Earthrise
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Hi, I'm Bryan Yeaton and this is the Weather Notebook. Sometimes, the moon is nothing more than a thin crescent above the setting sun. And if you look closely on a clear night, you might see the rest of the moon there,--but just barely.

What looks like a shadowy circle is actually a sign of sunlight bouncing off our own planet and then reflecting off the moon. It's called "earthrise," and scientists say it may tell us something about global climate change.

For the past three years, researchers at the Big Bear Solar Observatory, high above Los Angeles has been taking regular measurements of earthrise using a digital camera and a six-inch telescope. They can only measure earthrise on a few days each month--just before and just after a new moon. That's when sunlight is reflected from earth to the dark side of the moon, making it ever so slightly visible.

These scientists have learned a thing or two from this study, including some clues about global warming.

They've found that there's a little blip of extra earthrise when Asia rotates to face the moon, because that giant continent reflects more sunlight than the Pacific Ocean does. All in all, the earth reflects about 30% of the sunshine we get. But that number's changing. When these scientists looked back at some early readings from the mid-nineties, they found the earth isn't producing as much earthrise as it did just six years ago. That difference might be due to the solar cycle, or even to El Niño and its effect on clouds. But it could be a sign that the earth is holding on to more solar energy—and that would be further evidence that our planet is warming up.

Thanks today to writer Bob Henson of Boulder Colorado. The Weather Notebook is a production of the Mt. Washington Observatory and supported by Subaru.