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A satellite scheduled to launch from California later this month will measure sea level rise and provide other crucial data to scientists studying how global warming is affecting Earth’s oceans.
Melting ice has already caused sea levels to rise by about 8 inches since the 1880s, and the trend is accelerating. Earth’s oceans have absorbed the vast majority of the extra heat, and about a quarter of the extra carbon dioxide, that humans have generated by burning fossil fuels.
The new satellite, named Sentinel-6 Michael Freilich by the former director of NASA’s Earth Science division, will measure sea levels around the world for the next five years. At that point a second satellite of the same type will take over, providing scientists with a full decade of reliable data on Earth’s oceans. The mission is a collaboration between NASA and the European Space Agency.
“Sea level continues to rise and we can’t stop measuring it,” says Josh Willis, mission project scientist at NASA’s Jet Propulsion Laboratory. “Every year, every decade, we are renewing the climate and raising the sea level higher and higher.”
The satellite is the latest in a series of sea level measurement missions dating back to the early 1990s. The Sentinel-6 mission, with two state-of-the-art satellites over a 10-year span, is an indication of how much demand there is for reliable, high-resolution data on climate change.
“We know the oceans are rising due to human-caused interference with the climate. And, to see that, you really have to see sea levels rise across the planet,” says Willis. “This is what this satellite does best.”
Sentinel-6 will orbit about 800 miles high and use radar to measure the ocean’s surface. An instrument on the satellite sends a radar wave to Earth. The radar bounces off the ocean surface and returns to the satellite. By measuring how long it took the radar to go down and back – and by taking into account the humidity in the atmosphere that slows the radar down – scientists can measure how far the ocean surface is from the satellite.
In other words, the satellite can tell scientists on Earth how high the oceans are and how this height is changing over time.
“It’s really kind of an incredible technological feat,” says Willis. “We can accurately measure the water level with an accuracy of 1 inch from 800 miles and up.”
Rising seas affect coastal areas of the United States in tangible, often destructive, ways. Ocean water has seeped into drainage systems, flooded roads, and removed entire island communities from existence in the Chesapeake Bay, the Gulf of Mexico, and the Pacific coasts.
But higher and warmer water also affects people far from the coast. What happens in the oceans doesn’t stay in the oceans. For example, ocean currents and temperatures affect climate and fish populations.
And as water expands as it gets warmer, sea level data can help scientists understand more about the ocean.
“We can also use sea level measurements to understand how currents change, how the ocean stores heat,” says LuAnne Thompson, an oceanographer at the University of Washington. Thompson and her colleagues use data on sea level rise from satellites every day, and she says it is indispensable to her research on the amount of heat the oceans store.
“Knowing the sea level, we have an indication of how much the ocean has expanded due to warming,” explains Thompson.
There is still a lot that scientists don’t know about how the oceans will change in the coming decades. Climate models clearly indicate that sea levels will continue to rise rapidly and that sea level rise will accelerate as the Earth warms. But exactly how it will appear locally requires detailed and continuous data from both satellites and tide indicators on Earth.
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