Taking a Measure of Sea Level Rise: Gravimetry

Earth’s ice sheets and glaciers store a vast amount of water on land—as much as 69 percent of the planet’s fresh water, according to the U.S. National Snow & Ice Data Center. But when this ice melts and flows downslope, water once stored on land now contributes to the volume in the seas.  The planet’s seas have been rising for more than a century, with adverse effects such as increased coastal flooding, beach erosion, and saltwater intrusion into fresh groundwater supplies. There is more than one cause for the rise, but the largest contributor over the past few decades comes from the planet’s melting ice sheets and glaciers. One way to track how much sea level rise comes from melting ice sheets and glaciers is to measure how much mass they are losing. Scientists have been making repeat ground-based measurements at select sites for decades—an approach that continues today and extends important long-term records of change. Traditional field measurements are also important for calibrating models and for understanding what causes the changes observed by satellites. But research has shown that field measurements can overestimate ice loss when they are used to extrapolate over larger areas with few observations. - NASA