Sea levels are projected to rise 3 feet within 80 years, according to a new UN report. Hundreds of millions of people could be displaced.

Christian Aslund/GreenpeaceThe ship Arctic Sunrise surrounded by ice floes in the ocean near Svalbard, Norway.
  • Warming ocean water and unprecedented melting of the Arctic and Antarctic ice sheets could cause sea levels to rise by more than 3 feet by the end of the century, according to new report from the United Nations.
  • These rising waters could displace hundreds of millions of people who live on small islands and in coastal regions.
  • The report also found that most of the world’s warm-water coral reefs are in danger of deadly bleaching events.
  • Visit Business Insider’s homepage for more stories.

Sea levels could rise more than 3 feet within 80 years. Most warm-water coral reefs are expected to die. The oceans are heating up twice as fast as they were in 1993.

These are just some of the worrisome findings detailed in a new report from the United Nations’ Intergovernmental Panel on Climate Change (IPCC).

The assessment, compiled by more than 100 authors from 36 countries, focuses on the state of the world’s oceans and its cryosphere – the frozen parts of the planet. The findings revise projections for sea-level rise upwards – if Earth’s temperature increases by more than 3 degrees Celsius, the authors found, water levels would be an average of 3 feet higher by the year 2100.

The planet’s average temperature has already gone up by 1 degree Celsius, and sea levels have risen globally by about 6 inches (15 centimeters). But the rise is accelerating, the report found. The authors suggest that by the end of the century, higher seas are likely to displace or affect 680 million people who live in low-lying coastal zones, along with 65 million citizens of small island states.

The primary cause of this sea-level rise, the authors concluded, is the melting of the Antarctic and Greenland ice sheets.

“The biggest take-home message is the number of people who will be threatened by sea-level rise this century is extraordinary,” Margaret Williams, managing director of the World Wildlife Fund Arctic Program, told Business Insider. “Warming of oceans and the cryosphere presents a double whammy.”

Sea levels could rise 3 feet

Even if countries around the world achieve the goal set the Paris climate agreement – to keep the planet from warming more than 2 degrees Celsius – the new report suggests that sea levels could still rise up to 1.9 feet by the end of the century.

This sea-level rise comes from two primary sources: melting ice sheets and glaciers on the one hand, and rising ocean temperatures on the other (because water, like most things, expands when heated). But the former plays a larger role, the report shows.

Thwaites Glacier cavity antarcticaNASA/OIB/Jeremy HarbeckMelt from the Thwaites Glacier in west Antarctica contributes to 4% of sea-level rise worldwide.

Greenland’s ice is melting six times faster now than it was four decades ago, according to an April study – the ice sheet is sloughing off an estimated 286 billion tons of ice per year.

Two decades ago, the annual average was just 50 billion.

That melting alone has already contributed to more than half an inch (1.2 centimeters) of sea-level rise since 1972. Alarmingly, half of that increase came about in the last eight years.

GreenlandBob Strong/ReutersThe town of Kulusuk in east Greenland.

In Antarctica, meanwhile, the entire ice sheet is melting nearly six times as fast as it did 40 years ago. In the 1980s, Antarctica lost 40 billion tons of ice annually. In the last decade, that number jumped to an average of 252 billion tons per year.

The rate at which five Antarctic glaciers are losing ice has doubled over the last six years, according to a July study.

Specifically, sections of the Thwaites Glacier in western Antarctica are retreating by up to 2,625 feet per year, contributing to 4% of sea-level rise worldwide. The Thwaites is at risk of hitting a point of irreversible melting, after which the glacier could lose all of its ice in a period of 150 years. That, in turn, may set off a chain reaction of melting that could raise sea-levels an additional 8 feet on top of the 3 feet projected by the IPCC.

AntarcticaPauline Askin/ReutersMelting ice shows through at a cliff face at Landsend, on the coast of Cape Denison in Antarctica, January 2, 2010.

Additionally, the IPCC report found that other glaciers outside of Antarctica and Greenland are disappearing, too.

Smaller glaciers in the US, Europe, and the Andes mountains are projected to lose more than 80% of their current ice and snow by 2100, the authors concluded. That will “adversely affect recreational activities, tourism, and cultural assets,” they wrote.

Rhone swiss glacierDenis Balibouse/ReutersA view of Switzerland’s retreating Rhone Glacier, September 2018.

“Many small glaciers, for instance, in Washington state in the western US, will disappear within the next decades or within, at latest, a century,” Regine Hock, one of the report’s authors, said during a press conference.

Coral reefs are in trouble

The planet’s oceans absorb 93% of the extra heat that greenhouse gases trap in the atmosphere. Last year was the hottest on record for the oceans – 2018 broke the 2017 temperature record, which in turn smashed 2016’s. Scientists have never seen heat like this since they started measuring ocean temperatures in the 1950s.

According to the IPCC report, the ocean is expected to absorb two to four times more heat by 2100 than it did between 1970 and 2018 – and that’s if global warming is only limited to 2 degrees Celsius.

Marine heatwaves (defined as any day the sea’s surface temperature exceeds the local 99th percentile) have already doubled in frequency relative to 1982. If the Earth warms another 2 degrees Celsius, such heatwaves are expected to occur 20 times more often.

That’s especially problematic because warm water can cause coral to expel the algae living in its tissue, turn white, and eventually die. This is known as coral bleaching. At present rates, 60% of all coral reefs are expected to be highly or critically threatened by 2030, and 98% of reefs will be exposed to potentially fatal conditions every year.

As of last year, more than half of Australia’s Great Barrier Reef was dead as a result of bleaching.

Dean Miller/GreenpeaceAustralia’s Great Barrier Reef experienced its second major bleaching event in as many years in 2017.

Even if the most ambitious goal of the Paris agreement is met and the world’s temperature doesn’t rise by more than 1.5 degrees Celsius (a scenario that’s highly unlikely), almost all warm-water coral reefs are projected to suffer widespread extinctions, the IPCC report concluded.

The loss of ocean life impacts food security

Coral reefs cover less than 1% of the ocean floor, but the consequences of coral bleaching extend beyond that, since a quarter of all fish species spend some part of their life cycle in reefs. That means coral loss can have dire consequences for coastal communities that rely on reef ecosystems for sustenance, income from fishing, and tourism.

Approximately 3 billion people in the world rely on both wild-caught and farmed seafood as their primary source of protein, according to the World Wildlife Organisation. Coral reef fisheries are worth $US6.8 billion a year globally.

“Increases in the risks for seafood security associated with decreases in seafood availability are projected to elevate the risk to nutritional health in some communities highly dependent on seafood, such as those in the Arctic, West Africa, and Small Island Developing States,” the IPCC report says.

Salmon fishing boat alaskaLucas Jackson/ReutersCrew members sort salmon by species while delivering the day’s catch from the commercial salmon vessel F/V Renaissance in the waters near Kodiak, Alaska, August 1, 2008.

Warming can also cause food insecurity for Arctic residents, including Indigenous peoples, the report notes, since the changes disrupt herding, hunting, and fishing activity.

“There are short, fragile links between fish stocks plummeting, seals starving, whales disappearing, and human life in the Arctic,” Becca Robbins Gisclair, senior director of Arctic programs at the Ocean Conservancy, told Business Insider.

She added: “If we don’t act, food security for billions of people is at risk, entire ecosystems may disappear, coastal communities and low lying islands may be overrun by rising seas, and people won’t have the same opportunity to find wonder in the nature of our ocean.”

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