Mountains, Whitecaps Change Weather Models

What do the tallest mountains in the world have in common with whitecaps on a roiling sea?

Both, it turns out, have a far greater impact on global weather patterns than had been thought.

Two separate international teams of scientists have come up with evidence showing the majestic Himalayan Mountains can influence weather all over the Earth, and whitecaps on a wind-blown sea can reflect so much solar energy back into space that the entire climate system is altered.

Himalayas Contributed to Dust Storms

Scientists have known for a long time that the Himalayas have a dramatic impact on local weather patterns in Asia, but the latest research shows the impact is global in scale, and may even have precipitated the beginning of the ice age 2.5 million years ago.

And whitecaps have generally been left out of most computer models for global climate, because their effect was thought to be minimal, but the latest research will probably force scientists to remodel their models.

What it all adds up to is this: The Earth's climate is so complex, and subject to such wide reaching influences, that it's nearly impossible to comprehend it. Little wonder that meteorologists have trouble predicting the next day's weather, not to mention the long range impact of burning fossil fuel.

The Himalayas, it turns out, contributed to storms that carried dust from China and Mongolia's Gobi Desert to the United States last month, as I reported in a recent column. Even more important, that desert wouldn't even be there if it weren't for the mountains to the south.

That story is, quite literally, written in the sands of the desert, according to climatologist John E. Kutzbach of the University of Wisconsin-Madison, who returned to China this week to resume his research. Kutzbach, a member of an international research team, has been arguing for more than a decade now that the uplifting of mountain ranges has a profound impact on weather, and now, he says, he has the data to prove it.

The scientists collected ancient dust deposits in China, and deep ocean sediments from the North Pacific and Indian Oceans, to reconstruct the story of the Himalayas over the past eight million years.

The mighty range, which includes the world's tallest mountains and the Tibetan Plateau, actually began to form more than 50 million years ago when the tectonic plate that carried India crashed into Asia. The two huge land masses ground together, causing giant chunks of Earth to be thrust upward, giving rise to the Himalayas.

Digging in the Desert

Mountain building is a slow process, marked by occasional earthquakes, but about eight million years ago the Himalayas went through a dramatic growth process, according to geologists who have studied the region.

According to computer-driven models developed by Kutzbach, the growth of the mountains should have had two dramatic effects. "The Himalayas and the Tibetan Plateau form a barrier for moisture getting into the interior [of Asia,]" Kutzbach says. Just as the Rockies and the Sierras trap moisture on the seaward side of western North America, the Himalayas cause torrential rains to fall on the southern and eastern side of the plateau.

That heavy rainfall comes at the expense of inland regions and Kutzbach and his colleagues suspected that the relatively sudden growth of the Himalayas eight million years ago caused the deserts of Mongolia and interior China to form.

So they went to the deserts and dug deep into the sand.

"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.