Sea Level: it's worse than you know

Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century. 

A wholesale collapse of Pine Island and Thwaites would set off a catastrophe. Giant icebergs would stream away from Antarctica like a parade of frozen soldiers. All over the world, high tides would creep higher, slowly burying every shoreline on the planet, flooding coastal cities and creating hundreds of millions of climate refugees. 

All this could play out in a mere 20 to 50 years — much too quickly for humanity to adapt.

“With marine ice cliff instability, sea-level rise for the next century is potentially much larger than we thought it might be five or 10 years ago,” Poinar says.
A lot of this newfound concern is driven by the research of two climatologists: Rob DeConto at the University of Massachusetts-Amherst and David Pollard at Penn State University. A study they published last year was the first to incorporate the latest understanding of marine ice-cliff instability into a continent-scale model of Antarctica.

Depending on how we react to the CO2 pouring into the atmosphere there are different possible outcomes.

Instead of a three-foot increase in ocean levels by the end of the century, six feet was more likely, according to DeConto and Pollard’s findings. But if carbon emissions continue to track on something resembling a worst-case scenario, the full 11 feet of ice locked in West Antarctica might be freed up, their study showed.

Three feet of sea-level rise would be bad, leading to more frequent flooding of U.S. cities such as New Orleans, Houston, New York, and Miami. Pacific Island nations, like the Marshall Islands, would lose most of their territory. Unfortunately, it now seems like three feet is possible only under the rosiest of scenarios.

At six feet, though, around 12 million people in the United States would be displaced, and the world’s most vulnerable megacities, like Shanghai, Mumbai, and Ho Chi Minh City, could be wiped off the map.

At 11 feet, land currently inhabited by hundreds of millions of people worldwide would wind up underwater. South Florida would be largely uninhabitable; floods on the scale of Hurricane Sandy would strike twice a month in New York and New Jersey, as the tug of the moon alone would be enough to send tidewaters into homes and buildings.

And because we are doing nothing at all about the carbon dioxide in our atmosphere, the worst case scenario, 11 feet, is the most likely.

The three feet scenario is likely to occur in the next 20 years, but if we wait until then to do something about it, we will be headed for the worst case scenario no matter what we do about it.

There’s a recurring theme throughout these scientists’ findings in Antarctica: What we do now will determine how quickly Pine Island and Thwaites collapse. A fast transition away from fossil fuels in the next few decades could be enough to put off rapid sea-level rise for centuries. That’s a decision worth countless trillions of dollars and millions of lives.
“The range of outcomes,” Bassis says, “is really going to depend on choices that people make.”

And it's looking more every day what kind of choices people will make, to do nothing.