What's Wrong with the Weather?

By Philip Elmer-DeWitt

Just when summer should have been coming in, it snowed last week in Colorado, punctuating several days of unseasonable 32 degrees C (90 degrees F) weather with enough snowfall to close three mountain highways. Paris was hit with a torrential rainstorm -- the worst in a decade -- that crippled the city, poisoned the Seine with sewer effluent, and clogged the river with 300 tons of dead fish. In one hour in early May, a squall dumped a record 110 mm (4 1/3 in.) of rain on Hong Kong, turning steep city streets into rushing rivers and killing five. In the Middle East this January, the wettest, coldest winter in recent memory was capped by a storm that blanketed Amman, Damascus and Jerusalem with much more snow than anyone there had seen for 40 years.

If it continues as it has begun, 1992 could turn out to be almost as bizarre as 1991, a year in which North America's spring arrived in winter, its summer in spring and its winter in autumn. The period from December 1991 to March 1992 has already gone into the National Weather Service's record books as the warmest winter in at least 97 years. It hardly rained at all in rainy Seattle in May. Texas in January was swamped with twice as much precipitation as normal, and Southern California, where it never rains, was socked with floodwaters so powerful they carried cars out to sea. Africa is having its worst drought in 50 years, and eastern Australia, which is supposed to have summer when the northern hemisphere has winter, had to do without this year. Instead of balmy days and bright sunshine, Melbourne racked up a record 12 consecutive days of rain and the coldest January in 137 years, which is as far back as anyone Down Under kept track.

What is going on? Experts say fluctuations from normal readings are, well, normal and that weird weather is the rule, not the exception. But the highs and lows and wets and drys over the past two years have been so extreme that anxious questions are arising. Could these outbursts of wacky weather be related to those fires from the gulf war? That hole in the ozone layer? The global warming trend that environmentalists have been predicting for so many years?

The questions are more than idle speculation. This week at the Earth Summit in Rio de Janeiro, world leaders will be adding their signatures to a treaty to prevent climate change, a document that was significantly weakened during presummit negotiations, in part because of U.S. contentions that the threat of global warming has been overblown. But the Bush Administration's skepticism must contend with the direct experience of millions of citizens who are worried that when the weather gets as odd as it has been of late, something must be wrong.

Scientists, however, are more cautious than the umbrella-carrying public. Even climatologists who believe that global warming may eventually trigger extreme weather variations like the ones we are experiencing say it is too early to prove a direct connection. The outbreak of freakish weather could also have been partly caused by one or more of several large-scale atmospheric events now under way. The main suspects, in descending order of likelihood:

EL NINO. To meteorologists, the weather phenomenon named after the Christ child is not a theory but a recognizable and recurrent climatological event. Every few years around Christmastime, a huge pool of warm seawater in the western Pacific begins to expand eastward toward Ecuador, nudging the jet streams off course and disrupting weather patterns across half the earth's surface. The El Nino that began last year and is now breaking up has been linked to record flooding in Latin America, the unseasonably warm winter in North America and the droughts in Africa.

PINATUBO. The full effects of the eruption of Mount Pinatubo in the Philippines last June -- probably the largest volcanic explosion of the 20th century -- are starting to be felt this year. The volcano heaved 20 million tons of gas and ash into the stratosphere, where they formed a global haze that will scatter sunlight and could lower temperatures -- by half a degree Fahrenheit -- for the next three or four years. Smoke from the gulf-war fires, by contrast, never reached the stratosphere and had no measurable effect on the world's weather.

GREENHOUSE GASES. It is known that the level of CO2, methane and other heat- trapping gases in the atmosphere has increased 50% since the start of the Industrial Revolution. Measurements also indicate that the world's average temperature has increased 1 degree F over the past 100 years. The rest is conjecture. Computer models suggest that as the buildup of greenhouse gases continues, average temperatures could jump 3 degrees F to 9 degrees F over the next 60 years. Some scientists speculate that even a small rise in average temperatures could lead to greater extremes in weather patterns from time to time and place to place.

The problem with sorting out these influences is that they interact in complex ways and may, to some extent, cancel each other out. Pinatubo's cooling effects could counteract the warming caused by greenhouse gases, at least over the short term. At the same time, El Nino's warming influence seems to have suppressed the early cooling effects of Pinatubo's global haze.

Predicting the weather is, in the best of circumstances, a game of chance. Even with the most powerful supercomputers, forecasters will never be able to see ahead more than a couple of weeks with any accuracy. Climatologist Stephen Schneider of the National Center for Atmospheric Research compares the typical weather forecast to guessing what bumpers a pinball will hit after it has left the flipper. "What's happening now," he says, "is we're tilting the machine in several directions at once."

Of course, there have always been volcanic eruptions, and the tales of El Nino date back at least to the Spanish conquistadors. Old-timers can point to freak weather occurrences that put the Los Angeles floods to shame, like the 1928 storm that bombarded southwestern Nebraska with hailstones the size of grapefruit. Or the blizzard of 1888 that buried the Eastern Seaboard in snowdrifts the size of four-story buildings. "There is a record set somewhere every day," says Steve Zebiak, an atmospheric scientist at Columbia University's Lamont-Doherty Geological Observatory.

What is new is that for the first time some of the influences that shape our weather are man-made. Experts say it could be 20 or 30 years before they know for certain what effect the buildup of greenhouse gases, the destruction of ancient forests or the depletion of the ozone layer have had. Policymakers looking for excuses not to halt those trends will always be able to point to scientific uncertainty. As Schneider puts it, "We're insulting the system at a faster rate than we can understand." The risk is that by the time we understand what is happening to the weather, it may be too late to do anything about it.

With reporting by David Bjerklie/New York, with other bureaus