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Miami, Other Coastal Cities May Drown in 80 Years, Study Says

May 20, 2019, 7:00 PM

Today’s children could see Miami and the Earth’s other low-lying cities swallowed by the rising ocean within 80 years if the fossil fuel pollution causing climate change continues unabated.

That’s the conclusion of a study published May 20 in the Proceedings of the National Academy of Sciences that says rising seas could lead to the possible displacement of 187 million people as land totaling an area larger than Alaska is subsumed by the sea—a catastrophic climate scenario for which coastal communities must plan.

The research is likely to fuel ongoing political debate about how the U.S. should respond and adapt to climate change as the Trump administration rolls back carbon dioxide emissions regulations and dismisses the magnitude of the threat climate change poses to the U.S. even as scientists and United Nations officials describe global warming as an “emergency” and existential threat to humanity.

The study’s sea level rise figures roughly double the worst-case sea level rise estimates of the most recent United Nations climate report, the Intergovernmental Panel on Climate Change’s Fifth Assessment Report, published in 2014.

The researchers now estimate that global seas may rise by more than 1 meter (3.28 feet) because of global warming if greenhouse gas emissions are not cut, and there is a 5 percent probability that seas will rise by more than 2 meters by 2100.

“A SLR [sea level rise] of this magnitude would clearly have profound consequences for humanity,” the study concludes.

“5% probability is not really that low a probability: that’s a one-in-20 chance,” said study lead author Jonathan Bamber, a professor of physical geography at the University of Bristol.

“At two meters, many small island states and atolls in the Pacific will become effectively uninhabitable as will a large fraction of Bangladesh, the Nile Delta, Florida, Louisiana and many other low-lying coastal areas,” Bamber said.

Already, Miami and coastal cities in the U.S. are seeing increasing flooding and shoreline erosion as seas rise. High “king” tides are inundating Miami on a regular basis in areas that previously didn’t flood.

If countries cut their greenhouse gas emissions according to their targets under the Paris climate agreement and global warming is limited to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial temperatures, global seas may rise no more than 26 centimeters, or 10.2 inches, according to the study.

Countries, however aren’t yet cutting their emissions sufficiently to prevent global warming from exceeding 2 degrees.

Improved Modeling

Since the 2014 report was published, “the modeling has begun to improve and we have six more years of observations. Both point in the direction of accelerating ice loss and a larger contribution to sea level rise,” said study co-author Michael Oppenheimer, a geosciences professor at Princeton University and co-author of an earlier IPCC climate report.

The IPCC’s climate report gave only a “central prediction and a standard deviation” for rising seas as the climate warms, but the new study attempts to give a probability to some of the worst-case climate scenarios, said Peter Wadhams, head of the Polar Oceans Physics Group at Cambridge University whose book “A Farewell to Ice” explains how human-caused climate change is melting Earth’s polar ice caps.

Scientists are used to the IPCC’s predictions that global warming will raise the earth’s sea level by no more than 1 meter, but the new study shows that rising seas are much more dire, said Wadhams, who isn’t affiliated with the research.

“This would make a huge difference to [sea-level rise] impact on the planet—in fact, it would wipe out civilization—so we have to consider the possibility of having such high figures rather than shy away from them as IPCC does because they might frighten the horses,” Wadhams said in an email.

Time to ‘Rethink’ Coastal Living

As seas rise, the first impact will be increasingly episodic flooding as coastal storms surge sea water inland, such as during a hurricane or nor’easter, Oppenheimer said.

Tidal and storm surge flooding that may have historically inundated low-lying areas in Miami, Boston and New York City only once a year today may happen multiple times per year as the sea level rises to 2 meters, he said.

“Even normal high tides will create flooding where it was not previously concerning—daily,” Oppenheimer said via email. “This process has already begun. In NYC, flood heights that in the 19th century occurred once every 10 years now come once every five years.”

Risk-averse city planners need to prepare for such flooding by gearing up for continuous spending on adaptation, including enhancing wetlands and sand dune systems, and building large storm surge barriers, he said.

“It’s time to realize that sea level rise is going to be with us for centuries, so it’s time to rethink how we build and live along the coast,” Oppenheimer said.

Growing Uncertainty

Scientists have become less certain in recent years about how much the melting Greenland and Antarctic ice sheets will contribute to rising seas as the globe warms because of human fossil fuel pollution.

Polar regions of the earth are warming faster than the rest of the globe, destabilizing ice sheets in Antarctica and quickly melting the ice sheet that covers Greenland. Melt water from the diminishing ice sheets adds water to the ocean, which swells even further as it absorbs more and more heat as the atmosphere warms.

There is “HUGE uncertainty. We cannot rule out ice sheet collapse that is far more rapid than envisioned in this study, and sea level rise that is considerably greater and more rapid,” Michael Mann, an atmospheric scientist at Penn State University who is unaffiliated with the study, said in an email.

“Uncertainty is not our friend, and reason for even more concerted action in lowering carbon emissions,” Mann said.

Complex Dynamics

The dynamics of ice sheets and how they interact with the atmosphere are complex, and the more scientists learn about them, the less sure they are about how all the factors together will contribute to rising seas, according to the research.

The ice sheet covering Antarctica is probably too cold to fully melt, but it will decay as large chunks break off and flow as “rivers of ice” into the the sea, grating against the ocean floor in the process, Oppenheimer said.

Scientists don’t yet fully understand how much friction there is between the ice rivers and the bedrock at the ocean floor, or why there is warm water at the edge of Antarctica, and what that means for ice melt, he said.

“Computer models of ice sheets are not yet mature, and they are the only useful tool for detailed projection,” Oppenheimer said.

But the data seems to suggest that the melting will be worse than previously thought if greenhouse gas emissions continue unabated, he said.

The research was conducted by scientists at the University of Bristol; Princeton and Rutgers universities in the U.S.; Delft University in the Netherlands; Resources for the Future in Washington, D.C.; and Aspinall & Associates in the U.K.

To contact the reporter on this story: Bobby Magill at bmagill@bloombergenvironment.com

To contact the editors responsible for this story: Gregory Henderson at ghenderson@bloombergenvironment.com; Chuck McCutcheon at cmccutcheon@bloombergenvironment.com; Rob Tricchinelli at rtricchinelli@bloombergenvironment.com