VOA慢速英语2019--磁极的移动速度比科学家预想的快（在线收听）

Magnetic North Pole Moving Faster Than Scientists Expected

Earth’s north magnetic pole is moving, researchers say.

It has moved so much, so quickly that a group of scientists hurried to change a model that helps guide shipping, airplanes and submarines in the Arctic Ocean.

Last week, the scientists released new information on the north magnetic pole sooner than they had planned.

Compass needles point toward the pole. As a child, you might have received a simple compass as a gift. It has a magnetized pointer which shows the direction of magnetic north.

Liquid metal at the center of our planet produces the magnetic field. Unpredictable movements in the liquid mean the field and the location of magnetic north are always changing.

The World Magnetic Model records those changes. The model is a joint product of the British Geological Survey and the United States National Oceanic and Atmospheric Administration.

The two agencies were planning to report changes in the magnetic north pole, as they do every five years, at the end of 2019. But the pole has moved so quickly they had to release the information much sooner.

Scientists have found that the magnetic north pole is moving at a speed of about 55 kilometers every year. One hundred years ago, the pole was located near the coast of northern Canada. It crossed the International Date Line, the imaginary line running through the Pacific Ocean from the North Pole to the South Pole, in 2017.

Now, the magnetic north pole is in the middle of the Arctic Ocean and moving towards Russia.

Arnaud Chulliat is a scientist at the University of Colorado in Boulder, Colorado. He is also the lead researcher for the newly updated World Magnetic Model. Chulliat told the Associated Press the continuous movement of magnetic north is a problem for compasses in smartphones and other electronic devices.

Importance to navigation systems

Airplanes and boats mainly use Global Positioning System (GPS) instruments for navigation. GPS is not affected by the movements of the pole because it is satellite-based. But airplanes and boats do depend on magnetic north in emergencies, Chulliat noted.

The U.S. military needs to know the location of magnetic north for navigation and parachute drops. The American space agency NASA, the Federal Aviation Administration and U.S. Forest Service also use it.

Names for some airport landing areas are based on their direction toward magnetic north, and the names change when the pole moves. For example, an airport in Fairbanks, Alaska, renamed landing area 1L-19R to 2L-20R in 2009.

“The fact that the pole is going fast makes this region more prone to large errors,” Chulliat told Nature magazine.

Ciaran Beggan is with the British Geological Survey. He told the Reuters news agency the magnetic North Pole “didn’t move much between 1900 and 1980, but it’s really accelerated in the past 40 years.”

Since 1831, when the pole was first measured in the Canadian Arctic, it has moved about 2,300 kilometers toward Siberia. The speed of its movement has increased from about 15 kilometers a year to 55 kilometers per year since 2000.

The reason is movements in Earth’s liquid outer core, said University of Maryland geophysicist Daniel Lathrop. He was not part of the research team.

There is a hot liquid ocean of iron and nickel in the planet’s core, where the movement produces an electric field. Lathrop said the changes in movement of the liquid are similar to changes in the weather.

Possible reversal of Earth’s North and South Poles

Earth’s magnetic South Pole is moving far slower than the north.

In general, Earth’s magnetic field is getting weaker, leading scientists to say that it will eventually cause the north and south poles to change positions. Such a change has happened several times before, but not in the last 780,000 years.

“It’s not a question of if it’s going to reverse, the question is when it’s going to reverse,” Lathrop said.

The reversal will take 1,000 years or more to come into effect, experts said.

But Lathrop sees a reversal coming sooner, not later, because of the weakened magnetic field. An area over the South Atlantic has already reversed beneath Earth’s surface.

That could cause problems for birds that use magnetic fields to navigate. And a general weakening of the magnetic field is not good for people, especially astronauts. The magnetic field protects Earth from dangerous radiation, Lathrop noted.

Ciaran Beggan said the recent movements of the north magnetic pole would be unnoticed by most people outside the Arctic.

Navigation systems in cars or phones depend on radio waves from satellites high above the Earth to identify their position on the ground.

“It wouldn’t really affect anyone driving a car,” Beggan added.

I’m Pete Musto.

And I’m Anna Matteo.

Words in This Story

pole – n. either end of the imaginary line around which something, such as the earth, turns

compass – n. a device that is used to find direction by means of a needle that always points north

location – n. a place or position

navigation – n. the act, activity, or process of finding the way to get to a place when you are traveling in a ship, airplane or car

region – n. a part of a country or of the world that is different or separate from other parts in some way

prone – adj. likely to do, have, or suffer from something

accelerate(d) – v. to gain speed

core – n. the central part of something

reverse – v. to change something to an opposite state or condition