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Oceans have spared the world the worst of climate change, but those days may be over soon, according to a new United Nations report on climate change.

The ripple effect for Florida, whose economy depends on the bright blue waters that ring the state, could include more dramatic flooding, faster, as well as a scary new phenomenon that's killing coral reefs and reefs.

The Intergovernmental Panel on Climate Change report, released this week, said the ocean's days of soaking up excess carbon and insulating the world from the worst impacts of climate change are numbered.

"It is virtually certain that the global ocean has warmed unabated since 1970 and has taken up more than 90% of the excess heat in the climate system," scientists wrote.

In a world with carbon dioxide emissions run rampant, the new report paints a bleak picture, said Michael Oppenheimer, a Princeton University professor and coordinating lead author for the sea level rise chapter of the report, which includes the results of thousands of scientific papers reviewed by more than 100 scientists.

"Right now we're just headed in a very bad direction," he said. "We're building in more and more damage for ourselves while we think about what to do. And the only way to avoid that is to start cutting emissions."

Without severe emissions cuts, he said, sea level rise will outpace humanity's ability to adapt. The difference is severe. By 2100, "business as usual" emissions put the world on track for 31/12 feet of sea rise. If the world manages to cut emissions enough to keep the world below 2 degrees Celsius of warming—the magic number scientists said could limit the worst effects of climate change—that rise could be slashed in half.

The report said sea level rise is accelerating faster than expected and included revised curves that show the world is likely to see about 43 inches of sea rise by century's end if emissions aren't cut. That's a sharp jump from the 2013 version of this curve, which projected 31 inches of sea rise by 2100.

Ben Kirtman, a University of Miami professor who also served as the coordinating lead author of the 2014 IPCC report, said the 2019 projections involve a lot of new research, including some that shows glacial melt is now the biggest contributor to sea level rise.

If there's any good news for South Florida, it's that local leaders are already planning for worse sea level rise, faster.

South Florida expects two feet of sea rise by 2060, according to a 2015 unified sea rise projection by the South Florida Climate Compact, and more than five feet by 2100. This projection includes sea level rise curves created by NOAA and the U.S. Army Corps of Engineers, which predict more dramatic sea rise than the IPCC report. That projection is being updated for 2020.

Sea levels don't rise uniformly around the world, Kirtman said. It depends on geology, geography and ocean currents. Since 1982, Miami has seen about 6 inches of sea level rise, he said. Galveston, Texas, saw closer to 8 inches, while Honolulu saw about an inch and a half.

The report also found that places like Miami and Key West could see so-called "hundred-year floods," which have a 1% chance of happening every year, annually as soon as 2050. According to a Washington Post analysis, more than 1.2 million people in Miami-Dade live in 100-year flood zones. Florida alone has $714 billion of property in the 100-year floodplain.

"By 2100, almost everywhere where we have a tide gauge and can measure tide, we're expecting the historic 100-year tide level will be reached annually," Oppenheimer said.

And more extreme flood events, like the 500-year flood event in Houston after Hurricane Harvey, will happen more often.

Something else that could become more common? The relatively new phenomena of marine heatwaves.

Like a heatwave on land, marine heatwaves stress out fish and coral by making things too warm for too long. Warmer water also can't absorb gasses as well as colder water, so this hot water contains less oxygen, which all marine life relies on.

Hotter water has particularly deadly effects on coral reefs, said Mark Eakin, coordinator for NOAA's Coral Reef Watch. Hot waters turn the microscopic algae that live inside corals, which give corals color and food, toxic. In response, the corals spit out the algae in a process known as bleaching.

"This is literally a gut-wrenching experience," Eakin said.

Bleached corals lose their color and ability to make food, so they essentially starve to death. A twin danger of climate change, known as ocean acidification, can also harm corals. Ocean water gets more acidic as it absorbs carbon dioxide, and acidic water makes it harder for corals (or most shellfish) to grow, Eakin said. Acidification can also make some corals more susceptible to bleaching, which has become more common in a warming world.

"Back when severe coral bleaching events started to be reported in 1980s, they were once every 25 or 30 years," he said. "Now we're seeing events coming back every five to six years."

The IPCC report said bleaching events, and the marine heatwaves that precede them, will happen more often in a hotter world.

The most famous marine heatwave is a Pacific Northwest patch of warm water known as "the blob." The blob first appeared in 2013 and terrorized marine life from Washington to Alaska. Now it's back, Eakin said. "Some people are calling it return of the blob, the blob part two, son of the blob," he joked.

This time it's so big it's affecting Hawaii. If the four-month predictions are correct, Eakin said, "this is going to be the worst bleaching event ever in the main Hawaiian islands."

Despite record-breaking temperatures on land, South Florida's corals appear to have escaped a similar fate this year, thanks to the active storm season that cooled down Caribbean waters.

But a warmer world spells trouble for coral reefs around the globe, even in a best case scenario.

If the world managed to contain heating to under 1.5 degrees Celsius, an earlier IPCC report showed reefs are expected to decline 70 percent to 90 percent. If the world warms 2 degrees Celsius, the current goal of pacts like the climate agreement, 99% of coral reefs could die.

With two degrees of warming, sea levels could still rise a foot and a half, potentially displacing millions of people in coastal communities like Miami.

"If we're worried about this for 2050 we have to start now, because a lot of these measures—anything that involves concrete and steel—cannot be done overnight, including moving people in a politically acceptable way, which is getting them to move voluntarily," said IPCC author Oppenheimer. "Right now while we're twiddling our thumbs thinking about what we're going to do to adapt. We're going to be in a world with larger impacts and we've got to be ready."

©2019 Miami Herald
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