ESTIMATES OF EMISSIONS

Combined effect of the three greenhouse gases

The three gases ( CO₂, CH₄, and N₂O) differ in their warming effects. To compare their relative effects, therefore, their emissions are usually expressed as "CO₂ equivalents." One kilogram of N₂O has the warming effect of about 310 kg of CO₂ (when considered over 100 years), so it represents 310 CO₂ equivalents. Similarly, 1 kg of CH₄ represents 21 CO₂ equivalents.

According to best estimates, using the approaches described for each gas, Canadian agriculture had emissions of 67 Tg (million tonnes) of CO₂ equivalents in 1996 (Table 14). Of this amount, about two-thirds was as N₂O and about one-third as CH₄. By comparison, net emissions as CO₂ were almost negligible.

The estimates of CO₂ emission, however, exclude most of the CO₂ from fossil fuels used to produce inputs, power farm machinery, and transport products. These sources, which are included in inventories for transport and manufacturing sectors, emitted about 25 Tg (million tonnes) of CO₂ in 1996.

The emission of greenhouse gases from Canadian agriculture are increasing, according to current estimates (see Table 14). By 2010, emissions may be about 9% higher than those in 1996, unless producers adopt better management practices. These projected increases stem largely from predicted increases in livestock numbers and N inputs as fertilizer and manure. Emissions of CO₂ are expected to decline, but not nearly fast enough to compensate for predicted increases in the other gases.

Future emissions will depend on changes in farming practices that are hard to predict. Livestock numbers, crops that are grown, fertilization patterns, and manure management techniques can all change quickly, throwing off our current best projections.