Three cheers for those who planted trees or paid for the planting of trees. Hooray for people who take the time to recycle their paper products. Hallelujah for smart, effective environmental policies.

A new study from the National Academy of Sciences [1] tells us that reforestation — which can help counteract global warming [1] — is happening in several countries. Forests soak up carbon dioxide, reducing the greenhouse gases [1] that lead to climate change.

It didn't surprise scientists that forests had grown larger in prosperous parts of the world, such as North America and Western Europe. But it did surprise (and thrill) them to see regrowth in China, India, Turkey, and other countries that have established environmental policies.

Unfortunately, some of the world's largest forests — such as the tropical rain forests in Brazil and Indonesia — are still threatened. Along with global warming, experts fear the loss of biodiversity and the extinction of many species.

Twenty years ago, experts believed that deforestation was an irreversible problem and envisioned a scenario where the greatest forests on our planet [1] would be denuded, which would turn the earth into (as one scientist put it) a "skinhead."

I first heard the good news on a Science Friday podcast [2]. The same day that someone dropped a big, fat phone book to my front porch. Thanks to wifi, I no longer use a phone book, so it's still sitting outside my door till I find a place to recycle it.

Since much of the world is being re-greened, I have to admit that I'm now tempted to toss it in the trash. But, I'll hang onto it until the phone book recycling truck shows up at my grocery store. After all, it feels good that we're gaining ground.

But I can't vouch my actions once the tropical forests in the Amazon [2] start to bounce back.