Many environmental issues confront us today. This chapter discusses key environmental issues in four areas: atmospheric change, fresh water, spaces and species, and waste management.

Ozone Depletion

One of the issues motivating the environmental movement since its inception has been a concern for human health. Recently, worries about the harmful effects of a possible increase in the penetration of UV radiation into the biosphere have received much attention. This section summarizes the causes and consequences of the issue that is at the root of these concerns stratospheric ozone depletion.

Q3.1
What is ozone? Ozone is a form of oxygen. The oxygen we breathe is in the form of oxygen molecules (O2) two atoms of oxygen bound together. Ozone, on the other hand, consists of three atoms of oxygen bound together (O3). Most of the atmosphere's ozone occurs in the stratosphere. Ozone is colourless and has a very harsh odour.

Q3.2
Where is ozone found? Approximately 90 per cent of all ozone is produced naturally in the stratosphere. While ozone can be found through the entire atmosphere, the greatest concentration occurs at an altitude of about 25 km. This band of ozone-rich air is known as the "ozone layer".

Ozone also occurs in very small amounts at ground level. It is produced at ground level through a reaction between sunlight and volatile organic compounds (VOC) and nitrogen oxides (NOx), some of which are produced by human activities. Ground-level ozone is a component of urban smog a serious air pollutant.

Even though both types of ozone are exactly the same molecule, their presence in different parts of the atmosphere has very different consequences. Stratospheric ozone blocks harmful solar radiation all life on Earth has adapted to this filtered solar radiation. Ground-level ozone, in contrast, is simply a pollutant. It will absorb some incoming solar radiation, but it cannot make up for stratospheric ozone loss.

Q3.3
How is stratospheric ozone formed? Ozone is created in the stratosphere when highly energetic solar rays strike molecules of oxygen (O2) and cause the two oxygen atoms to split apart. If a freed atom bumps into another O2 it joins up, forming ozone (O3).

Ozone is also naturally broken down in the stratosphere by sunlight and by a chemical reaction with various compounds containing nitrogen, hydrogen and chlorine. These chemicals all occur naturally in the atmosphere in very small amounts.

In an unpolluted atmosphere there is a balance between the amount of ozone being produced and the amount of ozone being destroyed. As a result, the total concentration of ozone in the stratosphere remains relatively constant.

Q3.4
Why is the ozone layer important? Ozone's unique physical properties allow the ozone layer to act as our planet's sunscreen, providing an invisible filter to help protect all life forms the sun's damaging (UV) ultra- violet rays. Most incoming UV radiation is absorbed by ozone and prevented from reaching the Earth's surface. Without the protective effect of ozone, life on Earth would not have evolved the way it has.

Q3.5
Is the ozone layer evenly distributed around the Earth? No. The amount of ozone above a location on the Earth varies naturally with latitude, season, and from day-to-day. Under normal circumstances, the ozone layer is thickest over the poles and thinnest around the equator. The ozone layer over Canada is normally thicker in winter and early spring; it can vary naturally by about 25 percent between January and July. Weather conditions can also cause considerable daily variations.

Q3.6
What is ultraviolet radiation? Ultraviolet radiation is one form of radiant energy coming from the sun. The various forms of energy, or radiation, are classified according to wavelength, measured in nanometres (one nm is a millionth of a millimetre). The shorter the wavelength, the more energetic the radiation. In order of decreasing energy, the principal forms of radiation are gamma rays, X rays, UV (ultraviolet radiation), visible light, infrared radiation, microwaves, and radio waves. There are three categories of UV radiation:

• UV-A, between 320 and 400 nm

• UV-B, between 280 and 320 nm

• UV-C, between 200 and 280 nm

Q3.7
How harmful is UV (ultraviolet) radiation? Generally, the shorter the wavelength, the more biologically damaging UV radiation can be if it reaches the Earth in sufficient quantity.

• UV-A is the least damaging form of UV radiation and reaches the Earth in greatest quantity.

  Most UV-A rays pass right through the ozone layer.

• UV-B radiation is potentially very harmful. Fortunately, most of the sun's UV-B radiation is absorbed by ozone in the stratosphere.

• UV-C radiation is potentially the most damaging because it is very energetic. Fortunately, all UV-C is absorbed by oxygen and ozone in the stratosphere and never reaches the Earth's surface.

In summary, the danger from ultraviolet radiation comes mainly from the UV-B range of the spectrum, although UV-A poses some risk if exposure is long enough.

Q3.8
Do factors other than stratospheric ozone affect the amount of UV radiation that reaches the Earth? Yes. Although the ozone layer is the one constant defence against UV penetration, several other factors can have an effect:

Latitude. Since the sun's rays impact the Earth's surface at the most direct angle over the equator
they are the most intense at this latitude.

Season. During winter months, the sun's rays strike at a more oblique angle than they do in the
summer. This means that all solar radiation travels a longer path through the atmosphere to reach the Earth, and is therefore less intense.

Time of day. Daily changes in the angle of the sun influence the amount of UV radiation that
passes through the atmosphere. When the sun is low in the sky, its rays must travel a greater distance through the atmosphere and may be scattered and absorbed by water vapour and other atmospheric components. The greatest amount of UV reaches the Earth around midday when the sun is at its highest point.

Altitude. The air is thinner and cleaner on a mountaintop more UV reaches there than at lower
elevations.

Cloud cover. Clouds can have a marked impact on the amount of UV radiation that reaches the
Earth's surface; generally, thick clouds block more UV than thin cloud cover.

Rain. Rainy conditions reduce the amount of UV transmission.

Air pollution. Much as clouds shield the Earth's surface from UV radiation, urban smog can reduce
the amount of UV radiation reaching the Earth.

Land Cover. Incoming UV radiation is reflected from most surfaces. Snow reflects up to 85 per
cent, dry sand and concrete can reflect up to 12 per cent. Water reflects only five per cent. Reflected UV can damage people, plants, and animals just as direct UV does.

Q3.9
What is ozone depletion? Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction. Observations of an antarctic ozone "hole" and atmospheric records indicating seasonal declines in global ozone levels provide strong evidence that global ozone depletion is occurring. Although natural phenomena can cause temporary ozone loss, chlorine and bromine released from synthetic compounds are now accepted as the main cause of this depletion.

Q3.10
How long has ozone depletion been occurring? Based on data collected since the 1950s, scientists have determined that ozone levels were relatively stable until the late 1970s. Severe depletion over the Antarctic has been occurring since 1979 and a general downturn in global ozone levels has been observed since the early 1980s.

Q3.11
How much of the ozone layer has been depleted around the world? Global ozone levels declined an average of about 3 per cent between 1979 and 1991. This rate of decline is about three times faster than that recorded in the 1970s. In addition to Antarctica, ozone depletion now affects almost all of North America, Europe, Russia, Australia, New Zealand, and a sizeable part of South America.

Short term losses of ozone can be much greater than the long term average. In Canada, ozone depletion is usually greatest in the late winter and early spring. In 1993, for example, average ozone values over Canada were 14% below normal from January to April.

Q3.12
What human activities cause ozone depletion? Emissions of chlorine and bromine-containing synthetic compounds known as industrial halocarbons are the cause of stratospheric ozone depletion.

Q3.13
Why are industrial halocarbons so effective at destroying ozone? Industrial halocarbons are effective ozone-depleters for two reasons. The first is that they are not reactive, which means they survive long enough in the atmosphere to drift up into the stratosphere. The second is that they help the natural reactions that destroy ozone.

Unlike most chemicals released into the atmosphere at the earth's surface, industrial halocarbons are not "washed" back to earth by rain or destroyed in reactions with other chemicals. They simply do not break down in the lower atmosphere and they can remain in the atmosphere from 20 to 120 years or more.

Once they reach the stratosphere, UV-C radiation breaks up these molecules into chlorine (from CFCs, methyl chloroform, carbon tetrachloride) or bromine (from halons, methyl bromide) which, in turn, break up ozone (O3). Both chlorine and bromine activate and speed up the ozone destruction reactions without being altered or destroyed themselves. Thus, a single chlorine atom can destroy up to 100,000 ozone molecules before it finally forms a stable compound and diffuses out of the stratosphere.

Q3.14
What are the most widely used ozone-depleting halocarbons? CFCs are widely used as coolants in refrigeration and air conditioners, as solvents in degreasers and cleaners, and as a blowing agent in the production of foam. Emissions of CFCs account for roughly 80 percent of total stratospheric ozone depletion.

Did you know?
The term ozone "hole" refers to a large and rapid decrease in the abundance of ozone molecules not the complete absence of them. The Antarctic ozone "hole" occurs during the southern spring between September and November.

HCFCs (Hydrochlorofluorocarbons) contain chlorine but, unlike CFCs, they also contain hydrogen
(the H) which causes them to break down in the lower atmosphere. They are called transitional chemicals because they are considered an interim step between strong ozone-depleters and replacement chemicals that are entirely ozone-friendly.

Carbon tetrachloride is used as an industrial solvent, an agricultural fumigant, and in many other
industrial processes including petrochemical refining. It accounts for less than 8 percent of total ozone depletion.

Methyl chloroform is a versatile, all-purpose industrial solvent used primarily to clean metal and
electronic part. Methyl chloroform accounts for roughly 5 percent of total ozone depletion.

Halons are used primarily as fire suppressants. Halons account for only about 5 percent of global
ozone depletion, but the atmospheric concentration of these potent, long-lived ozone destroyers is rising by an estimated 11-15 percent annually.

Methyl bromide has been used as a pesticide since the 1960s. Today, scientists estimate that
human sources of methyl bromide are responsible for approximately 5 to 10 percent of global ozone depletion.

Q3.15
How does UV-B exposure affect people? Exposure to UV-B radiation causes skin cancer, hastens skin aging, and can cause eye damage. The human immune system can also be weakened by exposure to UV-B.

It is important to note, however, that UV-B radiation has always had these effects on humans. In recent years these effects have become more prevalent because Canadians are spending more time in the sun and are exposing more of their skin in the process. An increase in the levels of UV-B reaching the Earth as a result of ozone depletion may compound the effects that sunworshipping habits have already created.

Although fair-skinned, fair-haired individuals are at highest risk for skin cancer, the risk for all skin types increases with exposure to UV-B radiation. The effects of UV-B on the human immune system have been observed in people with all types of skin.

Q3.16
How does UV-B exposure affect plants and animals? Excessive UV-B inhibits the growth processes of almost all green plants. There is concern that ozone depletion may lead to a loss of plant species and reduce global food supply. Any change in the balance of plant species can have serious effects, since all life is interconnected. Plants form the basis of the food web, prevent soil erosion and water loss, and are the primary producers of oxygen and a primary sink (storage site) for carbon dioxide.

UV-B causes cancer in domestic animals similar to those observed in humans. Although most animals have greater protection from UV-B because of their heavy coats and skin pigmentation, they cannot be artificially protected from UV-B on a large scale. Eyes and exposed parts of the body are most at risk.

Q3.17
How much more ozone depletion will occur? No one knows for certain. Even if all nations meet their international commitments to phase out ozone-depleting substances, the levels of these chemicals will continue to build up in the stratosphere until at least the year 2000. CFCs are long-lasting chemicals and their effects will be with us for decades.

During the 1980s, the ozone layer over southern Canada thinned by an average of about 4 per cent. During the 1990s an additional loss of about 4 per cent is expected, meaning future depletions over southern Canada may reach an average loss of about 8 per cent.

It is important to note that scientific knowledge of the atmosphere and the processes that deplete the ozone layer is not complete. The sudden and unexpected appearance of the Antarctic ozone hole reveals that the ozone layer does not respond predictably to the quantities of industrial chemicals we are dumping into it.

Q3.18
Can ozone depletion be stopped and reversed? Yes. If concentrations of ozone-destroying chemicals are reduced the natural balance between ozone creation and destruction can be restored. However, this might require the complete elimination of CFCs, halons, carbon tetrachloride, methyl chloroform, HCFCs, and methyl bromide. In late 1991, scientists estimated that even with the current global schedule to eliminate ozone-destroying substances, the ozone layer would not return to 'normal' (pre-1980 chlorine levels) until the year 2060.

Q3.19
What can I do to protect myself and my family from the effects of ultraviolet radiation? A few simple steps will help protect us from the sun's harmful rays:

1. Keep sun exposure to a minimum, especially between the hours of 10:00 a.m. and 3:00 p.m. when the sun's rays are the most intense.

2. Wear wide-brimmed hats, UV-B blocking sunglasses, and long-sleeved shirts and pants.

3. Wear sunscreen with a Sun Protection Factor (SPF) of 15 or greater on any exposed skin. Re-apply every hour or after swimming or strenuous activity.

Action Step

In some cases, however, consumer products containing ozone-depleters are already in use in our homes and offices and cannot be easily replaced. A second strategy, therefore, involves proper care and maintenance of equipment to ensure that the CFCs they contain are never released to the stratosphere.

Smog

Despite improvement in recent years, smog remains a major concern for many Canadians. This section explains what smog is, where it comes from, and what effects it can have.

Q3.20
What is smog? Smog is a chemical mixture of gases that forms a brownish-yellow haze primarily over urban areas. Components of smog include ground-level ozone, nitrogen oxides (NOx), volatile organic compounds (VOC), sulphur dioxide, acidic aerosols and gases, and particulate matter. These gases result from a reaction between certain airborne pollutants and strong sunlight. Smog is most prevalent in the summer months, when there is the most sunlight and temperatures are the highest. In large enough quantities, it poses threats to animal, plant, and human life. The airborne pollutant which makes up 90% of all smog found in urban areas is ground-level ozone.

Q3.21
How is ground-level ozone formed? Ground-level ozone forms as a result of a chemical reaction between several distinct forms of pollutants and sunlight. Two groups of chemical pollutants are involved: nitrogen oxides (NOx), and volatile organic compounds (VOC). When stagnant air masses linger over urban areas, the pollutants are held in place for long periods of time. Sunlight interacts with these pollutants, transforming them into ground-level ozone. The ozone remains in the lower atmosphere until weather systems flush out a given area and dissipate them. An 'episode' of ground-level ozone can last from several hours to several days. Episodes are particularly severe in cities with high concentrations of NOx and VOC during periods of warm weather.

Q3.22
Is there a difference between ground-level ozone and stratospheric ozone? No. Ozone is the same chemical in the stratosphere and near the ground. Yet it has very different effects on life depending upon where it is located. Near the ground it is dangerous, in sufficient quantities, to the health of plants and animals. In the stratosphere, it protects animals and plants from dangerous ultraviolet radiation.

Q3.23
What are NOx and VOC? Nitrogen oxides are compounds formed of nitrogen and oxygen, and come from such processes as bacterial action in the soil, lightning, volcanoes, and forest fires, as well as from the burning of fossil fuels. Volatile organic compounds are organic gases and vapours that evaporate into the air easily. They are released by the decay of organic materials and during industrial professes that involve combustion, and as a result of the evaporation of liquid fuels, solvents, and organic chemicals (e.g., nail polish remover, barbecue fluid, gasoline fumes).

Q3.24
How much ground-level ozone is too much? Even without artificial sources of ozone at ground level, we find ozone in the lower troposphere in trace amounts. Some of this ozone is from air currents that bring ozone from the upper atmosphere down to the surface of the Earth, while the rest is from natural sources of NOx and VOC. In these small quantities, ozone poses no threat to humans or ecosystems. But there is a point at which ground-level ozone becomes a threat to the functioning of all living things. It has been determined that 82 parts per billion is the starting point for problems as a result of ozone exposure.

Did you know?
Fossil fuels and their by-products are responsible for 95% of NOx and 60% of VOC emissions.

Q3.25
Where is ground-level ozone found? High levels of ground-level ozone are found primarily in urban areas, particularly those with large industrial centres and high rates of traffic. With the exception of Saskatoon and Victoria, all major urban centres in Canada experience higher than acceptable levels of ozone during the peak periods of ozone formation. The formation of ozone depends greatly on the topography of the land, the prevailing weather systems, and the level of pollutants being emitted. However, ground-level ozone can also be found in rural areas far from its urban point of origin. While the transferral of ozone over long distances reduces its concentration, it can still pose a risk to plants, people, and wildlife.

Q3.26
What hazards does ground-level ozone pose to humans? The possible threats of ground-level ozone vary with exposure. During short-term, high-intensity exposure, health effects can include irritation of the nose and throat, coughing, painful breathing, and reduced lung function. People who exercise late in the afternoons and early in the evenings the time of day when smog is usually at its highest concentration can expect pain while inhaling, as well as the more common symptoms associated with ozone exposure. Long-term exposure to smog at low levels can affect lung elasticity and the lungs' ability to resist disease, effectively aging lungs prematurely. Children, the aged, asthmatics, and sufferers of other chronic lung diseases are more susceptible to smog effects than the general population.

Q3.27
What problems does ozone pose for plant and animal life? The effects of ozone on animals are similar to its effect on humans: decreased lung capacity and lung elasticity. As for plants, ozone damages leaf tissue. This can greatly affect the ability of plants to grow and thrive. Visible damage to leaf tissue includes discolouration, black and white spots, paper thin areas on the leaf, as well as leaf loss. Ozone damage can lead to 10 to 40% growth loss, premature aging, and a decrease in pollen lifespan. Damage can affect crop yields by as much as 20% in some cases.

Q3.28
What effect can ozone have on structures and materials? Ground-level ozone can have serious damaging effects on many human-produced materials; in particular, ozone can damage or destroy most forms of synthetic materials. With low-level exposure of only a few months, ozone can cause cracks in rubber and synthetic rubber products; with continued exposure, it can actually cause total disintegration. Ozone damages the integrity of cotton, acetate, nylon, polyester, and other textiles. It has been known to bleach materials, dyes, paints, and coatings.

Q3.29
What can smog-related problems do to the economy? Smog can have a major impact on many aspects of our economy.

• The health problems associated with smog lead to higher health care costs.

• Crops are damaged by smog. It is estimated that in Ontario alone, the damage done to food production through ozone exposure can be as high as $70 million per year.

• Ground-level ozone is linked with damage to Canada's red and sugar maple trees, as well as other species of trees that make up part of Canada's forestry industry.

• Although no estimates have been done in Canada, estimates in the U.S. blame ground-level ozone for up to one billion dollars annually in damage to materials exposed to the pollutant.

Q3.30
How can urban air recover from the stresses of pollution? Because ground-level ozone (and smog in general) results from a combination of pollutants, heat, and sunlight, the most effective way of combatting it is to reduce the level of these pollutants NOx and VOC. Since the main sources of NOx and VOC are vapours from hazardous products and the combustion of fossil fuels by vehicles and industry, the logical way to reduce smog is to be careful and efficient in our use of these products and resources.

Action Step

• using alternative transportation walking, cycling, mass transit, ride sharing;

• driving within the speed limit (optimum fuel economy is reached when driving from 50 to 70 km/h);

• maintaining your vehicle tune-ups, oil changes, and proper tire inflation all help.

• using alternative fuels such as ethanol, propane, and natural gas which emit a smaller amount of pollutants.

• using oil-based paints and solvents like gasoline and mineral spirits only when necessary.

• making your home energy efficient.

Climate Change

Climate change is potentially one of most serious environmental issues that we face today. Although there has been controversy over specific predictions and policies relating to climate change, we do know a lot about it. This section looks at the causes and likely consequences of climate change and global warming.

Q3.31
What is climate change? Climate change is a change in the 'average weather' a given region experiences, based both on the kinds of characteristics that the climatic zone exhibits, and the level of variability of those characteristics.

Q3.32
Is climate change natural? Yes. The Earth tends to experience dramatic changes in weather patterns every 100,000 years, with the cycles of glacial advance and retreat. This is coupled with other smaller cooling periods every 20,000 to 40,000 years. Canada's present climate was established around 10,000 years ago, when the last ice age ended. Since then, there have been several smaller fluctuations in temperature and weather conditions.

Q3.33
Can human actions affect climate change? Yes. Recently a concern has arisen that over the last 150 to 200 years certain human activities have influenced the rate of change in the climate system. Scientists believe that the natural system responsible for the warmth of the Earth's surface, commonly known as the 'greenhouse effect', has been enhanced by the emission of substances known as 'greenhouse gases' (see the chapter on climate in section 2 'The Biosphere - An Overview' for an explanation of the greenhouse effect). Many believe that this will lead to global warming beyond normal climate fluctuations.

Q3.34
What is the difference between climate change and global warming? Although the terms 'global warming' and 'climate change' have often been used inter-changeably, they are not identical. Climate change can imply both warming and cooling conditions, while global warming pertains only to those climate changes related to a temperature increase. Thus global warming is only one possible aspect of climate change.

Q3.35
Is increase in average temperature the only phenomenon associated with global warming? No. Other changes associated with global warming include:

• changes in the frequency, amount, and seasonal distribution of precipitation

• increased evaporation and drying of continental interiors

• increased melting of perma-frost, snow, sea ice and ice caps

• changes in oceanic currents

• rise in sea level.

Q3.36
How can human activity influence the greenhouse effect? For 1,000 years prior to the industrial revolution, the concentration of greenhouse gases in the atmosphere was relatively constant. This has changed in the last 200 years; industrialization brought with it emissions of large quantities of greenhouse gases. Other things being equal, the more greenhouse gases there are, the greater the greenhouse effect, and the higher the Earth's temperature. This increase in average temperature is a key part of the phenomenon known as 'global warming'. The enhancement of the greenhouse effect due to the emission of greenhouse gases is one important reason why global warming could occur.

Q3.37
What are the greenhouse gases, and where do they come from? Most greenhouse gases occur naturally. However, modern industry and lifestyles have led to new sources of greenhouse gases, as well as to the emission of entirely new greenhouse gases. Among the most important greenhouse gases are:

Water vapour. Water vapour comes from natural and human-induced respiration, transpiration,
and evaporation. The amount of water vapour released through evaporation increases as the Earth's surface temperature rises.

Carbon dioxide. Carbon dioxide comes from the decay of materials, respiration of plant and animal
life, and the natural and human-induced combustion of materials and fuels. It is removed from the atmosphere through photosynthesis and ocean absorption. Of the greenhouse gases, carbon dioxide is second only to water vapour in volume.

Methane. Although there is less methane than carbon dioxide in the atmosphere, methane is a
more potent greenhouse gas. It comes from the decay of matter without the presence of oxygen. Primary sources include wetlands, rice paddies, animal digestive processes, fossil fuel extraction, and decaying garbage. It is destroyed primarily through chemical reactions with other gases in the atmosphere.

Nitrous oxides. Soils and oceans are the primary natural sources, while humans contribute to
nitrous oxide emissions through soil cultivation and use of nitrogen fertilizers, nylon production, and the burning of organic material and fossil fuels.

Ozone. Ozone exists naturally in the lower atmosphere in minute quantities. It is also produced in
the lower atmosphere from a reaction involving several human-produced pollutants and sunlight.

Halocarbons. These human-produced chemicals are compounds containing members of the
halogen family (bromine, chlorine, and fluorine) and carbon. They are some of the most potent greenhouse gases of all. Most are used in various industrial and home uses, with chloroflurorcarbons (CFCs) being the most familiar example.

Q3.38
How much have concentrations of greenhouse gases increased in recent years? Over the past 200 years methane concentrations have more than doubled. Carbon dioxide concentrations are 20% higher today than the highest values of the past 160,000 years. And some greenhouse gases, such as halocarbons, have come into existence only in the last 100 years.

Q3.39
Will these increased concentrations of greenhouse gases have an effect on the global climate? Scientific theory predicts that they will. Using models of the world's climate, scientists have calculated that the Earth's average temperature should have risen by between 0.4oC and 1.3oC over the last 100 years. This prediction is based upon the amount of greenhouse gases human activities have added to the Earth's atmosphere. It also takes account of the fact that the Earth's climate system responds quite slowly to changes in the levels of greenhouse gases.

Q3.40
Has this predicted temperature increase in fact occurred? Yes, but just barely. An analysis of temperature records shows that the Earth has warmed an average of 0.5oC over the past 100 years. This is consistent with predictions of global warming due to enhancement of the greenhouse effect. Yet it is also within acceptable limits for natural variation in temperature. The fact that the seven warmest years during the twentieth century have occurred since 1980 lends support to the assumption that the Earth's climate is warming, but it may take another decade of continued increases in global temperatures to provide conclusive evidence that the world's climate is warming due to enhancement of the greenhouse effect.

Q3.41
How quickly do scientists expect temperatures to increase in the future? In 1990, the Intergovernmental Panel on Climate Change (IPCC) concluded that if human activities contributing to the greenhouse effect are not slowed, global mean temperatures during the next century will rise an average of between 0.2oC and 0.5oC per decade. This means that the likely rise in global temperature will be 3oC before the end of the next century. Such a change might seem insignificant, but it should be borne in mind that it is a global average. A climatic shift of this magnitude and rapidity has not been experienced since the last de-glaciation some 10,000 years ago; the difference between average global surface temperatures now and at the peak of the last ice age is a mere 4oC to 5oC. Global warming could thus have a significant impact on all of the Earth's ecosystems.

Q3.42
Do all scientists agree with these predictions? While there has been much debate over climate change, it is generally agreed that:

• There is a natural greenhouse effect that keeps the Earth warmer than it would be without it.

• Human activities are enhancing this process by releasing gases such as carbon dioxide and methane into the atmosphere.

• An enhanced greenhouse effect will result in global warming.

  What is less certain is how quickly temperature changes will take place, and what the effects of global warming will be on particular regions or locales.

Did you know?
The Earth's seven warmest years since 1881 have been: 1981, 1983, 1987, 1988, 1989, 1990, and 1991. The year 1991 was the second warmest ever recorded.

Q3.43
Why are there variations in global warming predictions? The basic science is not in dispute; the heat-trapping properties of greenhouse gases are well known, and their build-up in the atmosphere is well documented. However, predicting the rate of global warming is extremely complex. Uncertainties arise from our imperfect knowledge of:

• future rates of human-made greenhouse gas emissions

• the response of the global climate to these emissions.

Anticipating future rates of emission of human-made greenhouse gases requires predicting complex political, socio-economic, and technological factors. Scientists deal with this problem by making predictions for a number of different possible scenarios, varying key assumptions for each scenario. The Intergovernmental Panel on Climate Change's 'business-as-usual' scenario, for example, assumes a coal-intensive energy supply, only modest increases in energy efficiency, continued deforestation, modest curbs on carbon monoxide, and no controls on agricultural emissions of methane and nitrous oxide. Other scenarios make more hopeful assumptions: shifts toward lower carbon fuels, greater increases in energy efficiency, reversal of deforestation, etc.

The second source of uncertainty is our understanding of climate processes themselves. Scientists deal with this sort of uncertainty by giving their climate predictions as ranges. Under the 'business-as-usual' scenario, for example, the best estimate for global warming is a temperature increase of 0.3oC per decade, within an uncertainty range of 0.2oC to 0.5oC. Each scenario has a best estimate and an uncertainty range.

Q3.44
What effects would global warming have on Canada's natural ecosystems? Ecosystems and species must either adapt to climate change, move, or disappear. If the changes are gradual, migrations usually proceed with minimal disruption. Rapid change, allowing less time for adaptation or migration, could significantly lower some species populations. For example, climate change models suggest relatively quick temperature and precipitation changes in comparison to tree species' migration rates. Thus, despite higher carbon dioxide concentrations, longer and warmer growing seasons, and milder winters, the total area covered by trees in Canada is expected to decrease.

Q3.45
What effects would global warming have on Canadian agriculture? The higher concentrations of carbon dioxide which contribute to global warming are likely to have a beneficial effect on most plants, since carbon dioxide is a plant nutrient and improves plant water-use efficiency. Temperature increases will allow the expansion of agriculture northward, and lengthen the growing season in present cropping areas. However, much of Canada's northern land consists of soil that is unsuitable for supporting crops. As well, higher temperatures will significantly increase evaporation, greatly reducing soil moisture in some areas. It is also believed that drought years, occurring everywhere as part of natural year-to-year climate variability, will become more frequent and more severe.

Q3.46
What effects would global warming have on Canada's water resources? Current climate models agree on the following points:

• During the winter, precipitation is likely to increase across Canada.

• The snow season will be significantly shorter. Except for the North, snow accumulations will be less.

• During the growing season, precipitation is likely to increase in northern Canada and decrease or remain relatively unchanged in southern Canada.

Water resources in northern Canada are likely to become more abundant, which could increase the potential of northern hydro-electric production operations. However, drier conditions in the south are expected to increase demands for large-scale water diversions. Another possible effect is lower stream flow and lake levels, which would cause the disappearance of many wetlands, a deterioration in water quality, and increased shipping costs by water, as large vessels would be forced to carry lighter loads in order to pass through shallow waterways.

Q3.47
What effect would global warming have on snow and ice in Canada? Lowered duration of ice cover on lakes and oceans would make northern Canada much more accessible to marine navigation and activities such as fishing and resource exploitation. On the other hand, increased snow accumulation may accelerate glacial flow and iceberg formation. Permafrost melting in the north will reduce the stability of land, disrupting transportation. In southern Canada, winter transportation would benefit from more navigable waterways and less required snow removal. While the season for winter recreational activities would shorten, the season for summer recreation would lengthen.

Q3.48
What effect would global warming have on Canada's coastal regions? The mean levels of the world's seas have been rising slowly over the past 100 years at a rate of nearly 1.5 cm per decade. As the global climate warms, this rate is likely to increase due to the melting of ice on land and the expansion of sea water as it warms. Expected effects include:

• increased beach erosion and loss of coastal wetlands

• increased frequency and extent of coastal flooding

• damage to coastal structures, port facilities, and water management systems

• loss of agricultural and habitable land.

Although Canada's rugged coastline makes it less vulnerable to coastal flooding than many other countries, the country's coastal areas will not escape harmful effects if sea levels rise. In Charlottetown, for example, a one-metre rise would flood the harbourfront at high tide; major storms, which occur about once every 20 years, would flood large parts of the downtown residential and commercial district.

Action Step

• using motor vehicle transportation less often and more efficiently

• making their homes energy efficient

For more details on how not to contribute to climate change please see the action guide.

Acid Rain

Despite progress in recent years, acid rain remains a significant environmental and economic concern for many regions of Canada. This section explains what acid rain is, where it comes from, and what its effects are.

Q3.49
What causes acid deposition? Acid deposition commonly called acid rain is caused by emissions of sulphur dioxide and nitrogen oxides. Although natural sources of sulphur oxides and nitrogen oxides do exist, more than 90% of the sulphur and 95% of the nitrogen emissions occurring in eastern North America are of human origin. These primary air pollutants arise from the use of coal in the production of electricity, from base-metal smelting, and from fuel combustion in vehicles. Once released into the atmosphere, they can be converted chemically into such secondary pollutants as nitric acid and sulphuric acid, both of which dissolve easily in water. The resulting acidic water droplets can be carried long distances by prevailing winds, returning to Earth as acid rain, snow, or fog.

Q3.50
Is acid deposition always wet? No. The acids can be transformed chemically into sulphur dioxide gas or into sulphur and nitrogen salts. In this form they are deposited 'dry', causing the same damage as when they land dissolved in rain or snow. In this form they can also do internal damage to plants as they are taken up from the soil.

Did you know?
About 40% of nitrogen oxides come from transportation (cars, trucks, buses, trains), about 25% from thermo-electric generating stations, and the balance from other industrial, commercial, and residential combustion processes.

Q3.51
Is natural precipitation acidic? Yes. Water solutions vary in their degree of acidity. If pure water is defined as neutral, baking soda solutions are basic (alkaline) and household ammonia is very basic (very alkaline). On the other side of this scale, there are ascending degrees of acidity; milk is slightly acidic, tomato juice is slightly more acidic, vinegar is mediumly acidic, lemon juice is still more acidic, and battery acid is extremely acidic.

If there were no pollution at all, normal rainwater would fall on the acid side of this scale, not the alkaline side. Normal rainwater is less acidic than tomato juice, but more acidic than milk. What pollution does is cause the acidity of rain to increase. In some areas of Canada, rain can be as acidic as vinegar or lemon juice.

Q3.52
If rain is naturally acidic, why does it matter if pollution makes it more acidic? The problem is one of balance; nature depends upon balance. Normal precipitation reacts with alkaline chemicals derived from the region's bedrock and found in the air, soils, lakes, and streams and is thereby neutralized. However, if precipitation is more highly acidic, then acid-buffering chemicals can eventually become depleted. In this case, the buffering effect will no longer occur, and nature's ability to maintain balance will have been destroyed.

focus
The pH scab: Acidity is measured in terms of pH, on a scale that runs from zero, the most acidic, to 14,
the most alkaline. A change of one unit on the pH scale represents a 10-fold change in acidity. Organisms generally thrive near pH 7, the neutral point, and function less successfully toward either end of the scale.

Q3.53
Do all regions have the same acid-neutralizing capacity? No. Different types of bedrock contain variable amounts of alkaline chemicals. Regions with bedrock containing less alkali have a lower capacity for reducing acidity, and thus are more sensitive to acid deposition.

Q3.54
What happens when this buffering effect is disrupted? When the environment cannot neutralize acid rain, damage occurs to forests, crops, lakes, and fish. Toxic metals such as copper and lead can also be leached from water pipes into drinking water.

Did you know?
About 46% of Canada's surface area is considered highly sensitive to acid deposition. Much of this area lies in the Canadian Shield which contains a large proportion of this country's wealth of lakes and wetlands.

Q3.55
How does acid deposition affect aquatic ecosystems? The interactions between living organisms and the chemistry of their aquatic habitats are extremely complex. If the number of one species or group of species changes in response to acidification, then the ecosystem of the entire water body is likely to be affected through the predator-prey relationships of the food web. At first, the effects of acid deposition may be almost imperceptible, but as acidity increases, more and more species of plants and animals decline or disappear.

• As the water pH approaches 6.0, crustaceans, insects, and some plankton species begin to disappear.

• As pH approaches 5.0, major changes in the makeup of the plankton community occur, less desirable species of mosses and plankton may begin to invade, and the progressive loss of some fish populations is likely, with the more highly valued species being generally the least tolerant of acidity.

• Below pH of 5.0, the water is largely devoid of fish, the bottom is covered with undecayed material, and the nearshore areas may be dominated by mosses.

• Terrestrial animals dependent on aquatic ecosystems are also affected. Waterfowl, for example, depend on aquatic organisms for nourishment and nutrients. As these food sources are reduced or eliminated, the quality of habitat declines and the reproductive success of the birds is affected.

Q3.56
How does acid deposition affect terrestrial plant life? Both natural vegetation and crops can be affected.

• It can alter the protective waxy surface of leaves, lowering disease resistance.

• It may inhibit plant germination and reproduction.

• It accelerates soil weathering and removal of nutrients.

• It makes some toxic elements, such as aluminum, more soluble. High aluminum concentrations in soil can prevent the uptake and use of nutrients by plants.

Q3.57
How does acid deposition affect animal life? The effects on terrestrial wildlife are hard to assess. As a result of pollution-induced alteration of habitat or food resources, acid deposition may cause population decline through stress (because of decreases in available resources) and lower reproductive success.

Q3.58
What are the socio-economic consequences of acidification?

• Lower productivity in fisheries, forestry, and agriculture translates to lower profits and fewer jobs for some of Canada's important industries.

• Acid deposition causes accelerated corrosion, fracturing, and discolouration of buildings, structures, and monuments.

Q3.59
How does acid deposition affect human health?

• We eat food, drink water, and breathe air that has come in contact with acid deposition.

• Canadian and U.S. studies indicate that there is a link between this pollution and respiratory problems in sensitive populations such as children and asthmatics.

• Acid deposition can increase the levels of toxic metals such as aluminum, copper, and mercury in untreated drinking water supplies.

focus
It has been estimated that acid rain causes $1 billion worth of damage in Canada every year. Thousands of lakes have been damaged; a large part of the salmon habitat in the Maritimes has been lost; a significant proportion of eastern Canada's forests has been affected; and considerable damage to buildings and monuments has been documented.

The Canadian Council of Resource and Environment Ministers in 1983 established 20 kg/hectare per year as the target for Canadian sulphur dioxide loading. In eastern Canada, 96% of the land with high capability for forestry is subject to acidic deposition in excess of 20 kg/ha per year. In recent years, important instances of dieback and declines in growth rate have been noted in sugar maple groves in parts of Canada that receive high levels of these and other air pollutants, such as ozone. Significant growth declines in northern Ontario forests, most notable over the past 30 years, coincide with a period of rapidly increasing industrialization and urbanization across much of the province.

Did you know?
More than 80% of all Canadians live in areas with high acid rain-related pollution levels.

Q3.60
Is acid deposition occurring to the same extent across Canada? No. Sulphur emissions tend to be concentrated in relatively few locations, while the sources of nitrogen emissions are widely distributed; however, where they are deposited depends on more than just where they are produced. Airborne acidic pollutants are often transported by large scale weather systems thousands of kilometres from their point of origin before being deposited. In eastern North America, weather systems generally travel from southwest to northeast. Thus, pollutants emitted from sources in the industrial heartland of the mid-western states and central Canada regularly fall on the more rural and comparatively pristine areas of the northeastern U.S. and southeastern Canada.

Action Step

by reducing the amount of energy used in the home (energy efficiency)

by reducing the stress your driving habits put on the environment.

For more information on how not to contribute to acid rain please refer to the action guide.

Did you know?
It has been estimated that about 50% of the sulphate deposited in Canada is derived from sources in the U.S.

Important Notices and Disclaimers Page Last Updated: 2001-10-05