Ozone Depletion and Climate Change

Environment Environnement Canada Canada OzoneOzone DepletionDepletion andand ClimateClimate Change:Change: UnderstandingUnderstanding thethe LinkagesLinkages Angus Fergusson Meteorological Service of Canada Published by authority of the Minister of the Environment Copyright © Minister of Public Works and Government Services Canada, 2001 Catalogue No. EN56-168/2001E ISBN: 0-662-30692-9 Également disponible en français Author: Angus Fergusson (Environment Canada) Editing: David Francis (Lanark House Communications) David Wardle / Jim Kerr (Environment Canada) Contributing Authors: Bruce McArthur (Environment Canada): Bratt Lake Observatory David Tarasick (Environment Canada): Canadian Middle Atmosphere Model Tom McElroy (Environment Canada): MANTRA Project Special thanks for comments to: Vitali Fioletov (Environment Canada) Hans Fast (Environment Canada) Pictures: Angus Fergusson (Environment Canada) John Bird (Environment Canada) Brent Colpitts Ray Jackson Layout and Design: BTT Communications Additional copies may be obtained, free of charge, from: Angus Fergusson Science Assessment and Integration Branch Meteorological Service of Canada 4905 Dufferin Street Downsview, Ontario M3H 5T4 E-mail: [email protected] Table of Contents Summary 2 Introduction 4 The Atmosphere and its Radiative Effects 6 The Dynamics of the Atmosphere 10 The Chemistry of the Atmosphere 12 Biogeochemical Linkages: The Impact of Increased UV Radiation 14 Canadian Research and Monitoring 16 Implications for Policy 20 The Research Agenda 22 Making Connections 26 Bibliography 28 Figure 1. Compared to the earth itself, the earth’s atmosphere as seen from space looks remarkably thin, much like the skin on an apple. In this photograph, the two lowest layers of the atmosphere, the troposphere and the stratosphere, are clearly visible. The stratosphere is home to the ozone layer that protects life on earth from intense ultraviolet radiation. The troposphere is the layer where most weather activity takes place. The top of the thundercloud has flattened out at the tropopause, the boundary between the two layers. Interactions between the troposphere and stratosphere provide a number of important connections between ozone depletion and climate change. Figure 1 Source: NASA 1 Summary zone depletion and climate which are a key factor in the depleting substances covered by Ochange have usually been development of polar ozone the Montreal Protocol.To under- thought of as environmental holes. stand these connections better, issues with little in common Enhancement of the green- researchers are now looking other than their global scope and house effect may also be causing more closely at how the tropo- the major role played in each by changes in circulation patterns in sphere and stratosphere interact CFCs and other halocarbons. the troposphere that are, in turn, (Figure 1).Environment Canada With increased understanding of altering the circulation in the scientists are contributing to this these issues, however, has come a stratosphere. It is suspected that research in a variety of ways, growing recognition that a num- these changes are increasing the including the monitoring of ber of very important linkages cooling forces acting on the ozone concentrations and solar exist between them. These link- stratosphere over the poles and radiation levels and collaboration ages will have some bearing on are thus making the formation of in balloon-based stratospheric how each of these problems ozone holes more likely.There is research and atmospheric and the atmosphere as a whole evidence as well that changes in modelling. evolve in the future. the stratospheric circulation may Both greenhouse warming and Some of the most important of be altering weather patterns in the thinning of the stratospheric these linkages involve the way the troposphere. Other linkages ozone layer are a result of human that ozone-depleting substances between climate change and activities that have changed the and greenhouse gases alter radia- ozone depletion are related to composition of the atmosphere in tion processes in the atmosphere the effect of increased levels of subtle but profound ways since so as to enhance both global ultraviolet radiation on sun-driven the beginning of the industrial warming and stratospheric ozone chemical reactions in the atmo- revolution more than 200 years depletion.These changes result sphere and to changes in biologi- ago. By taking an integrated in a warming of the troposphere cal processes that affect the approach to ozone depletion and (the bottom 8–16 km of the composition of the atmosphere. climate change, governments and atmosphere) and a cooling of the The net effect of these link- scientists will have a better stratosphere (the layer above that ages is an intensification of both chance of understanding and extends to an altitude of about climate change and ozone moderating the enormous 50 km and contains the ozone depletion and possibly a delay in changes that human activities layer). Stratospheric cooling the recovery of the ozone layer have had and will continue to creates a more favourable environ- as it responds to diminishing have on the atmosphere. ment for the formation of polar levels of CFCs and other ozone- stratospheric clouds (PSCs), Ozone Depletion and Climate Change: Understanding the Linkages • 2 emp. Change (ºC) T Data from thermometers (red) and from tree rings, corals, ice cores and historical records (blue). The shaded area indicates the margin of error in the measurements. Figure 2a Source: Adapted from IPCC, 2001 Figure 2a. Greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, affect climate by retaining heat near the earth’s surface. Concentrations of these gases began to rise in the 19th century and have increased exponentially in the 20th, paralleling the expansion of industrial economies and the growth of the human population. Over the past century the average global temperature has increased by about 0.6ºC, and significantly greater increases are expected for the 21st century. Warming of the atmosphere is also expected to cause changes in other aspects of climate, including changes in precipitation and evaporation, circulation patterns, and weather extremes. Figure 2b. Thinning of the stratospheric ozone layer has been caused largely by long-lived chlorine and bromine compounds, such as CFCs and halons, that eventually make their way into the stratosphere. Use of these compounds increased considerably in the 1960s and 1970s. Evidence of ozone depletion in the stratosphere began to appear in the 1980s. Atmospheric concentrations of most ozone-depleting substances peaked, or their growth rate began to slow, as a result of the phasing out of these chemicals under the Montreal Protocol. Concentrations of ozone-depleting substances are expected to decline over the coming century, bringing a gradual recovery of the ozone layer. Figure 2b Source: J. Elkins, NOAA 3 Introduction limate change and the deple- stratosphere, the layer of stratified, can have important and surprising Ction of the stratospheric relatively stable air that houses results.To take account of the ozone layer have been leading the ozone layer and extends from many complicated interactions environmental issues for more the top of the troposphere to an that occur in the atmosphere, than a quarter of a century. For altitude of about 50 km.Yet, as scientists and policy makers are much of that time, they have been scientists have come to under- increasingly taking a more holistic treated as separate and distinct stand more about these issues approach to atmospheric issues. problems, with researchers setting and the complex physical and The most obvious linkage up separate programs to investi- chemical processes that drive between ozone depletion and gate the underlying scientific them, they have also become climate change is the fact that questions and governments increasingly aware of a number ozone itself and some of the establishing separate international of important connections between more important ozone-depleting arrangements to coordinate them. substances such as chlorofluoro- control measures. Recognition of these connec- carbons (CFCs) and hydro- In many ways, of course, these tions parallels a growing aware- chlorofluorocarbons (HCFCs) are issues are quite distinct. Climate ness among scientists and policy also powerful greenhouse gases. change is concerned with how makers that atmospheric issues But ozone depletion and climate carbon dioxide, methane, and cannot be dealt with in isolation change are linked in many other other greenhouse gases emitted from each other. The human ways as well, particularly through by human activities are altering activities that contribute to climate their effects on physical and the climate system (Figure 2a). change and ozone depletion, or to chemical processes in the Consequently, research into cli- any other air pollution problem atmosphere and on interactions mate change has focused largely, for that matter, affect the same between the atmosphere and though not exclusively, on trends atmosphere.And because the other parts of the global and processes within the tropo- atmosphere is a very complex ecosystem. sphere, the layer of turbulent air, entity, changes to one aspect of it some 8–16 km deep, that is closest can often initiate changes that to the earth’s surface. Ozone affect other aspects of the atmo- depletion, on the other hand, is spheric system. Consequently, about how certain industrially

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