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100-Year Floods Could Hit Miami and Key West Yearly by 2050, U.N. Climate Author Warns

Charles Trainor JR. /Miami Herald
William Potash paddles a canoe with friends through flooded streets in Davie in 2017.

A new United Nations climate reportreleased in Monaco this week paints another grim picture for the planet and Florida.

Seas are not only rising, but accelerating and worsening flood threats.

The diversity and abundance of ocean life is declining and marine heat waves are multiplying with the increase in ocean temperatures. More carbon soaked up by oceans is deepening acidification.

Even if carbon is reduced to limit some global warming, lead author Michael Oppenheimer told reporters Thursday that Key West, Miami and Jacksonville could see 100-year flood events occurring every year in three decades.

“Even under those low scenarios, by 2050 many cities and other locations around the world are going to be getting their historic hundred year high water level every year,” said Oppenheimer, a geoscientist at Princeton University. “Let me repeat that: historic hundred year events in terms of flooding will occur annually.”

Oppenheimer warned that it’s likely too late to alter changes baked into the atmosphere through 2050. But scaling back emissions could slow the pace.

Credit Emily Michot/Miami Herald
Emily Michot/Miami Herald
Flooding in Miami Beach threatened homes in 2017.

The report is the latest in a series periodically issued by the UN’s International Panel on Climate Change to update threats and projections for impacts like rising seas and melting ice. About 100 scientists helped compile the information and warned that the accelerating pace of changes is alarming.

“Sea level rise is now about twice as fast as it was over the past century. And it's projected to just keep rising through 2100 at an accelerating pace if we remain on a business as usual emissions trajectory,” Oppenheimer said.

Since 1970, the report says oceans have absorbed 90 percent of the planet’s excess carbon. That’s caused warming temperatures to double since 1993, which helps push up sea levels along with melting ice sheets.

Protective measures like flood walls take time, so governments need to begin work now, Oppenheimer warned.

“The important thing to realize is if we’re worried about this for 2050, you have to start now because a lot of these measures, particularly because hard protection — anything that involves concrete and steel — cannot be done overnight," he said. "The same thing with moving people in a politically acceptable way; getting them to volunteer to move essentially, out of harm’s way.”

Earlier this month, the U.S. Army Corps of Engineers released an early look at plans for cities and neighborhoods around Biscayne Bay that would include flood walls and flood gates, increasing natural barriers like reefs, and elevating buildings. Corps officials say they will also consider buying out property owners. A final plan is expected by September 2021.

Besides flooding, the ocean conditions are also worsening. This is the first time IPCC scientists have documented the number and duration of marine heat waves. That’s causing fish to move, which could make them more vulnerable and affect fisheries globally and in Florida.

“Like the report says, we have begun to document species distribution changes,” said Neil Hammerschlag, a shark researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

Fish rely on their surroundings to regulate their temperature, he said. If they move to cooler water, they may leave behind ranges best suited for finding food, hiding from predators and reproducing.

“They’ve got to find a match between the optimal temperatures for their own internal functioning and physiology, but also make sure that overlaps with places that are good habitat,” Hammerschlag said.

Since 1950, the report says many species, including birds and mammals, have shifted their ranges in response to warming temperatures, loss of sea ice and changes in ocean chemistry like oxygen loss. Some have benefited: albatross have been able to take advantage of increasing winds to widen hunting grounds. But others, like snakes and sea turtles, are suffering: reducing hatchling sizes or, in the case of turtles, influencing the sex of offspring. Scientists have already linked the movement of Atlantic cod and salmon in the Pacific to warming waters.

They warn a poleward shift of fish to cooler water will likely decrease the richness of the ocean.

Other changes noted by the report include:

  • The ocean is taking up twice as much heat as it did before 1993. If no changes are made, by 2100, the ocean could be five to seven times warmer.
  • Rising ocean temperatures have caused surface waters to become less dense compared to deeper waters. That’s limited the movement of surface and deeper water, which can help cool temperatures.
  • The upper levels of the ocean are losing oxygen. Scientists say it’s likely between 0.5 and more than 3 percent have been lost between 1970 and 2010. By 2031 to 2050, up to 80 percent of the ocean could be affected by this oxygen loss.
  • The movement of fish is leading to more feeding on reefs and seagrass meadows, which are also being threatened by rising temperatures. A May reportfrom the U.S. Geological Survey put the value of flood protection from reefs between Fort Lauderdale and Miami during severe storms at $1.6 billion.
  • Warming water and other changes could decrease the amount of life in the ocean by as much as 15 percent by 2080 compared to 1986 to 2005.
Jenny Staletovich is WLRN's Environment Editor. She has been a journalist working in Florida for nearly 20 years. Contact Jenny at jstaletovich@wlrnnews.org
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