By the year 2100, two billion people will be displaced from coastal areas due to rising sea levels. Now sociologists are beginning to talk about the real dangers that will ensue from what they call "residential retreat."

By 2060, there may be 9 billion people on Earth, and by 2100, 11 billion. If current estimates hold, about one-fifth of the world's population will have to move from areas near the ocean to inland sites.

Charles Geisler of Cornell and Ben Currens at Kentucky have begun to look at the issues that face all these people as they move inland.

Global Mean Sea Level Rise (GMSR) is increasing, with melting of polar and cap ice of deep concern for both scientists and governments. The loss of coastal lands, and especially the loss of coastal cities will have a deep impact on human life, say the professors.

People who must move inland will be climate refugees.

Geisler and Currens focus on impediments to land resettlement--what barriers humans will face as they relocate inland to non-coastal hinterlands. They have identified three types of barriers.

First, climate refugees will face depletion zones, areas where natural resources, including space and arable land, will be at a premium. As refugee numbers swell these areas will be the sites of social conflict. War, desertification, and habitat destruction will be issues that will require excellent human management to contain or avoid. It is not only coastal areas that will be affected by climate change--inland areas may suffer drought or heat that make them less habitable than now.

Second, there will be win-lose zones. When people flee coastal areas and move to cities there is risk for massive urban sprawl. If this happens there will be reduced land for food production, resulting in possible food shortages or famine.

Finally, in the extreme, cities or towns may create no-trespass zones, building walls and entry stations to regulate who gets in or out. Imagine a medium-sized city in Texas, which will have millions of climate refugees, building a fence or wall around its borders and posting guards to keep people out.

Yes, this is dramatic, but the two researches have by their own admission written a serious paper of worse-case scenarios. They have called their predictions "draconian." But the authors point out that current solutions to GMSR are misguided. Building ocean barriers or sea wall are solutions that in the past were used to reclaim the sea. But the issues are different now. Instead of us mastering the coast, the coast will master us, say the team, and we must recognize the severity of the issue.

They point to some positive actions that deal directly with residential retreat. Four counties in South Florida have developed evacuation plans based on shared data of the effects of sea level rise. The team suggests that we must break traditional political, and geopolitical, boundaries. Only then can we adapt to the displacement of up to 2 billion people as the oceans rise.