Melting Glaciers, Ice Caps Causing Seafloor To Rise, Sink Around Earth

Climate change is quite distinct from weather, and studies like this could help President Donald Trump understand the difference, if he were interested in learning about it. To put it simply, weather cannot cause the seafloor to subside or rise, but climate change can, and that is precisely what scientists have found.

As rising temperatures cause glaciers and ice caps to melt, and the meltwater flows into seas and oceans, the increased weight of the larger volume of water pushes down the seafloor at the bottom, effectively increasing the total height of the water column, adding — quite literally — another dimension to the idea of rising sea levels, which are usually measured by satellite imagery.

A study found an 8 percent difference between the measurements taken by satellites — using altimeters that measure the ocean surface from the center of Earth — and those taken by tide gauges — instruments placed at the bottom of the sea to measure surface change relative to the bottom — in sea level changes measured from 1993-2014.

That means our satellite measurements of how much sea levels have actually risen are off by about 8 percent from how much they actually have. But the researchers behind the study, led by Thomas Frederikse from Delft University of Technology in the Netherlands, explained only 4 percent can be attributed to the ocean floor subsiding, because half the increase in sea level rise is an effect of warming temperatures, which cause the same amount of water to expand and occupy more space.

There are significant regional variations in this change, since more ice is being lost in the Northern Hemisphere compared to the south. So, the Arctic Ocean gained 1 millimeter more per year in that 21-year period than satellite data showed, while the South Pacific rose by 60 percent less, or 0.4 millimeter a year, during the same period, according to the study.

“The effect is systematic and relatively easy to account for. In a future warming climate, the sea level rise induced by ice sheets will increase, and therefore, the magnitude of the bias due to elastic ocean bottom deformation will grow,” the authors wrote.

While the ground is sinking in some places, it is also rising slightly in some others — places where the glaciers are melting, reducing their weight on the ground beneath them. Given the almost clear-cut distinction of ice loss along hemispheres, almost all of the Northern Hemisphere is undergoing a small uplift of the ocean floor.

Titled “Ocean Bottom Deformation Due To Present-Day Mass Redistribution and Its Impact on Sea Level Observations,” the most recent version of the study appeared online Monday in the journal Geophysical Research Letters.

“The Earth itself is not a rigid sphere, it’s a deforming ball,” Frederikse told Earther. “With climate change, we do not only change temperature.”