Rise in sea-level slowed by land storing extra water: study

Climate change has caused Earth's parched land masses to soak up increasing amounts of water in the last decade, slowing the pace of sea level rise, according to a new NASA study.

The study shows that while ice sheets and glaciers continue to melt, changes in weather and climate over the past decade have caused Earth's continents to store an extra 3.2 trillion tonnes of water in soils, lakes and underground aquifers, temporarily slowing the rate of sea level rise by about 20 per cent.

New measurements from a NASA satellite have allowed researchers to identify and quantify, for the first time, how climate-driven increases of liquid water storage on land have affected the rate of sea level rise.

The water gains over land were spread globally, but taken together they equal the volume of Lake Huron, the world's seventh largest lake.

Each year, a huge amount of water evaporates from the ocean, then falls over land as rain or snow, and returns to the ocean through runoff and river flows.

Scientists have long known that small changes in Earth's water cycle could lead to large, although temporary, changes in the rate of sea level rise.

By measuring the distance between the two satellites to within the width of a strand of human hair as they orbit the planet, researchers can record changes in Earth's gravitational pull that result from water moving across its surface.

Careful analysis of these data, allowed the scientists to measure the change in water storage over land.

"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 NASA's Jet Propulsion Laboratory (JPL).

"What we didn't realise 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," said Reager, who began the research project as a graduate student at the University of California, Irvine (UCI).

"This is the first study to observe these changing water storage patterns on land and their impact on modulating current rates of sea level rise," said senior author Jay Famiglietti, professor at UCI.

"Our work will certainly sound the alarm about the possible effects of climate change on shifting patterns of freshwater availability, as well as the potential for modulating future rates of sea level rise by managing the amount of freshwater stored on land," Famiglietti said.

The study is the first to observe global patterns of wetting and drying on land, with wet areas getting wetter and dry areas getting drier.

The research was published in the journal Science.