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Atmospheric Ozone - Relation to Scale2018-Nov-20  10:15:30 AM
Exceeding Maximal Sustainable Scale Maximum sustainable scale is the highest level of material throughput which allows all essential ecosystem functions to be maintained. The material throughput of ODCs has disrupted the ecosystem’s capacity to maintain the normal balance of atmospheric ozone creation and destruction; maximum sustainable scale has been exceeded. ODC use in the global economy has led to greater than normal amounts of atmospheric ozone destruction, resulting in a net loss. The result is harmful to living things dependent on protection from ultraviolet radiation.

Maximum Scale Maximum scale is a level of material throughput beyond that of maximum sustainable scale, where the very processes of atmospheric ozone creation and destruction would be irrevocably disrupted. Fortunately, we have not reached this point. The apparent success of the Montreal Protocol in reducing global production of ODCs indicates that material throughput of these compounds may well be reduced to the level required to reestablish maximum sustainable scale with respect to ultraviolet radiation protection. However, this process will take several decades to accomplish, and the possibility of reversals still exists.

Optimal Scale Optimal scale is that level of material throughput which provides an adequate safety margin in terms of not exceeding maximum sustainable scale. In the case of ODCs, optimal scale appears to be identical to, or very close to, maximum sustainable scale. Nature has provided a global, dynamic and effective mechanism for the natural creation and destruction of atmospheric ozone, the result of which provides the balance necessary to protect living things. The optimal strategy for human policies and activities is to ensure this natural process is not disrupted.

Continuing Risks Thinking about scale requires us to consider both material throughput of ODCs in the global economy and a variety of ecosystem impacts. It is clear that the optimal level of ODC throughput is zero or close to zero – any ODC emissions threaten the natural balance for atmospheric ozone. While the Montreal Protocol seems to have succeeded in reducing ODC production toward this optimal scale target, a number of potential risks remain with regard to ecosystem services.

There are at least four kinds of risk remaining to be explored. The first relates to whether the current planned reduction of ODCs will succeed; the second relates to the possible identification of yet unknown consequences of UV exposure; and the third relates to potentially critical ecosystem services associated with the atmospheric ozone layer other than UV protection that may not yet be identified. The fourth risk has to do with the impact of other scale problems as they might affect atmospheric ozone depletion.

Will Maximum Sustainable Scale be Reestablished? While the Montreal Protocol appears to be working, it will be decades at best before normal, sustainable levels of atmospheric ozone are restored. There is no assurance that this is inevitable. The UN’s “Scientific Assessment of Ozone Depletion: 2002” report states “The ozone layer will remain particularly vulnerable during the next decade or so, even with full compliance.” The same report goes on to say “… because of changes in other influencing factors, such as changes in cloud cover, aerosols, or snow/ice cover, UV radiation may not (italics added) return exactly to pre-ozone-hole values.”

There are many scientific and political uncertainties involved: new data are emerging regularly about the complex atmospheric processes involved; black market trading and production of some ODCs may be increasing; and the United States has recently asked for exemption from the phasing out of a known and previously agreed upon ODC - methyl bromide. The longer the term over which the recovery must be managed, the more likely something can retard or reverse the process. Just such a reversal occurred when the Reagan administration relaxed CFC restrictions after they were initially banned in aerosol cans. This lead to an increase in CFC emissions in the mid and late 1980’s, and a worsening of the impact from atmospheric ozone depletion.

UV Protection for What Ecosystem Functions? Scientific understanding of the important role the atmospheric ozone layer plays in terms of UV protection is relatively new, stimulated in part by the discovery of ozone depletion. The various life support functions affected by UV protection are still being explored and new discoveries are likely. It is conceivable that some essential life support functions resulting from UV protection are more subtle, or take longer to express themselves, than the ones currently known. Maximum sustainable scale may already have been exceeded for these ecosystem services but not yet been detected. It is also possible that the continued exposure to UV radiation over the next few decades will result in exceeding maximum sustainable scale for a critical ecosystem function. For example, could the result of reduced UV protection significantly affect the supply of ocean phytoplankton, and in turn the entire ocean food chain? The ubiquitous role of atmospheric ozone in the evolution of life over hundreds of millions of years suggests such impacts are at least possible; and underscores the importance of research into the basic life supports functions of global ecosystems.

Does the Atmospheric Ozone Layer Do More than Provide UV Protection? The third kind of risk has to do with functions other than UV protection that the ozone layer might provide. We know that global ecosystems such as the atmospheric ozone layer are complex and usually provide a variety of services. Are there ecosystem functions (in addition to UV protection), that the atmospheric ozone layer provides either on its own, or in conjunction with other ecosystems? Given the global nature of the atmospheric ozone layer, and its long term role in the evolution of life, this should at least be considered. A potential implication is that we have already exceeded maximum sustainable scale for some unknown but vital ecosystem function performed by this layer. When global systems are involved it would seem prudent to at least explore this issue. For example, could the role the atmospheric ozone layer plays in global climate regulation be limiting the climate’s ability to adapt to changing circumstances induced by rising GHG concentrations?

How Might Other Scale Problems Affect Restoration of an Atmospheric Ozone Balance? The fourth type of risk to be considered is how other global scale problems might impact the atmospheric ozone layer. Global ecosystems evolved together over billions of years and it is to be expected that they are intimately interconnected in complex ways. For example, a 2002 study by NASA suggests that increases in various GHG emissions are offsetting some of the improvements from reduction of ODCs. It is also reported that the increased GHG induced warming of the lower stratosphere, where most of the ozone occurs, may be speeding up chemical reactions that destroy ozone. In addition, methane, also a GHG, is known to destroy atmospheric ozone independently of any warming effect. The NASA study suggests that climate change may retard the anticipated recovery of atmospheric ozone expected from the Montreal Protocol.

The issues of ozone depletion and climate change are interconnected in many complex ways. On the one hand, the reduction of some ODCs will reduce the contributions of those compounds to greenhouse warming. On the other hand, increased use of substitutes such as HFCs will contribute to greenhouse warming. In addition, atmospheric ozone depletion acts to cool the climate system, so that successful recovery of the ozone layer will contribute to global warming. These complex interdependencies of global ecosystems are a major reason for ensuring that all such systems remain within maximum sustainable scale. They point out the dangers of exceeding scale in any single area, and the compounded threats from exceeding sustainable scale in multiple areas at the same time. The longer the duration over which material throughput exceeds maximum sustainable scale, the greater the likelihood of critical ecosystem disruptions.

IN SUMMARY, despite the welcomed successes of the Montreal Protocol the level of atmospheric ozone depletion will continue to exceed maximum sustainable scale for several decades. Damage to living things will continue as long as levels remain above maximum sustainable scale. In addition, the possibility of atmospheric ozone depletion exceeding maximum scale with respect to some ecosystem services cannot be ruled out. These remaining risks underscore the importance of policies and practices which emphasize the Precautionary Principle regarding any decisions which might affect a return of atmospheric ozone to traditional levels of optimal scale. The variety, complexity, potential magnitude, and extended duration of these risks also highlight the importance of implementing policies to ensure maximum sustainable scale is not exceeded in the first place.

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