Atmospheric issues in Canada

Six atmospheric ‘issues’ are currently being assessed by scientists, modellers and policy analysts in Canada: climate change; stratospheric ozone depletion (including UV-B radiation increases); acidic deposition; smog (e.g. ground-level ozone episodes); suspended particulate matter; and hazardous air pollutants. This paper provides a brief historical review of how these particular issues came to the forefront internationally and in Canada. Then the characteristics of the issues are described, revealing the wide range of space and time scales involved, as well as the several different ecological systems and socioeconomic sectors affected. Historically each air issue has been treated as a separate problem — from root causes, through the atmospheric processes involved, through the impacts on the biosphere and society, and finally to the design of policies to slow down or eliminate unwanted impacts. In recent years, however, recognition has been growing that the six air issues are interrelated through complex feedbacks, lags and synergisms. For example, replacing CFCs may slow down stratospheric ozone depletion, but the replacement gases may contribute to climate warming. The lesson to be learned by both scientists and policy analysts is therefore that strategies for dealing with a particular issue may not be optimal for the whole. Two examples are given to illustrate the point. (1) With respect to policies to reduce greenhouse gas emissions, the warming potentials of all such gases should be assessed, and the effects of proposed strategies on the other five air issues should also be included. (2) With respect to regional land-use planning, a long-term perspective (decades) should be taken, and the effects of global and regional atmospheric change on the region should be included in the assessment. Because the future is difficult and often impossible to predict, an adaptive strategy is recommended in which options are kept open, and the assessment document is revisited periodically (at 2–5-year intervals).