Earth Has "Spare Tire"—And Ice Melt's Keeping It That Way

Earth isn't losing its "spare tire" as fast as it should be, according to new research—and it's definitely not because the planet's not getting enough water.

Researchers have long known that Earth isn't a perfect sphere. Rotational forces cause the planet to bulge at its waistline. A person standing at the North Pole, for example, is about 13 miles (21 kilometers) closer to the center of Earth than someone at the Equator.

That difference has been shrinking, at least over the long term. Ever since scientists have been measuring the equatorial bulge, it's been retracting at a rate of seven millimeters (about a quarter of an inch) a decade—part of a long rebounding from the Ice Age, which lasted from about 2.6 million to 11,700 years ago.

During the Ice Age, "all that ice is sitting there, and it's sitting there for tens of thousands of years," study co-author John Wahr said. At the Poles, "it pushes down on the Earth, and the Earth sinks down underneath it."

The extra Ice Age weight even squished Earth's malleable mantle outward, further enlarging the planet's bulge.

Once the Ice Age ice melted, though, the Poles began to slowly spring back, and they've been doing so ever since.

But now "there's something else going on that offsets [the bulge's shrinkage]," said Wahr, a geophysicist at the University of Colorado.

Straight to the Waistline

Beginning in the 1990s, the post-Ice Age rebound began to slow and now appears to have stopped, according to the new study, which relied on data from the twin Gravity Recovery and Climate Experiment (GRACE) satellites. GRACE takes ultra-precise readings of Earth's gravitational field, allowing for researchers to gauge, for example, changes in ice mass and the amount of water in the ocean.

The culprit? "It looks like that is Greenland and Antarctica losing mass," Wahr said.

According to Wahr and his collaborator Steve Nerem, the two regions are losing a combined 382 billion tons of ice a year.
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The Original Car Fuel

Biofuels have been around as long as cars have. At the start of the 20th century, Henry Ford planned to fuel his Model Ts with ethanol, and early diesel engines were shown to run on peanut oil.

But discoveries of huge petroleum deposits kept gasoline and diesel cheap for decades, and biofuels were largely forgotten. However, with the recent rise in oil prices, along with growing concern about global warming caused by carbon dioxide emissions, biofuels have been regaining popularity.

Gasoline and diesel are actually ancient biofuels. But they are known as fossil fuels because they are made from decomposed plants and animals that have been buried in the ground for millions of years. Biofuels are similar, except that they're made from plants grown today.

Much of the gasoline in the United States is blended with a biofuel—ethanol. This is the same stuff as in alcoholic drinks, except that it's made from corn that has been heavily processed. There are various ways of making biofuels, but they generally use chemical reactions, fermentation, and heat to break down the starches, sugars, and other molecules in plants. The leftover products are then refined to produce a fuel that cars can use.

Countries around the world are using various kinds of biofuels. For decades, Brazil has turned sugarcane into ethanol, and some cars there can run on pure ethanol rather than as additive to fossil fuels. And biodiesel—a diesel-like fuel commonly made from palm oil—is generally available in Europe.

On the face of it, biofuels look like a great solution. Cars are a major source of atmospheric carbon dioxide, the main greenhouse gas that causes global warming. But since plants absorb carbon dioxide as they grow, crops grown for biofuels should suck up about as much carbon dioxide as comes out of the tailpipes of cars that burn these fuels. And unlike underground oil reserves, biofuels are a renewable resource since we can always grow more crops to turn into fuel.
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