NASA uses 30-year satellite records to track and project rising seas

Observations from space show that the rate of sea level rise is increasing. Knowing where and how much uplift occurs can help coastal planners prepare for future hazards.

The average global sea level has risen 0.11 inches (0.27 centimeters) between 2021 and 2022, according to a NASA analysis of satellite data. That’s the equivalent of adding water from a million Olympic-size swimming pools to the ocean every day for a year, and is part of a decades-long trend of rising seas.

Since satellites began observing sea surface height in 1993 with the US-French TOPEX/Poseidon mission, the average global sea level has risen 3.6 inches (9.1 centimeters), according to NASA’s Sea Level Change science team . The annual rate of rise — or how fast sea levels are rising — that researchers expect to see has also increased from 0.08 inches (0.20 centimeters) per year in 1993 to 0.17 inches (0.44 centimeters) per year in 2022 Based on long-term satellite measurements, the projected rate of sea level rise will be 0.26 inches (0.66 centimeters) per year by 2050.

“We have a clear picture of recent sea level rise — and can better predict how much and how fast the oceans will continue to rise — because NASA and Center National d’Études Spatiales (CNES) have accumulated decades of ocean observations. data with measurements from the rest of NASA’s fleet, we can also understand why the ocean is rising,” said Karen St. Germain, director of NASA’s Earth Science Division in Washington.

“These fundamental climate observations help shape the operational services of many other federal and international agencies working with coastal communities to mitigate and respond to rising waters.”

The increase in 2022 was less than the expected annual rate due to a mild La Niña. During years with a particularly strong La Niña climate pattern, mean global sea levels may even drop temporarily as weather patterns shift in such a way that more rainfall falls over land rather than over the ocean.

“With an increasing demand for accurate and timely climate information, NASA is committed to providing annual sea level observations and future projections to help vulnerable communities around the world better understand the risks they face in a new climate,” said Nadya Vinogradova Shiffer, a NASA ocean science program scientist. “Timely updates are essential to show what climate trajectory we are on.”

Despite natural influences such as La Niña, sea levels continue to rise due to human-induced climate change, driven by the excess amounts of greenhouse gases such as carbon dioxide that society is pumping into the atmosphere. Climate change is causing the Earth’s ice caps and glaciers to melt, adding more fresh water to the ocean, while warming causes sea water to expand. Both effects contribute to rising sea levels, negating many natural effects on sea surface height.

“Tracking the greenhouse gases we’re adding to the atmosphere tells us how hard we’re pushing the climate, but sea levels show us how much it’s responding,” said Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory in Southern California. “These measurements are a critical measure of how much people are reshaping the climate.”

A long-standing record

Sea surface height measurements, which began 30 years ago with TOPEX/Poseidon, have continued on four successive missions led by NASA and partners including the French space agency CNES, ESA (European Space Agency), and the US National Oceanic and Atmospheric Administration.

The most recent mission in the series, Sentinel-6/Jason-CS (Continuity of Service), consists of two satellites that will extend these measurements to 2030. The first of these two satellites, Sentinel-6 Michael Freilich, was launched in 2020. with the second slated to go into orbit in 2025.

“The 30-year satellite record allows us to see through the shorter-term shifts that occur naturally in the ocean and helps us identify the trends that tell us where sea level is headed,” said JPL’s Ben Hamlington, a researcher. at sea level who leads NASA’s Sea Level Change science team.

Scientific and technical innovations by NASA and other space agencies have given researchers a better understanding of the current state of the ocean on a global scale. In particular, radar altimeters have helped produce increasingly accurate measurements of sea level around the world. To calculate sea level height, they bounce microwave signals off the ocean surface and record the time it takes for the signal to travel from a satellite to Earth and back, as well as the strength of the return signal.

When height measurement data from all ocean basins are combined with more than a century of observations from coastal surface sources, they combine to dramatically expand and improve our understanding of how sea surface height changes on a global scale. And when those sea level measurements are combined with other NASA data sets about ice mass, land motion and other earth changes, scientists can decipher why and how seas are rising.