The "dominant contributor” is ice loss, primarily from Greenland and Antartica. Recently, using data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, Robert Nere and John Wahr found reduction of the bulge had slowed and recently stopped. This is mostly due to recovery from the last ice age which ended only about 12,000 years ago and the massive ice sheets covering most of the Earth's surface. Scientists have been observing that bulge, noting that it has been reducing at a rate of about one quarter inch each year. This number is used in a variety of calculations to adjust the force of gravity based on latitude as well as determining satellite orbits. Measure these images straight from NOAA weather satellites and you'll come up with ratios very close to the 0.99665 ratio of the equator to the poles. Though look closely at images larger than 5000x5000 pixels and you’ll find it occupies a pixel or more of the image side to side than it does top to bottom. Looking at full disk images produced by weather satellites or NASA missions, the Earth looks quite round. The greater the rotational force and the more fluid the planet (including its atmosphere, oceans and body), the more oblate the planet.
Oblateness is caused by rotational forces and the tendency to redistribute the oceans and even the body of the planet itself along the equator. Think of it this way: standing on the equator, you are about 13 miles further from the center of the Earth than someone standing at one of the poles.
The difference in diameters measured at the poles and at the equator is very slight, only about 26 miles. Looking over the conference agenda, they did get one point right: the Earth is not round.Īn oblate spheroid is a sphere slightly squashed at the poles and a bit wider at the equator.
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