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Understanding Climate Change

Over the course of the last century, the average temperature on Earth has increased by 0.6^°C, and this warming appears to be picking up speed. The 20th century was the warmest in the past 1000 years. The 1980s were the warmest decade on record – until the 1990s, which were warmer still. The trend is continuing with the 21st century having some of the warmest years on record.

"There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities."

Intergovernmental Panel on Climate Change

Most scientists agree that human activities are a major factor in this warming, particularly the increase in average global temperatures observed since the middle of the 20th century. This is the conclusion of the Intergovernmental Panel on Climate Change (IPCC), an international organization of hundreds of the world's top climate scientists. The IPCC projects average global temperatures will continue to rise by 1.4^°C to as much as 5.8^°C during this century.

As the average global temperature rises, it will lead to more and more changes in weather in Canada and around the world. The warmer it gets, the more dramatic – and disruptive – other changes in climate are likely to be.

What Is Climate Change?

When we talk about climate, we are talking about the typical kind of weather that a certain location or region can expect to have from one season to the next, from one year to the next, and even from one decade or one century to the next.

Climate change is a term used to describe a shift in the climate of a specific region or even the entire planet from one period to another. This is what we are seeing now. Increasingly, the weather we are getting – the amount of precipitation we receive and when it falls, and the temperature ranges through the year, for example – is no longer the sort of weather that would be expected, based on records from previous centuries and earlier.

Higher temperatures lead to higher rates of evaporation and precipitation, more frequent heat waves, less frequent cold snaps, and generally more energy for storms and other extreme weather events. Thus, as the Earth warms, experts expect, for example, that the frequency of very heavy and extreme precipitation events and of local flooding could increase in some areas. In other areas, increased drought could occur. The number of tornadoes and the intensity of thunderstorms and related extreme wind and hail events could also increase in some areas.

How do we know about past climate?

Modern temperature records go back only to about 1860 but, by studying sediment cores from the bottoms of oceans and lakes, tree rings, glacier ice cores and other data, scientists can tell how climate has changed over thousands of years. As they are created over many years, such things as tree rings and layers of glacial ice exhibit certain chemical and physical properties according to the conditions that existed at the time they were formed. By studying these properties and others, such as the concentrations of different gases in air bubbles trapped in glacial ice, scientists can gain insight into what the climate and the atmosphere were like at different times in the distant past.

Human Activities and the Greenhouse Effect

This increase in average global temperatures is occurring because the greenhouse effect is getting stronger.

When heat energy from the sun enters the Earth's atmosphere, about a third of it is reflected back to space. Of the remaining two thirds, some is captured by the atmosphere, but most is absorbed by the surface of the Earth. As it warms, the Earth, in turn, emits heat energy. Some of this escapes to space but, because it is emitted at longer wavelengths (infrared radiation), some of it is absorbed and re-emitted by clouds and greenhouse gases (GHGs), such as water vapour, carbon dioxide, methane and nitrous oxide. This is the natural greenhouse effect, and it is vital to life as we know it.

Without the natural insulation provided by these GHGs, the average temperature on Earth would be -18^°C, instead of the current average of about 15^°C, a difference of 33^°C.

The proportion of GHGs is less than 1 percent of the total gases in the atmosphere. Although the concentrations of these gases are low, it is still possible for human-caused emissions to have a drastic effect on the surface temperatures on Earth.

We need GHGs to make our planet liveable, but it is possible to have too much of a good thing. Because the concentration of GHGs in our atmosphere is increasing, our natural greenhouse is becoming more efficient at keeping the heat in.

James J. McCarthy
Harvard University
Co-Chair 2001, Intergovernmental Panel on Climate Change

GHGs occur naturally, of course, but more are created when fossil fuels – such as coal, oil and natural gas – are burned. Since the Industrial Revolution, we have been burning ever-increasing quantities of fossil fuels – to power our industries, generate electricity, heat and cool our homes, and drive our vehicles. Other human activities, such as the clearing of forested land for agriculture and urban development, and waste disposal methods such as landfill, can also lead to an increase in the concentration of GHGs.

Since the 1850s, concentrations of carbon dioxide in the atmosphere have increased by more than 30 percent. The concentration of methane in the atmosphere has increased by more than 150 percent since pre-industrial times, while nitrous oxide concentration is about 17 percent higher.

Greenhouse gases

Water vapour is the most common GHG. However, three others are of special importance to climate change because they are so often produced by human activities:

• Carbon dioxide (CO2) is released into the atmosphere through natural processes of plant and animal life and through human activities, primarily the burning of fossil fuels and other materials. It is the main contributor to climate change and accounts for about two thirds of the GHGs produced by human activities. Photosynthesis, the process by which plants take in CO2, removes CO2 from the atmosphere.

• Methane (CH4) is not as abundant as CO2 but is 21 times more effective at trapping heat. It is created when vegetation is burned, is digested or rots in an oxygen-free environment – buried in a landfill, for example. Wetlands, rice paddies, animal digestive processes and decaying garbage are the greatest sources of CH4 in our atmosphere.

• Nitrous oxide (N2O) occurs naturally in the environment, but human activities are increasing the quantities. This gas is most often released when chemical fertilizers and manure are used in agriculture.

Climate Change and Our World

On a global scale, climate change is expected to bring some benefits – for example, more precipitation could lead to greater food security in some regions, and longer growing seasons could enhance agricultural productivity in others. However, the net impacts of climate change are projected to be negative.

• One third of the world's population, close to 2 billion people, already suffers from a shortage of water, and this number is expected to increase dramatically as the global population increases. Climate change could add to the stress on fresh water supplies. Drought-prone areas could receive even less precipitation; glaciers and mountain snowcaps that feed rivers and streams in many parts of the world are already retreating. In Africa, for example, more than 80 percent of the ice field that existed on Mount Kilimanjaro has melted since 1912.

• In regions where growing food is already difficult, reduced water resources would make it even harder to feed growing populations. This could lead to the migration of millions of "climate-change refugees" to other countries.

• Because water expands as it gets warmer, and as more ice in the Arctic and Antarctic melts, sea levels will rise, possibly as much as 88 centimetres by the end of this century. Adapting to this change would entail major economic costs, and millions of people would be affected as coastal lands and islands are eroded and even submerged by rising oceans.

• Some types of severe weather – such as the heat wave blamed for the deaths of over 15 000 people in Europe during the summer of 2003 – are projected to become more common.

• As global temperatures rise, tropical and sub-tropical insects that spread serious diseases, such as malaria and dengue fever, could expand their range as habitat permits, potentially putting more people at risk. The impacts would be greatest in countries that do not have well-developed public health systems to deal with such outbreaks of disease.

Climate Change and Canada

"... Children in Canada are more likely to be hospitalized for respiratory problems resulting from exposure to air pollutants than due to any other cause."

"Changing Habits, Changing Climate: A Foundation Analysis" Canadian Institute of Child Health Report available at cich.ca

As with other parts of the world, climate change could bring some benefits to Canada, including milder winters and extended growing seasons. But most of the impacts of climate change on Canada are expected to be more detrimental to our health, our safety, our economy and our environment:

• More intense heat waves may cause an increase in heat-related illnesses and deaths, particularly in large cities in southern Canada.

• Air pollution and smog are already significant public health concerns – numerous studies have shown that air pollution can lead to premature death, increased hospital admissions, more emergency room visits and higher rates of absenteeism from work and school. Ground-level ozone, the primary ingredient of smog, results from a chemical reaction that occurs when airborne pollutants come together with sunlight and heat. As climate change pushes temperatures higher across the country, we can expect more smog days, especially in major urban areas.

• Changes in wind and weather patterns can also change the amount of plant pollen and mould spores in the air, making conditions worse for people with allergies.

• Climate change may cause severe weather events – hurricanes, tornadoes, thunderstorms, ice storms, floods and droughts – to occur more often and be more intense. Beyond the often large economic cost of these events, severe weather can cause injury and death, as well as serious emotional distress, as people are forced from their homes and into emergency shelters, see their property destroyed or face the loss or injury of loved ones. Surface water can also become contaminated during heavy rainstorms and floods by storm sewer overflows.

• Higher temperatures, if not balanced by higher precipitation, would lead to greater evaporation of our fresh water resources. This could result in lower flows of water that could, in turn, lead to an increase in water-borne diseases and to poor water quality due to increased concentrations of pollutants. Lower water levels will also affect the use of lakes and rivers for transportation, recreation and fishing, as well as our ability to generate hydroelectric power. Some glaciers in the Rocky Mountains, a vital source of fresh water, could be gone in as little as 20 years as climate change progresses.

• Sea levels on all three of Canada's coasts are predicted to rise as much as 9 centimetres each decade over the next 100 years. This would mean more erosion and flooding of Canadian communities, as well as increases in the already destructive and dangerous effects of storm surges.

• Fish, including valuable commercial species such as salmon and cod, are very sensitive to temperature. Changes in water temperature in the oceans, lakes and rivers would likely impact on fish growth, health and distribution, with potentially serious impacts on commercial and recreational fishing in Canada.

• As the weather in some regions of Canada becomes warmer and drier, we can expect more and bigger forest fires. The danger of fires in some areas is already increasing, as is damage to Canada's forest resources due to growing infestations of the mountain pine beetle, an insect normally kept in check by our cold winters. Smoke from forest fires is also detrimental to human health.

• Hot weather can cause micro-organisms to grow more quickly and can cause outbreaks of illnesses at recreational beaches, as well as contamination in shellfish. It can also increase chances of food-poisoning outbreaks if foods are not handled and stored properly.

• The Canadian Arctic is already experiencing impacts of climate change with higher temperatures, melting permafrost and declining sea ice. As these trends continue and are magnified, the economic, environmental and social consequences for communities in the circumpolar Arctic would be serious and wide-ranging. For example, Tuktoyaktuk, the major port in the western Canadian Arctic, is highly vulnerable to increased coastal erosion due to the reduced extent and duration of sea ice, accelerated thawing of permafrost and sea-level rise. Erosion is already a serious problem in and around Tuktoyaktuk, threatening cultural and archaeological sites and causing the abandonment of an elementary school, housing and other buildings. Successive shoreline protection structures have been rapidly destroyed by storm surges and accompanying waves.

"Some of our communities are eroding into the ocean in front of our eyes because of the decrease in the multilayered ice, which is allowing for larger storms to roll in."

Duane Smith, President Inuit Circumpolar Conference (Canada)

Over the present century, the increase in average temperatures in some regions of Canada, particularly the Far North, could be as much as 7^°C. That may not sound like a big difference, but when we consider that today's average global temperatures are only about 5^°C warmer than they were during the last Ice Age, we realize that even small changes can have a major impact. In North America, that 5^°C change in global average temperatures was enough to melt the vast sheets of ice that once covered much of the continent.

SOURCE: Government of Canada