Great Plains: Global Changes

Global Changes

Considerable concern has been expressed over the potential for global warming arising from the accumulation of radiatively active gases in the atmosphere. Carbon dioxide and nitrous oxide have been identified as contributors to global climate warming through the greenhouse gas effect in the upper atmosphere. The concentration ratios of these two gases in the atmosphere before the industrial revolution have been estimated as having increased by 26 percent and 8 percent, respectively ¹. Uncertainty remains as to what climate changes would eventually arise as the concentration of these gases increases. As the content of carbon dioxide in the atmosphere increases, plants respond with increased rates of photosynthesis and reduced rates of evapotranspiration.

Three strategies for dealing with prospective climate change are possible: do nothing and accept whatever change arises; adopt policies which facilitate adaptive responses; or adopt policies designed to reduce greenhouse gas emissions ². The degree to which greenhouse warming is occurring remains a matter of debate. Natural capacities to adapt to the change will reduce the impact of any climatic change. Agriculture is expected to be more affected by climate change than many other sectors of the economy.

Regardless of the strategy adopted for dealing with potential climate change, increased attention is being given to the effects of the individual gases, their source, and how to reduce their emissions. The development of prairie agriculture has contributed to the concentration of both carbon dioxide and nitrous oxide over time.

Following the commencement of cultivation of the prairies, large reductions in the level of organic carbon in the soil occurred. While the proportion of the organic carbon lost was substantial, it accounts for only a few percent of the carbon dioxide generated worldwide by land clearing activities. However, the rate of loss of carbon as the cultivation period lengthens declines quickly and soon approaches a steady state, becoming neutral with respect to carbon dioxide emissions. Farming practices with the greatest potential for retention of carbon in the soil include reduction in summer fallow and use of minimum tillage. Indeed, proper management practices have been shown to increase the amount of carbon in the soil, removing carbon dioxide from the atmosphere in the process ³. The extent to which such management practices can abate the greenhouse effect can only be estimated at present. The effects associated with these practices, (change in fossil fuel consumption in tillage and in the manufacture of inputs) have to be considered in relation to the amount of carbon dioxide absorbed. It is worthy to note that these management practices also contribute to the sustainability of agriculture.

Less information is available on nitrous oxide emissions from prairie soils. Denitrification losses from prairie soils have arisen under cultivation but the extent to which these have taken place is unknown. In order to understand the role of agriculture with respect to nitrous oxide emissions, it will be necessary to determine the effects of different tillage practices. Nitrous oxide from application of fertilizer can contribute to the total level of emissions. On the other hand, the net impact of agriculture on the accumulation of radiatively active gases in the atmosphere can be expected to be minimal. Most of the accumulation arises from the combustion of fossil fuels.

Canada has made a commitment to stabilize emissions of carbon dioxide and other greenhouse gases at 1990 levels by 2000. If this commitment and similar ones made by other nations are met, dangerous human impact on the climate would be avoided. The greenhouse effect is real, being based on scientific principles. Greenhouse gases keep the earth warm enough to be habitable but the continuing increase of greenhouse gases of human origin, such as those arising from the burning of fossil fuels, holds the potential to raise the global annual-mean surface air temperature to unacceptable levels. It is, however, uncertain as to the rate at which any warming will occur. Existing forecasting models are not consistent in their projections. Indeed, accurate predictions of future greenhouse gas concentrations are limited by an incomplete understanding of the biospheric processes that control the sources and sinks and of the way they may change in the future ⁴. It is therefore prudent to limit increases of greenhouse gases of human origin.

The potential impact of any foreseen increase in global warming upon agriculture on the prairies appears limited ⁵. The effects of warming on the prairies would be of three types: the direct physiological effect of increased carbon dioxide and other greenhouse gases on crops and weeds; the effects caused by changes in climate; and indirect effects of changes in world agricultural markets induced by the global pattern of climate change⁶. Warming would result in the extension of agriculture northward, but the land there is not suitable for grain production. Extreme droughts could be expected on occasion while the carrying capacity of rangelands would decrease. While yield losses could be expected in some crops, on the whole, losses could be offset by development of drought tolerant and disease resistant crops. Global change elsewhere would decrease cereal production in current high cereal production areas leading to greater demand for cereals of Canadian origin.

The global issue cannot be restricted to the potential impacts of climate change. There is an international development aspect. Development elsewhere can be expected to have a major impact on the sustainability of agriculture as presently understood in the prairie region. Such development has five sustainability dimensions, namely, environmental, economic, political, social and cultural ⁷. Environmental sustainability is closely linked with population. Existing resources must be allocated wisely. Achievement of development and environmental sustainability in the developing countries can be expected to be aided by increased agricultural production. Such will reduce the need for imports of food, particularly grain, from a country such as Canada. This reduction may well make mandatory a reorientation of agriculture on the prairies, since a substantial proportion of the grain exported goes to these countries. Sustainability must be considered in the global context. The following quotation appears highly relevant:

"The pursuit of sustainability is also linked across nations. The globalization of the world economy has eroded the ability of all countries to pursue independent economic policies. The global nature of major environmental threats led to unprecedented international cooperation to address common problems, such as depletion of the ozone layer. As a result of modern communications, political change on one continent can influence change on another. The same communications technology has allowed the dominant cultures to project their values and lifestyles well beyond their national boundaries. The growing interdependence of the community of nations implies that sustainable development must in time become a global goal." ⁸

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