Global Warming: Overview & Debates

Feature by Jay Makarenko || Feb 1, 2007

Global warming and climate change have become major environmental and political issues, both internationally and within Canada. This article provides an introduction to the scientific claims and debates concerning global warming. More specifically, it focuses on key scientific theories concerning the meaning of global warming, its causes, and potential impact on Canadians, in addition to exploring some of the scientific debates surrounding these theories and their political implications.

What is Global Warming?

Warming of the air temperature

Global Warming & the Greenhouse Effect

Theories on the causes of global warming

Impact of Global Warming on Canada

Potential consequences for Canadians

Debates on the Science of Global Warming

Scientific debate & political implications

Sources & Links for Further Information

List of article sources, links for more on this topic


What is Global Warming?

An explanation of what global warming is

Changing Weather & Climate

What precisely does global warming mean?  It’s useful to begin first with a brief look at the ideas of weather, climate, and climate change. Weather is the condition of the air or atmosphere (the huge blanket of gas that circles the entire Earth) at a particular place and time. Weather is usually measured in terms of wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. A snow flurry or rainstorm is weather. A clear sunny day is weather.

Climate is the “average weather” in a given location over a long period of time. For example, Vancouver has a wet and moderate climate. The area receives a high level of annual precipitation and temperatures are relatively moderate. In contrast, the Canadian Arctic has a dry and cold climate. The region receives relatively low levels of annual precipitation and experiences regular cold temperatures.

Climate change refers to shifts in the climate or average weather. This involves more than simply the annual changing of the seasons from summer, fall, winter, and spring. Instead, climate change involves significant and relatively permanent shifts in the average weather of a geographical location. If, for example, a region experiences a drastic and recurring drop in its annual precipitation, then we would say that its climate is changing (it is now a “dryer” climate). Similarly, if an area experiences several decades of abnormally cold temperatures, we would again say its climate has changed (it has changed to a “colder” climate).

Definition of Global Warming

Global warming is the scientific claim that the temperature of the air on the earth’s surface is increasing, making the planet warmer (hence, the term “global warming”). Moreover, this scientific claim has to do with the earth’s climate or average weather, as opposed to simply changes in the seasons. The global warming claim is not that the earth’s air temperature is warmer today than it was six months or a year ago. It is, instead, a claim that the average annual temperature of the earth’s air is increasing (the average temperature of all the days in one calendar year). Two important components of this global warming claim can be further distinguished. Firstly, global warming holds that the earth’s air temperature has increased significantly in the past. In other words, the average annual air temperature is warmer today than it was 50 or 100 years ago. Secondly, and more significantly, the claim also holds that the earth’s air temperature will continue to rise in the future. That is to say that the average annual temperature 50 or 100 years from now will be even warmer than it is today. This distinction is important because each component is based on different scientific evidence (see below) and comes with varying implications for the planet – and its inhabitants.

Scientific Basis for Global Warming

The claim of global warming has been based, in large part, on two different types of scientific evidence. On the one hand, there is the instrumental record. For over 150 years, scientists have been using instruments (such as thermometers) to observe and record daily air temperatures across the earth. These instrumental recordings have then been used to calculate the average temperature of the earth for each year, and then compared on a year-to-year basis. Using these recordings and comparisons, scientists have found that the earth’s annual average temperature has increased by approximately 0.6 degrees Celsius between the years 1861 and 2000, with major increases occurring in two periods: 1910 to 1945, and 1976 to 2000 (IPCC, Climate Change 2001: The Scientific Basis: 2001).

For more information on instrument-based estimates of global warming: IPCC: Climate Change 2001: The Scientific Basis: Summary for Policymakers (PDF)

In addition to instrumental recordings, scientists have also constructed climate models or simulations to estimate past and future climate changes. Climate models for the Northern Hemisphere have indicated that the temperature increase of the 20th century is likely to have been the largest of any century between the years 1000 and 2000 (with the 1990s likely being the warmest decade, and 1998 the warmest year). Moreover, these climate models have suggested this global warming trend will likely accelerate in the future. The Intergovernmental Panel on Climate Change, a United Nations agency that reports on climate change, has reported that current climate models project the earth’s average temperature will likely increase by an additional 1.4 to 5.8 degrees Celsius between 1990 and 2100 (IPCC, Climate Change 2001: The Scientific Basis: 2001).

For more information on model-based estimates of past and future global warming: IPCC: Climate Change 2001: The Scientific Basis: Summary for Policymakers (PDF)


Global Warming & the Greenhouse Effect

Theories on the causes of global warming

Leading theories on global warming suggest that the rise in the earth’s temperature is the result of a process called the ‘enhanced’ greenhouse effect, and, moreover, that this process is the result of human activities.

Normal’ Greenhouse Effect Theory

It is important to distinguish the ‘normal’ greenhouse effect from the ‘enhanced’ version. The normal greenhouse effect is a scientific theory concerning the regulation of the air temperature around the earth’s surface. Central to this theory is the idea that planets in our solar system are constantly being bombarded by energy radiated by the sun. In most situations, this energy simply bounces off a planet and back into space. In the case of the earth, however, a special process (the greenhouse effect) occurs by which much of the energy is trapped on the planet’s surface. This results in the earth having warmer air temperatures than it otherwise would.

How does this process work? Located in the earth’s atmosphere (the layer of gases and materials that surrounds the planet) are materials called greenhouse gases (such as water vapour, carbon dioxide, ozone, methane, nitrous oxide, and chlorofluorocarbons, or CFCs). These gases have important properties. On the one hand, they allow some of the sun’s radiated energy to pass through the atmosphere and hit the earth’s surface. On the other hand, they block that energy from bouncing off the earth’s surface and heading back out into space. The result: a trapping of energy along the earth’s surface, which, in turn, warms the earth’s air temperature. This process operates much like a vegetable greenhouse in someone’s backyard (hence the reference to the “greenhouse effect”).

This normal greenhouse effect is naturally occurring, and has taken place on earth for millions of years. It is also a critical element for the development and continuation of many forms of life on this planet. Without the greenhouse effect, the earth would be a much colder planet and would not be able to support many of the plants, animals, and other organisms that exist today.

Enhanced’ Greenhouse Effect Theory

When scientists assert that global warming is the result of the greenhouse effect, they are actually referring to another related theory called the ‘enhanced’ greenhouse effect. This theory holds that over the last few hundred years, the normal greenhouse effect has become much more powerful than it was before. This, in turn, has resulted in more of the sun’s energy being trapped on the earth’s surface, and higher air temperatures – resulting in global warming.

What is causing the process to become more powerful? According to the theory, the enhanced greenhouse effect is the result of higher amounts of greenhouse gases in the earth’s atmosphere. The basic idea is that the ‘energy-trapping’ property of the atmosphere is directly related to the total amount of greenhouse gases it contains. As the level of greenhouse gases in the atmosphere grows, the stronger the greenhouse effect becomes, and the warmer the air on the earth’s surface becomes.

Global Warming & Human Activities

If the enhanced greenhouse effect theory is correct, then it raises an important question: why are there higher levels of greenhouse gases in the atmosphere? Many scientists have pointed to human beings as the primary cause. This view contends that as human societies have developed and become more industrialized, they have created greater levels of greenhouse gases (and carbon dioxide in particular) to be emitted into the earth’s atmosphere. This, in turn, has resulted in the enhanced greenhouse effect and global warming.

How do humans contribute to greenhouse gas levels? On the one hand, human beings are large producers of greenhouse gases, through such activities as the burning of fossil fuels (which produces carbon dioxide); agricultural production (which generates methane and nitrous oxide); and waste dumping, coal mining, and natural gas production (which all involve the production of methane). Moreover, human beings have also impacted the planet’s ability to naturally absorb these gases before they enter the atmosphere. The earth’s forests, for example, are major consumers of carbon dioxide, taking in the gas and releasing oxygen in exchange. Over the last 100 years, humans have developed large-scale forestry industries, resulting in high levels of deforestation. Fewer trees, it is argued, mean lower levels of carbon dioxide consumption and higher amounts being emitted into the earth’s atmosphere.


Impact of Global Warming on Canada

Potential consequences for Canadians

Global Warming & the Inter-dependent Planet

The earth’s ecosystem is a complex and inter-dependent process. Changes in one constitutive part (such as air temperature) can often lead to significant changes in other parts of the ecosystem. As such, there is much concern in the scientific community regarding global warming and what it might mean for the planet as a whole.

One area of concern is the affect of global warming on other climate trends. Some scientists, for example, have predicted that higher air temperatures could lead to changes in annual precipitation, shifting wind and cloud patterns, as well as changes in incidents of extreme weather (including hurricanes, tornadoes, hailstorms, and lightning storms). Such broad-based climate change would vary from region –to region, with some areas actually benefiting (such as from greater rainfall), and others facing difficult challenges (such as greater incidents of drought).

Another area of study involves the affect of global warming (and the wider climate change that may accompany it) on the planet’s physical and biological systems. Higher average temperatures may, for example, result in a rise in sea levels across the planet, which would drastically affect coastlines. Changes in precipitation could also impact river, stream, and lake systems (involving higher or lower levels of water flow). These climate and physical changes could, in turn, have implications for biological life on the planet, as plants, animals, insects, and micro-organisms adapt to their changing environment. Even human societies may face opportunities and/or challenges stemming from global warming (see below for more on the possible consequences of global warming for Canadians).

It is important to note, however, that the precise impacts of global warming and climate change are not certain. Our understanding of global warming, and its relationship with other physical and biological processes, while growing, is far from complete, and is often based on scientific theories and models that can only provide “best estimates.” Thus, when considering the potential implications of global warming, it is important to view current scientific assessments (such as those summarized in this article) as tentative projections, which are open to modification as new evidence becomes available.

See the Scientific Debate on Global Warming section of this article for more information on the debate surrounding global warming and its impacts.

Consequences of Global Warming for Canadians

What are some possible consequences of global warming for Canadians? In 2004, the Government of Canada released a comprehensive report on climate change, entitled Climate Change Impacts and Adaptation: A Canadian Perspective. Before summarizing key conclusions of the Report, some background is essential.

The Report was delivered under the Government of Canada’s Climate Change Impacts and Adaptation Program, which provides funding for research and activities to “improve our knowledge of Canada’s vulnerability to climate change, to better assess the risks and benefits posed by climate change, and to build the foundation upon which appropriate decisions on adaptation [to climate change] can be made.” (Climate Change Impacts and Adaptation Program: 28 November 2006). The Report is a summary of research literature from 1997 to 2002 in two primary areas of study: a) the potential impacts of climate change across Canadian regions and economic sectors, and b) possible strategies for adapting to these impacts

The Report adopts, as its basis, several important scientific claims. Firstly, it accepts the conclusion that the earth’s average temperature has increased by an estimated 0.6 degrees Celsius between the period 1861 and 2000. Secondly, it recognizes current projections by climate models and simulations are plausible. These models predict that the earth’s average temperature will further increase by 1.4 to 5.8 degrees Celsius between 1990 and 2100, and will bring with it broader climate and environmental changes (such as changes in precipitation, wind and cloud patterns, and sea levels). Thirdly, it recognizes human-caused increases of greenhouse gas levels in the atmosphere as a potential (but not necessarily definitive) cause of global warming.

The following section provides a summary of four key areas discussed by the Report:
1) water resources, 2) coastal zones, 3) natural resource sectors, and 4) human health and wellness. For the full text of the 2004 Report, please see:

Water Resources

According to the Report, global warming and its associated climate change could have a significant impact on water resources, and particularly water availability and water quality. Regarding water availability, the hydrological cycle (the natural cycle of water through the air and on land) is greatly influenced by air temperature; even small changes can have a large impact on water flows and supplies. According to the Report, some regions of Canada may experience higher rates of water shortage and droughts (especially in the summer months) due to greater water evaporation and reduced levels of precipitation. Some regions may also face water quality issues; higher air and water temperatures could result in greater incidents of water-borne diseases (such as E. coli), as well as contamination of water reservoirs due to increased flooding and heavy rainfall events.

Coastal Zones

Another potential consequence highlighted by the Report is a rise in sea levels along Canada’s coastal areas. Sea levels may rise because of several global warming–related factors. On the one hand, warmer average temperatures mean that the planet’s glaciers (large bodies of frozen water) will begin to melt into the oceans, causing sea levels to elevate. At the same time, higher air temperatures mean warmer water temperatures, which will also expand the total volume of the planet’s oceans and seas. According to the Report, the global sea level is projected to rise by anywhere from 8 to 88 centimetres between 1990 and 2100 (although, precise changes in sea levels would vary regionally).

If this rise in sea level were to occur, each of Canada’s coastal areas would face significant challenges. Many regions along the Atlantic coast, for example, are identified as highly sensitive to a rise in sea level, with key issues being higher incidents of surge flooding, permanent submerging of parts of the coast, accelerated levels of coastal erosion, and the degradation of coastal wetlands. While most of the Pacific coast would be generally unaffected by a rise in sea levels, some small but important (and highly populated) areas would be at high risk, including the Queen Charlotte Islands, the Fraser Delta, and parts of Victoria and Vancouver. Main issues there include the breeching of dykes, flooding, and coastal erosion. Finally, some areas of the Arctic coastline would face amplified coastal erosion stemming from rising sea levels in combination with decreased ice cover and permafrost degradation (which would also result from global warming).

According to the Report, there are several different strategies for dealing with rising sea levels, each with their own social and economic impacts. One option is to protect coastal areas through the construction or improvement of seawalls and dyke systems. Such a strategy would involve high capital costs. Another option is accommodation, which would involve adapting infrastructure, industry, and agricultural practices to deal with higher incidents of flooding (which would again involve capital costs). A third option is to retreat and abandon coastal regions affected by rising sea levels, which would entail significant social and economic costs associated with uprooting communities and businesses.

Natural Resource Sectors

According to the Report, global warming may also have significant consequences for several Canadian natural resource sectors, including agriculture, forestry, and fisheries.

Regarding the agriculture sector, global warming is projected to bring both advantages and disadvantages. Warmer temperatures would significantly increase the length of the growing season in many Canadian regions, and could result in increased yields in certain crops. This would, in turn, lead to higher levels of agricultural production and a more robust agricultural industry. Warmer temperatures (and other associated climate changes), however, may also lead to higher rates of crop damage in some regions due to heat stress, water shortages, extreme weather events, and insect problems.

The impact of global warming on the forestry sector could vary considerably between regions in Canada. Warmer temperatures would lead to longer growing seasons and increased plant growth, particularly in northern regions and those at higher elevations. Moreover, some species of trees would adapt more readily to global warming and its associated climate changes (such as higher levels of carbon dioxide), resulting in a proliferation of certain tree species and a decline in others. Warmer temperatures may also lead to higher incidents of forest fires and greater outbreaks of forest pests (such as spruce budworms and mountain pine beetles), with negative environmental and economic consequences.

Finally, global warming is also expected to have large impacts on the fisheries sector. An increase in average air temperatures would lead to changes in water temperatures, water levels, ice cover, extreme weather events and fishery diseases, all of which could have an impact on fresh and seawater fish populations and sustainable harvests. As with the agricultural and forestry sectors, these impacts on the fisheries could vary greatly between regions and bring both advantages and disadvantages to the industry.

Human Health & Wellness

While recognizing that a range of demographic, social, and economic factors influence physical health and wellness in the population, the Report concludes that changes in climate could have important ramifications for such factors as rates of death, illness, and injury. In some cases, these potential consequences would be direct. For example, higher average temperatures are expected to increase the occurrence of heat-related illness, such as heat exhaustion and heat stroke, and exacerbate existing conditions related to circulatory, respiratory, and nervous system problems. Global warming may also lead to increases in heat waves, particularly in urban areas, which may result in more deaths. As for beneficial impacts, higher average temperatures may result in decreased extreme cold events during winter months, and a fall in cold-weather-related fatalities.

Global warming could also have several indirect impacts on human health and wellness. These involve broad climate and environmental changes, which may be induced by a rise in the average air temperature. For example, global warming could lead to changes in wind patterns, cloud cover, and incidents of forest fires. This, in turn, may impact average and peak air pollution levels, with consequences for persons with respiratory disorders. Higher average temperatures may also encourage the migration and proliferation of insect species, leading to higher rates of insect-borne diseases such as malaria and West Nile virus. Moreover, global warming may also lead to higher incidents of heavy rainfall events and flooding in some regions, which would also encourage water- and insect-borne diseases. In other regions, however, global warming could lead to more arid climate conditions, which would then reduce the rates of these diseases in those areas.

The Report further goes on to detail the consequences related to adapting to these health and wellness issues. Some adaptation initiatives include the development of vaccines against emerging diseases, the reduction of global warming-related health risks through public education programs, an improvement of emergency preparedness measures, and an improvement of water protection and management systems (all of which may require substantial capital costs). 


Debates on the Science of Global Warming

Scientific debate & political implications

Throughout this article, mention has been made of the ‘uncertainty’ and ‘tentativeness’ of the claims associated with global warming and climate change. While there exists widespread (but not absolute) agreement that global warming is a real possibility, there remain gaps in our understanding of its scope and precise environmental and social consequences. Moreover, some in scientific and political circles have challenged the existence of global warming entirely, as well as the notion that it represents a substantial and pressing threat to the planet and its inhabitants. The following section offers an introduction to key issues and debates in this regard, as well as the political implications of these debates.

Existence of Global Warming

One point of contention is the existence of global warming itself. It is important to note, however, that this is a very complex debate with several important nuances. Most in scientific and political circles recognize the evidence of the instrumental record and its conclusion that the earth’s temperature has increased between the period 1861 and 2000 (see the What is Global Warming? section of this article for more on the instrumental record). There has, however, been some disagreement concerning the implications in the broader context.

Some have observed that the instrumental record alone does not prove that the earth is experiencing a prolonged and relatively permanent period of global warming. It may, instead, simply indicate a temporary rise in average air temperature, which will naturally correct itself over time. In response, supporters of the global warming thesis point to other forms of evidence, such as climate models and simulations, which suggest not only that the current rise and level of the air temperature is a unique event over the last 1,000 years, but also that it will continue (and even accelerate) in the foreseeable future.

This line of thinking, however, does raise questions concerning current climate models. Most in the scientific community (including the Intergovernmental Panel on Climate Change, the United Nation’s agency that reports on climate change) recognize the possibility that current models may not be absolutely accurate. (This is due, in large part, to the fact that scientists today cannot completely account for all the possible variables associated with changes in air temperature). Accordingly, critics of the global warming thesis often argue against using these models as evidence of global warming. In response, supporters often contend that current models are reliable enough to be taken seriously. In this vein, supporters often point to the fact that current models are highly consistent with the instrumental record. The basic idea behind this argument being that, if these models correctly reflect the observed rise in temperature over the last 150 years, then their estimates regarding previous and future temperature changes should be taken seriously.

Global Warming & Human Activities

Another issue often raised by critics concerns the causes of global warming, and, in particular, the claim that it is the result of human activities. Leading scientific theories hold that global warming is the result of the ‘enhanced’ greenhouse effect in the earth’s atmosphere, and, moreover, that this effect is connected to human activities, such as the burning of fossil fuels and deforestation.

See the Global Warming & the Greenhouse Effect section of this article for more information on global warming, the greenhouse effect, and human activities.

These leading theories, however, draw much of their evidence from climate models and simulations (actual experiments on the earth’s atmosphere would be impractical and highly dangerous). As discussed above, most scholars acknowledge that these climate models may not be absolutely accurate. Accordingly, critics often dismiss the connection between human activities and global warming (or, at the minimum, call it into question), on the basis that the evidence is far from reliable. Again, supporters of the connection counter by arguing that, while not perfect, current climate models are sophisticated and reliable enough to be taken seriously.

Consequences of Global Warming

A third issue, and possibly the most contentious, concerns the precise impact of global warming. Most in scientific and political circles would agree that if global warming were to occur to a significant extent, then other components of the planet’s ecosystem would be impacted. However, there is often significant disagreement concerning the precise nature and extent of these impacts.

Again, much of this disagreement is based on the soundness of climate and environmental models and theories. Our understanding of the precise extent of global warming, and its relationship with other physical and biological processes, is far from complete, and is often based on models and theories that can only provide “best estimates.” For some, this uncertainty means we should be cautious of current studies and reports, especially those that project drastic environmental and social consequences. For others, these reports and studies, while far from conclusive, represent well-educated projections, and, as such, should be taken seriously until disproved by additional evidence.

Political Implications of these Scientific Debates

Finally, it is important to recognize the political implications of these debates. If, on the one hand, the earth is in fact experiencing a human-induced period of global warming, and if this represents a situation that should be avoided, then there would seem to be very strong grounds for political action and change. Such a situation would provide an important justification for the creation of international agreements (such as the Kyoto Protocol on Climate Change), as well as higher levels of spending and regulation by societies and their governments to reduce greenhouse gas emissions and stall the global warming process.

If, however, the reality is that recent changes in the earth’s average air temperature are simply temporary, or beyond the control of human beings, or will not result in significant environmental and/or social changes, then the political implications are much different. Such a situation would seem to undercut the necessity of agreements such as the Kyoto Protocol. The same would also seem to be true of expensive government programs aimed at limiting the emission of greenhouse gases, as well as greater social regulation of personal and industry behavior.

In sum, the debate on global warming is much more than simply a scientific project. It also entails important, and very real, political and social implications.


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