The level of the world’s seas and oceans is rising at rates never before seen, threatening coastal cities like New York, Shanghai and Dhaka, along with the very existence of some island nations.
As with a host of other modern-day environmental calamities, the cause of the crisis is clear: the accumulation of greenhouse gases in the atmosphere from the burning of fossil fuels.
The seas have been a reliable heat sink over the past five decades, absorbing more than 90% of global heating. But, as water warms, it also expands. Additionally, the unprecedented melting of the Earth’s glaciers and polar ice sheets only adds to the volume of water, causing the oceans to overflow even more.
“This is a crazy situation: rising seas are a crisis entirely of humanity’s making. A crisis that will soon swell to an almost unimaginable scale, with no lifeboat to take us back to safety,” U.N. Secretary General António Guterres said on Tuesday in Nuku’alofa, capital of the Pacific island nation of Tonga.
Guterres pointed to a pair of U.N. studies by the World Meteorological Organization and the U.N.'s climate action team, saying they cast the issue in “sharp relief.”
The reports document how ocean water temperatures continue to shatter records. Marine heatwaves are growing more intense and prolonged, while rising sea levels result in more frequent and severe storm surges and coastal flooding.
'Coming for us all'
Globally, the average rate of sea level rise has more than doubled since the 1990s, up more than 10 centimeters. In the Pacific, it’s even worse, and in some places the rise exceeds 15 centimeters.
That could spell disaster for islands where the average elevation is only a meter or two above sea level and 90% of the people live within five kilometers of the coast, the U.N. says.
“Without drastic cuts to emissions, the Pacific islands can expect at least 15 centimeters of additional sea level rise by mid-century, and more than 30 days per year of coastal flooding in some places,” Guterres says.
It doesn’t end there. As the Earth inches toward a three-degree rise in temperatures above pre-industrial levels, seas and oceans will continue to rise at alarming rates, foretelling disaster for Tonga and well beyond.
People living in the coastal zones of densely populated countries like Bangladesh, China, India, the Netherlands and Pakistan will be at risk and potentially suffer catastrophic flooding. Also at risk are major cities on every continent, including Bangkok, Buenos Aires, Lagos, London, Mumbai, New York and Shanghai.
“Surging seas are coming for us all,” the U.N. chief says.
Guterres is calling on the world’s major polluters to step up and provide more money and aid for the most vulnerable nations: “We need a surge in funds to deal with surging seas.”
In its report, WMO says the global mean sea level will continue to rise not only for the foreseeable future but “for centuries to millennia” due to continuing deep ocean heat uptake and the increasing decadal ice mass losses from the Greenland and Antarctic Ice Sheets, which together contain more than 99% of freshwater ice on Earth.
Even if the world manages to cut greenhouse gas emissions, marine heatwaves will likely become more frequent and last longer, experts say. As the seas absorb more carbon, they become more acidic, with major impacts on the marine food chain.
