What’s Up With Sea Level Rise?

National Geographic Rising Seas Cover Sept 2013

National Geographic Magazine's September 2013 issue cover.

This post is the first in a five part blog series on sea level rise, being developed concurrent with the new IPCC climate report, Florida  Atlantic University’s Sea Level Rise Summit in Fort Lauderdale, Florida, Oct. 16 – 17, and the anniversary of Hurricane Sandy’s landfall on Oct. 29. See the whole series here.

The topic of sea level rise has recently gained considerable media attention, including Rolling Stone’s article, “Goodbye, Miami” and National Geographic Magazine’s cover story last month. So what’s up with sea level rise? Why are we hearing about it so much and why should we care?

The short answer is that there have been a lot of recent developments in climate change literature, policy, and climate action campaigns, and given that sea level rise is perhaps the riskiest impact of climate change, people are sitting up and paying more attention.

In this series, we’ll provide a succinct briefing on all the latest information and reports on sea level rise. In this post and others in the coming weeks, we will outline the basic mechanisms and impacts of sea level rise, how governments and businesses are responding, and lastly what you as an individual can do to help slow the rising of the seas.

So what is sea level rise?

Sea level rise is the phenomenon of seas rising due to global warming. Carbon pollution and other emissions from power plants, our transportation sector and industrial processes trap heat in the earth’s atmosphere, causing the earth to warm.  As the planet warms, sea levels rise because of two primary mechanisms: 1) glaciers melt and flow from the land to the sea; and 2) as the oceans absorb more heat, they expand in size.

What are the impacts of sea level rise?

Saltwater Intrusion Illustration - FAU Resilient Waters

As the sea level rises, downward pressure moves the saltwater/freshwater dispersion zone farther inland and sometimes into freshwater wellfields. Image courtesy Florida Atlantic University's Resilient Waters report.

A few of the primary impacts of sea level rise are:

  • increased risk of flooding
  • salt water intrusion
  • coastal erosion
  • and eventual inundation

Flood risk and salt water intrusion are two sides of the same coin–as the sea level rises, the height differential between fresh water on land (or under land) and the sea water (where fresh water drains to) is diminished. This means that when it rains, stormwater drains more slowly because there’s just nowhere for the rainwater to go. Also salty sea water can creep farther inland and higher in the water table since there’s not as much water pressure to keep the salty water at bay. Flood risk is also exacerbated by sea level rise in that when there are flooding storms, the flood level is that much higher over where it would have been minus the higher sea. This phenomenon was particularly evident with Hurricane Sandy’s impact last year. Sea level rise contributes to coastal erosion by the simple fact that more of the coast and buffer elements such as dunes or wetlands is being lapped by the tides and storms. Of course the final risky outcome of sea level rise is the eventual inundation of areas that are above the high tide mark today, but may be gradually overtaken.

There are many other secondary impacts, such as financial effects that are important to consider as well. Some of these impacts include the costs of water management, beach renourishment (the process of dumping sand on beaches to replace what has washed away), decreased real estate investment and property values, and insurance impacts such as higher premiums.

Given the proportion of population living on the coast–roughly 39% of the U.S. population and perhaps a quarter of the global population (depending on how you define “coastal”)–these impacts will affect hundreds of millions, if not billions, of people in coming decades. Already, stories of climate change refugees are beginning to bubble to the surface as peoples are displaced by sea level rise. A couple of the more publicized stories of climate refugees include the Alaskan towns of Newtok and Kivalina as well as small Pacific islands such as the Cartaret Isalnds, Kiribati, and the Maldives. While these places are on the forefront of being massively impacted by sea level rise, here in the Southeast, the effects are showing themselves slowly but surely.

How do we know sea level rise is happening?

Tide gauges that have measured the actual sea level have been in place for over a century in some places on the U.S. east coast and have measured observed sea level rise. The graph below shows the measured historic sea level change at Charleston, SC, which has been keeping track since 1899. Tide gauges along the coastal Southeast, such as this one in Charleston, have observed a historic rise of about 1 foot in the past century.

This high tide floods the streets of Fort Lauderdale in September 2008. Photo courtesy Robert Giordano.

But it doesn’t take a scientist to know that sea level rise is happening. Day-to-day living on the coast seems to confirm the reality of higher tides. In many Southeastern coastal communities, road flooding is now commonplace even without a heavy rain. A particularly high tide with no rainfall will allow sea water to find its way up through drain pipes or over seawalls to flood the streets of Miami Beach, Fort Lauderdale, and the Charleston Battery. In fact, simple high tides are now so severe that the City of Fort Lauderdale issued a notice to citizens about high tide impacts just last week. Add in stormwater on top of a high tide and we’re talking some serious flooding occurring on a regular basis. While some people are able to make light of the situation and take a paddle down the flooded streets in a kayak or on a paddleboard (see video and photos below), for most people, it’s a major headache, and a costly one too.

How much will the sea rise in the future?

Answering this question is tricky and perhaps the best response is “it depends.” Many factors will determine the extent of sea level rise and scientists don’t yet understand exactly how each of those factors will play into complex, sea level rise scenarios. Tune in to our blog post next week as we examine this question and in future weeks as we will talk about how governments and businesses are responding, and how you can make a difference.

Kayaking in the Flooded Charleston Market

Bold adventurers face the surf in the middle of Charleston's market during a flood event in August 2012. Photo courtesy Charles Merry.

 

Kayaking Flooded Downtown Charleston Market Street

Bold adventurers face the surf in the middle of Charleston's Market Street during a flood event in August 2012. Photo courtesy Charles Merry.

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