The town of Pacifica, Calif., just south of San Francisco, is ground zero for the issue of coastal erosion. On Jan. 20, 2019, the combination of ocean surge and a king tide caused high waves. Some homes and apartment building were destroyed. (Carolyn Cole/Los Angeles Times/TNS)

The planet is in hot water – literally – and that will have dire consequences for humanity, warns a new United Nations report on the state of the world’s oceans and ice.

Over the next century, climate change will make the oceans warmer and more acidic. Melting ice sheets will drive up sea levels at an accelerating pace. Marine heat waves will become 20 to 50 times more frequent, harming sensitive ecosystems. And the total biomass of animals in the sea could drop by as much as 15 percent, according to the sobering assessment by the U.N. Intergovernmental Panel on Climate Change.

“The oceans and ice are in trouble, so we’re all in trouble,” said Michael Oppenheimer, a climate scientist at Princeton and a lead author of the report.

But while some damage is inevitable at this point, the report makes clear that society’s efforts to reduce greenhouse gas emissions in the coming decades will determine how bad things ultimately get.

It’s “the difference between an unmanageable problem and one that humans can deal with,” Oppenheimer said.

The analysis, released Wednesday at a meeting of scientists and policymakers in Monaco, follows close on the heels of the U.N. Climate Action Summit in New York, which failed to elicit ambitious commitments from the world’s biggest polluters. Yet the report underscores just how costly delaying action will be.

Thus far, the world’s oceans have been the quiet hero of our warming world. They have absorbed about a quarter of the carbon dioxide humans have pumped into the atmosphere since the dawn of the industrial revolution, and 90percent of the resulting heat.

“But it can’t keep up,” said Ko Barrett, the deputy administrator for research at the National Oceanic and Atmospheric Administration and a vice chair of the Intergovernmental Panel on Climate Change, or IPCC.

The report illustrates how climate change has already started to alter the chemistry and circulation of the oceans, and how that exacts heavy toll on marine ecosystems. Coastal communities, which will be home to a billion people by 2050, are also feeling the impacts, starting with rising seas.

Over the last century, sea level rise was primarily driven by runoff from melting mountain glaciers in places like Alaska and the Andes, as well as by the expansion of seawater as it warmed. 

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