Researchers have examined data collected by NASA’s Gravity Recovery and Climate Experiment (GRACE)  satellite mission during the period 2002 to 2016 to track freshwater trends worldwide. In a new report, they claim that data shows access to freshwater will be the biggest challenge to humanity in the 21st century. The GRACE data made it possible for the researchers to track changes in freshwater resources around the world even in areas where local data has been scarce or unavailable, according to a report in The Guardian.