Will rising sea levels affect me?

Dear Dr. Rock,

I heard recently that with global warming, many coastal cities will one day be underwater. Is this true? Is San Diego, where I live, one of those cities? Which cities will "go under" first? Is this something that might happen in the next decade or so? Or how long?

Doug Montigale

San Diego

Doug,
I don't want to get mired in the politics of climate change. It is a topic we need to think seriously about. Sea level change due to global warming is real, though perhaps not the most critical effect (that might be weather: drought, crop failure, drinking water...). But let's attend to Doug's question.This is not, strictly speaking, a geology question, since the science of climate change is multidisciplinary. I was just looking at the new National Geographic's article titled "Rising Seas" down at the barber shop. It has a fold out map [web version here] showing sea level if ALL the world's ice melted and sea level consequently rose 216 feet*. No one is saying that climate change is going to cause that. That would be bad, but it has happened in the geologic past, when the earth was much warmer during the Eocene, first instance, and glaciers were very rare or nonexistent on Earth.
Observations show that sea level has been rising since at least 1880. Between 1901 and 2010, global sea levels rose by 19 centimeters (7.6 inches) - an average of about 1.7 millimeters (1/14 inch) per year. But looking at the last few decades, it's clear sea level rise is speeding up. Between 1993 and 2010, sea levels rose by 3.2 mm (1/8 inch) per year - nearly twice the long term average.**
Small potatoes, huh? Yeah, but that is 1 inch every 8 years, one foot in less than 100 years. Still small potatoes? That doesn't account for any increase in the newly measured 1/8 inch rate. Current projections by the National Oceanic and Atmospheric Administration (NOAA) call for sea level rise of about 6 feet globally if carbon emissions are not drastically curtailed.

The view from my deck on a sunny day in Bellingham,
WA, USA. Elevation 133 feet above the bay. Alaska
Ferry terminal in the middle ground. Click to enlarge.

What does that mean? Is San Diego going to "go under" as Doug puts it? Well, no, only those places that are less than 6 feet above sea level, and certainly not in the next decade. The Silver Strand, with the North Island Naval Air Station, is going to be submerged, or at least very precarious. In my town, Bellingham Washington, on the Salish Sea, that means that the Alaska Ferry dock will need to be repositioned, the city's waterfront parks will be submerged, the busy marina on the bay will need to replace pilings and add to the breakwater. The former site of the Georgia Pacific paper mill on the waterfront, currently being redeveloped by the city and port, will need to be designed to have a higher level grade (elevation of sea level) than at present. Bellingham is a small city. Multiply that by every coastal city in America, and you are looking at big bucks. Studies show that New York City has assets of 2+ trillion dollars at risk. Miami is worse: $3 trillion. Hurricane Sandy nearly a year ago was pretty bad. Add 6 feet to that storm surge! Then extend that to the rest of the world. Read the National Geographic article for more data and the human story. Here is a University of Arizona website with detailed maps of some coastal US cities under various sea level increases. Read a pre-Sandy New York Times article (March 13, 2012) on the expected effects of sea level rise in the near future on Americans.


University of Arizona sea level forecast map for SE USA. Click to enlarge

The principal contribution of geologists to climate change theory is showing that the geological record (that  is, rocks) demonstrate that climate change has happened in the past. Evidence for climate change is preserved in a wide range of geological settings, including marine and lake sediments, ice sheets, fossil corals, stalagmites and fossil tree rings. Nearly all the world's geological societies, which represent most professional geologists, have issued statements of concern (at the mildest) or warnings that continued carbon emissions will only increase the threat from global warming.

* That would be the pits. My home, on a hill with a nice view of Bellingham Bay, seems far above the bay at an elevation of 133 feet. Hard to imagine my lot could some day be under 83 feet of water! Even worse, those snooty neighbors a couple blocks up the street would have waterfront property! I can only hope their boat's anchor fouls on my chimney.
 **The source for my information is an analysis of the 2013 IPCC report posted on the The Carbon Brief Blog. The report is based on observations, so the data is not 'wrong'. If you don't believe in the global warming theory, fine, but you can't refute the observed data. In the immortal words of Daniel Patrick Moynihan (US Senator 1927-2003), "Everyone is entitled to his own opinion, but not his own facts." 

Are there any rock outcrops in Florida?

Dave,
I often vacation in Florida during the winter. I don't recall ever seeing a rock outcrop! Why is that? Where can I go to see rocks in Florida?
Joan Osborne
Cleveland, Ohio

Dear Joan,

The short story: there are a few areas of Florida with exposed bedrock. Virtually all of it is limestone. Your best bet is in the northeast part of the state. You won't find any bed rock in Miami, for instance. Much of the state is covered in unconsolidated clay or sand. The clays were eroded from the Appalachian highlands and deposited on top of the limestone by rivers entering the shallow sea. The sand is beach deposits. For roadside locations, see Roadside Geology of Florida by Brian, Scott and Means, and  Florida's Geological Treasures by Iris T. Comfort. I confess I haven't read any of these books, but they seem like a good place to start.

I found this map at http://www.floridacaving.com/pages/misc/karst1.htm

Dark brown areas are where limestone is at or near the surface.

This is a fossil coral from Florida. It is preserved

on a pillar in the Westlake Mall in downtown

Seattle (yep, no kiddin'! I write about it in my up-

coming book, Geology Underfoot in

Western Washington.)

The long story: It wasn't that long ago that all of Florida was below sea level, beneath the shallow warm waters of the Caribbean. Limestone is the fossilized remains of animals, many of them microscopic, that have shells made of calcium carbonate. Clams, oysters and crabs are large animals with calcium carbonate shells. When these animals die, their shells sink to the seafloor and accumulate hundreds of feet thick. With sufficient thickness, water is driven out of the spaces between the shell and they become cemented together (calcium carbonate makes great cement). If the seafloor is lifted above sea level, the limestone is exposed. The highest point in Florida is only 345 feet above sea level, so little erosion has cut into the bedrock to expose it. Your best bet to see rock in Florida is in a few road cuts, or in caves.

Florida is proud of its high

point, and has erected a

roadside sign so you don't

miss it as you drive by. It's near

Lakewood in Walton County.

The limestone in northern Florida is very young, around 50-60 million years old. It is exposed in the northern portion of the state only because the rocks have been slightly folded along a north-south axis which raised some of the rocks high enough to allow the clay and sand to largely erode away, exposing the rock beneath. The Florida Keys have some limestone, too, though it is much younger, only around 130-150,000 years old. Some was quarried to build the buildings of the Keys.

Limestone is dissolved in fresh water that is slightly acidic. The result is a swiss-cheese type of topography called 'karst'. The famous limestone caves of Florida result from this chemical weathering. Some caves must be explored by diving, but there are dry caves in the northern part of the state.