Tuesday, November 27, 2007

Ask The Green Miles: Most Vulnerable to Sea Level Rise?

A question from The Green Miles' dad:
Is there a place that would show a rising ocean first and most dramatically? Would it be Florida, Holland, Venice, Bangladesh, some Pacific Island group, or where? Or is it too soon for that kind of extrapolation?
Too soon? The impacts are already right here in my backyard. No fewer than 13 islands in the Chesapeake Bay have already been swallowed up by rising sea level. According to a recent National Wildlife Federation report, over the last century air temperatures in the Bay region have risen 1.4 degrees, water temperatures are up two degrees, and sea levels have risen two feet. That's due mostly to thermal expansion (warmer water takes up more space than cooler water), not melting glaciers or ice caps as commonly though.

But back to the question. Obviously I am not a scientist, so my answer will be more subjective based on what I've seen and read, but this is a blog and you should know this already. In the US, the these are the areas that are most screwed when it comes to rising sea levels:
- New Orleans (I know, you're shocked). It's below sea level already and still sinking due to subsidence, the natural compression of land composed of flood deposits. Why hasn't this been a problem until now? Because before people came along, the land would sink, then Mississippi would flood and retreat, leaving a layer of sand and silt to build it back up. Then we decided to put levees up and build on the floodplain. Now there's just sinking, no silting.
- Hampton Roads, VA (Hampton/Norfolk/Newport News/Virginia Beach), just a few feet above sea level and home to major naval installations.

- Miami, three feet above sea level.
- Lower Manhattan and its hundreds of miles of subway tunnels.
All of the above are not only below or right at sea level but are in prime hurricane landfall zones. But let's be honest - as the richest country in the world, America can afford to build flood barriers or even relocate key populations without a devastating economic impact. Globally, it's the poor nations that can't afford to adapt that will be hit the hardest.

Island nations just a few meters above sea level like The Maldives face grave threats, but for total number of people threatened, I'd have to go with Bangladesh. Not like they're so safe and sound to begin with - a recent cyclone killed 3,400 people, about twice as many people as killed by Hurricane Katrina. One estimate says just a 1.5 meter rise in sea level could affect 17 million people in Bangladesh.

The most frightening part about sea level rise is that no one can truly say how fast it will occur. The human brain tends to think of everything as rational and directly related - a 1% rise in temperature will result in a 1% rise in sea level. But as anyone who has ever, say, made ice knows, at the margin a one degree difference is all it takes to go from solid ice to water.

How will we know if and when we're approaching a similar tipping point? The United Nations International Panel on Climate Change has more or less punted on the issue, focusing on sea level rise probability due to known factors like thermal expansion. Now Arctic Sea ice is retreating faster
than even the most pessimistic projections. Can anyone say definitively that Greenland's ice sheet, with its potential to raise sea levels 20 feet, won't beat expectations as well?

Wikipedia can tell you
much more about sea level rise. And if you have a question about the environment, ask The Green Miles!
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