IntroductionFire is a topic on which most people can comment. Fire is a widespread phenomenon. Most of us have seen fires in natural vegetation, or their effects; stark, blackened vegetation or a smoke pall.
Because fires such as these can have damaging economic and social effects, can spoil forestry timber, can burn down houses and farms, and can kill people and animals, there has been a lot written about wildfires. Added to this wide perception of the damage that can be caused by wildfires, there has been increasing publicity given, since the 1950’s, to the active use of fire as a management tool, particularly in protecting against severe wildfires. The introduction of a policy of deliberate burning as a management tool has a fascinating history, especially in the United States Forest Service, but the ecological effects of prescribing a fixed burning regime on large tracts of land are increasingly being questioned (Lyons, 1985, 3). To an ecologist, fire can be treated as just one of the many factors in an environment. It compares with droughts, floods, hurricanes and other physical disturbances because of the direct impact it makes on organisms. Unlike these physical factors, however, fire as a disturbing force is itself influenced by the biota, particularly the plant community.
Alteration of the vegetation by any number of factors can influence the nature of a subsequent fire. Fire has similarities to grazing as a force on vegetation because of such feedback effects (Whelan, 1995, 20). Fire HistoryWhen cavemen learned to make and use fire, they could start to live in civilized ways. With fire, they were able to cook their food so that it was easier to eat and tasted better.
By the light of torches, men could more easily find their way at night. They could also improve their wooden tools by hardening the points in fire. With fire to keep them warm, they could live in the colder regions and spread out over the Earth (CD-ROM, 1996). It is supposed that early people got fire accidentally from trees set ablaze by lightning or from spouting volcanoes. Then they carefully kept it burning in huts or caves. As far back as the study has gone, primitive peoples have never been found without fire for warmth and cooking.
Fire also protected them from wild beasts (CD-ROM, 1996). In time people discovered how to create fire by rubbing dry sticks together. Then they invented bow drills to aid the process. When they began to chip flint to make axes, they found that hot sparks came from the stone. From this they later developed the flint-and-steel method of fire making.
Later it was found that fire could be made by focusing the sun’s rays with a lens or curved mirror (CD-ROM, 1996). People remained ignorant of the true character of fire until 1783. In that year the great French chemist Antoine Lavoisier investigated the properties of oxygen and laid the foundation for modern chemistry (CD-ROM, 1996). Lavoisier showed that ordinary fire is due to the chemical process called oxidation, which is the combination of a substance with oxygen. He disproved the earlier “phlogiston” theory. The phlogiston theory held that when an object was heated or cooled it was due to a mysterious substance (phlogiston) that flowed into or out of the object in question (CD-ROM, 1996).
Since fires are due to oxidation, they need air to burn properly, and a flame will go out after it has used up the oxygen in a closed vessel. Almost anything will combine with oxygen if enough time is allowed. Iron will rust if exposed long to damp air, and the rust is simply oxidized iron. When the chemical combination is so rapid that it is accompanied by a flame, it is called combustion (CD-ROM, 1996). Ignition Point or Kindling TemperatureHeat is required to start combustion. The degree of temperature at which a substance will catch fire and continue to burn is called its ignition point or its kindling point.
A substance that can be ignited in the air is said to be flammable (or inflammable). The flash point of a flammable liquid is lower than its ignition point. The flash point is the temperature at which it gives off sufficient vapor to flash, or flame suddenly, in the air. It is not the temperature at which the substance will continue to burn (CD-ROM, 1996). When primitive peoples rubbed two sticks together to kindle a fire, they discovered without knowing it that the ignition point of wood is usually quite high.
They had to use enough energy to create a good deal of heat before flames appeared. The tip of a match is composed of chemicals that, under ordinary circumstances, have a low ignition point. The heat created by scratching it once on a rough surface is enough to start combustion. It must be remembered, however, that the temperature needed to sustain combustion can vary with the condition of the substance and the pressure of the air or other gases involved, as well as with laboratory test methods (CD-ROM, 1996). Lowering the Temperature Puts Out FireAfter a fire has started, it will be self-supporting only when the temperature created by the combustion of the burning substance is as high or higher than its ignition point. This is one of the most important laws of fire.
Some very hard woods, such as ebony, require a great deal of heat to burn. If the end of a stick of ebony is placed in a coal fire, it will burn. When it is drawn out, the fire of the smoldering ebony itself is lower in temperature than the ignition point of the wood. The flames thus will die (Lyons, 1985, 5).
This principle explains why a match can be blown out. One’s breath carries away the heat, and the temperature falls below the ignition point of the matchstick. The stream of water from a firefighter’s hose cools the burning walls of a building with a similar result (Lyons, 1985, 5). The heat of a fire depends on the speed with which chemicals combine with oxygen.
This speed depends generally on the quantity of oxygen present. If a lit match is touched to a small piece of iron wire, it will not burn. If a tip of a match is fastened to the end of the wire, struck, and plunged quickly into a jar of pure oxygen, the wire will catch fire and burn, with bright sparks shooting off briskly (Lyons, 1985, 6). Fire Without FlameFire may burn either with or without flames.
A flame always indicates that heat has forced gas from a burning substance. The flames come from the combination of this gas with oxygen in the air. When a coal fire flames, it does so because gas is being forced from the coal, and the carbon and hydrogen in the gas combine with oxygen. If kept from burning, such gas can be stored. Manufactured gas is forced from coal in airtight kilns, or retorts. The product left after the gas is extracted from coal is called coke.
Coke will burn without flame because no gas is driven off. In order to burn, the carbon in the coke combines directly with oxygen (Lyons, 1985, 8). It is the gas given off by the heated wax in a candle that produces the bright flame. When a burning candle is blown out, for example, a thin ribbon of smoke will arise.
If a lighted match is passed through this smoke an inch (2. 5 centimeters) above the wick, a tiny flame will run down and relight the candle (Lyons, 1985, 8). The brightest flames are not always the hottest. Hydrogen, which combines with oxygen when burning to form water, has an almost invisible flame even under ordinary circumstances. When it is absolutely pure and the air around it is completely free of dust, the hydrogen flame cannot be seen even in a dark room (Lyons, 1985, 9). Whenever a flammable gas is mixed with air in exactly the quantities necessary for complete combination, it will burn so fast as to create an explosion.
This is what takes place in a gasoline engine. The carburetor provides the air mixture, and the electric spark sets it on fire. The small explosions that sometimes occur after the burners of a gas stove are turned off are from the gas remaining in the pipe. Air creeps in through the air valve until the mixture becomes explosive, and the tiny flame that remains on the burner fires back (Lyons, 1985, 9).
Legends and Worship of FireTribal legends of the North American Indians say various animals showed the Indians’ ancestors how to make fire. Other early peoples said that fire came down from heaven in magic ways. According to a myth of ancient Greece, Prometheus, a member of the giant race of Titans, stole fire from the sun and carried it to the Earth. There is much evidence that primitive peoples used fire for some time before they learned how to kindle it. When they captured fire, they tended it carefully so that it would not go out (CD-ROM 1996).
Gradually the legends of the magic origin of fire and the tending of perpetual fires were associated with religious practices. Fire worship was often associated with sun worship. Fire was said to be the earthly representative of the sun-god. Sacred fires were preserved in temples by the Egyptians, Greeks, and Romans. Priests or certain special people watched the fires. Among the most famous were the Vestal Virgins in the Temple of Vesta in Rome.
The Mayas and Aztecs kept sacred fires burning on top of high pyramids or fire altars. The Iranian religion Zoroastrianism maintains a sacred fire that must be fed at least five times a day (CD-ROM 1996). The history of fire is the history of progress. As people have learned how to tame fire and make it their servant, they have been able to develop the forces of nature. Fire has yielded the power of steam.
It has extracted metals from rocks. It has helped make rubber from the gum of a tree and hard brick from soft clay. It is essential to a wide variety of manufacturing processes (CD-ROM 1996). Forest Fires on the Home FrontForest fires are a natural part of a forest’s life cycle. Indeed, the extreme weather and forest fires we are experiencing this spring and summer are not unique — Canadians have endured forest loss, flooding and heat waves for many, many years.
But what is new and alarming is the frequency at which these events are now occurring. In the last fifteen years, we have experienced five of the seven worst forest fire years in recorded Canadian history. And, not surprisingly, in that same period we have lived through eight of the warmest years on record (UNEP, On-line, 1998). Canadians can continue to expect more fires, more often and earlier in the season. While there are fluctuations in forest fire activity from year to year, the trend is clearly upward. Since the early eighties, there has been a two-fold increase in forest fire activity.
From 1920 to 1980, the average annual amount of forest loss due to fire was about one million hectares. Since then,the average has been around 2. 2 million hectares (UNEP, On-line, 1998). Relationship between Forest Fires and Climate ChangeGlobal warming is not the only cause of what is happening in the forests of northern Canada.
Obviously aging timber stands, changing forest policies, climate variability, spark-driven forest machinery and careless people are considerable factors. Even our historical success at fighting fires may be a factor since intervention often cause debris and deadwood to build up,become dry, flammable and a contributing source of many fires. But, these factors alone are not enough to adequately explain the dramatic increase in forest fire activity. There have to beother explanations and climate change is one of them (Whelan, 1995, 12). In 1989, Environment Canada scientists first suggested a link between fire and climate change. Based on what was then known about climate change, they predicted there would be changes in the length and severity of forest fires in Canada.
They predicted, for example, that northern Canada would experience a fire season with two peak periods; the first in late spring,and the second late in the summer. Unfortunately, this is exactly what is happening in northern Canada now (UNEP, On-line, 1998). We have also been saying that when temperatures increase, so does the stress on our forests: moisture levels decrease, bogs dry up, lakes shrink, trees die, dry up and become fire fuel. Under these conditions, fires are more frequent, more intense and more severe.
The number and rate at which fires are occurring are also an indication that there is a dramatic change underway in our forests. Fire is transforming many of our forests into grasslands — permanently (UNEP, On- line, 1998). Losing trees is bad news for the economy and environment. Canada’s economy has always depended heavily on natural resources. Right now, the forestry generates $42 billion in economic activity and employs 779,000 Canadians — one out of every 16 jobs.
Severe and frequent forest fire activity puts these people, and our economy, in real jeopardy (UNEP, On-line, 1998). For the environment, forest loss has an ironic twist — while growing trees recycle carbon dioxide, burning trees release it. Obviously, if the current trend of forest fire activity continues to rise, so will carbon dioxide levels and global warming (On-line, 1998). This summer’s devastating fires are reminders of what we can expect in the future unless we collectively adopt a global warming action plan. This summer, nature is teaching us a lesson. Earth’s Climate system is dynamic, and extremely complex.
It is an entirely solar-powered system, dependent on complex interactions between radiation from the sun, gases in the atmosphere, reflectivity of the earth’s surface, currents of wind and water, and other factors. Everything works together in a delicate balance that is sensitive to even minor changes. As we now know, changes in the concentrations of certain trace gases in the atmosphere can trigger a significant response from the Earth’s climate system (On-line, 1998). What is climate?Before describing what climate is, let’s start by describing what it is not. Climate is not weather. Weather is what today’s daytime high temperature, this morning’s humidity or the cold front that went through last night.
Weather is short-term variations in atmospheric conditions for a specific locality. Weather can change in hours or minutes. On the other hand, climate is the long-term average of atmospheric conditions for a region. For example, you would notice that Calgary is much drier than Vancouver. This expresses a climatic difference between these two cities. Changes in climate are only noticeable only over long distances, and over decades and centuries of time.
We can describe weather and climate by analyzing information about such factors as temperature, rainfall, and winds, gathered at thousands of locations all over the world. Meterologists use this information to predict what the weather will be like for the next few days or hours. Climatologists use some of the same information to describe climate in various regions by figuring out the long-term averages for conditions like rainfall, humidity and temperature (On- line, 1998). The Natural Greenhouse EffectOn a planet with no atmosphere, the infrared radiation emitted by its surface would go straight out to space.
But on Earth, things are very different. The Earth’s atmosphere has several gases that have the ability to absorb infrared radiation. This means that much of the infrared radiation emitted by the surface is captured before it gets out to space. As they absorb long-wave energy from the surface, these gases heat up, making the air warmer. This is roughly the same thing that happens inside a greenhouse on a sunny day, and why it is called the greenhouse effect.
As you might expect, the gases that do this are called greenhouse gases (On-line, 1998). The atmosphere’s main greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and water vapor (H2O). Together they make up less than one-tenth of one percent of the atmosphere’s total volume. The rest of the atmosphere contains mostly nitrogen (78%) and oxygen (21%), neither of which trap much heat.
The greenhouse gases are present in the atmosphere in just trace amounts. Even so, they have an extremely important role in determining climate. By trapping heat, they keep Earth’s thermostat set at an average temperature of +15 C. Without greenhouse gases, the average temperature would be 33C colder than it is now, and Earth would be a lot more like Mars-a frozen, dusty, lifeless planet (On-line, 1998). The natural greenhouse effect gives Earth an average temperature of +15C.
Obviously, it isn’t a steady +15 C everywhere on the planet. Some places are perpetually frozen, such as the polar ice caps. Others are constantly hot and humid, as in the tropical rain forests. Other regions, like here in Canada, have highly variable seasonal climates-warm, wetsummers; long, cold winters. What is clear is that climate varies widely from place to place on the planet (On-line, 1998).
Why do climates vary so much from place to place? The differences arise because the sun’s heat is not distributed evenly over the entire planet. Complicated interactions between the greenhouse effect, wind and ocean currents, land masses, elevation, and the many other factors distribute this heat around the planet in a way that creates the wide diversity of climates we can see. The interactions are so complex that they are nearly impossible to describe accurately, even with the help of the most powerful supercomputers (On-line, 1998). Natural Climate ChangeWe are surrounded by clues that climates have been different in the past.
Many landscapes in Canada show traces of the last Ice Age, a time when climates were much colder than now. At the same time, fossils of tropical plants and animals have been found all over Canada, even in the high arctic. Clearly, the climates we now experience are different than those in the past. When did climate change in the past, and by how much (On-line, 1998)?The following graph shows the variations in global temperatures, going back one-million years.
It shows that warm periods occurred roughly every 100,000 years, with colder periods in between. It was during those cold periods that the great continental ice sheets advanced, spreading over much of the North American continent each time (On-line, 1998). Figure 1 Variations in Global Temperatures Over the Last Million Years (On-line, 1998). The next graph shows how climates have changed in the past 1000 years. It shows that around 800 years ago, there was a 300-year warm spell. This was a time when Greenland was actually green (Europeans were farming there), and grapes and other warm-climate fruits could be grown on the British Isles (On-line, 1998).
Figure 2Global Temperatures Over the Last 1000 Years (On-line, 1998)The graph above also shows that around 400 years ago, the global climate was approximately 1-2 degrees colder than now. It was a time when winters were longer, and glaciers advanced dramatically. The Vikings had to abandon their farms on Greenland, and withdraw from Eastern Canada, where they had also settled. This period is known as the “Little Ice Age.
” It is clear that climates change naturally on their own. What has caused these changes’scientists all over the world are studying this problem, and are coming up with many theories. Many natural events appear to have altered global climates, including meteorite impacts, volcanic eruptions, and changes in the compositions of the earth’s atmosphere (On-line, 1998). The most important factor seems to be composition of the atmosphere, which affects the intensity of the Earth’s greenhouse effect. Scientists now know that many changes in past climates seem to occur at the same time that changes in the concentration of CO2 also occurred. When the Earth’s average global temperature has risen or fallen, CO2 concentrations have moved in a similar pattern (On-line, 1998).
The last graph shows changes in temperature have been mirrored by changes in the two important greenhouse gases, carbon dioxide and methane. It shows that for every peak in average global temperature, there was a corresponding peak in greenhouse gases (On-line, 1998). The relationship between global temperatures and composition of the atmosphere has scientists extremely concerned. Human activities are rapidly increasing the concentration of greenhouse gases in the atmosphere. In fact, scientists now believe that if anthropogenic (human-caused) emissions of greenhouse gases are not significantly reduced, the Earth will warm at a rate faster than at any time in the 10,000 years that represent human history (On-line, 1998). Climate is usually something humans take for granted.
It changes far too slowly for us to notice on a day-to-day basis. But by looking at long-term climate records, and with new techniques for determining ancient climates from ice, sediments, and other natural deposits, we can see climates have changed dramatically in the past. We can also see that some of the changes humans are making to the atmosphere and to landscapes are beginning to have noticeable effects on global climates. We now have to think about protecting the Earth’s climate system the same way we do about protecting other important parts of the environment, like water, air and soil (On-line, 1998).
Figure 3Location of t he Principle F ire Events in 1 998 (On- l ine, 1998)ConclusionsFire provides the material well-being of the people in the industrial countries of the world. Heat from the burning of fuel converted into electrical and mechanical energy does practically all the work of these economies. However, the world’s population has a fire problem. Americans and Canadians lose property and life to fire at twice the rate of people in comparable circumstances in other industrial nations.
The table below illustrates the fatalities due to fire in various nations (Payne, 1989, 56). Table 1Fire Caused Fatalities in Various Nations (Deaths per 100,000 pop. ) (Payne, 1989, 56)Nation19741976-78Latest ReportCanada3. 63.
22. 9United States2. 92. 92. 8Sweden 1.
61. 51. 6Japan1. 5——–1. 5United Kingdom1.
51. 51. 5France 1. 51.
51. 5Australia1. 5——–0. 8Germany0. 90.
90. 9Switzerland0. 70. 60. 7ReferencesCompton’s Interactive Encyclopedia: On compact disc (1996) CD-ROM.
Lyons, John W. (1985). Fire. New York: Scientific American Library.
Payne, Charles A. , Falls, William R. , & Whidden, Charles J. (1989). Physical Science (5thed. ).
Iowa: Wm. C. Brown Publishers. Whelan, Robert J. (1995).
The Ecology of Fire. Great Britain: Cambridge UniversityPress. United Nations Environment Program. On-line. Available:http://www.
grid. unep. ch/fires/On-line. Available:http://www.piad.ab.ca
