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Destructive changes already set in motion could see a steady decline in fish stocks, a hundred-fold or more increase in the damages caused by superstorms, and hundreds of millions of people displaced by rising seas, according to the Intergovernmental Panel on Climate Change (IPCC) “special report” on oceans and Earth’s frozen zones, known as the cryosphere.

As the 21st century unfolds, melting glaciers will first give too much and then too little to billions who depend on them for fresh water, it finds.

Without deep cuts to manmade emissions, at least 30 percent of the northern hemisphere’s surface permafrost could melt by century’s end, unleashing billions of tonnes of carbon and accelerating global warming even more.

The 900-page scientific assessment is the fourth such tome from the UN in less than a year, with others focused on a 1.5-Celsius (2.6-Farenheit) cap on global warming, the state of biodiversity, and how to manage forests and the global food system.

All four conclude that humanity must overhaul the way it produces and consumes almost everything to avoid the worst ravages of climate change and environmental degradation.

Governments meet in Monaco next month to vet the new report’s official summary. While the underlying science—drawn from thousands of peer-reviewed studies—cannot be modified, diplomats with scientists at their elbow will tussle over how to frame the findings, and what to leave in or out.

The final advice to policymakers will be released on September 25, too late to be considered by world leaders gathering two days earlier for a summit convened by UN Secretary-General Antonio Guterres to extract stronger national commitments in confronting the climate crisis.

Guterres may be disappointed by what the world’s major greenhouse gas emitters put on the table, according to experts tracking climate politics in China, the United States, the European Union and India………..

1,000-fold flood damage increase

By 2050, many low-lying megacities and small island nations will experience “extreme sea level events” every year, even under the most optimistic emissions reduction scenarios, the report concludes.

By 2100, “annual flood damages are expected to increase by two to three orders of magnitude,” or 100 to 1,000 fold, the draft summary for policymakers says.

Even if the world manages to cap global warming at two degrees Celsius, the global ocean waterline will rise enough to displace more than a quarter of a billion people.  The report indicated this could happen as soon as 2100, though some experts think it is more likely to happen on a longer timescale………

Marine heatwaves

Oceans not only absorb a quarter of the CO2 we emit, they have also soaked up more than 90 percent of the additional heat generated by greenhouse gas emissions since 1970.

Without this marine sponge, in other words, global warming would already have made Earth’s surface intolerably hot for our species.

But these obliging gestures come at a cost: acidification is disrupting the ocean’s basic food chain, and marine heatwaves—which have become twice as frequent since the 1980s—are creating vast oxygen-depleted dead zones.

In the Tasman Sea, for example, a 2015-16 heatwave lasted for 251 days, causing disease outbreaks and a die-off of farmed shellfish.https://phys.org/news/2019-08-oceans-friend-foe-landmark-climate.html