Sea Level Rise

July 11, 2012

Scams and swindles were rampant long before the Internet. One of the more prominent of these was the sale of Florida swampland. Florida is a low-lying state, and home of the Everglades, so there are many swampy areas on which it is impossible to build.

Florida has always been a popular tourist and retirement location, so scammers in the 1960s and 1970s would advertise swampland for sale without revealing its true nature. Just as for today's Internet scams, they just needed a small percentage of people to buy into the scheme to make a huge profit. If the Internet didn't exist, perhaps I would get junk mail advertising land for sale on a Nigerian oil field.

The green arrows indicate positive sea level change along the Florida coastline. All stations report rising seas of about two mm/year; for example, Miami Beach 2.39 ± 0.43; Pensacola 2.1 ± 0.26; St. Petersburg 2.36 ± 0.29; Fernandina Beach (Jacksonville) 2.02 ± 0.20 (NOAA, ref. 1).

As shown in the figure above, the Florida swampland business will be booming in a few decades due to sea level rise. There's no question that sea level is rising, since that's an observation, not a conjecture. It's important to understand the cause of such a rise, since we don't want our descendants living in a waterworld (perhaps I exaggerate).

My house is fortunately about 725 feet above sea level, but others are not as lucky. North Carolina has a long coastline and many thousands of square miles of low-lying land, and a recent study by the U.S. Geological Survey has projected a worrying trend. Sea level on the Atlantic seaboard, on which North Carolina and quite a few US states sit, seems to be rising 3-4 times faster than elsewhere. The projection is for a possible one meter rise by the end of the century.[2]

So what has North Carolina done to prepare for all this? They've decided to legislate the problem away. Apparent pressure from real estate lobby groups has influenced the North Carolina legislature to attempt to enact a law that requires projected sea level rise to be based on historical trends, only, and not on any scientific projection of an accelerated rate.[2] In the end, a compromise measure was passed that prevented any North Carolina agency from using extrapolated data for the next few years, while a state study is conducted.[3]

A valid question is whether a study like this should take so much time. Everyone realizes that this is just a delaying tactic. The shame of the process is that lawmakers in North Carolina have ignored, and even ridiculed, science. For an idea of what a meter's rise in sea level means to North Carolina and other states, see the interactive application in ref. 3.[3]

What processes are causing the sea level to rise? Is it possible to slow or stop this process? Even if we ignore the melting of polar ice and glaciers, there's another physical principle at work. That's the thermal expansion of water caused by a global temperature rise. The average depth of the Atlantic Ocean is a little more than three kilometers, so a meter's change in depth is just 0.033% (330 ppm), and the volumetric thermal expansivity of water at 20 °C is 207 ppm/°C

Scientists from the National Center for Atmospheric Research (Boulder, Colorado), Climate Central (Princeton, New Jersey), and the Centre for Australian Weather and Climate Research (Melbourne, Australia) have published a paper in Nature Climate Change that says that sea level change from this thermal expansivity will happen no matter what we do.[4-5] If we are able to constrain global warming to just 2-3°C above pre-industrial levels, sea level would rise for centuries thereafter.[4] Our only option at this point is to slow the rise enough to allow mitigation strategies;[3] e.g., everyone to higher ground.

Global temperature is rising at a rate of about 0.17°C/decade, and the warming is penetrating into greater sea depths as time goes on.[5] Even if we were fortunate enough to bring about a major cooling of the atmosphere, by 0.83 °C in 2100 and 0.55 °C by 2300, the thermal expansion of the oceans will still cause a sea level rise of 4.2 cm in 2100, and 24.2 cm in 2300.[5]

A worst-case scenario of a 3.91 °C rise in 2100 would give a thermal expansion increase of 32.3 cm, jumping to 139.4 cm by 2300.[4] All this is in addition to whatever ice melt there may be.

Map showing the first year when an ice melt was detected at a region of Antarctica. Darker shades indicate more persistent melting. (NASA image, via Wikimedia Commons).

References:

1. Sea Levels Online, NOAA Center for Operational Oceanographic Products and Services.
2. Wade Rawlins, "North Carolina lawmakers reject sea level rise predictions," Reuters, July 3, 2012.
3. Leigh Phillips, "Sea versus senators," Nature, vol. 486, no. 7404 (June 28, 2012), p. 450.
4. Global Sea Level Rise Map, Geology.com.
5. Gerald A. Meehl, Aixue Hu, Claudia Tebaldi, Julie M. Arblaster, Warren M. Washington, Haiyan Teng Benjamin M. Sanderson, Toby Ault, Warren G. Strand & James B. White III, "Relative outcomes of climate change mitigation related to global temperature versus sea-level rise," Nature Climate Change, Published Online, July 1, 2012.
6. Nina Chestney, "Rise in sea level can't be stopped: scientists," Reuters, July 1, 2012.