Drought Stirs Storm of Theories on Its Origins : Lack of Volcanic Activity, Greenhouse Effect, El Nino All Offered as Cause of Long Dry Spell

Picture a vast river of air 60 miles wide, a mile thick, 10 miles above the ground and moving at speeds as high as 200 m.p.h. Normally in the spring and summer, this river called the jet stream crashes across the northern Rockies and sweeps eastward through the Great Plains, bringing storms from the Pacific Ocean and drawing up other storms from as far away as the Gulf of Mexico to quench the thirsty agricultural fields of the Midwest.

But not this year.

This spring, for reasons that still have scientists mystified, the jet stream split into two parts--one swooping as far north as Hudson Bay, one veering along the southern border of the United States--before rejoining far out over the Atlantic.

These two branches trapped a massive high-pressure ridge over the central United States, locking out cooling storms and producing the heat wave and drought that have devastated America’s heartland.

And despite the temporary respite resulting from a Pacific storm that forced its way through the high-pressure ridge at the end of June, weather forecasters say the jet stream has not significantly altered its position and the drought could continue for another month or more.

“We don’t know why it’s splitting like that, and we don’t know why it is staying so long,” said meteorologist David Miskus of the National Weather Service in Camp Spring, Md. “If we knew why, we’d be millionaires.”

Many researchers are offering partial explanations, however.

Some say the drought is caused by volcanoes--or more specifically the lack of recent volcanic activity. Others say it is a lingering effect of El Nino, a massive body of warm water off the Pacific Coast of South America. Some link it to solar cycles.

A few say the heat and drought are the first stages of the long-predicted “greenhouse” warming caused by the burning of fossil fuels--although virtually all agree that the heat and drought foreshadow what conditions will be like when greenhouse warming does arrive.

There seems little doubt that temperatures this year will set a record. Climatologist James E. Hansen of the NASA Goddard Institute for Space Studies in New York City last month told a Senate committee that the first five months of the year were “so warm globally that we conclude that 1988 will be the warmest year on record unless there is a remarkable, improbable cooling in the remainder of the year.”

Most scientists agree that Earth is slowly warming, with global temperatures having risen by as much as 1.25 degrees Fahrenheit since the mid-1800s and with the four hottest years in history having occurred in the 1980s. Hansen caught the attention of the world when he said he was 99% certain that greenhouse warming has already begun.

But the greenhouse effect is a broad brush that paints only the wide background of climate. The finer details, such as droughts in the U.S. heartland and monsoons in India, must be superimposed, painted in by transient localized conditions. As physicist Paul Handler of the University of Illinois in Champaign-Urbana asked: “If the greenhouse effect is here this year, why wasn’t it there last year? Nineteen eighty-seven was a very warm year globally, but it didn’t produce any droughts in the U.S.”

Most researchers say the current drought is simply part of normal climate variability produced by volcanoes and El Ninos as well as other factors.

‘Every Year Is Abnormal’

“Normal climate is a 30-year average,” said atmospheric scientist Michael E. Schlesinger of Oregon State University. “It’s like saying the normal family has an average of 2.2 children. No family has 2.2 children, so every family is abnormal and, in the same way, every year is abnormal.”

Handler thinks this summer’s drought is caused by a lack of volcanic activity near Earth’s Equator. In fact, he predicted the drought last fall--apparently the only researcher to do so publicly. The University of Illinois, in a press release, circulated the prediction at the time.

Volcanic eruptions spew sulfur dioxide gas into the stratosphere, the upper layer of Earth’s atmosphere. In the presence of sunlight, the sulfur dioxide is converted into sulfuric acid, which condenses with water to form extremely small particles called aerosols.

These aerosols are rained out of the stratosphere over a period of two to five years. But while they are there, they absorb a small fraction of the sunlight striking Earth and prevent it from reaching the ground.

If the volcano is in the mid-latitudes, from about 25 degrees north of the Equator to 25 degrees south, one effect--through a complicated mechanism--will be a slight cooling and increased rainfall in the central United States.

But if there is no aerosol, the sun’s full radiation warms the equatorial belt and the land heats up faster than the ocean. The cooler water offshore, Handler said, would stabilize high-pressure ridges such as that now over the central United States.

“If you go back to the year 1866, when the U.S. Department of Agriculture first started keeping records of corn yields,” Handler said, “one can show that whenever there was low-latitude stratospheric aerosol, the corn yield in the states of Indiana, Illinois and Iowa was always above average.

“There was very little stratospheric aerosol during the 1930s. The stratosphere was just very, very clear, and that may be a possible explanation of why there was a drought then. The same was true during the 1950s.”

The April, 1982, eruption of El Chichon volcano, about 400 miles south of Mexico City, was followed by unusually good corn yields in the United States, Handler said. But now, he added, virtually all the aerosol from that eruption is gone and subsequent eruptions in the mid-latitudes have not been strong enough to add any, allowing sunlight to shine through with its full intensity and create the drought.

Handler noted that weather conditions in West Africa and India are even more sensitive to the effects of volcanoes and that volcanic eruptions are a particularly good tool for predicting the severity of monsoons in India.

Researchers in Australia and the United Kingdom have concurred with Handler’s theory, but his work is not widely accepted in the United States. “I’m pretty much sitting out here all alone,” he said.

One researcher who does support him is climatologist Reid Bryson of the University of Wisconsin at Madison, who compared the current drought to that of the 1930s. “If we want to find a cause of this drought,” he said, “we should find a cause common to both of them. About the only common denominator I can see is that both droughts occurred during periods of very low volcanic activity.”

Another who agrees is marine geologist Gerald Kuhn of the Scripps Institution of Oceanography in La Jolla. Kuhn noted that all major volcanic eruptions in the mid-latitudes have been followed immediately by cool and wet periods in the central United States and then by droughts.

Other researchers, however, consider Handler’s results “too qualitative” and unproven.

“When you are dealing with slow-moving events such as droughts and monsoons, you often get the appearance of relationships . . . but that doesn’t mean causality,” cautioned climatologist Nicholas E. Graham of Scripps.

But Graham was impressed with Handler’s prediction of the drought. “He has a real coup there,” he said.

Graham is one of a growing number of scientists who have been studying the link between climate and El Nino, a recurring event whose name--a reference to the Christ Child--was coined by Spanish fisherman because the phenomenon typically begins around Christmas. Because the phenomenon also involves changes in atmospheric pressure over the Pacific and Indian oceans, scientists often refer to it as the El Nino-Southern Oscillation, or ENSO.

Meteorologist Jerome Namias of Scripps believes that ENSO is linked to the current drought through a convoluted chain of events that, he concedes, would be virtually impossible to prove.

The link is that the 1986-87 ENSO event may have helped establish large bodies of cooler-than-normal water in the Pacific and Atlantic oceans. These, in turn, may have a role in maintaining “troughs” of stormy low-pressure air off both coasts that are helping to lock dry air into place over the central United States.

“We don’t understand how those cold bodies would maintain these troughs, but the fact that they are sitting there now and are . . . cold enough would give one a strong feeling that there is a connection there to be made,” said Bill Holland, head of the oceanography section at the National Center for Atmospheric Research in Boulder, Colo.

Others were skeptical about such a connection between ENSO and the drought but conceded the possibility that it could exist.

The “teleconnection” between ocean-atmosphere events in the Pacific--the ocean that most influences the world’s weather--and weather thousands of miles away would go like this:

Two-and-a-half years ago, warm surface water began traveling westward along the Equator in the Pacific Ocean--the classical ENSO phenomenon. In 1982-83, a similar, but much stronger, event had devastated fisheries off the U.S. Pacific coast.

Lasted Longer Than Expected

Although the 1986-87 ENSO was weaker than the 1982-1983 version, it lasted much longer than most scientists had expected. It also was unusual in that it left behind a huge pool of cooler-than-normal surface water in the northern Pacific.

With temperatures as much as 5 degrees Fahrenheit below normal, the cool water stretched from the Pacific Coast to Japan and from Vancouver Island to Baja California last summer and fall. Today, the water has drifted slightly northward and warmed a bit, but it remains more than one degree below normal.

Last fall, some meteorologists suggested that this cool water was the key factor in a weather pattern that made the fall and winter unusually dry in the Pacific Northwest and cut snowfalls in the Cascade Range and the Sierra Nevada. Instead of looping farther southward, the jet stream stayed stuck in its summer position well into the fall.

The pattern not only kept the West Coast dry but also dumped snow in the East earlier than usual, in early November.

These early storms and others later would have funneled cold air off the East Coast and cooled down the Atlantic along the East Coast--where, indeed, an unusual body of water about one degree cooler than normal has been building since last fall.

It is this body of cool water and the cool water in the Pacific that might--and climate researchers emphasize that it is only speculation--be strengthening the low-pressure systems that are helping to keep the ridge of dry, high-pressure air stuck over the central United States.

That meteorological sandwich of a high-pressure ridge between near-shore low-pressure systems is the classic pattern seen during the 1930s droughts, Namias said. But, he noted, those droughts did not closely follow ENSO events.

Researchers have been less successful in trying to connect the drought to sunspots or solar cycles. Dendrochronologist (a scientist who dates events by studying tree rings) Charles Stockton of the University of Arizona has found recurring cycles of drought in various areas of the United States, including the Midwest, that operate on 22-year cycles--twice the 11-year period for ebbing and waning of sunspots.

Connection to Sunspots

But the connection to sunspots has been exceptionally difficult to document. Furthermore, noted meteorologist Michael Smith of WeatherData Inc., in Wichita, Kan., the next dry period from that cycle should occur in the 1990s, so the current drought “is not associated with that.”

Smith, like many others, argues that the current drought is linked to normal variability of the weather. “Mother Nature generally doesn’t let us have too many wet years in a row or too many dry years in a row. The weather in the Midwest has been pretty good for a couple of years . . . so we are more or less overdue for a dry period.”

And how long will the drought last? Only Handler is willing to make a prediction: If there is not a volcanic eruption near the Equator, he said, next summer will be just like this one.