What is the Issue of Climate Change?

The Changing Climate

The earth's climate has been forever changing. As shown in Figure 1, over the past 400 000 years, the earth's temperatures have changed significantly and periodically. From a warm climate to an ice age, the changes took place on millennial time scales. There is also evidence of large regional changes on time scales of decades. Closely correlated to the temperature changes have been the changes in the atmospheric concentration of carbon dioxide (CO₂) over the same period. Studies suggest that CO₂ is an important feedback in the process that strongly amplifies changes that were likely triggered by solar changes due to orbital variations.

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Figure 1. Temperature and Atmospheric CO2 Concentration Over the Past 400 000 Years

Over the past 150 years, abundant scientific data has demonstrated that the earth's climate has become warmer, and that the warming has been accelerating over the past two decades (Figure 2). This change in the climate has become a global issue of concern. According to a widely-accepted scientific consensus, the increases in the atmospheric CO₂ concentration over the same period (roughly since about 1860), as shown in Figure 3, are correlated to the rise in average temperature during the same period. The increases in CO₂ concentrations are very largely due to increases in emissions of CO₂ as a result of fossil fuel use and other activities of human societies (such as deforestation and soil cultivation). In the foreseeable future, the continued increase in anthropogenic emissions is projected to cause the continued rise of the earth's surface temperature; a rise which will likely have overwhelming negative effects on the earth's living beings.

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Figure 2. Changes in the Earth's Surface Temperature Relative to 1961 to 1990 Temperature Normals

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Figure 3. Changes in the Atmospheric Concentration of Greenhouse Gases

Greenhouse Gas Emissions and Climate Change

The earth's atmosphere is like a greenhouse. As shown in Figure 4, certain atmospheric gases, called greenhouse gases (GHG), trap infrared radiation being reflected back into space, thus warming up the earth's surface to the range that is suitable for living beings. Naturally occurring greenhouse gases, including water vapour, carbon dioxide, ozone, methane and nitrous oxide, together create a natural, delicately balanced, greenhouse effect.

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Figure 4. The Greenhouse Effect

Over the past century, the process of industrialization has lead to the extensive use of fossil fuels and the massive conversion of forested areas into agricultural lands or urban lands. As a result, as shown in Figure 5, significant additional quantities of greenhouse gases (mainly CO₂) have been released into the atmosphere. Once released, all of these types of gases remain in the atmosphere for long periods of time (for example, about a century for CO₂). This has intensified the natural greenhouse effect, and is believed to have induced the global warming that has become evident during the past century.

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Figure 5. The Main Greenhouse Gases

As the industrialized countries seek increasingly higher standards of living, and the developing countries strive to become industrialized, it is anticipated that, without significant changes in human activities, anthropogenic GHG emissions will keep increasing. This will result in doubling the concentration of greenhouse gases in the atmosphere before the end of this century, as compared to the pre-industrial level.

In its Third Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) presents six GHG emission scenarios for the coming century. The highest emission scenario is SRES A1 F1, which assumes low population growth, high economic growth and new and efficient technology. SRES B1 is the lowest emission scenario: it assumes low population growth, low economic growth, and rapid technology development. The IS92a and IS92b scenarios (Figure 6), which have been used in many past model studies, fall between these two extremes. Based on these and other scenarios, the latest climate models project that the global mean surface temperature could rise by about 1.4 to 5.8 Celsius degrees by 2100 (Figure 7).

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Figure 6. Greenhouse Gas Scenarios

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Figure 7. Projected Changes in Global Annual Mean Temperature

Potential Consequences of Climate Change

The increases in the earth's surface temperatures will lead to changes in many other aspects of the climate system, including precipitation, wind patterns, and the frequency and severity of extreme weather in a particular area. According to the IPCC, these changes will potentially have wide-ranging effects on natural ecosystems and on human societies. Figure 8 shows some of the anticipated impacts that have been estimated. Because of the interrelations between the sub-components within each of the natural ecosystems and the human community, as well as the complex human-nature interactions, the potential consequences are expected to be cumulative, therefore more complicated and far-reaching. Even more threatening and unpredictable, the changes in the climate may take place non-linearly, as observed from the paleoclimate record, if certain triggering points for the climate system should be reached. For example, if the thermohaline circulation slows down, there may be major changes in ocean circulation. Changes of this type could have catastrophic effects on climates of particular regions.

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Figure 8. Potential Impacts of Climate Change

Alleviating climate change

To minimize climate change and, thereby, to avoid the (poorly understood) disruption of the Earth's environment, the human community is taking actions around the globe. The ultimate goal is to sharply reduce greenhouse gas emissions, so that, as illustrated in the green curve in Figure 6, the CO₂ concentrations in the atmosphere will become stabilized. In 1992, the United Nations Framework Convention on Climate Change was signed by over 160 countries. A protocol to this Convention, the Kyoto Protocol was agreed to by over 160 countries in 1997. In July 2001, at Bonn, over 180 countries further reached a broad agreement for the implementation of this Protocol.

The legally-binding Kyoto Protocol commits the industrialized countries to reduce greenhouse gas emissions by an average of 5.2% below 1990 levels by the period 2008 to 2012. Canada's reduction target is 6 percent below 1990 levels for the same period. Based on the current projections of emission growth, this target equates to about a 26% reduction of greenhouse gas emissions for Canada in a decade (Figure 9), posing a major challenge for Canada.

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Figure 9. Canada's Greenhouse Gas Reduction Target for the Kyoto Protocol (Mt: millions of tonnes of CO2 Equivalent)

To meet Canada's commitment, the federal government has announced an Action Plan on Climate Change. Through a large set of measures, this Plan is expected to bring Canada one-third of the way toward meeting its emission reduction goal. The Government will invest up to $500 million on measures to reduce GHG emissions. Combined with the $625 million for climate change-related activities for the next five years that was announced in Budget 2000, this investment results in a commitment of $1.1 billion to reduce GHG emissions in Canada. This builds on the $850 million the Government of Canada has spent on climate change since 1995.

Governments at all levels, industry, communities, schools and non-governmental organizations are all involved in the actions to alleviate climate change. The short-term strategy is to improve the efficiency of energy use in Canada. For the longer term, investments are being made in technological innovation for the development of renewable energy forms and clean technologies, as well as in increases in the capacity of forest and soils to act as carbon sinks. At the same time, understanding climate change and its impacts and developing adaptation strategies have become a major focus of scientific research for the federal government.

More detailed accounts for Canada's actions in addressing climate change can be found in several climate change Web sites:

• Government of Canada
• Environment Canada
• Natural Resources Canada