The accelerating thaw of Antarctica might drive sea levels up by more than five metres by 2300 unless governments act quickly to cut greenhouse gas emissions, a UN report said on Wednesday.
Many fish, corals and other marine life are suffering in ever warmer waters, with more frequent underwater heatwaves, acidification caused by man-made carbon dioxide in the atmosphere and a decline in levels of oxygen, the world’s leading climate scientists said.
“Over the 21st century, the ocean is projected to transition to unprecedented conditions,” the Intergovernmental Panel on Climate Change (IPCC) said in a special report about the oceans and the cryosphere – the world’s frozen regions. It was compiled by more than 100 authors from 36 nations.
The report is the most detailed look at the impact of climate change ranging from melting glaciers on the world’s highest mountains to the depths of the oceans that cover 71% of the Earth’s surface.
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“The open sea, the Arctic, the Antarctic and the high mountains may seem far away to many people,” said Hoesung Lee, chair of the IPCC. “But we depend on them and are influenced by them directly and indirectly in many ways.” Melting Himalayan glaciers, for instance, provide water to grow crops or generate hydropower before flowing into the oceans.
The report points to alarming signs of an accelerating melt of Antarctica that could herald an irreversible thaw from the world’s biggest store of frozen ice, ahead of Greenland.
Even so, sea level rise could be limited to 43cm by 2100, and around a metre by 2300, if the world sharply cuts greenhouse gas emissions in line with a goal set by almost 200 nations in the 2015 Paris Agreement to limit warming to 2C above pre-industrial times, it said.
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But a future with no meaningful action and rising greenhouse gas emissions could push up sea levels by 84cm by 2100, about 10cm higher than estimated in the most recent IPCC global assessment in 2014 because of Antarctica’s quickening melt.
On that track, seas could rise by anywhere between 2.3 and 5.4 metres by 2300, it said. That would redraw maps of the world, make entire low-lying nations in the Pacific Ocean uninhabitable and swamp coasts from Bangladesh to Miami.
Lee said that there were worrying signs that the world was losing the race against climate change. “We need to take immediate and drastic action to cut emissions right now,” he said.
“Humanity is exacting a terrible toll on the ocean,” Norway’s prime minister Erna Solberg and Palau president Tommy Remengesau Jr. wrote in CNN on Monday. “Global warming, combined with the negative impacts of numerous other human activities, is devastating our ocean, with alarming declines in fish stocks, the death of our reefs, and sea level rise that could displace hundreds of millions of people.”
Authors said those different futures for rising seas highlighted stark choices now.
“Although many of the messages may seem depressing … there are actual, positive choices that can be made to limit the worst impacts of climate change,” said Michael Meredith, of the British Antarctic Survey.
Nerilie Abram, of Australian National University, also said: “We see changes in all of these areas, from the tops of high mountain to the depths of the oceans and the polar region …We see two very different futures ahead of us.”
The report was published two days after leaders failed to match UN secretary general Antonio Guterres’ call for nations to cut global greenhouse gas emissions by 45% below 2010 levels by 2030 at a summit in New York.
Global CO2 output continues to rise. Guterres said such immediate action was needed to get on track to limit warming to 1.5C, the toughest goal of the Paris Agreement. Global average temperatures are already up about 1C.
Delegates to the IPCC said Saudi Arabia, OPEC’s top oil producer, had repeatedly sought changes at the Monaco meeting, partly to weaken links to an IPCC report in 2018 that examined ways to achieve the 1.5C goal.
Largely at Saudi insistence, Wednesday’s text, for instance, merely said it “follows” the 1.5C report and another about climate change and land issued this year. Many other delegates had favoured the word “complements” to underscore that the reports are part of a family of scientific studies.
Delegates said the Saudis pushed to water down any wording that would link this report to the IPCC’s 1.5 degrees report. In Katowice, the COP only “noted” the 1.5C report, under pressure from Saudis, Americans etc, stopping short of “welcoming” it.
Saudi Arabia seemed to worry that the Santiago COP may “welcome” this new report. If so, it could implicitly endorse the findings in the 1.5C report if they were strongly connected in the text, so they wanted to loosen any links.
Some authors said wrangling over wording ended up helping because authors tightened the scientific findings.
Martin Sommerkorn, an author with the WWF conservation group, said that “the report ended up stronger because of a defence of the science.”
Delegates said the wrangling contributed to delay the meeting, with an all-night session lasting into Tuesday, from a scheduled finish on Monday.
They also said that the US delegation did not stand in the way of the science, even though US president Donald Trump plans to pull out of the Paris Agreement.
Among other findings, the report said the maximum catch of fish in the oceans, already falling because of factors including over-fishing and pollution as well as warming waters, would fall by between 20 and 24% this century unless governments take strong action to rein in greenhouse gas emissions.
And fish stocks would be driven polewards or to the depths as the waters warm, perhaps causing conflicts over dwindling resources.
The report said extreme high tides or storm surges that historically happened only once a century could become at least annual events by 2100, exacerbated by rising sea levels. And a melt of permafrost could release methane and undermine infrastructure in mountains or polar regions.
“The impacts of human-made carbon emissions on our oceans are on a much larger scale and happening way faster than predicted,” said Taehyun Park, global climate political advisor with Greenpeace East Asia.