Peter Grier (email@example.com) and James N. Thurman (firstname.lastname@example.org), Staff writers of The Christian Science Monitor
WASHINGTON - Some of the worst weather of the 20th century has occurred at its end.
This year, torrential rain and mudslides have devastated Venezuela. Last year, hurricane Mitch hit Honduras just as hard. In 1992, the southeastern US was raked by hurricane Andrew - possibly the costliest storm ever recorded.
Despite this burst of killer storms, as yet there is no hard evidence that extreme weather is becoming more frequent around the globe, say many meteorologists.
What has changed over the past 100 years is the pattern of human habitation and behavior. Coastal condos, massive deforestation, hillside shantytowns - all have led to an explosion in what might be called unnatural disasters.
"The affluent want to be by the sea. Mega-cities of the third world are often situated in vulnerable locations," says John Topping, head of the Climate Institute in Washington.
The disaster in Venezuela, where the death toll could top 30,000, has been a case in point.
An estimated 3 million Venezuelans live in shacks perched precariously on mountain slopes near the capital of Caracas. Many of these flimsy neighborhoods are now buried.
Environmental Vice Minister Ricaurte Leonett singles out deforestation and heavy development of the Vargas side of the Avila mountain range as prime causes of the destruction.
At the same time, the largely green and untouched slopes on the southern Caracas side helped mitigate damage in the capital.
"If it weren't for the fact that the mountain's status as a national park is more respected on the southern side, the north of the capital might have been destroyed," says Mr. Leonett.
The Venezuelan mudslides may well rank as the worst weather disaster to ever strike Latin America. They come one year after hurricane Mitch killed 11,000 - the greatest loss of life from a tropical storm in the Western Hemisphere since 1780.
Other major global weather events of the 1990s, according to the US National Oceanic and Atmospheric Administration (NOAA), include Bangladesh Cyclone 02B, a 1991 storm that killed 138,000, and China's Yangtze flood of 1998.
Five of the top 10 US weather events of the 20th century, as judged by NOAA, occurred in the 1990s. They include hurricane Andrew, with an estimated $25 billion cost; the Oklahoma/ Kansas tornado outbreak of May1999, the worst in the nation's history; and the 1993 Midwestern floods.
It is true that the world has seen an unusual number of severe weather events in the 1990s, say meteorologists. But most are hesitant to draw any conclusions from that fact.
"We usually have episodes of extreme events ... in intense periods of two to three years. Then we might go through another 10-year period without any anomalies," says Louis Uccellini, director of the National Centers for Environmental Prediction.
The 1950s and '60s were a period of intense hurricane activity, for instance, notes Dr. Uccellini. Then the Caribbean quieted down for some 20 years.
Now the Western Hemisphere is again seeing a pattern of active hurricane seasons.
The weather has also been particularly warm in recent years. Last month was the warmest November ever recorded in the contiguous 48 states of the US. This year is almost certain to join 1998 as one of the two warmest years on record worldwide.
Most scientists believe that humanity has helped create this century-long warming trend by emitting increasing amounts of heat-trapping gases such as carbon dioxide. Some experts believe this global warming is helping to cause weather extremes.
"With high temperatures ... you roll the dice by heating up the water cycle," says Seth Dunn, a research associate at the Worldwatch Institute here.
The cost of weather extremes is clearly rising. As of earlier this year, the insurance industry had paid out almost $92 billion in claims from weather-related natural disasters in the 1990s - four times more than it paid out in the 1980s.
But human behavior is the likely the main cause of this increase. The world has more people and things than it did in 1900.
Environmental degradation hurts, too. The toll of Bangladesh's 1991 cyclone was increased by deforestation in coastal swamps, which had previously slowed storm surges. China's government has now ordered reforestation along parts of the Yangtze to help mitigate constant flooding problems.
"Increasing financial losses from weather extremes are primarily due to a variety of societal changes," says a paper on weather extremes in a recent issue of the Bulletin of the American Meteorological Society.
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