The same oceans that nourished human evolution are poised to unleash misery on a global scale unless the carbon pollution destabilising Earth’s marine environment is brought to heel, warns a draft UN report.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 man made emissions, at least 30 per cent 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.Irreversible change Donald Trump — a no-show at the G7 climate segment this week — wants the US to exit the Paris Agreement and has taken a chainsaw to predecessor Barack Obama’s climate policies.India is rapidly developing solar power, but continues to build up coal-fired capacity at the same time. The European Union is inching toward a mid-century ‘net zero’ emissions goal, but several member states are dragging their feet.Long seen as a leader on climate, China — which emits nearly as much CO2 as the US, EU and India combined — is also sending mixed signals.1,000-fold flood damage increaseBy 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.“Even if the number is 100 or 50 million by 2100, that’s still a major disruption and a lot of human misery,” said Ben Strauss, CEO and chief scientist of Climate Central, a US based research group. “When you consider the political instability that has been triggered by relatively small levels of migration today, I shudder to think of the future world when tens of millions of people are moving because the ocean is eating their land.”Earth’s average surface temperature has gone up 1C since the late 19th century, and is on track — at current rates of CO2 emissions — to warm another two or three degrees by century’s end.The Paris Agreement calls for capping global warming at “well below” 2C. Sea level rise will accelerate rapidly moving into the 22nd century, and “could exceed rates of several centimetres per year” — about 100 times more than today, according to the report. “If we warm the planet by 2C, by 2100 we will only be at the beginning of a runaway train ride of sea level rise,” said Strauss, whose research informs the report’s conclusions.Marine heatwavesOceans 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.