Due to climate change, the world's oceans are getting warmer, rising higher, losing oxygen and becoming more acidic at an ever-faster pace and melting even more ice and snow, a grim international science assessment concludes.
But that's nothing compared to what Wednesday's special United Nations-affiliated oceans and ice report says is coming if global warming doesn't slow down: three feet of sea rise by the end of the century, many fewer fish, weakening ocean currents, even less snow and ice, stronger and wetter hurricanes and nastier El Nino weather systems.
"The oceans and the icy parts of the world are in big trouble and that means we're all in big trouble too," said one of the report's lead authors, Michael Oppenheimer, professor of geosciences and international affairs at Princeton University.
"The changes are accelerating."
These changes will not just hurt the 71 per cent of the world covered by the oceans or the 10 per cent covered in ice and snow, but it will harm people, plants, animals, food, societies, infrastructure and the global economy, according to the special report by the Intergovernmental Panel on Climate Change.
The oceans absorb more than 90% of the excess heat from carbon pollution in the air, as well as much of the carbon dioxide itself. The seas warm more slowly than the air but trap the heat longer with bigger side effects and the report links these waters with Earth's snow and ice, called the cryosphere, because their futures are interconnected.
"The world's oceans and cryosphere have been taking the heat for climate change for decades. The consequences for nature and humanity are sweeping and severe," said Ko Barrett, vice chair of the IPCC and a deputy assistant administrator for research at the U.S. National Oceanic and Atmospheric Administration.
And for the first time, the international team of scientists is projecting that "some island nations are likely to become uninhabitable due to climate-related ocean and cryosphere change."
"Climate change is already irreversible," French climate scientist Valrie Masson-Delmotte, a report lead author, said in a Wednesday news conference in Monaco.
"Due to the heat uptake in the ocean, we can't go back. " But many of the worst-case projections in the report can still be avoided depending on how the world handles the emissions of heat-trapping gases, the report's authors said.
The IPCC increased its projected end-of-century sea level rise in the worst-case scenario by nearly four inches (10 centimeters) from its 2013 projections because of the increased recent melting of ice sheets in Greenland and Antarctica.
The new report projects that, under the business-as-usual scenario for carbon emissions, seas by the end of the century will rise between two feet (61 centimeters) and 43 inches (110 centimeters) with a most likely amount of 33 inches (84 centimeters). This is slightly less than the traditional 1 meter (39 inches) that scientists often use.
"Sea level continues to rise at an increasing rate," the report said. "Extreme sea level events that are historically rare (once per century in the recent past) are projected to occur frequently (at least once per year) at many locations by 2050."
And sea level will rise two to three times as much over the centuries to come if warming continues, so the world is looking at a "future that certainly looks completely different than what we currently have," said report co-author Hans-Otto Portner, a German climate scientist.
The Nobel Prize-winning IPCC requires nations meeting this week in Monaco to unanimously approve the report, and because of that the group's reports tend to show less sea level rise and smaller harms than other scientific studies, outside experts said.
"Like many of the past reports, this one is conservative in the projections, especially in how much ice can be lost in Greenland and Antarctica," said NASA oceanographer Josh Willis, who studies Greenland ice melt and wasn't part of the report.
"We're not done revising our sea level rise projections and we won't be for a while." Willis said people should be prepared for a rise in sea levels to be twice these IPCC projections.
The oceans have become slightly more acidic, but that will accelerate with warming. In the worst case scenario, the world is looking at a "95% increase in total acidity of the oceans," said study co-author Nathan Bindoff of the University of Tasmania.
Even if warming is limited to just another couple of tenths of a degree, the world's warm water coral reefs will go extinct in some places and be dramatically different in others, the report said.
"We are already seeing the demise of the warm water coral reefs," Portner said.
"That is one of the strongest warning signals that we have available." The report gives projections based on different scenarios for emissions of heat-trapping carbon dioxide. One is a world that dramatically decreases carbon pollution and the worst case is where little has been done. We are closer to the worst-case situation, scientists said.
Outside scientists praised the work but were disturbed by it.
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