The surge next time: Every inch makes difference

Roll on, deep and dark blue ocean, roll. Ten thousand fleets sweep over thee in vain. Man marks the Earth with ruin, but his control stops with the shore. – Lord Byron

Here’s a thought experiment for you to try:

Imagine that the overflow drain in your bathtub has become plugged and you’re running a bath. You’re called away and when you return, you find the tub is overflowing and there is one-eighth of an inch of water on your bathroom floor. Big mess, huh?

You quickly put a towel in the bathroom doorway to keep the water from spreading into the hallway, and spend the next half hour mopping the bathroom.

Now, imagine that your house is surrounded by water standing 8 inches higher than your floor level, and you open the front door. Water rushes in with such force that it’s hard to close the door again, and in about one minute, the entire first floor of your house is flooded to a depth of eight inches. Now that’s a big mess.

There are two lessons to learn from this exercise. One, while an 8-inch-high wave or water surge might not seem like much, it can, in fact, be extremely destructive. Two, the sea level along the North Atlantic coast has risen about 8 inches since 1870 because of global warming, and that deceptively modest increase needs to be taken very seriously because of its contribution to storm surges.

Although the North Atlantic sea-level rise had been responsible for a variety of problems such as coastal erosion and increased saltwater incursion into estuaries, its potential for increasing storm surge damage wasn’t widely appreciated until Hurricane Sandy struck Oct. 29. Sandy’s winds pushed water 9.15 feet higher than the average high-tide level, with an 8-inch cap on the surge, so to speak. What difference did the extra 8 inches make?

Sea-level rise expert Ben Strauss – developer of an innovative and highly useful online “surging seas tool” for analyzing flooding and storm surges (http://sealevel.climatecentral.org) – recently was quoted by science writer Chris Mooney as saying, “The footprint of the flood was bigger, based on roughly eight extra inches of depth.”

Meteorologist and sea-level expert Scott Mandia, co-author of the book Rising Sea Levels: An Introduction to Cause and Impact, estimates that the larger footprint translated into 6,000 more people impacted by the storm for each additional inch of water height. Thus about 48,000 more people were affected by Sandy.

Those at the outer edge of the surge would experience relatively light impacts. But, as Strauss explains, “(even) an inch or two (of water) could be enough to get over a home’s threshold and down into the basement, or make it into one or more subway entrance.” And, of course, those a little closer to the shore would be hit by the full 8 inches of fast-flowing water, an amount sufficient to flood workshops, factories and stores, upend the elderly and drown small children and pets.

Sea levels are expected to continue rising in the coming years because of two effects of global warming: 1) thermal expansion of the oceans caused by additional heating, and 2) the melting of landlocked ice sitting on Greenland and Antarctica and from glaciers everywhere. Both of these processes have accelerated in recent years, as has sea-level rise.

The average projected North Atlantic sea-level rise, based on several studies, is 1½ feet by 2050 and 3 feet by 2100. However, those projections could be “dated” because they were made before this summer’s dramatic loss of Arctic sea ice and the consequent Arctic region temperature increases. (To clarify, sea ice floats in water and displaces its own mass, so it does not contribute to sea-level rise as it melts.)

If Greenland’s entire land-based ice sheet melts, sea levels will rise by 21 feet. That much melting could take centuries, but if Greenland’s current record-breaking melt rate continues to accelerate because of rising arctic region temperatures, some scientists believe we could see a 3- to 4-foot rise by mid-century and 5 to 8 feet by 2100.

Don’t think for a minute that the rising tides won’t affect everyone, even those living on the continent’s interior, as they displace tens of millions of people from the coasts of our ecological house.

Philip S. Wenz, who grew up in Durango and Boulder, now lives in Corvallis, Ore., where he teaches and writes about environmental issues. Reach him via email through his website, www.your-ecological-house.com.

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