Mysteries of nature.

While everybody seems focussed on looking for human causes behind global warming, natural climate changes may be far more significant

True, we've been changing the world for thousands of years -- ever since we started farming about 10,000 years ago. We stopped wandering around hunting and gathering to survive and started to root ourselves, as well as our food, in farming communities. We cleared land, depleted the soil of its nutrients, created deserts, and moved on to more fertile areas, thinking there was an endless supply. Skipping thousands of years, we eventually ended up not only using nature to meet our needs but poisoning it with excessive gases and chemicals that the natural world can't absorb. Chopping down [CO.sub.2]-absorbing trees without replacing them only adds to the problem.

While we've clearly created some problems, many see global warming as a largely natural phenomenon. The Fraser Institute quotes a survey in which nine of 10 climatologists agreed that "scientific evidence indicates variations in global temperature are likely to be naturally occurring and cyclical over very long periods of time" and 89% agreed that "current science is unable to isolate and measure variations in global temperatures caused--only by man-made factors." "

After all, the global climate has changed radically during periods long before humans entered the scene.

The average worldwide temperature rose by about 0.4 [degrees] C between 1910 and 1940, before most of the increases in greenhouse eases. So, it seems reasonable to conclude that most of the warming early in this century came from natural causes of climatic change. In a survey of 1,500 experts in climatology carried out in 1990 for the magazine Nature, 71% of respondents said they believed the temperature rises experienced over the last 100 years are within the natural range of fluctuation.

The sun could have something to do with it. Some scientists have found a strong connection between the temperature history of the northern hemisphere during the 20th century and the history of solar activity during the same period. One estimate suggests that about half of the warming since 1850 is a result of solar changes.

The surface magnetism on the sun, and corresponding variations in brightness, has an 11-year cycle. It's thought that the sun dims during the magnetically low periods and brightens during magnetically high intervals. The changes would be small but enough to change global temperatures.

It's also thought that every two centuries or so, the sun's magnetism drops to very low levels for several decades. One of those drops, between 1640 and 1720, might have contributed to the "Little Ice Age," when the average global temperature was about 1 [degrees] C cooler than it is today. Some records show that six out of seven cold spells over a 5,000-year period coincided with long-term lulls in solar magnetism. Going back 10,000 years, records from Scandinavia found the same links in 17 out of 19 cold spells.

In addition to changes in the sun, volcanic activity can affect climate. The eruption of large volcanoes can raise enough dust into the stratosphere to help cool things off. Studies have shown that when dust levels are low, global annual temperatures tend to be high, and when dust levels are high, temperatures appear to be lower. Scientists have found that more than 20% of the variation in the global temperatures can be explained by stratospheric dust.

Other naturally occurring events such as large warm pools or cold pools of ocean water can influence global temperatures too. El Nino and La Nina -- in the eastern portion of the tropical Pacific Ocean -- have made plenty of headlines.

El Nino arrives every two to seven years, when a build-up of warm water from the western Pacific mysteriously parks off the western coast of South America, altering global weather.

Back in 1991, weather experts warned that El Nino was about to reappear in the equatorial Pacific. It had caused flooding in Peru and Ecuador and brought droughts to Southeast Asia eight years earlier.

Scientists said rising water temperatures off the coast of South America and changes in rainfall patterns in Pacific Basin countries were setting the stage for another onslaught. In June 1991, snow fell in Chile's northern Atacama Desert. A month later, torrential rains destroyed crops in eastern Ecuador.

In 1982-83, floods caused $3 billion (U.S.) in damage to Peru; warm waters destroyed cold-water fish and ruined the country's fish-meal industry; coastal desert regions that normally received no rainfall suddenly were swamped by three metres of rain; Ecuador suffered loss of lives through landslides and its shrimp industry was hard hit; droughts were reported around the world, as well as damaging storms.

A decade later, in 1992, the normally harsh winter of the Canadian Prairies became one of the warmest on record with average temperatures 10 degrees above normal.

The warmest Christmas season -- when El Nino usually hits -- was in 1877. But the phenomenon warmed the Prairies with its 1982-83 appearance and in 1986-87 as well. El Nino has been blamed for African and Australian droughts, typhoons in Indonesia, and mudslides along coastal South America.

It was blamed for another heat wave in Western Canada in December 1997, torrents of rain in central Ontario, and avalanches in British Columbia. At the same time, it brought drought and forest fires to parts of southeast Asia, and bitter cold and snow to normally balmy Mexico.

Overall, according to the United Nations weather agency, El Nino made 1997 the world's hottest year on record, as well as causing major disasters worldwide.

It also has its name on the ice-storms in January 1998 that made Montreal, Ottawa, and communities from Kingston, Ont., to Nova Scotia's Annapolis Valley look like battle zones. In 1998 it parched Hawaii, which normally gets more than three metres of rain on its eastern end, and drenched Pacific Coast states and Florida, causing devastating floods and landslides in California, and a series of tornadoes in Florida.

According to the U.S. National Oceanic and Atmospheric Administration's Climate Prediction Center in Washington, 1997-98 saw "the most significant El Nino event of the century."

We can't blame everything on El Nino. It made 1997 the hottest year since records were first kept in 1860. But the previous record, which was only 0.06 [degrees] C cooler, occurred in 1995 when there was no El Nino.

Clearly, the reasons behind global climate are not simple. Even experts admit there are a lot of unanswered questions.

Like life, one of the certainties of climate is change. Ice ages hit about every 100,000 years. Then, warm periods last 10,000 to 12,000 years. And, there are wild fluctuations even during the warm periods. Between 5,000 and 8,000 years ago, Earth went through long periods that were two to three degrees hotter than today. The Prairies turned wet about 800 years ago after 1,500 years of dust-bowl conditions. The Sahara Desert is said to have been home to water-loving hippos and crocodiles in the past, and England once was warm enough to produce some tasty wines (at another time England's Thames River was used as skating rinks). But, many experts say it's all part of the natural scheme of things.

In his book The Heated Debate, climatologist Robert C. Balling, Jr. points out that our five-billion-year-old planet has had huge temperature changes over the last 850,000 years, with a range of more than 6.5 [degrees] C.

"The pattern is one of rather abrupt jumps in temperature -- there is little evidence of climate stability in the past, and it is not logical to expect the modern-day climate to remain stagnant, with or without the addition of the greenhouse gases," he writes.

Dr. Balling says scientists simply do not understand why these past variations have occurred. Nor are they sure "where the climate of the twentieth century was headed in the absence of the build-up of the greenhouse gases."

SUGGESTED ACTIVITIES:

1. The World Wildlife Fund reported that more forests around the world were burned in 1997 than in any other year in recorded history. At least five million hectares of forest and scrub -- an area about half the size of Newfoundland -- burned in Indonesia and Brazil, along with vast areas of Papua-New Guinea, Colombia, Peru, Tanzania, Kenya, Rwanda and the Congo. Do a research paper describing these fires and explaining what caused them.

2. There were a lot of reports about El Nino 1997 and 1998. In mid-1998, climatologists warned that La Nina was about to make a return appearance. Appoint a team of students to research how these two phenomena affect the weather in Canada

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