Sea levels are rising, swamping roads and homes in South Florida. And it鈥檚 picked up the pace in recent years.
In the last 80 years, sea level rise has risen about a foot, with 8 inches of that total in the last 30 years, said Brian McNoldy, a senior research associate at the University of Miami鈥檚 Rosenstiel School of Marine, Atmospheric and Earth Science.
According to the National Oceanic and Atmospheric Administration鈥檚 best estimates, that pace is expected to speed up 鈥� dramatically.
It took about 80 years for the first foot. The second one will only take 30 years. The next, 20 years. And Florida could see the next foot in merely a decade after that.
鈥淪ea level rise is beginning to speed up a bit,鈥� McNoldy said. 鈥淚f you draw a straight line it starts to not look so straight in recent decades.鈥�
That鈥檚 according to NOAA鈥檚 鈥渋ntermediate-high鈥� projection of sea level rise. The agency created a range of predictions 鈥� low, intermediate-low, intermediate, intermediate-high and high 鈥� to estimate what sea level rise could look like in places like Florida.
So far, scientists have found that we鈥檙e trending toward the high end of those predictions.
鈥淧resently, sea level is tracking in the intermediate-high to high, the two fastest,鈥� said Randall Parkinson, a coastal geologist with Florida International University. 鈥淭he other three scenarios, you might not even think about because we鈥檙e already rising faster than that.鈥�
Those are used by South Florida governments when deciding how high to build new developments. But after a , local governments hoping for state money for sea rise projects have to only consider the intermediate-low and intermediate scenarios, a downgrade from previous legislation that asked them to consider intermediate-low and intermediate-high scenarios.
What goes into a sea rise projection?
Two feet of sea rise by 2060, compared to present-day levels, would be a shock to the system for Miami, where the average elevation is three feet. That鈥檚 why local governments 鈥� and the state 鈥� are spending billions to keep streets dry.
However, pinning down exactly how much sea rise South Florida could experience is a tough task.
Researchers know the two main factors in sea level rise are the temperature of the ocean and how much the ice sheets melt. As burned fossil fuels trap more heat in the atmosphere, that heat is largely being absorbed by the ocean. Hotter water physically takes up more space than cold water, so a hotter ocean means higher sea levels. A hotter atmosphere also means gigantic ice sheets in Greenland and Antarctica are melting, pouring tremendous amounts of now-liquid water into the sea.
Those two issues make up the lion鈥檚 share of impact to rising sea levels, but South Florida also has its own unique challenges that add to rising water levels.
There鈥檚 the fact that some parts of the land are actually sinking, a process known as subsidence. However, it鈥檚 not very much 鈥� the depth of two credit cards stacked on top of each other over half a decade in one spot in Miami Beach.
鈥淚t does add to an already dire situation, but it isn鈥檛 a driving force,鈥� Parkinson said.
The one big unknown in South Florida鈥檚 future of sea level rise is likely the water rushing offshore. The Gulf Stream, a massive current that moves hot water from the tropics to the frigid depths of the Arctic, has a little offshoot that runs between Florida鈥檚 east coast and the Bahamas.
The Florida Current, as it鈥檚 known, has an impact on Miami鈥檚 water levels. When the current is stronger, water levels are generally a bit lower in Miami. And when it鈥檚 weaker, they have been shown to rise.
A new paper from Lisa Beal, professor of ocean sciences at UM鈥檚 Rosenstiel School, and Chris Piecuch, a physical oceanographer at the Woods Hole Oceanographic Institution, found for the first time that this current may be slowing down.
鈥淲e found that there is a weakening. It鈥檚 small,鈥� she said.
The article, , suggested that the Gulf Stream has slowed by about 4% in the last 40 years, although it did not directly link that change to global warming.
Beal said the findings were significant for Florida.
鈥淲e shouldn鈥檛 get carried away that weakening of the Gulf Stream is going to double sea level rise in Miami. It isn鈥檛,鈥� she said. However, 鈥渨hen you鈥檙e so low-lying like South Florida, you鈥檇 kind of want to know because it means you reach thresholds of flooding much more quickly.鈥�
But perhaps the biggest uncertainty in future sea level rise boils down to one thing: exactly how much more pollution the world will continue to spew into the atmosphere. The lower-end predictions account for a world in which governments stop burning fossil fuels quickly, and the higher-end predictions are based on a situation where we burn even more than we are now.
鈥淥ne of the great unknowns is, the world needs to be attempting to slow down the release of greenhouse gasses,鈥� McNoldy said.
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, 港澳天下彩Public Media and the Tampa Bay Times.
