(GRAPHIC) SÖNKE DANGENDORF, ADAPTED BY N. DESAI /SCIENCE; (DATA) DANGER ET AL., CHANGE CLIMATE CHANGE, 9, 705 (2019); LEGEAIS ET AL., EARTH SYSTEM SCIENCE DATA, 10, 281 (2018)
Oceanographers are set to gain a clearer picture of the trends thanks to the Michael Freilich Sentinel-6 satellite, which NASA and the European Space Agency plan to launch on November 21 from Vandenberg Air Force Base in California. Named after the former head of NASA’s Earth Science program, who died this year, the satellite will work similarly to its predecessors, using reflected radar pulses to measure ocean altitude. But higher-resolution measurements will allow him to measure the height of the ocean within 300 meters of the shoreline, far closer than before.
Coasts are where rising sea levels reach home – and where large local variations can obscure the global average. In a paper published last month in Scientific data, Ani Kazenave, an ocean geophysicist at the International Space Science Institute, and colleagues re-analyze satellite imagery and show sea level rise in 20% of coastal sites studied in Europe, Asia and Africa is significantly different from that of the open ocean. . “We have to explain that,” she said.
Part of the variation reflects the vertical movement of the earth itself, due to the slow jump of continental plates that “float” on a viscous mantle. Coastal ocean currents, freshwater from nearby rivers and weather patterns can also bring variability, causing water to accumulate or recede from continents, Kazenave said.
But Dangendorf believes that currents in the open ocean drive much of this variable mess, directing rising water from the open ocean – where there is more water to warm and expand – to shoreline. For example, a reconstruction of the Norwegian sea level from 1960 to 2015 showed that changing currents are the best explanation for mysterious and frequent 20-millimeter swings in height. Dangendorf is currently tracking sea level rise in nine coastal regions to their ocean sources and finds that they are usually 500 to 1,000 kilometers away; much of the sea level rise in the northern half of the east coast of the United States, for example, comes from waters swept away by the Labrador Sea.
The trends are worrying. Aimée Slangen, a climate scientist at the Royal Dutch Institute for Marine Research, and colleagues are integrating recent forecasts from climate models to predict when sea levels will rise by 25 centimeters above 2,000 levels, a moment when 100-year floods in some coastlines may be close to the annual occurrence. In an unpublished paper, Slangen finds that the threshold will be reached sometime between 2040 and 2060. Efforts to slow climate change will not contribute much to delaying it, given the inertia of ocean warming and melting ice, although it may later century. And this short-term security, while scary, is “pretty good for decision-making,” Slangen said.
Dangendorf, who joined Old Dominion late last year, took first place in the action. The university is in Norfolk, Virginia, part of the US coast, where the crust sinks as fast as the oceans rise. “I watch the coastal flood every week,” he said. “I see him from my balcony.”