Recent studies reveal that Earth’s rapid soil moisture loss is contributing to global sea level rise and altering the planet’s rotation, underscoring the profound impacts of climate change.

The amount of water stored on lands across Earth’s continents has declined at such staggering levels that changes are likely irreversible while humans are alive, a study published Thursday found.

The losses in soil moisture — a result of the planet’s climate conditions and prolonged droughts — already pose issues for farming, irrigation systems, and critical water resources for humans. But it also affects sea-level rise and Earth’s rotation — datasets the research team used to better track water storage for decades longer than previous studies.

“What we were looking for was evidence of changing hydrology around the world,” said Jay Famiglietti, co-author of the study, published in Science. “What we found was this unprecedented decrease in soil moisture in the early part of the 21st century, which took us by surprise.”

The team found that from 1979 to 2016, the largest soil moisture losses occurred between 2000 and 2002, resulting in the loss of approximately 1,614 gigatons of water from the land. The team estimated that it contributed to global mean sea-level rise at a rate of roughly 1.95 millimeters per year.

The startling contribution to rising sea levels was more significant than Greenland’s ice loss around that time. Greenland contributed about 0.8 millimeters a year in recent decades. Between 2002 and 2006, it lost approximately 900 gigatons.

“The rate of water dumping into the oceans was bigger from terrestrial water storage than from what we normally think of as the biggest source, which was the melting of Greenland,” said Clark Wilson, a co-author and geophysicist at the University of Texas at Austin.

Famiglietti agreed that “soil moisture depletion is playing a bigger role in sea level rise than we previously thought.”

The most significant drops in soil moisture during that period occurred in extensive regions of East and Central Asia, Central Africa, and North and South America. The study showed that the decline was primarily driven by changes in precipitation patterns and increased drying power from the atmosphere due to rising temperatures.

“Remarkably, the global-scale drought that occurred between 2000 and 2002 was largely unnoticed at the time,” said Ki-Weon Seo, lead author and geophysicist at Seoul National University. “This study suggests that greater attention should be paid to drought events”

The drop in soil moisture from 2000 to 2002 is interesting because it’s not well depicted in computer models depicting Earth’s past water storage, Wilson said. One well-known computer model predicted a global drought, but its accuracy was unclear. The study’s findings, however, he said, confirm the observation and will help refine models better.

Soil moisture continued to decrease following 2002, although not at that same intense rate. Satellite observations from NASA’s Gravity Recovery and Climate Experiment revealed that approximately 1,287 gigatons of water on land were depleted between 2005 and 2015, equivalent to about 3.52 millimeters of global mean sea-level rise.

“There is continuing loss of moisture of water stored on land,” Wilson said. From our perspective of human timescales, we may not have witnessed the kind of rainfall events that would be crucial in recharging the land.

Evidence of a global shift in water storage

Tracking Earth’s global water storage on land is a challenging task.

Scientists were previously limited to regional measurements and models, but the launch of GRACE enabled new global views of water storage, ranging from the surface to below ground. However, it was only launched in 2002, leaving scientists in the dark about what it looked like in prior decades.

In the new study, Seo and his colleagues extend this record back to 1979 and provide the first “evidence of a permanent shift in Earth’s hydrological cycle due to climate change,” said hydrologist Luis Samaniego, who was not involved in the study and wrote a review article on the research.

Since direct observations of global water storage on land were scarce before 2002, the team examined two other, more extensive datasets as indicators: global sea-level rise and Earth’s tilt.

Global sea-level rise is primarily driven by the melting of glaciers and ice sheets, but it is also influenced by changes in the amount of water on land. When water leaves the continents, it ends up in the oceans, Famiglietti said.

At the same time, moving water from one part of Earth to another can affect the planet’s rotation around its axis. Earth spins on an imaginary line between the North and South poles, but the exact position of the line isn’t fixed. The points where Earth’s axis of rotation meets Earth’s surface wobble and drift a few meters each year — called polar motion. (These changes aren’t noticeable to people but are perceptible by GPS systems on phones.)

Previously, Famiglietti and his colleagues found that removing groundwater shifted the Earth’s tilt by 31.5 inches to the east. In the new study, the team also found that polar motion underwent observable changes due to global groundwater loss from 1993 to 2010.

Samaniego said the new study validates a long-term trend in Earth’s water cycle, as seen in models using not just one, but three completely independent global datasets — “an impressive scientific feat.”

These declines have been seen on a regional level, but he said this is the first “conclusive” evidence of a global shift in water storage.

As of 2021, the team said soil moisture still has not recovered and likely won’t under the current climate conditions. Prolonged droughts, which are increasing in a warming world, will prevent soil moisture from bouncing back on the given course — at least in our lifetimes.

Soil moisture “that has left the soil layers and hasn’t been replenished for decades is unlikely to return to its original levels,” said Samaniego, a researcher at Helmholtz Centre for Environmental Research.

The conclusion, researchers say, is that societies must learn to practice more innovative and sustainable water resource management.

“Climate change is not only about rising temperatures but also about long-term impacts on water availability, affecting agriculture, ecosystems, and societies alike,” Samaniego said.

https://www.washingtonpost.com/climate-environment/2025/03/27/earth-soil-moisture-drying-sea-level-study/