Over a Thousand Gigatons Lost in Three Years: Freshwater Depletion and Rising Sea Levels

A recent study reveals a significant reduction in the amount of freshwater stored on land, as ocean levels continue to rise. This alarming trend was particularly pronounced during a three-year period, highlighting a shift in the Earth's water distribution that has been exacerbated by climate change.

The research, conducted by an international team led by Ki-Weon Seo from Seoul National University and published in the journal Science, indicates that terrestrial water loss has had a more immediate impact on sea levels than the melting glaciers of the Arctic. The findings suggest that the frequency of droughts has increased in recent decades, adversely affecting agriculture and various ecosystems. This increase may be linked to intensified evaporation due to rising air temperatures and decreased rainfall linked to persistent high-pressure systems over continents.

Between 2000 and 2002, approximately 1,614 gigatons of soil moisture were lost, a figure that underscores the challenges in assessing changes in global water resources, particularly regarding groundwater levels and soil moisture. The research team utilized data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and global gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) satellites, which provide insights into the amount of freshwater stored on land.

The study noted that the most significant water loss occurred from 2000 to 2002, with about 1,614 gigatons of moisture vanishing from the terrestrial environment, excluding Greenland and Antarctica. While the rate of loss slowed between 2003 and 2016, an additional 1,009 gigatons of soil moisture were still lost during this period. In comparison, the Greenland ice sheet, a critical factor in rising sea levels, lost around 900 gigatons of mass from 2000 to 2006.

Measurements of sea levels corroborate these findings, indicating that the decline in soil moisture contributed approximately 1.95 millimeters per year to the rise in sea levels from 2000 to 2002. This rate decreased to about 0.2 millimeters annually from 2003 to 2016. Regions heavily impacted by this water loss include East and Central Asia, Central Africa, South America, and the eastern United States.

The reduction of terrestrial water has also influenced polar movement, causing a slight shift in the Earth's rotational axis due to the redistribution of mass. By 2012, the pole had moved an estimated 45 centimeters. The researchers attribute this phenomenon to altered precipitation patterns since 2000, combined with a deficit in atmospheric vapor pressure, which effectively removes moisture from the soil.

The evidence gathered supports the conclusion that the sudden changes in soil moisture are genuine and likely driven by a warming climate. According to Luis Samaniego from the University of Potsdam, the study provides compelling evidence of a significant shift in the Earth's hydrological cycle, primarily influenced by climate change.