ATMOSPHERIC CHANGE IN CANADA: ASSESSING THE WHOLE AS WELL AS THE PARTS Introduction to This Volume

Abstract

Over the past decade there has been increasing interest in methodologies for undertaking environmental assessments that are regional, continental or global in scale. These have generally focused on single issues such as acidic deposition and climate warming, although multiple type of receptors (people, vegetation, buildings, etc.), may be involved. The word ‘assessment’ implies an activity that is at the interface between science and policy; it is different from, and does not replace, scientific research. Assessment is difficult, and the difficulty should not be disguised when one tries to reconcile scientific uncertainties with the needs of policy-makers for firm answers. In Toronto, 27–29 March 1995, a Workshop was held on this general topic, the goal being to extend current knowledge and practice on single-issue atmospheric assessments to multi-issue ones. The Workshop was titled Atmospheric Change in Canada: Assessing the Whole as Well as the Parts, the idea being to look at methods of examining a suite of inter-related atmospheric issues: acidic deposition; climate change (global warming); stratospheric ozone depletion (increasing UV-B radiation); tropospheric ozone episodes; hazardous air pollutants; and suspended particulate matter. For example, how would a proposed policy to reduce acidic deposition affect the frequency of tropospheric ozone episodes or the rate of climate warming? To a large extent, scientists and policy analysts have addressed each of these issues separately, the net result being that although a policy may be optimal for a single issue, it is often not so for a range of issues, and in some cases it may have negative consequences. Yet these issues are inter-related, and attempts to resolve them individually may lead in some cases to conflicting policies and regulatory actions. For example, sulphate aerosols cause acidic deposition while at the same time absorbing and scattering solar radiation, thus partially compensating for greenhouse warming. Similarly, catalytic automobile converters reduce emissions of tropospheric ozone precursors (NOx and VOC) but release N2O, a greenhouse gas. The need to understand the scientific commonalities and linkages amongst these issues and their multiple effects on the biosphere and society is of major importance.