WunderBlog Archive » Dr. Ricky Rood's Climate Change Blog

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By: Dr. Ricky Rood, 9:04 PM GMT on June 18, 2007

Sea Level: Past and Future

About 10 years ago I went to Portchester Castle on the coast of England. This castle is built at sea level and has a moat that is filled with tidal water. The first enclosure is Roman, built in the third century. What strikes a climate person is that sea level has been stable for a long time. Here is great aerial photo of the castle from Goggle Maps.

Figure 1: Aerial photo of Portchester Castle

In the 10 April 2007 issue of EOS (The Transactions of the American Geophysical Union ), there was an article by John Day Jr. and co-authors on the emergence of civilizations after sea level stabilized following the last ice age. This article shows that cities and complex societies started to form about 1000 years after the sea level rise stabilized. The argument was that in this amount of time coastal ecosystems stabilized. This was a source of relatively easy food, hence calories, and having excess caloric energy is what allows people to move away from being primarily food collectors. This is one of several pieces of evidence of the co-evolution of thriving humanity and climate.

We have evolved, and we have changed our relationship with coastal ecosystems. We exploit ecosystems far from our homes. We have depleted the natural resources of coastal ecosystems, and we use aquaculture to generate food. Still, rapid sea level will be disruptive to this ecosystem and those who depend on it.

Looking into the future, however, brings a new problem. The Day et al. article cited above shows the development of cities along the coasts. Today people are moving to the cities, and more than half of the world's population lives in cities. By 2030 more than 60% of the people are projected to live in cities. (Here are current and projected urban centers from the consulting firm Demographia .) We have seen the emergence of mega-cities. A majority portion of population will live on a very small percentage of the land. And, like 6000 years ago, many of these cities are on the sea. Hence, when we think about the impact of climate change on people, we need to think specifically about how cities are impacted. Already stressed resources, like fresh water, are subject to additional stresses from climate change. Harbors, airports, roads, and buildings will be more vulnerable to storm damage and outright flooding. With the projected rise in sea level, we once again, link the stability of sea level rise to the stability and success of societies. Since significant sea level rise will occur, this leads to the question of adaptation--potentially relocation.


Day et al., 2007: The Emergence of Complex Societies after Sea Level Stabilized. EOS, Transactions of the American Geophysical Union, pp 169-170.

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