Moon's Dark Side Gives Climate Hints

"We have found surprisingly large — up to 20 percent — seasonal variations in Earth’s reflectance," says Philip R. Goode, leader of the New Jersey team and director of the Big Bear Solar Observatory. Everyone expected some seasonal variation, because the amount of ice, snow and cloud cover changes with the seasons, but Koonin says the variation was four or five times larger than had been expected.

"That is a bit of a mystery right now that we want to understand," Koonin says.

But that’s only the tip of the iceberg, so to speak. The data also reveals what Goode calls a "hint" of a 2.5 percent decrease in the Earth’s albedo over the past five years.

The researchers are a little cautious on this point, because their equipment is not quite precise enough to be definitive, but Koonin points out that if the decrease is only one percent, that’s a major change.

In fact, it’s too much of a change to be the result of greenhouse warming.

It would take all of the greenhouse gases released since pre-industrial times to push the Earth’s albedo down by 2.5 percent, and their data indicates that the drop occurred over just five years.

But What's the Reason?

Clearly, there must be another explanation. The scientists note that the drop occurred during a period when the magnetic activity on the sun that produces sun spots rose from minimum to maximum.

That’s fascinating to solar physicists, because it has long been hypothesized that the sun’s magnetic field plays a role in the Earth’s climate. Nobody has been able to prove that, but now scientists have a new tool.

It would be nice if Earthshine could settle the debate over how much damage we are doing to our planet by burning fossil fuels, but that’s not likely to be the case. The subject is just too complicated for any one approach. Still, it is a "good diagnostic" tool that could help fill in a lot of blanks, Koonin says.

"Greenhouse gases are one perturbation of the climate system, and hence will cause climate change," he says. "In order to assess whether they are significant or not, we need to understand all perturbations of the climate system."

It’s a little like trying to assess your health just by taking your blood pressure, he says. You also need to look at the level of sugar in your blood, your pulse and respiration, as well as other things that can reflect the condition of the entire system.

So toward that end, the scientists are expanding their project into a global network of earthshine telescopes. Each system will cost about $20,000, and three are expected to begin operations in Asia in the coming months.

Together, the telescopes will provide a continual and precise record of the intensity of the light reflected back from the moon, an ongoing measurement of how much solar energy the Earth is keeping to itself.

"It’s really amazing, if you think about it," Koonin says, "that you can look at this ghostly reflection on the moon and measure what Earth’s climate is doing."

Yeah, but if Leonardo were still here, he probably would wonder why it took us so long.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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