Consequences, they say, collect in low places.
A new NASA analysis, using data collected from different specialized satellites, reports that sea levels rose more than expected in 2024. But as any earth scientist will emphasize, the data in any particular year isn’t nearly as important as the long-term trend. And the agency’s analysis shows that global sea levels have gone up over 10 centimeters, or about four inches, since 1993 when satellites started measuring ocean height, and this rate is increasing. (Overall, sea levels have risen some eight to nine inches since 1880.)
“Every year is a little bit different, but what’s clear is that the ocean continues to rise, and the rate of rise is getting faster and faster,” Josh Willis, who researches sea level rise at NASA’s Jet Propulsion Laboratory, said in a statement.
After reporting on sea level rise — which stokes increased flooding and storm damage while threatening coastal infrastructure from sewage plants to water supplies — over the past decade, the most common responses I receive on the topic (beyond the unprintable) are either essentially “that’s barely any sea level rise” or “stop sensationalizing sea level rise.” It’s true that four inches of sea level rise over the last few decades may not be concerning or noticeable to some people. And just four inches itself, occurring in a temporal vacuum, doesn’t spell a serious problem. The problem, however, is it’s not stopping at four inches.
In a previous report authored by top researchers at a diversity of U.S. agencies — the National Oceanic and Atmospheric Administration (NOAA), NASA, the Department of Defense, and beyond — scientists project sea levels will rise by some 10 inches to a foot along the U.S. coast over just the next three decades. And again, it won’t stop there, either. The U.S. could see several feet of sea level rise by the century’s end. (Different longer-range sea level rise scenarios are shown later in this story.)
The new NASA graphic below shows the picture captured by satellites since 1993. Importantly, the rate of sea level rise increase has doubled over this period. Satellites, like the Sentinel-6/Michael Freilich spacecraft, use radar altimeters to observe sea level rise by beaming radio waves from space to the surface, which reflect off the ocean and return to the satellite.
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Sea level rise as measured by earth-observing satellites since 1993.
Credit: NASA / JPL-Caltech
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There are two main contributors to sea level rise. The largest contributor, at some two-thirds, is melting ice. Globally, nearly all mountain glaciers are shrinking, and much glacial water ultimately enters the ocean. What’s more, the colossal ice stores on Greenland and Antarctica are melting enormous amounts of water into the sea. (The Greenland Ice Sheet, about three times the size of Texas, lost some 200 gigatons annually between 2003 and 2019. A gigaton equals 1 billion metric tonnes.) The second is thermal expansion: As the seas absorb more heat, they expand.
In 2024, however, thermal expansion played a larger role, which is little surprise as 2024 was Earth’s hottest year on record (the seas absorb over 90 percent of the heat humans trap on Earth). This boosted sea level rise a bit above current annual expectations, to nearly a quarter inch. (Rising surface temperatures are part of another clear trend: The last 10 consecutive years have been the warmest 10 on record, NASA says.)
In the coming years, however, Earth’s melting ice sheets will play an outsized role in sea level rise. “The ice sheets are just getting warmed up,” NASA’s Willis previously told Mashable.
“The ice sheets are just getting warmed up.”
There is uncertainty about how much sea levels will rise by the century’s end because humanity has never seen such human-caused melting before. How much water, for example, will Antarctica’s destabilized, Florida-sized Thwaites Glacier dump into the oceans in the coming years? “Thwaites is the one spot in Antarctica that has the potential to dump an enormous amount of water into the ocean over the next decades,” Sridhar Anandakrishnan, a professor of glaciology at Penn State University who researches Thwaites, told Mashable in 2021.
Four inches since 1993 is really just the beginning as Earth continues to warm.
The following five long-term (2050-2150) sea level rise scenarios, compiled by U.S. agencies in the comprehensive report cited above, cover a wide range of possibilities. The “low” scenario — involving an extremely ambitious climate target — requires global nations to stabilize Earth’s warming at around 1.6 degrees Celsius (2.8 degrees Fahrenheit) above 19th-century temperature levels by mid-century. Compared to sea levels in 2000, the “Intermediate” scenario for the U.S. below, which projects 1.3 feet of sea level rise by 2050 and several feet by 2100, is a world warmed by around 2 degrees C (3.6 degrees F) by mid-century.
Five potential sea level rise scenarios for both the U.S. and the globe.
Credit: NOAA 2022 Sea Level Rise Technical Report
Ultimately, the amount of sea level rise experienced by our descendants is up to the choices made by the most unpredictable part of the climate equation — us.