As crucial as it is for the future of humanity, calculating the rate of sea level rise has never been easy, and new measurements by NASA satellites have added a new twist to the equation. Careful study of the data from NASA’s twin NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites helped show how climate-driven increases of liquid water storage on land have affected the rate of sea level rise.
In the past decade, Earth’s land masses have soaked up an extra 3.2 trillion tons of water in soils, lakes and underground aquifers, temporarily slowing the rate of sea level rise by about 20 percent, according to the new study published in Science. But that doesn’t mean it’s time to stop worrying — by most projections, rising seas will swamp many coastal cities where millions of people live in the near future.
The research will help scientists make more accurate predictions on sea level rise by showing how climate change affects the global water cycle. Even small changes in the cycle, like persistent regional changes in soil moisture or lake levels, for instance, can affect the rate of sea level rise from what we would expect based on ice sheet and glacier melt rates.
“We always assumed that people’s increased reliance on groundwater for irrigation and consumption was resulting in a net transfer of water from the land to the ocean,” said lead author J.T. Reager of JPL, who began work on the study as a graduate student at UC Irvine. “What we didn’t realize until now is that over the past decade, changes in the global water cycle more than offset the losses that occurred from groundwater pumping, causing the land to act like a sponge … at least temporarily,” Reager said.
The sensitive satellite sensors can detect changes in Earth’s gravitational pull that result from regional changes in the amount of water across Earth’s surface. With careful analysis of these data, JPL scientists were able to measure the change in liquid water storage on the continents, as well as the changes in ice sheets and glaciers.
“These results will lead to a refinement of global sea level budgets, such as those presented in the Intergovernmental Panel on Climate Change (IPCC) reports, which acknowledge the importance of climate-driven changes in hydrology, but have been unable to include any reliable estimate of their contribution to sea level changes,” said JPL senior water scientist Jay Famiglietti, senior author of the paper and a UCI professor.
Famiglietti also said the study is the first to observe global patterns of changes in land water storage, with wet regions getting more wet and dry areas getting drier.
“These patterns are consistent with earlier observations of changing precipitation over both land and oceans, and with IPCC projections of changing precipitation under a warming climate,” he said. “But we’ll need a much longer data record to fully understand the underlying cause of the patterns and whether they will persist.”