ATMOSPHERIC ISSUES IN CANADA

Six atmospheric 'issues' are currently being assessed by scientists, m odellers and policy analysts in Canada: climate change; stratospheric ozone depletion (including W-B radiation increases); acidic deposition ; smog (e.g. ground-level ozone episodes); suspended particulate matte r; and hazardous air pollutants. This paper provides a brief historica l review of how these particular issues came to the forefront internat ionally and in Canada. Then the characteristics of the issues are desc ribed, revealing the wide range of space and time scales involved, as well as the several different ecological systems and socioeconomic sec tors affected. Historically each air issue has been treated as a separ ate problem - from root causes, through the atmospheric processes invo lved, 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 deplet ion, but the replacement gases may contribute to climate warming. The lesson to be learned by both scientists and policy analysts is therefo re that strategies for dealing with a particular issue may not be opti mal for the whole. Two examples are given to illustrate the paint. (1) With respect to policies to reduce greenhouse gas emissions, the warm ing potentials of all such gases should be assessed, and the effects o f proposed strategies on the other five air issues should also be incl uded. (2) With respect to regional land-use planning, a long-term pers pective (decades) should be taken, and the effects of global and regio nal atmospheric change on the region should be included in the assessm ent. Because the future is difficult and often impossible to predict, an adaptive strategy is recommended in which options are kept open, an d the assessment document is revisited periodically (at 2-5-year inter vals). (C) 1997 Elsevier Science B.V.