Ask AP: Global warming and the Earth's rotation

That's one of the mysteries solved in this edition of "Ask AP," a weekly Q&A column where AP journalists respond to readers' questions about the news.

If you have your own news-related question that you'd like to see answered by an AP reporter or editor, send it to newsquestions@ap.org, with "Ask AP" in the subject line. And please include your full name and hometown so they can be published with your question.

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What oil companies, if any, do not import oil? I would buy from them alone if I knew who they were.

Sue Copeland

Kilgore, Texas

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You'd be hard-pressed to find an oil company involved in refining that doesn't import oil.

The bottom line is they don't produce enough oil on their own to run their refineries and produce gasoline, diesel and other products. According to the Energy Information Administration, which keeps energy statistics for the federal government, less than 40 percent of the crude oil used by U.S. refineries was produced in the United States.

John Porretto

AP Business Writer, Houston

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As we know, the ice in the polar caps is melting, changing into water. Ice is lighter than water. This ice, at the top and bottom of the globe, is spreading around the globe as water, causing sea levels to rise.

So the question is: Will this change in the location of all this water affect either the tilt of the Earth on it axis, or the Earth's path around the sun?

Richard Driscoll

Winnsboro, S.C.

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As the polar ice melts and sea level rises, it will slightly affect the rotation of the Earth, but not our path around the sun. But even in the scenario of a major, rapid polar ice melt, the effects of the changes in rotation and tilt would barely be noticeable -especially compared to the effects of the accompanying sea rise.

As the ice melts, the water indeed redistributes elsewhere around the globe, essentially giving the Earth a bit more of a bulge near the middle. Just as an ice skater with her arms extended slows down, a bulgier Earth spins slower.

Not that you'd notice it. The daily rate of slowdown is about 76 one-millionths of one second for every inch of sea level rise, according to calculations by physicist Jerry X. Mitrovica, director of the University of Toronto's Earth Systems Evolution Program.

Since 1993, sea level has risen at rate of about one inch every eight years, but scientists fear that will speed up. If the ice sheets in Greenland and West Antarctica melt, the sea level could rise by 33 to 39 feet -something that could take anywhere from several decades to several centuries to happen.

That would cause a slowdown in the Earth's rotation of about one thirtieth of a second a day, which translates into about one second a month, 12 seconds a year, or about two minutes every decade.

That's on top of the thicker level of carbon dioxide in the atmosphere that a 2002 study found slows the Earth down by about 1.7 millionths of a second a year.

And because of various physics and ice dynamics, the location of the axis around which the Earth spins would also change slightly with Greenland's melt, Mitrovica said. To put it another way, both the North Pole and the South Pole -the two ends of that rotational axis -would end up in a slightly different place.

Scientists aren't worried about what the relocated axis or the slowing of the Earth would do, but they regularly monitor those changes as indicators of the greater and more dangerous effects of global warming. Putting it another way: They say don't worry about the longer day -worry about the rising seas that cause the longer day.

Seth Borenstein

AP Science Writer, Washington

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An e-mail request for data from the Federal Bureau of Labor Statistics shows that more people are employed now than at any prior time in our nation's history. So why have so many recent news stories about the economy talked about "strains in the labor market" and described employment conditions as "weak"?

Don DeVan

Knoxville, Tenn.

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Economists look at a variety of barometers to judge the health of the nation's labor market, which Federal Reserve Chairman Ben Bernanke and his colleagues have described as "softened."

Employers have cut jobs for four months in a row, wages, when adjusted for inflation, have fallen over the past year, workers' hours have been trimmed, the number of part-time workers has gone up sharply and the number of unemployed people is higher now than a year ago. The unemployment rate is now at 5 percent, up from 4.5 percent a year earlier.

The statistical survey used to calculate the unemployment rate showed the number of people employed stood at 146.3 million in April, the second-highest level on record, said Gary Steinberg, a spokesman for the Labor Department's Bureau of Labor Statistics. However, that high number has a lot to do with the growing U.S. population.

Because of population growth, the number of employed people needs to grow by about 125,000 a month for employment to remain stable.

Jeannine Aversa

AP Economics Writer, Washington

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Have questions of your own? Send them to newsquestions@ap.org.