Harold Wanless on sea level rise in South Florida

South Florida is less than 12 feet above sea level and home to over 5 million people. It’s one of the most vulnerable regions in the U.S. to rising seas from global warming. Harold Wanless is an expert on sea level rise at the University of Miami. He told EarthSky that, since the mid-1990s, sea level in South Florida has been rising faster each year, due to melting ice in Greenland and Antarctica.

Basically, what we see is accelerating sea level because ice melt is accelerating. And we are confident, unfortunately, that sea level will be three to six feet above present level at end of century.

Dr. Wanless said that today, the sandy barrier islands that border South Florida – such as Miami Beach – are becoming destabilized by storms washing over them.

The problem with sea level rising over a sandy barrier island, is that sand is mobile. And so as sea level rises, storms will rework it.

In other words, the islands will erode away after years of strong storms. He told us:

What’s happening now is that every aspect of our environment in South Florida, and elsewhere, is starting to change significantly, because of rising sea level.

Wanless said that with projected sea level rise of 6 feet, only 44% of South Florida’s developed area would still be above high tide by the end of this century. Dr. Wanless said that mangrove forests – growing in the margins of salt and freshwater marshes along the coast – are moving inland as salt water undermines the sediment they grow on. And these forests aren’t the only things that will need to move inland. Wanless said that three to six feet of sea level rise would make a big difference to people living in South Florida, especially developments on islands and near the coast. Wanless said:

With a six-foot rise in sea level, it would mean there is only 44% of the developed area still above normal high tide. Of that 44% left, 73% is less than 2 feet above sea level. South Florida has become an incredibly risky place to live.

He said the rate of sea level rise has significantly accelerated in South Florida – and worldwide – since the 1930s. He said:

Since 1930, South Florida and the global ocean has had about a 10-inch rise of sea level. That rise is mostly because of warming of the ocean.

In other words, global warming is warming the atmosphere, and a warmer atmosphere is gradually warming the surface waters of the ocean. Warm water expands. Much of our rise of sea level up until this century was because of warming, and expanding, water. Then in the mid 1990s, the reason behind sea level rise began to shift, Wanless said.

Since the mid 90s, a new component of sea level rise has become more important, and that is the melting of the continental ice sheets. They’re huge masses of ice, on land, and as they’re melting and washing into the ocean, they are accelerating the rate of sea level rise.

February 25, 2011

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