We identified not one but three sets of processes that are crucial -- and melting of the global cryosphere especially Greenland over the course of the 20 th century is one of them.
In general, the redistribution of mass on and within Earth -- like changes to land, ice sheets, oceans and mantle flow -- affects the planet's rotation. As temperatures increased throughout the 20 th century, Greenland's ice mass decreased. In fact, a total of about 7, gigatons -- the weight of more than 20 million Empire State Buildings -- of Greenland's ice melted into the ocean during this time period.
This makes Greenland one of the top contributors of mass being transferred to the oceans, causing sea level to rise and, consequently, a drift in Earth's spin axis.
While ice melt is occurring in other places like Antarctica , Greenland's location makes it a more significant contributor to polar motion. Previous studies identified glacial rebound as the key contributor to long-term polar motion. And what is glacial rebound? During the last ice age, heavy glaciers depressed Earth's surface much like a mattress depresses when you sit on it. As that ice melts, or is removed, the land slowly rises back to its original position. Groundwater is stored under land but, once pumped up for drinking or agriculture, most eventually flows to sea, redistributing its weight around the world.
In the past 50 years, humanity has removed 18tn tonnes of water from deep underground reservoirs without it being replaced. Some scientists argue that the scale of this impact means a new geological epoch — the Anthropocene — needs to be declared. Since the midth century, there has been a marked acceleration of carbon dioxide emissions and sea level rise, the destruction of wildlife and the transformation of land by farming, deforestation and development.
Or it could be a star with the mass of a thousand suns. In either case, an object's axis runs through its center of mass , or barycenter. An object's center of mass is a point where an outside force acting on the object acts as if the object were located at just that point—where the object appears "balanced.
Ocean tide s shift the center of mass, although not enough to radically shift the planet's axis. Each planet in our solar system rotates on its axis.
So, each planet has a North and South Pole , the points where an axis meets the planet's surface. The time it takes for a planet or other celestial object to complete one spin around its axis is called its rotation period.
Earth's rotation period is about 24 hours, or one day. Axial Tilt Some planets, such as Mercury, Venus, and Jupiter, have axes that are almost completely perpendicular , or straight up-and-down. Earth's axis is not perpendicular. It has an axial tilt , or obliquity. Axial tilt is the angle between the planet's rotational axis and its orbital axis.
A planet's orbital axis is perpendicular to to the ecliptic or orbital plane , the thin disk surrounding the sun and extending to the edge of the solar system. Earth's axial tilt also known as the obliquity of the ecliptic is about Due to this axial tilt, the sun shines on different latitude s at different angles throughout the year. This causes the season s.
Uranus has the largest axial tilt in the solar system. Its axis is tilted about 98 degrees, so its north pole is nearly on its equator. Astronomer s suspect that this extreme tilt was caused by a collision with an Earth-sized planet billions of years ago, soon after Uranus formed.
Axial Precession Earth's axis appears stable, but it actually wobbles very slowly, like a spinning top. It takes Earth's axis about 26, years to complete a circular "wobble. Currently, for instance, Earth's axis points toward a star called Polaris. Polaris, which gets its name because it is almost directly above the North Pole, is the current North Star. Polaris will not always be the North Star, however.
The Earth's axis is slowly wobbling away from Polaris. In another 13, years, it will point toward the new North Star, a star called Vega.
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