Mountains, Whitecaps Change Weather Models

"It turns out now that there's an eight-million-year accumulation of sediments and the base date is thought to be when you started having central Asian aridity," he says.

In other words, the deserts started to form just when the mountains began to grow even higher, and those two events had to have been related.

"That's where the modeling comes in," Kutzbach says. "If you have the geologic dates, you sort of know when the mountains formed and you know when the sands started accumulating. Can you connect these two things?"

So they fed the data into their computer model to see what would have happened if the mountains had grown taller eight million years ago.

"If you take a small plateau, and turn it into a big plateau, then you do get stronger monsoons in the south and greater aridity in the north," according to the model, he says. And that's exactly what has happened.

Clues to an Ice Age?

In addition, the winds whistling down the northern slopes of the mountains can be so fierce that they pick up dust from the deserts and carry it around the world. And that, the scientists argue, could mean that dust stirred up by the Himalayan winds could have added so many sun-blocking particulates to the Earth's atmosphere that the air grew cooler, contributing to the beginning of the ice age.

That's far from conclusive, they admit, but it fits neatly with the other part of this complicated story. Anything that reflects solar radiation back into space is bound to have some impact on the Earth's weather system.

Scientists at Scripps Institution of Oceanography at the University of California, San Diego, decided to take a closer look at whitecaps to see just how much impact they might have on weather. Whitecaps, because they are white, reflect sunlight, thus keeping it from warming the sea, but that has been ignored by most climate models.

Whitecaps, after all, usually don't last very long, and tend to be regional, so how could they have much impact on the weather?

One of the scientists, Robert Frouin, had previously found that whitecaps reflect more energy than had been thought, so the team decided to find out just how much. Using satellite data and other measurements, they found that in some cases the effect can be quite significant.

Whitecaps on the Indian Ocean, which is constantly stirred by winds caused by the Himalayas, reflect several times more solar radiation than most areas, they found.

It is a significant finding, the researchers contend, because it indicates that changing events can have an accumulative effect on overall weather patterns. If global climate change causes more wind in some areas, for example, it would increase whitecaps, which in turn would lower temperatures, and that could contribute to dramatic changes in the weather.

The researchers site the Arabian Sea, noted for its cloudless skies and great wind speed, "two important factors in increasing the role of whitecaps."

But the overall effect, the scientists conclude, is very difficult to determine.

"Many competing effects and feed-backs may be involved, and are difficult to untangle," says Frouin.

Like most of us, he sounds a bit bewildered by a global weather system that is so complex it's almost impossible to predict.

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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