Although climate scientists have been warning us for some time now that sea levels are rising and will continue to do so, things may not be quite as dire as we’ve feared. Sea levels are rising slower than expected, and should continue to do that, because the land is acting like a sponge and soaking up a lot of that water.
More accurately, the rate of sea level rise has been temporarily slowed by about 20%. Each year the global hydrological cycle brings vast amounts of evaporated seawater to the land in the form of snow and rain. That water subsequently runs off and returns to the ocean. However, an increase in reliance on groundwater for irrigation and consumption, meaning that water we use is coming out of the ground instead of from the sky, has allowed the land to soak up more of that rain and snow.
Lakes, underground aquifers, and soil has been soaking up more water than normal to replace the water lost to human activity. In all, over the last decade about 3.2 trillion tons more water has been stored than normal, which is about the volume of Lake Huron, the seventh largest lake on the planet.
Scientists have long expected that water being “soaked up” by land could offset some amount of sea level rise, but they weren’t sure how much. Until 2002, there were no instruments to measure that, but with the launch of NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, we were able to begin collecting data on exactly that. The measurements come from measuring the distance between the two satellites, down to the width of a human hair, as they orbit. That distance is determined by changes in the gravitational pull on those objects by the amount of water stored on land.