A Season in Hell

By Philip Elmer-DeWitt

It was an unpopular week for weathermen. In almost every corner of the country last week, the news was bad and the forecast was for more of the same. In the Midwest -- where the swollen Mississippi continued to turn streets into rivers and fields into lakes -- the floodwaters reached record heights and just kept climbing. In the South and the East -- where the temperature hit triple digits in many cities -- weather reporters were reduced to frying eggs on sidewalks and reprinting lame jokes ("How hot was it?" asked the New York Post. "So hot, Grant's Tomb had the front door open"). Even the breaks in the weather were bad. It snowed (in July!) in Colorado, but the white stuff melted too fast in most places to do skiers much good. In South Carolina, which had been spared the Midwest's drenching downpours, the total rainfall for June was .74 in. instead of the normal 4.8 in., causing millions of dollars in argicultural losses.

But meteorologists have more than just last week to answer for. In March, 20 states from Florida to Maine were briefly paralyzed by an atmospheric oddity that scientists called an extratropical cyclone -- a blizzard with hurricane- strength winds that blanketed parts of North Carolina with 50 in. of snow. In early winter, some Southwest cities got a year's supply of rain in six weeks. A record number of tornadoes (1,381 in all) touched down on U.S. soil last year, as well as the nation's costliest weather disaster, Hurricane Andrew, which destroyed $20 billion worth of property in Florida alone.

Nor is the outrageous weather limited to North America. Hailstones the size of tennis balls last week bombarded France, a country whose precious vacation time has been marred of late by blazing springs, cool summers and snowless ski slopes. Farmers in western Queensland, Australia, are currently suffering through the state's longest and most widespread drought. New Delhi recorded ^ its hottest day in more than 40 years in June; Rome last week had its hottest day of this century. Torrential rains have become so severe in Hong Kong that meteorologists coined a new term -- black rainstorm alert -- to signal their approach. Weather-related losses at Lloyd's of London are staggering. Says underwriter Richard Keeling: "From what we have experienced over the past four or five years, we have either been very unlucky or things are getting worse out there."

What is going on? Scientists have a standard reply to questions like this. It is the nature of weather, they say, for wild fluctuations to occur. Their proof: there is a record broken every day somewhere in the world. But after last week's weather -- which showed every sign of being this week's weather as well -- the standard reply starts to wear a little thin. Why are so many records being set in so many places right now? Could it have anything to do with the holes we've drilled in the ozone layer? The forests we've leveled? The greenhouse gases we've pumped into the atmosphere?

Experts caution against drawing too many conclusions from a few weeks of heat and rain. The conditions that caused this weather pattern in the U.S. are easy to understand and not that extraordinary, says Edward O'Lenic of the National Weather Service. The system's basic engine is the jet stream -- the river of atmospheric air that flows from west to east between banks of cold, dry polar air to the north and wet, tropical air to the south. At this time of the year, the jet stream usually runs in a fairly straight line across the U.S., tracking the Canadian border in the West and passing over the coast of Maine in the East.

In the weather system that locked into place two weeks ago, the jet stream has been diverted by a high-pressure ridge over the Northeast and a wall of cold air planted over Greenland (see map). Result: a giant heat pump that is drawing moisture up from the Gulf of Mexico and dumping it onto the Midwest. Meanwhile, a dome of hot air -- the so-called Bermuda high -- has parked itself over the Eastern seaboard like the top to a pressure cooker, melting city pavements and turning suburbs into saunas.

This in itself is not terribly unusual, especially in July. What made the summer rains in the Midwest so destructive this time is that the region was still feeling the effects of an unusually wet fall and an even wetter spring -- weather events that may have had their origin on the other side of the globe.

The primary suspect is El Nino, a huge pool of warm seawater in the western Pacific that expands eastward every few years toward Ecuador, nudging the jet stream off course and disrupting weather patterns around the world. The El Nino that began two years ago, triggering droughts in Africa and unseasonably warm winters in North America, was supposed to break up last summer. But new satellite pictures show that a second, smaller pool of warm water has joined the first and is likely to extend the effects of the current El Nino. Some scientists believe it was the effects of this one-two El Nino punch, dousing the Midwest with two consecutive seasons of unusually wet weather, that saturated the Mississippi Valley and set it up for this week's devastating floods.

Another suspect is Mount Pinatubo, the giant Philippine volcano that heaved 20 million tons of sulfur dioxide into the stratosphere two years ago and veiled the earth with a global haze. Scientists report that this haze lowered temperatures around the world about 1 degreesF and may have contributed to last year's unusually mild summer. This may have resulted in less evaporation -- and thus wetter ground conditions -- contributing to the Midwest's soggy woes. But the Pinatubo haze is breaking up rapidly now, and most scientists do not think it is a major factor in this week's weather.

No reputable scientist will say that what we are experiencing now is the early effects of global warming -- even if a few privately suspect it to be so. The theory that the buildup of CO2, methane and other heat-trapping gases can raise global temperatures -- like the glass in the walls of a greenhouse -- is well established, but no one knows how much warming will occur or how soon. While early computer models suggested that average global temperatures could jump 3 degreesF to 9 degreesF by the middle of the next century, recent studies have cast doubt on those estimates. Even a small change in average temperatures can trigger big changes in local weather patterns, but there is no evidence that climate changes are to blame for the weather we are suffering through right now.

What makes these influences so hard to sort out is that they interact in complex ways. Some scientists think that any global heating will be eased by the buildup of clouds, which tend to block sunlight. Indeed, a recent study showed an increase in nightly minimum temperatures over the past decade but little increase in daily maximums -- precisely what you would expect if clouds were cooling the earth by day (by blocking sunlight) and warming the earth at night (by trapping heat).

The latest twist in the global-warming equation involves the effects of the tiny droplets of sulfuric acid that gather in the atmosphere wherever fossil fuels are burned. These droplets help reflect sunlight, counteracting the effects of greenhouse gases. But the cooling may not be concentrated in exactly the same place as the heating, says Stephen Schneider, a climatologist at Stanford. He notes that unlike greenhouse gases, which disperse rapidly around the globe, the sulfate droplets tend to concentrate over industrialized regions -- the U.S., Europe, the former Soviet Union. The result, he says, may be a localized skewing of the weather similar to that caused by El Nino. "Not only are we forcing the system to change at a fast rate," says Schneider, "but we are forcing it to change in ways that are likely to play havoc with regional weather patterns."

Weather prediction is, in the best of circumstances, a crap shoot. Meteorologists, with their satellites and supercomputers, have become pretty good at forecasting the weather five to 10 days in advance. But offering definitive explanations for long-range atmospheric complexities is something no scientist can do. The world's weather is a prime example of the phenomenon of chaos -- a cause-and-effect system so devilishly complex that it becomes inherently unpredictable.

Much of what seems like extraordinary weather this year may actually be a return to conditions that seemed quite ordinary only a few years -- or a few decades -- earlier. The heavy precipitation that fell in the West last Christmas, for example, seemed like a return to the rainy winters of the early 1980s, before the recent drought set in. Similarly, hurricanes like Andrew may hark back to the storms that lashed the East Coast in the 1940s and '50s. As strange as the weather may seem this week, it hasn't produced anything like the tale of the tornado that traveled over a Southern lake in the 1950s, moved a few miles inland, and then started dropping fish at the feet of startled residents standing on their lawns.

What is new about today's weather is that, for the first time, some of the factors that help shape it may be man-made. Experts say it may be decades before we are certain what effect the buildup of greenhouse gases or the depletion of the ozone layer has had on the global climate. Last week's flooding and heat wave served as a warning that if we wait for the weathermen to tell us what's wrong with the weather, it may be too late to do anything about it.

With reporting by Adam Biegel/Atlanta and Madeleine Nash/Chicago, with other bureaus