Burning coal for energy adds planet-warming carbon dioxide(CO2) to Earth's atmosphere. As the planet heats up, experts warn that simply cutting greenhouse gas emissions（排放） will not be enough to avoid global warming. CO2 must also be remcved from the atmosphere.

Existing experimental machines that pull CO2 directly from the air are too expensive to be widely used. But a new effective technology to remove CO₂ already exists. It is not expensive and easy. It is forests. Planting trees and watching forests are effective ways to clean the air.

Forests used to cover large areas of the Appalachian Mountains in the eastern United States. In the state of West Virginia, coal mining left the land there bare, without trees. Over the years, coal mining and cutting forests took over 90 percent of the red spruce（云杉） forests.

Chris Barton works for the University of Kentucky. He started a group called Green Forests Work, aiming to put trees back on the roughly 400 , 000 hectares of land.

However, Barton explains the land has problems. "If you planted trees on these places, they just didn't grow. The ground was too hard. Water didn't infiltrate（渗透）. The trees can't root. Oxygen can't circulate in those environments. "Using heavy equipment, workers tear the ground. In this way, the trees put down roots.

Barton says not everyone believes the solution is a good idea. "We've had a lot of doubtful look at us twice from people. But after we do it, there's no question that it was the right thing to do. "And it has worked. Forests are coming back to the grounds.

Scientists say that, in West Virginia alone, restoring red spruce forests to the area could send what is equal to 56 million barrels（桶）of oil into the ground. But it will take time—a long time. Around the world, experts say, nature offers powerful tools to fight climate change. But patience is needed. Nature works, but slowly, in its own time.

As the economic crisis goes worse, some reader are turning to bookstores for advice on how to manage their own finances. Below are the top-ten selling books in both categories for the week ended Oct.18 at Barnes & Noble Inc., the country’s largest book retailer (零售商). Here readers are buying books whose titles feature such words as “failed”, “crisis” and “danger”.

1. The total Money Makeover by Dave Ramsey. A primer on how to cut debt, save money and create a financial strategy.

2. Debt Cures ‘They’ Don’t Want You to Know About by Kevin Trudeau. A look into the dangers of credit card spending and how to reduce your expenses.

3. Women & Money: Owning the Power to Control Your Destiny by Suze Orman, Ms. Orman writes about how women can gain better control of their finances by better understanding their relationship with money.

4. The Money Book for the Young, Fabulous & Broke by Suze Orman. A book on what the young need to know now about money management.

5. The Smart Cookies’ Gude to Making More Dough by the Smart Cookies with Jennifer Barrett. The book’s advice: Take charge and get out of debt.

6. The Forgotten Man: A New History of the Great Depression by Amity Shlaes. A look at what happened during that other crisis.

7. The Partnership: The Making of Goldman Sachs by Charles D. Ellis. An inside look at the famed investment-banking firm.

8. “Bad Money: Reckless Finance, Failed Politics, and the Global Crisis of American Capitalism by Kevin Phillips. Mr. Phillips documents the unreaveling of the U.S. economy.

9. The New Paradigm for Financial Markets: The Credit Crisis of 2008 and What It Means by George Soros. An analysis of the issue behind the crisis and their implications.

10. The World is Cured: Hidden Dangers to the Global Economy by David M. Smick. An inside look at what went wrong with the banking system here and abroad.

Across the world, more and more people are volunteering online. What encourages them to help strangers without expectation of money or even thanks?

Radha Taralekar helped teach Imelda how to protect herself from HIV, though the two have never met, and neither knows the other’s name. Taralekar received no payment for the job. She is one of a number of talented people who regularly donate their time online. But what is driving them to help total strangers, while asking for nothing in return? For Taralekar, the project gave her the chance to us her professional experience. “I want to serve people with my medical knowledge,” she says.

For some, the inspiration to volunteer online was far more personal. After losing his wife to cancer, Tony Selman spent many hours online helping Cancer Research to collect data on the disease. “Seeing how painful she was when my wife was dying, I determined to help scientists find a cure for cancer,” he says.

Interests and hobbies are also one of the factors (因素). In 2011 Sam Luk, a designer, joined other online volunteers to try to help the police solve a murder case. The police posted them online, calling for volunteers to help them make sense of the messages. “I’m interested in patterns and I love Sherlock Holmes,” says Luk.

For writer Clay Shirky, some large online volunteering projects benefit millions of people, giving him a sense of achievement. He helps write Wikipedia, the world’s biggest encyclopedia (百科全书), which is written entirely by people willing to donate their professional knowledge without any reward.