One of the most pressing issues facing governments and industries today is global warming and the associated global climate change. Considerable debate is ongoing on what are the right policy instruments to use to reduce the emissions of carbon dioxide (CO₂) and other gases such as methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. These gases, also known as greenhouse gases (GHG), have been linked to a rise in the earth’s average temperature, termed global warming resulting in global climate change.

It is a well-established fact that the concentrations of CO₂ in the atmosphere have been increasing steadily. The average concentrations of CO₂ in the atmosphere reached 358 parts per million by volume (ppmv) in 1994, compared to the pre-industrial level of 280 ppmv. Despite the great uncertainty of its effect on global temperature increase and the impact on climate, the magnitude of the problem is potentially so huge that the government and industry must take “appropriate” actions now, rather than later.

In December 1997, more than 150 nations assembled in Kyoto, Japan; and agreed to a Protocol to cut greenhouse gas emissions. However, before it can become a binding agreement, the Protocol must be ratified individually in the signature countries. The overall target for CO₂ under the Protocol is to reduce emissions in industrialized nations to 5.2% below 1990 levels, no later than 2012. Canada is a signature party to the Protocol, with an emission reduction target at 6% below 1990 levels averaged over the years 2008–2012. This reduction target is a formidable task.

This paper provides an initial look at large carbon-dioxide sinks with respect to their capacities, retention/residence times, rates of uptake, and relative costs of utilization, at three scales – international, national (Canada), and provincial (Alberta). The authors expect that substantial refinement of the data presented here will take place in the future. By providing these preliminary data, it is hoped that it will provide a starting point for the policy makers in assessing the appropriate mechanisms to support in the planning of reduction measures.

In 1995, Canadians contributed about 619 million tonnes CO₂ equivalents (619 Mt CO₂ E) of anthropogenically-generated greenhouse gases to the atmosphere, about 2% of total global emissions. Carbon dioxide contributed approximately 81% of this, or 500 Mt CO₂. By this time, carbon dioxide emissions had already increased about 8% from the 1990 level of 464 Mt CO₂ and total greenhouse-gas emissions about 10% from the 1990 level of 564 Mt CO₂ E. A major cause of this change is attributed to increased economic activity. Canada’s commitment under the Kyoto Protocol calls for a 6% decrease in emissions from the 1990 level to 436 Mt CO₂ annually by the year 2012 (averaged over the previous 5 yr). Assuming that Canada wishes to achieve compliance, a course will have to be charted and implemented. Canada cannot wait until 2012 to start reducing greenhouse gas emissions. Here, a simple scenario is considered where Canada wishes to drop its emissions to 6% below 1990 levels in 2008 and keep them at this level for the next 5 yr. Accepting the Canadian government’s projections, the national CO₂ emissions level will have reached approximately 565 Mt CO₂ by 2010. Then, cumulatively over the 5-yr period, this gap translates to approximately 650 Mt CO₂ emissions that will need to be mitigated nationally in the period 1998–2012. Obviously uncertainties are large and other scenarios are possible. For example, due to unexpected closures of nuclear power plants in Ontario and predicted major development of oil sands in Alberta, emissions from these two provinces are expected to be much higher than predicted and will substantially contribute to the national total.

Alberta’s CO₂ contribution to the national totals in 1990 was the second highest of the provinces at 127 Mt CO₂ (27%), only exceeded by Ontario. In 1995, Alberta’s share had increased to approximately 30% of the national total (151 Mt CO₂). The gap between projected emissions for Alberta and a reduction target equivalent to the national target (6%) is difficult to project into the future without large uncertainty. Cumulatively, this gap translates to approximately 250 Mt CO₂ emissions that will need to be mitigated within the province for the period 1998–2012 if the national scenario described above is used (i.e. Alberta’s emissions track national emissions at the 30% level). What is not addressed in these predictions, is the ownership of the emissions. As Alberta exports much of its fossil fuel to the US for their consumption, a case could be made that the emissions from extraction/transport/refining of oil and natural gas in Alberta should be debited against the country who is the end-user.

The main sources of anthropogenic CO₂ include fossil-fuel utilization, cement production, and land-use changes. Sources of anthropogenic CO₂ can be centralized, as in a power generating station, or diffuse, as in the use of motor vehicles. No single method of CO₂ emissions reductions will be adequate to meet international, national or provincial reduction objectives, since no single method can address the issues related to both large central and diffuse emission generators.

Reduction of anthropogenic CO₂ emissions into the atmosphere can be achieved by a variety of means, which has been summarized by Herzog and can be expressed in a form of the Kaya identity.

CO₂ =POP×GDP/POP×BTU/GDP×CO₂/BTU?CO₂,

where CO₂ is the total CO₂ released to the atmosphere, POP is population, GDP/POP is per capita gross domestic product and is a measure of the standard of living, BTU/GDP is energy consumption per unit of GDP and is a measure of energy intensity, CO₂/BTU is the amount of CO₂ released per unit of energy consumed and is a measure of carbon intensity, and CO₂ is the amount of CO₂ sequestered in biosphere and geosphere sinks. Of the first two measures, reducing the population or the standard of living is not likely to be considered. Consequently, only the three remaining methods can be employed (i.e. reducing energy intensity, reducing carbon intensity and carbon sequestration).

A very attractive and cost effective solution (which will reduce energy intensity) is energy conservation, although it will require tough policy measures. Solutions are to improve energy and material efficiency or modify industrial processes, which will lead to a lowering of the rate of CO₂ generation. An option to reduce carbon intensity is to increase the use of renewable resources. However, until such energy sources can be developed and applied on a large-scale, fossil energy resources will continue to be the primary energy sources around the globe. During this period, reduction in carbon intensity could be achieved by switching to low carbon alternative fuels (for example switching to natural gas). While most of these options are probably solutions for the long term, more short and medium term solutions need to be found to deal with the problem of increasing CO₂ emissions. We are in agreement with Turkenburg, that the issue of emissions reduction is a complex one, and will only be solved by innovative responses that include both reducing the quantities of these gases emitted by anthropogenic activities, and enhancing and using greenhouse gas sinks. For the latter solution, a first step is to describe the attributes of these sinks quantitatively.

Carbon dioxide sinks can be grouped into three broad classes based on the nature, location and ultimate fate of CO₂ as depicted in Fig. 1. These groupings are:

• Biosphere sinks, which are active, environmentally sensitive, natural reservoirs for CO₂. The oceans, forests, and soils (agricultural) ecosystems are members of this class.

• Geosphere sinks, which are natural reservoirs for CO₂, but require anthropogenic intervention in order to make use of the sink. Members of this class include oil reservoirs suitable for enhanced oil recovery (EOR), coal beds, depleted oil and gas reservoirs, and deep aquifers.

• Material sinks, which are anthropogenically created/generated pools of carbon. This class includes durable wood products, chemicals and plastics as members.