As pollution from burning fossil fuels continues to heat the atmosphere, the world’s glaciers are melting at an accelerating rate. Scientists widely agree that this meltwater has been a major factor in raising global sea levels about seven inches over the 20th century...
The movement of all that water is affecting the Earth’s rotation, according to a study published Friday in the journal Science.
“If you are melting glaciers from high latitudes—in Alaska, Greenland, or Iceland—you move mass away from the pole, toward the equator, which slows the Earth down,” said Jerry Mitrovica, the study’s lead author and a Harvard geophysicist who specializes in studying sea level change. “The change in the distribution of the mass from the poles to lower latitudes also causes the rotation to wobble slightly, because it’s being redistributed unequally.”
That change in rotation added a microsecond to the course of a day over the 20th century.
The study showed that “glacier melt over the 20th century would have increased the duration of a day by maybe a millisecond,” said Mitrovica. While small, the change “can tell you something about how things are melting,” he said, and is a striking example of how human activities are altering Earth’s systems.
For the first time, researchers have mathematically detected glacier meltwater’s movement from higher altitudes to the ocean basins in the speed of the Earth’s rotation.
The finding is yet more proof that greenhouse gas emissions are having an enormous impact on the Earth’s climate. “This very subtle effect, Earth’s rotation, is a way to monitor how much ice sheets are melting and adds to how we are monitoring sea level rise,” Mitrovica said.
“And more important, it shows that even these very subtle effects support the scientific consensus that we’re affecting the climate, and that effect is accelerating,” he added.
In the study, Mitrovica and his colleagues updated and corrected how scientists calculate the known impacts on the Earth’s spin and axis resulting from the end of the last ice age. In the process, they may have solved a 13-year-old conundrum in earth science called “Munk’s enigma,” which asked why the influx of water from melting glaciers wasn’t apparent in measurements of the Earth’s rotation.
“It is an important additional tool in understanding the mass balance of ice sheets, and we need as many of those as we can get,” Mitrovica said.
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