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 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 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 20

The Research Agenda 22

Making Connections 26

Bibliography 28 Figure 1. Compared to the 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 and the , are clearly visible. The stratosphere is home to the layer that protects on earth from intense radiation. The troposphere is the layer where most 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 and 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 .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 . 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 are a result of that ozone-depleting substances between 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 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 (PSCs),

Ozone Depletion and Climate Change: Understanding the Linkages • 2 emp. Change (ºC) T

Data from thermometers (red) and from tree rings, corals, 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 , , and , 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 . Warming of the atmosphere is also expected to cause changes in other aspects of climate, including changes in and evaporation, circulation patterns, and weather extremes.

Figure 2b. Thinning of the stratospheric ozone layer has been caused largely by long-lived and 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 . 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 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- (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 (Figure 2a). change and ozone depletion, or to chemical processes in the Consequently, research into cli- any other air 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 . 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 human activities that alter the produced chemicals containing atmosphere, even in very chlorine or bromine are damaging subtle ways, the earth’s protective ozone layer, thus increasing the intensity of ultraviolet radiation at the earth’s surface (Figure 2b). Research into ozone depletion has therefore focused largely, though not exclusively, on trends and processes within the

Ozone Depletion and Climate Change: Understanding the Linkages • 4 Figure 3

Figure 3. The contrasting temperature patterns in the troposphere and stratosphere are the result of differences in the way radiative is transferred to the atmosphere. The stratosphere is heated from the top down as intense ultraviolet radiation is absorbed by and ozone. The troposphere is heated from the bottom up as the earth’s surface warmed by incoming , emits longwave radiation, which is then absorbed and re-emitted by greenhouse gases in the air above. A small amount of heat is also transferred directly to the air by direct contact with the surface and by the evaporation and condensation of moisture. Because the troposphere generally becomes cooler with altitude, the warmer and lighter surface air rises easily. As a result, the air in the troposphere is often turbulent and well mixed. The stratosphere, on the other hand, tends to be quite stable because the increase of temperature with altitude inhibits vertical mixing of the air.

Figure 4. The basis of the can be seen if we compare the wavelengths at which different atmospheric gases absorb radiation with the wavelengths at which radiation enters and leaves the atmosphere. The sun, because it is very hot, emits shortwave radiation, and although the shortest of these wavelengths are absorbed by oxygen and ozone, most solar radiation is not absorbed by atmospheric gases. The earth, because it is much cooler, emits longwave, infrared radiation, but most wavelengths in this part of the spectrum are readily absorbed by vapour, carbon dioxide, methane, nitrous oxide, ozone, and other greenhouse gases. The atmosphere thus provides a very wide window through which incoming sun- light can penetrate but only a very narrow window through which infrared radiation can depart.

Figure 4 Source: adapted from Jacob, 1999

5 The Atmosphere and its Radiative Effects

adiative processes have an beneficial byproduct of these of this greenhouse effect, the Renormous influence on the processes is that most of the ultra- earth’s average temperature is some behaviour of the atmosphere violet radiation that is harmful to 33ºC warmer than it would other- because they govern the amount and animal life on earth is wise be and the planet is able to of energy entering and leaving the filtered out in the stratosphere and support life (Figure 4). earth-atmosphere system and does not reach the earth’s surface. Because it is heated in this way, hence the amount of energy avail- Some additional heating of the air in the troposphere is generally able to heat the air, evaporate stratosphere also occurs because warmest at the surface and moisture, and drive the movement ozone absorbs infrared radiation becomes cooler with increasing of air masses.This energy initially emitted by the earth’s surface. altitude. Since warm air is less enters the atmosphere as short- In the troposphere, in contrast, dense than cool air, the warm air wave radiation from the sun, but it very little of the incoming solar rises and cooler air moves in at is transferred to the troposphere radiation is absorbed directly by the surface to take its place. This and stratosphere in very different the atmosphere. Instead, the short- simple convective flow is modified ways, giving these two layers of wave radiation warms the earth’s by the earth’s rotation, by surface the atmosphere very different surface, which then transfers heat features, and by temperature structures and characteristics energy to the atmosphere in a vari- differences between the equator (Figure 3). ety of ways – partly through direct and the poles.The end result is a The stratosphere is heated from contact between the surface and rather turbulent layer of the atmo- the top down and is therefore the air, partly through the evapora- sphere in which air circulates in warmer at the top than it is at the tion and condensation of moisture, complicated and variable patterns, bottom. Consequently,the densest but mostly through the emission of moving energy and moisture from air in the stratosphere is at the longwave infrared radiation, which place to place. bottom, there is little vertical mix- is absorbed by water vapour and ing of the air, and the stratosphere other greenhouse gases in the air is very stable. Heat is added to such as carbon dioxide, methane, the stratosphere when strong nitrous oxide, and ozone. By ultraviolet-C (UV-C) radiation from re-emitting some of this longwave the sun is absorbed by oxygen radiation back towards the earth’s molecules and causes them to split. surface, these gases retain heat at One of the results of this process is the bottom of the atmosphere and the production of ozone and the help to make it warmer. As a result formation of the ozone layer in the stratosphere. More warming occurs when the ozone molecules intercept and are destroyed by intense but slightly less powerful ultraviolet-B (UV-B) radiation. A

Ozone Depletion and Climate Change: Understanding the Linkages • 6 Figure 5

Figure 5. The stratosphere has cooled significantly since about 1980, mostly as a result of ozone loss but also because of the accumulation of greenhouse gases in the troposphere. Over the middle latitudes of the Northern Hemisphere, the cooling trend has been noticeably greater in the middle and upper stratosphere than in the lower stratosphere.

Figure 6. Polar stratospheric clouds such as these, photographed over Sweden during the of 2000, form in the lower stratosphere when temperatures drop below about –80ºC. These clouds support chemical reactions that change stable bromine and chlorine compounds into more active, ozone-destroying substances. Cooling of the stratosphere as a result of climate change and ozone depletion increases the possibility that these clouds will form.

Figure 6

7 When ozone-depleting chemicals gas concentrations increase, the into much more active chemicals. are released into the atmosphere, downward flow of longwave It is these chemicals that cause however, these radiative processes radiation increases and the rapid ozone destruction when are modified in a variety of ways: upward flow diminishes, thus sunlight returns to the polar • Because the most effective exerting a warming force on the regions in the spring. PSCs are a ozone-destroying substances, troposphere and a cooling force key factor in the severe ozone- such as CFCs and HCFCs are on the stratosphere (Figure 5). depletion that occurs over polar also strong greenhouse gases, Although all greenhouse gases regions in the spring. the greenhouse effect is contribute to warming in the The different heating and cool- enhanced and the earth’s sur- troposphere, the effect of individ- ing forces that arise as a result of face and the lower troposphere ual greenhouse gases on the ozone layer depletion and become warmer. stratosphere can vary consider- increasing concentrations of • Warming by CFCs and HCFCs ably, depending on whether they greenhouse gases have been is partially offset, however, by cause a greater reduction in measured globally and studied the ozone losses that these upward emissions at the bottom using computer models.These chemicals cause in the lower of the stratosphere or at the studies indicate that the net stratosphere. Because ozone is top. Carbon dioxide has the result of all of these contending a , a loss of greatest cooling effect on the forces is a warming at the surface stratospheric ozone weakens stratosphere, while CFCs actually (due mainly to increased concen- the natural greenhouse effect have a warming effect on it. trations of greenhouse gases), a and cools the stratosphere. Nevertheless, the net result of an slight or negligible temperature • Thinning of the ozone layer increase in concentrations of all increase in the middle to upper also means that less heat is greenhouse gases is a cooler troposphere, and a cooling of the available to the stratosphere stratosphere. stratosphere (due mainly to the from the absorption of UV-B Cooling of the stratosphere loss of ozone). radiation by ozone molecules. has important consequences for However, the effects of green- That also has a cooling effect ozone depletion, because it con- house gases and ozone depletion on the stratosphere. tributes to the formation of polar on the radiative balance are very • With fewer ozone molecules stratospheric clouds (PSCs).These complex and many available in the stratosphere clouds (Figure 6), which form still remain. A number of research to absorb UV-B radiation, more only at extremely low tempera- efforts are now under way in of that radiation reaches the tures in the lower stratosphere an attempt to resolve these ground. That contributes to during the sunless polar winter, uncertainties. additional warming of the provide a medium for chemical earth’s surface and the lower reactions that change stable troposphere. chlorine and bromine compounds An increase in the abundance of greenhouse gases produces similar results.As greenhouse

Ozone Depletion and Climate Change: Understanding the Linkages • 8 9 The Dynamics of the Atmosphere

s greenhouse gases accumu- warmer.The energy that drives inside the becomes an Alate in the atmosphere, they this circulation comes from extremely favourable environment alter temperature differences atmospheric waves that penetrate for the formation of PSCs and between different parts of the upward from the troposphere. rapid ozone depletion. Before it globe and different levels of the These waves are caused by large- finally dissipates in the spring, atmosphere and in this way scale atmospheric disturbances however, the vortex may occasion- change atmospheric circulation that are a result of differences in ally be broken down by the action patterns.There is good reason to the way that and water and of strong atmospheric waves, thus believe that these circulation different types of land surfaces allowing a temporary incursion of changes may be enhancing ozone affect the heating and movement warmer air that makes conditions depletion over the poles by of the air.They tend to be stronger less favourable for the rapid weakening some of the warming in the Northern Hemisphere destruction of ozone. Because forces that act on the polar because of its greater land area, atmospheric wave action is stratosphere. and thus cause the stratosphere stronger in the Northern Hemi- One of these forces is known to be warmer on average over the sphere, the vortex tends to as dynamical heating, and it is Arctic than it is over the . be less stable than the Antarctic associated with a slow general Atmospheric waves also affect vortex. Consequently, massive circulation pattern in the strato- the stability of a feature known as ozone holes, such as those that sphere in which air gradually rises the .This is a wind form regularly over the Antarctic in the tropics, moves towards the system that circles around each of in spring, have not yet occurred in poles, and then slowly sinks over the poles in winter and isolates the Arctic. the poles (Figure 7).The compres- the polar stratosphere, preventing There is evidence from climate sion of the air as it descends over the influx of warmer air and model studies, however, that the the poles causes it to become ozone from the lower latitudes. warming of the atmosphere Because of this isolation, the area near the earth’s surface and the

Figure 7. Air in the stratosphere flows poleward from the equator, its movement driven largely by the Figure 7 force of waves created by storms in the troposphere. Air enters the strato- sphere at the equator, where the hot surface generates strong upward currents and thunderstorms. The tropopause, the boundary between the two layers, disappears over the poles in winter, allowing stratospheric air to sink back into the troposphere. Although the tropopause tends to block the movement of air between the troposphere and stratosphere, air exchanges in both directions also occur in the mid-latitudes and the polar regions as a result of the actions of planetary waves. The breakup of these waves in the lower stratosphere creates a “surf zone” where some mixing of air occurs.

Ozone Depletion and Climate Change: Understanding the Linkages • 10 circulation changes resulting from output varies by only about 0.1% changes in stratospheric airflow it may be weakening these plane- across the entire cycle. Recent also affect the flow of energy tary wave motions and thus their studies have shown, however, that downward into the troposphere, warming effect on the polar strato- the variation in is where it can have an impact on sphere. If so, this would have the much greater in the UV-C portion pressure and circulation patterns. effect of enhancing ozone deple- of the spectrum, where the sun’s Such changes may affect the tion over both poles, but especially output can vary by as much as position of the , which over the Arctic. Such a develop- 10% during the cycle.This is controls the path of weather ment would slow the recovery enough to have a noticeable effect systems in the troposphere. A of the ozone layer that should on ozone amounts in the strato- small change in the path of the jet occur over the coming decades as sphere, which have been shown to stream can cause very noticeable concentrations of ozone-depleting be about 1.5% greater at the solar changes in regional . compounds in the stratosphere maximum (when the number of Initial studies with models, for decline. is greatest) than at the example, suggest that increases in Research is also revealing solar minimum (when the number stratospheric ozone could have mechanisms through which of sunspots is least). These changes the effect of directing more changes in the composition of the in ozone amounts cause corre- storms into Canada. Further study stratosphere can affect the move- sponding changes in the tempera- is needed, however, to determine ment of air in the troposphere. ture of the stratosphere, which how long-term depletion of the Meteorologists have long known in turn result in changes in air ozone layer is affecting surface that atmospheric pressure patterns pressure and wind flow. weather patterns. at the earth’s surface vary with the Recent computer simulations at solar cycle, but they have NASA’s Goddard Institute for had trouble explaining the connec- Space Studies have shown that tion, since the sun’s total energy

Smog over the lower Fraser Valley

11 The Chemistry of the Atmosphere

zone depletion is largely radiation reaches the earth’s sur- ozone-depleting methyl chloro- Oa matter of atmospheric face, the photochemical reactions form and gases such as chemistry, but chemical processes that produce ground-level ozone hydrochlorofluorocarbons (HCFCs) play an important part in climate can proceed more vigorously. and (HFCs) that change as well, particularly in the Average ozone amounts over are both ozone depleters and generation and breakdown of Canada are now about 6% greenhouse gases. In addition, OH some greenhouse gases.The below pre-1980 values. Scientists reacts with a host of other pollu- chemistry of ozone depletion and estimate that this decrease has tants, including , that associated with climate resulted in a corresponding volatile organic compounds, and change interact significantly in at increase of about 7% in the various oxides of .There is least two ways. amount of UV-B radiation reach- some concern that the demands on One way is through photo- ing the earth’s surface. Recent the hydroxyl in a heavily chemistry – chemical processes computer model research indi- polluted atmosphere may lead to a that are driven by energy from cates that an increase in UV radia- decline in OH concentrations and the sun. Many reactions in the tion will result in an increase in thus a reduction in the efficiency atmosphere are of this kind, and ground level ozone in polluted with which methane and various the amount of ozone in the strato- urban areas where there are ozone-depleting compounds are sphere affects the rate at which high concentrations of nitrogen removed from the atmosphere. these reactions occur, because it oxides, carbon monoxide, and Slower removal of these com- determines how much of the . pounds would intensify the sun’s high-energy UV-B radiation The other linkage involves a process of climate change and reaches the atmosphere near the short-lived, highly reactive mole- slow the recovery of the ozone ground.This has important cule known as the layer.Although global hydroxyl consequences for climate change, (OH), which is produced by the amounts cannot be estimated with because ground-level or tropo- photochemical breakdown of a high degree of certainty, some spheric ozone, a significant green- ozone in the presence of water recent evidence suggests that a house gas and a major constituent vapour. OH is an atmospheric significant decline in hydroxyl of , is photochemically scavenger that reacts with many concentrations has taken place produced (Figure 8). As the ozone and removes them from during the and that further layer thins and more ultraviolet the atmosphere.These include the declines can be expected in the greenhouse gas methane as well as coming decade. Figure 8 Source: Ontario Ministry of the Environment (ozone) and Environment Canada (UV Index) Figure 8. Ultraviolet-B radiation provides Ground-level Ozone and UV Index at Etobicoke South July 14, 15, & 16, 1999 the energy for the chemical reactions that 120 9 lead to the formation of ground-level

8 ozone, which is both a major component 100 of smog and a greenhouse gas. 7 Measurements taken during a smog

80 6 episode in Toronto in July 1999 show a close relationship between UV levels and 5 Ozone 60 ground-level ozone concentrations. UVI 4 Computer models suggest that higher UV Index levels of UV-B could lead to an increase 3 40 in ground-level ozone formation in highly

Ozone (parts per billion) 2 polluted areas. Such an increase would 20 not only make smog problems worse 1 but would also add to warming from 0 0 greenhouse gases. 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 July 14 July 15 Ju ly 16

Ozone Depletion and Climate Change: Understanding the Linkages • 12 13 Biogeochemical Linkages: The Impact of Increased UV Radiation

hanges in climate and through the burning of fossil Similarly,biological changes Cchanges in the intensity of and the clearing of , initiated by changes in climate ultraviolet radiation can both is largely responsible for the might have some effect on ozone have substantial impacts on the modern increase in atmospheric depletion. Methyl chloride and biological, geological, chemical, concentrations of carbon dioxide, methyl bromide, for example, are and physical processes that the most abundant anthropogenic two ozone-depleting compounds control the exchange of matter greenhouse gas. One of the more whose production and use are now and energy between the major important links in the carbon being phased out under the components of the environment– cycle from an atmospheric per- Montreal Protocol. However, the atmosphere, the , spective is the so-called “marine because natural sources of these the , and the litho- .” This is a gases are larger than the human sphere. Probably the most familiar process in which plankton, the industrial sources, anything affect- of these exchanges is the carbon microscopic and animals ing the and natural cycle, in which carbon is trans- that live near the surface of the processes that produce these gases ferred continuously between the and freshwater lakes, could also have consequences for atmosphere, the oceans, living remove carbon from the air and the ozone layer. Much has yet to be things, and the rocks and , then transfer it to the bot- learned about these natural sources, changing from an almost purely toms and lakebeds when they but coastal marshes appear to be elemental form, as in charcoal or die. Ozone depletion, particularly important contributors. Fungi, anthracite, to a simple gas like severe episodes such as the crops such as rapeseed, and soils carbon dioxide, or to one of spring ozone holes in the rich in organic matter are also numerous organic compounds as Antarctic, present a potentially thought to be substantial sources. it moves from one environmental serious threat to this process, Warming of the atmosphere and reservoir to another. because plankton cannot take oceans or changes in level The is of central shelter from solar radiation. A seri- could affect all of these sources importance in the climate change ous decline in their numbers as a by altering the ecosystems and issue because human disruption result of exposure to more intense climatic conditions that support of the natural carbon cycle, ultraviolet radiation could there- the natural production of these fore decrease the rate at which gases. Climate change could also carbon dioxide is removed from affect the rate at which these gases the atmosphere. are removed from the atmosphere by the oceans. Studies of the natural production and removal of these gases are still in their early stages, however, and it is not yet to predict how climate change might affect the quantities of these gases in the atmosphere.

Ozone Depletion and Climate Change: Understanding the Linkages • 14 , ,

Figure 9

Figure 9. Ozonesonde data collected over Eureka in 2000 show the annual ozone cycle, with highest levels occurring in the winter and early spring and lowest levels in summer. The plot also shows unusually low levels of ozone in late March and early April between about 15 and 20 km. This depleted area is believed to be the result of high levels of chlorine and bromine in a very cold Arctic stratosphere.

Figure 10. At Environment Canada’s observatory at Alert on in the High Arctic, background concentrations of greenhouse gases, ozone-depleting substances, and are monitored daily.

Figure 10

15 Canadian Research and Monitoring

hrough its Experimental data for use in producing UV The Alert observatory is an offi- TStudies Division, Environment Index reports and forecasts. cial baseline station for the Canada’s Air Quality Research These ground-based measure- Meteorological Organization’s Branch is involved in a number of ments are supplemented by data (GAW) activities that are contributing to gathered by small balloon-borne program and is one of about 20 a better understanding of ozone sensors known as ozonesondes. such stations around the world.The depletion and its interactions Weighing about 3 kg, these instru- objective of the GAW program is with climate change. Some of ment packages provide continu- to make available ongoing back- these activities are research pro- ous measurements of ozone ground concentration measure- jects designed to provide new concentrations up to an altitude ments of selected atmospheric knowledge about atmospheric of about 20 km (Figure 9). constituents and related physical constituents and processes. conditions for every major region Others are long-term monitoring Arctic observatories of the globe.The Canadian Baseline programs whose function is to In 1992 Environment Canada Program began at Alert in 1975 provide a long and continuous built the High Arctic stratospheric with simple measurements of - record of atmospheric conditions ozone observatory near the Eureka bon dioxide. By 1998, the program that can be used as a reliable basis weather station on Ellesmere had expanded to include measure- for identifying trends and changes Island.The observatory is the main ments for other greenhouse gases, in the atmosphere’s composition centre for atmospheric research in such as methane, ozone, and and behaviour.These activities, the Arctic and is also a primary chlorofluorocarbons. which also assist in evaluating the component of the international effectiveness of controls under Network for the Detection of Radiation studies the Montreal Protocol and help to Stratospheric Change, a series of (Bratt’s Lake Observatory) set strategies for the future, are high quality, ground-based stations The Bratt’s Lake Observatory, carried out through the following that measure the physical and located about 20 km south of key facilities and programs. chemical state of the stratsphere. Regina, is the Canadian link in The Eureka observatory operates the World Climate Research Ground-based ozone instruments that measure ozone, Programme’s Baseline Solar monitoring and ozonesondes nitrogen dioxide, and other sub- Radiation Network.This is a Canadian scientists have been stances important to atmospheric network of approximately 40 using ground-based instruments chemistry. Canada also maintains stations, spread across all seven to measure total ozone amounts an observatory at Alert on that take very accurate since the 1950s.These measure- Ellesmere Island (Figure 10) that measurements of solar and ments are now taken at 12 sites provides continuous monitoring infrared radiation (Figure 11). across Canada, using the of background concentrations of Since shortwave radiation from Canadian-developed Brewer greenhouse gases, ozone-depleting the sun and the longwave infrared ozone spectrophotometer.Three substances, and aerosols (atmo- radiation emitted by the earth’s of the instruments are in the High spheric particles).Analysis of surface and atmosphere provide Arctic, at Resolute Bay, Eureka, this data provides information the energy that drive the earth’s and Alert.The Brewer network is a about the long-term variability climate system, this information fundamental source of informa- of these substances and furthers can provide evidence of how tion about changes in the state understanding of the impact changes in radiative energy flows of the stratosphere. At a more of human activities on the atmo- are affecting regional and global practical level, it also provides sphere. climate change. The Bratt’s Lake

Ozone Depletion and Climate Change: Understanding the Linkages • 16 ) 2 Radiant Exposure (MJ m

Figure 11 Figure 12 Source: B. Arthur, Environment Canada Source: de Grandpré 2001

Figure 11. Measurements of daily amounts of solar and infrared radiation reaching the earth’s surface should allow the detection of trends over time. The four-year plot shown here indicates little change in either solar or infrared radiation from one summer to another. Over the four , however, solar radiation has declined and infrared radiation has increased. These changes may be the result of increased cover during the winters. Many more years of data will be needed, however, before it can be determined whether this pattern is part of a longer-term trend or simply a result of the climate’s natural short-term variability.

Figure 12. While increasing concentrations of greenhouse gases lead to warming at the earth’s surface, they cause cooling in the stratosphere. The plot shown here shows the potential effects of a doubling of atmospheric carbon dioxide concentrations on summer temperatures and winds in the stratosphere, as estimated by the Canadian Middle Atmosphere Model. Temperature changes are indi- cated by the dashed lines in degrees Kelvin (1ºK is the same as 1ºC, but the Kelvin scale starts at absolute zero or –273ºC). Wind speed changes are shown by the coloured areas. The model shows the greatest cooling occurring near the top of the stratosphere, with temperatures in the upper stratosphere over the Antarctic cooling by as much as 14ºK.

Figure 13. The graph shows the average daily amount of ultraviolet-B radiation received at Toronto, Edmonton, and Churchill for each year since 1965. Values from the late 1980s on are derived from actual measurements. Earlier values are estimates derived from related meteorological information by a statistical model. UV-B amounts begin to increase noticeably at all locations in the early 1980s, shortly after the thinning of the ozone layer is believed to have started. The increase at Churchill, however, has been greater than at the other two locations. This is thought to be due to climatic factors, although it is as yet unclear whether these are related to long-term climate change.

Figure 13 3600 Source: V. Fioletov, Environment Canada ) 2 - m 3200 J ( n o i at

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2400 CIE Toronto Edmonton Churchill 2000 1965 1970 1975 1980 1985 1990 1995 17 Observatory, which has been The Canadian Middle UV and Research operational since the mid-1990s, Atmosphere Model Measurements of the strength of provides researchers with a relat- Computer modelling is an impor- UV radiation at the earth’s surface ively non-polluted environment tant tool that helps researchers were not taken on a regular basis in an area where the climate is improve their understanding in Canada until the introduction of expected to change significantly of atmospheric processes, study the Brewer spectrophotometer in as greenhouse gases increase. the impact of natural and human- the late 1980s.When Environment induced changes in the atmo- Canada researchers set out a Balloon-based ozone research sphere, and make long-term decade later to estimate long-term Over the past 20 years, Environ- predictions about atmospheric trends in UV radiation, the length ment Canada has worked with change.The Canadian Middle of the data record was still too the Canadian Space Agency and Atmosphere Model (CMAM), short to yield reliable results. To partners in the universities and developed jointly by scientists overcome this problem, they industry to collect data about reac- from Environment Canada and the developed statistical models that tive nitrogen compounds, chlorine universities, provides a sophisti- estimated the UV irradiance from and bromine compounds, ozone, cated representation of important a combination of earlier data on aerosols, and other substances that physical and chemical processes solar radiation, total ozone levels, play a critical role in the chem- in the upper troposphere and the dew point temperature, and istry of the upper troposphere and stratosphere.The model has cover. Using this method, they the stratosphere.This work is co- recently been used to study how estimated that the strength of UV ordinated under the Middle the middle atmosphere would radiation at the earth’s surface Atmosphere Nitrogen Trend change if the atmosphere con- has increased by an average of Assessment program or MANTRA. tained twice as much carbon about 7% across Canada since the To collect the data, researchers dioxide as it does now. Results of late 1970s when the thinning of use large polyethylene balloons, this study suggest that an increase the ozone layer appears to have about 20 stories high, that carry in carbon dioxide will lead indi- started. instruments to of, typic- rectly to a cooling of the middle Results of the study also show a ally, 30–40 km.The instruments atmosphere as more radiation is possible climatic influence on the scan the earth’s horizon at various emitted to space from other areas pattern of UV changes in Canada altitudes and record the spectra of the atmosphere.These results (Figure 13).When results from produced by scattered sunlight. At are consistent with observations different locations in the country the end of the flight, the instru- taken over the past few decades were compared, Churchill showed ment payload is separated from the that show a cooling trend in some a much stronger increase in UV balloon and descends to earth by parts of the middle atmosphere. than either Edmonton or Toronto. parachute, where it can be recov- Although most of the observed The difference is likely due to ered.Analysis of the recorded data cooling of the stratosphere is variations in surface reflectivity then provides information about thought to be a result of ozone caused by increases in snow cover the chemical composition of the loss, part could also be the result and decreases in . atmosphere at different altitudes. of increased concentrations of These changes may, in turn, reflect Information from the MANTRA carbon dioxide (Figure 12). The a shift in the average position of flights not only contributes to a results also show small but signifi- the polar jet stream. better understanding of strato- cant changes in the distribution of spheric processes but also helps ozone throughout the middle governments determine the effec- atmosphere as a result of the tiveness of controls on ozone- increase in carbon dioxide. depleting substances under the Montreal Protocol.

Ozone Depletion and Climate Change: Understanding the Linkages • 18 19 Implications for Policy

hanks to the Montreal Pro- recovery of the ozone layer, mainly But further problems remain. Ttocol of 1987 and the various through their effects on strato- What, in particular, should we do amendments made to it in subse- spheric cooling and the formation about HFCs and any other green- quent years, concentrations of of polar stratospheric clouds. house gases now being promoted CFCs, halons, and other major Recent computer simulations sup- as alternatives to CFCs and ozone-depleting substances in the this notion and suggest that HCFCs? Although concentrations atmosphere are now decreasing. expected increases in greenhouse of these gases in the atmosphere As these concentrations decline gas concentrations could cause are as yet fairly low, they are further over the rest of century, severe polar ozone depletion to expected to increase significantly the effects of stratospheric ozone continue for about 10–20 years over time if the use of these sub- depletion on climate change can longer than it would if concentra- stances is not controlled. Canada be expected to diminish gradually. tions of greenhouse gases had has adopted the position that the Full compliance with the Protocol remained at earlier levels.These use of HFCs should be restricted would see concentrations of studies are very preliminary,how- to the replacement of ozone- ozone-depleting substances fall by ever, and further investigation with depleting substances. Canada the end of the century to the more refined models is needed. also wants emissions of HFCs point where they would no From a policy perspective, it is controlled through mandatory longer be a significant threat to clear that actions to mitigate recovery and , safe the ozone layer. However, it is global warming can have positive disposal, and the use of other unlikely that full compliance will effects on ozone depletion and emission control measures.At the be achieved; therefore, recovery vice versa. However, care must be tenth meeting of the Parties to the of the ozone layer will almost taken to avoid solutions to one Montreal Protocol and the Fourth certainly take longer.The effects problem that make the other Conference of the Parties to the of ozone depletion on climate worse. Policy makers and scien- Climate Convention, the technical change will also continue longer tists are now wrestling with this and scientific authorities of each if CFCs are replaced by substi- difficulty as they look for long- body were asked to provide guid- tutes such as hydrofluorocarbons term alternatives to CFCs, halons, ance on limiting emissions of (HFCs), which are also potent and other ozone-depleting sub- HFCs and other greenhouse gases greenhouse gases.The greenhouse stances whose use has been that might be used as CFC replace- effect of these gases, moreover, phased out under the Montreal ments.Their investigation of the would be in addition to that of Protocol. Current restrictions on options is now under way. older ozone-depleting substances HCFCs, which have a lower that remain in the atmosphere. ozone-depleting potential than While atmospheric concentra- CFCs but are strong greenhouse tions of ozone-depleting gases, illustrate acceptance of the substances are declining, concen- need to consider the implications trations of important greenhouse for both issues. gases, such as carbon dioxide and methane, that have no direct connection with ozone depletion, continue to increase. Higher concentrations of these gases may have the effect of prolonging the

Ozone Depletion and Climate Change: Understanding the Linkages • 20 At the Bratt Lake Observatory, the Brewer spectrophotometer in the foreground measures ultraviolet radiation and the depth of the ozone layer while the solar trackers in the background measure diffuse solar radiation.

21 The Research Agenda

n the research side, more could, in turn, affect the height earth’s surface. In addition, with Oneeds to be known about of convection currents within more sunlight more ultraviolet how the troposphere and the the troposphere, such as those radiation will also reach the stratosphere interact.The associated with thunderstorms, earth’s surface. Since ultraviolet following are some of the more and could possibly affect the radiation contributes to the for- important questions now being intensity of those storms. It mation of ground-level ozone, pursued. might also alter the positions which is both a greenhouse gas • What are the major coupling of the planet’s jet streams and and a major constituent of mechanisms between the thus the movement of weather smog, reduction in sulphate troposphere and the strato- systems. concentrations could further sphere and how do they • How will changes in tropo- intensify greenhouse warming affect climate? We know, spheric concentrations as well as lead to more ozone for example, that the vertical affect solar radiation at the pollution in many areas. temperature structure of the earth’s surface? Aerosols are • How will stratospheric cooling troposphere is sensitive to tiny atmospheric particles affect the formation of ozone changes in the vertical tempera- and droplets. They come from holes? Since their discovery ture structure of the strato- both natural and human-related in 1985,Antarctic ozone holes sphere.We also know that sources. For most of the twen- have become increasingly waves propagating upwards tieth century, industrial activi- larger.The hole that formed in from the troposphere reach ties substantially increased September 2000 was, at the into the stratosphere and affect the atmospheric loading of time of writing, the largest yet temperatures and circulation aerosols, especially sulphates. recorded, covering an area of there. Similarly, waves generated Because sulphates contribute 28.3 million square kilometres, in the stratosphere can pene- to acid as well as human a little bit bigger than trate downwards and affect health problems, emissions and weather in the troposphere. of them have been reduced slightly smaller than Further study of such mecha- substantially in and (Figure nisms will improve our under- North America since the 1970s. 14).The hole standing of how conditions in Although emissions have extended as the stratosphere affect climate increased with industrialization far north in the troposphere and vice in other parts of the world, it as the versa. is expected they too will even- • How do changes in the tually fall for the same reasons. vertical temperature structure Sulphate aerosols reflect solar of the troposphere and radiation back to space, thus stratosphere affect climate? exerting a cooling force at the During the past three decades, earth’s surface and reducing researchers have measured a the amount of ultraviolet cooling of the stratosphere and radiation that penetrates the a warming of the lower tropo- atmosphere.As the amount of sphere.These changes could sulphate aerosol in the atmo- affect the height of the sphere declines, however, tropopause, the boundary surface warming may increase, between the troposphere and as more sunlight reaches the the stratosphere. Such a change

Ozone Depletion and Climate Change: Understanding the Linkages • 22 UV Index at Ushuaia,

12

10

8

6 UV Index 4

2

0 12345678910111213141516171819202122232425262728293031 Date: October 2000

Figure 14 Source: NASA (top); Servicio Meteorológico Nacional, Argentina (bottom)

Figure 14. The Antarctic ozone hole reached its largest extent yet in October 2000, and for the first time extended over sizeable settled areas in southern . UV Index values in Ushuaia, Argentina, were close to or greater than 8 on five different days and reached 10.1 on October 12. UV Index values for October in Ushuaia are normally around 4. Values greater than 10 are usually found only in tropical areas.

23 southern tip of South America, vapour in the atmosphere and and their Role in Climate, and the subjecting Ushuaia,Argentina that could have important con- project embraces a number of and the of in sequences for both climate and studies designed to improve scien- , with a population of over ozone depletion. Scientists tific understanding of the physical, 100,000 people, to very high therefore need to determine chemical, and radiative connec- ultraviolet radiation levels for whether the amount of water tions between the troposphere that time of year. Since the early vapour in the atmosphere is and the stratosphere and their 1990s, severe ozone depletion actually increasing and, if so, effects on climate. SPARC’s current has also been detected in some how it is distributed in differ- research agenda includes such years in the Arctic stratosphere. ent parts of the atmosphere. areas as stratospheric indicators of In the spring of 2000, for exam- • How will decreases in the climate change, the physics and ple, ozone levels in the Arctic atmospheric loading of chlorine chemistry of ozone depletion, the were depleted by almost 60% at and bromine affect climate influence of ozone changes on an altitude of 18 km. Ozone change and ozone depletion? climate, energy and gas exchanges depletion over the poles should As the amount of chlorine and between the troposphere and the decrease as the quantity of bromine in the stratosphere stratosphere, and atmospheric ozone-depleting substances in decreases, ozone concentra- waves. the atmosphere diminishes, but tions in the stratosphere should Another important area of researchers need to know more gradually increase towards activity,and one in which SPARC about how changes in green- natural levels.At the same time, is heavily involved, focuses on house gas and stratospheric however, atmospheric tempera- improving the way in which com- ozone concentrations will affect tures will be affected as the puter models of the atmosphere temperatures in the polar strato- cooling effect of ozone loss and represent important linkages sphere before they can confi- the warming effect of ozone- between ozone depletion and dently predict future trends in depleting greenhouse gases climate change.These improve- ozone hole formation. diminish. Data from monitoring ments include better representa- • How will changes in the systems that track ozone tion of the stratosphere in the amount of water vapour in concentrations and other impor- general circulation models used to the atmosphere affect climate tant atmospheric characteristics study climate change and better change and ozone depletion? will help to verify that expected representation of atmospheric Water vapour is the most abun- changes are taking place and waves. Inclusion of these refine- dant greenhouse gas in the expand our understanding of ments will give us not only greater atmosphere. In the strato- other changes that may be insight into how ozone depletion sphere, water vapour in polar occurring. and climate change interact but stratospheric clouds also acts as Many of the research initiatives will also provide a better under- a catalyst that enhances ozone that are probing these and other standing of how these linkages, in depletion. Since the atmo- related questions are taking place common with all the other factors sphere can hold more water under the World Climate affecting atmospheric change, will vapour when it is warmer, Programme’s SPARC project, influence the future state of both greenhouse warming could launched in 1992.The acronym the ozone layer and the surface increase the amount of water stands for Stratospheric Processes climate.

Ozone Depletion and Climate Change: Understanding the Linkages • 24 An integrated approach to atmospheric issues is also necessary because ecosystems and human health are affected not by just one of these issues but by all of them. The puzzling decline of populations, for example, may be a result of multiple stresses related to , persistent organic pollutants, and a number of other pollution issues. Increased UV levels (caused by ozone depletion) and changes in shallow water levels (caused by climate change) may also be contributing to the decline, as they make amphibian eggs more susceptible to water mould, which kills the embryos.

25 Making Connections

ncreasingly both science and integrated approaches to ozone Ipolicy are being driven by the depletion and climate change – recognition that the atmosphere and to other atmospheric issues cannot be seen as a collection of as well – is now enhancing our separate compartments in which ability to understand and moder- different things happen in isola- ate the enormous changes that tion. Instead, researchers and human activities have imposed on policy makers are adopting a the earth’s atmosphere over the more comprehensive view of the past two centuries. Not only will atmosphere, seeing it as a single these approaches help us deal dynamic whole whose state at more effectively with today’s any given time depends on a problems, but they will also give maze of interactions not only us a much better chance of between its different parts and anticipating and controlling any processes but also with those of further human threats to the other parts of the ecosphere. atmosphere that might occur in To take proper account of these the future. interactions, atmospheric scien- tists are increasingly thinking outside the confines of their particular specialties and collabo- rating more closely with experts in other areas.The of

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Ozone Depletion and Climate Change: Understanding the Linkages • 28