwindling resources and climate change has the potential to converge in the next century with catastrophic results.
Watch "Earth 2100," a two-hour television event, Tuesday, June 2, at 9 p.m. ET.
In order to plan for the worst, we must anticipate it. In that spirit, guided by some of the world's experts, ABC News' "Earth 2100," hosted by Bob Woodruff, will journey through the next century and explore what might be our worst-case scenario.
But no one can predict the future, so how do we address the possibilities that lie ahead? Our solution is Lucy, a fictional character devised by the producers at ABC to guide us through the twists and turns of what the next 100 years could look like. It is through her eyes and experiences that we can truly imagine the experts' worst-case scenario -- and be inspired to make changes for the better.
For more information on the climate change war game featured in Earth 2100, click HERE.
By 2015, there are expected to be hopeful signs. Experts predict alternative energy solutions that are currently in their infancy will gain momentum. Windmills may sprout up everywhere. Off the coast of Scotland, a sprawling wave farm will harvest renewable energy from the ocean. Vatican City will meet all of its energy needs with solar power. And the U.S. will produce cleaner, more fuel efficient vehicles in accordance with newly unveiled emissions guidelines.
But will it be enough? In 2015, global demand for fossil fuels could be massive and growing, but experts say oil will be harder to find and far more expensive to consume.
"We have no new source of energy on the horizon that's currently capable of being developed on a large enough scale to replace the supply of oil in any near- term framework," says Michael Klare, professor of peace and world security studies at Hampshire College.
If the cost of gasoline skyrockets, few may be able to afford to maintain the lifestyles to which we've grown accustomed. There may be a mass exodus from the suburbs, as driving gas-fueled cars becomes nearly impossible economically. But will that convince us to change our ways?
"Until we have a crisis of some kind, I don't think we're going to be motivated to make the really deep changes in the way we use energy, the technologies we use, the density of our cities, our travel patterns," says Thomas Homer-Dixon, a political science professor and author of "The Upside of Down."
The imagined crises in Lucy's futuristic world come in the forms of earthshaking hurricanes spawned by over-reliance on climate-damaging coal and other nonrenewable resources. What if climate change in our world is actually much closer than we think? Many experts say we have to start seriously reducing greenhouse gas emissions by 2015, or we may pass a point of no return.
"If we continue on the business as usual trajectory, there will be a tipping point that we cannot avert," says John P. Holdren, science advisor to President Obama. "We will indeed drive the car over the cliff."
Scientists predict that by 2020, global catastrophes may well begin to accelerate. The human population is expected to explode and animal species may be dying off at a rapid rate. As the world becomes more chaotic, the costs of mending it would grow more and more daunting. By 2030, gradually rising temperatures may have shifted rainfall patterns around the globe, and many experts warn much of the world may face serious shortages of our most basic need -- water.
"By 2030, two-thirds of the world's population will be under water stress," says Janine Benyus, science writer and founder of the Biomimicry Institute.
Some cities will have the forethought to plan ahead. Starting in 2009, San Diego began building huge desalination plants to turn ocean water into an abundance of fresh water. But in the middle of the country, people may be running out -- and there may well not be funds to transport it from the coast. If and when a place like Tucson, Ariz., runs dry, people will panic.
"Something that will catch people's attention is the first rich city that just runs out of water," says Homer-Dixon.
Americans may well meet these challenges with resourcefulness and work hard to keep the threats at bay. But even as things stabilize on the home front, experts predict hundreds of thousands of environmental refugees may begin streaming through Europe, fleeing droughts and famines. Millions of Latin Americans could align on the U.S. border seeking entry, and some could encounter violent resistance.
"I can't imagine the horrors that will take place on the border as millions of refugees try to get into the United States," says Klare.
In the history of Earth, there have been five mass extinctions in which at least half the species on the planet disappeared. Scientists believe the extinctions were brought on by natural disasters -- massive volcanic eruptions, rapid climate changes and meteors hitting Earth.
Today, scientists say we are in the middle of a "sixth extinction" -- and for the first time, it's being caused by one species -- us. It seems inconceivable that we could do so much damage to our planet that we actually cause society as we know it to collapse. But historical precedent shows that it is, in fact, a very real possibility.
"Every society that collapsed thought it couldn't happen to them," says Joseph Tainter, an expert in anthropology and societal collapse. "The Roman Empire thought it couldn't happen. The Maya civilization thought it couldn't happen. Everyone thought it couldn't happen to them. But it did."
These populations grew too much and exhausted their resources -- and their climate suddenly changed. People were forced to fight each other for what little was left or face starvation. Entire societies broke down.
"Civilizations in the past have lost the fight," says climatologist Heidi Cullen. "They have collapsed as a result of the inability to deal with several different events going on at once. I think the takeaway is that honestly, we are not that special."
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.