1. Lesson 4 "Ozone Depletion: The future?"
This lesson is intended to discuss what has been done about ozone depletion and what will happen in the future.
Note: One misconceptions many Australian have is that ozone depletion is getting worse, with no end in sight.
Ozone module prepared by Eugene C. Cordero

2. Outline What are current levels of ozone depletion?
Is the ozone hole getting worse?
What has been done about ozone depletion?
What is going to happen in the future?
Ozone module prepared by Eugene C. Cordero

3. Global Ozone Trends
Ozone trends from a NASA satellite shown in percent change per decade. The horizontal scale is time, in months from January through December, while the vertical scale is latitude from the South Pole to the North Pole. The colors denote larger negative ozone trends, while the white shading indicates no ozone trend.
For example, over Southern Australia main population centers (25-35S), trend is at most 2-4% per decade, although less during some seasons. In Northern Australia such as Cairns (17S), there is no observable ozone trend, in a statistical sense.
Most of Australia does not have large negative ozone trends
Ozone module prepared by Eugene C. Cordero

4. How has ozone changed over other parts of the Earth?
Globally, ozone has been decreasing over the last 15 years.
Largest ozone change over Antarctica
~ -8% per decade or more
No ozone change over Tropics
Over Australia
Melbourne: decreasing at 2-3%/decade
Darwin: No significant change
Global ozone trends show decreasing ozone levels at higher latitudes, while no statistical significant trends over the Tropics. Besides the ozone hole, there appears to be other ozone destroying mechanisms acting in the middle latitudes to destroy ozone. However, research still continues to quantify these. However, our understanding of what causes the ozone hole is very good.
Note that only Southern Australia has significant negative ozone trends, while Northern areas of Australia have not measurable trend.
Ozone module prepared by Eugene C. Cordero

5. Is the ozone hole getting worse?
(Optional)
Many students (and the public) have the perception that the ozone hole (and ozone in general) is getting much worse. This is likely due to press reports that usually say, ‘the ozone hole reached it’s largest size…’ The reality is that in the last decade, the size and severity of the ozone hole have stayed about the same, compared to rapid changes seen in the middle 1980’s.
Year to year variations in the depth and severity of the ozone hole is really a function of the atmospheric weather conditions (I.e. the colder the winter, the more greater the ozone loss). In addition, the ozone hole is about as bad as it can get. Between km, all the ozone is essentially destroyed during spring over Antarctica, so it couldn’t get much worse. Thus, we don’t expect the size and depth of the ozone hole to change dramatically in the future. Rather, it is expected that the size of the ozone hole is about as big as it’s going to get, and with time (10 or more years) and reduced chlorine levels, we should start to see the size of the ozone hole get smaller.
Thus, this graphic is intended to illustrate how in the 80’s, the size of the ozone hole increased rapidly, while in the 90’s and 2000, things stabilized.
Ozone module prepared by Eugene C. Cordero

6. What is being done about ozone depletion?
Montreal Protocol (1988): international agreement to phase out ozone depleting chemicals
Further amendments accelerated the phase out.
Developed countries have switched to HCFC’s (more ozone friendly) instead of CFC’s.
Developing countries has until 2010 to phase out CFC’s.
This was also discussed also in lesson 2.
Ozone module prepared by Eugene C. Cordero

7. Is the Montreal Protocol working?
Observations indicate that chlorine is beginning to decline in the atmosphere. (Good news!)
Still large uncertainties about illegal trade/use of CFC’s (??’s)
Future
Atmospheric models suggest that:
atmospheric chlorine will return to pre-80’s in next 50 to 100 years.
a slow ozone recovery will follow decreasing chlorine concentrations
These are the predictions for future ozone levels. It is mainly good news, but there are still large uncertainties.
Good news.
Chlorine levels in the atmosphere have begun to decline, as observed by measurements. These declines in chlorine suggest that the Montreal Protocol is starting to work.
Models suggest that ozone levels will begin to recover as Chlorine starts to decline.
Hard Truth:
Chlorine levels are not expected to reach pre 1970’s values until at least the This is because CFC’s remain in the atmosphere for many years (50-100). Therefore, even though we do not release any more CFC from today on, CFC’s will still be in the atmosphere for a long time, and will be destroying ozone. So, although the atmosphere is ‘self healing’, it takes a long time.
Tough questions:
Some of the big questions are whether countries will continue to follow the Montreal Protocol legally. In the US, CFC’s are a large contraband substance due to demand from old car air conditioners. In addition, developing countries like China have legally produced more CFC’s than originally expected, thus slowing the rate of ozone recovery. Whether countries continue to follow the protocol will determine how quickly ozone recovers.
The role of global warming adds another level of complexity. With surface temperatures rising (due to increased CO2), the upper atmosphere appears to be cooling. Recalling our ozone hole recipe calls for cold temperatures means that in a world with more CO2, we could expect a colder upper atmosphere, and thus more ozone depletion. At present it is difficult to estimate how this will slow the ozone recovery.
Ozone module prepared by Eugene C. Cordero

8. What is going to happen in the future?
Model simulations suggest:
atmospheric chlorine will return to pre-80’s in next 50 or more years.
a slow ozone recovery will follow decreasing chlorine concentrations
Still many questions!!!
Phase out and use of CFC’s
Contribution from global warming
Prediction for the future are always difficult, and this is no exception. At present, models predict that in the next 50 or more years, ozone levels should recover to their pre 1980’s levels. But this assumes that all participating countries abide by the Montreal Protocol, that developing countries are able to convert their technology, that illegal use of CFC’s is controlled, and that climate change (I.e. global warming) does not increase too quickly (more on that later). There are natural uncertainties, but our best guess at the moment is around the 50+ year mark (I.e recovery of ozone layer).
Ozone module prepared by Eugene C. Cordero

9. Graph of CFC’s levels starting to fall off
Optional
These are estimates of future total chlorine abundances from Du Pont, one of the major producers of CFC’s and HCFCs. Since that time, the projection for the reduction of chlorine have been pushed back some years
Ozone module prepared by Eugene C. Cordero

10. Chlorine in the future? Optional
These are estimates of future total chlorine abundances from Du Pont, one of the major producers of CFC’s and HCFCs. Since that time, the projection for the reduction of chlorine have been pushed back some years
Ozone module prepared by Eugene C. Cordero

11. Potential Chlorine growth
Optional
This figure shows how different scenarios of Chlorine growth. The red curve, show if CFC’s were allowed to grow unrestricted. Thus, by 2100, the atmosphere would have had nearly 10 times the 1975 level of chlorine. The other curves show the various agreements (Montreal Protocol, London amendment to Montreal, and Copenhagen further amendment.
Ozone module prepared by Eugene C. Cordero

12. Ozone depletion and global warming
No direct connection between these environmental issues.
However: Global warming may enhance ozone depletion
global warming produces
Tropospheric warming & stratospheric cooling
Therefore, if the stratosphere cools, then ozone destroying chemistry (e.g. ozone hole), will increase.
(optional)
There exists lots of confusion between ozone depletion and global warming, not just with students, but with the general public. Many people confuse the cause and effect, saying that automobile pollution cause ozone depletion, or that holes in the ozone layer allow more radiation to enter, thus causing global warming. These are not true.
One may think of ozone depletion and global warming as two separate environmental issues, with almost no overlap. Ozone depletion comes from CFC’s, or air conditioner refrigerants, fire retardants, aerosols etc. Global warming comes from increases in CO2, due to coal power plants, automobile exhaust etc.
The only relationship between the two issues is: If global warming continues, as expected, then the earth’s surface will continue to get warmer. A consequences of a warmer surface is a cooler upper atmosphere. Recall, from our ozone hole recipe, that cold temperatures are one of the prerequisites for an ozone hole. Thus, if the upper atmosphere does cool off, this could enhance ozone depletion. What this means is that even though we are cleaning up the atmosphere of chlorine, the recovery of the ozone layer will take longer if the upper atmosphere gets cooler.
It seems that we are now seeing evidence of a cooler upper atmosphere. Measurements of stratospheric temperatures show that the stratosphere has cooled 1-2K in the last two decades. The consequences of this may be occurring over the Arctic, where cooler temperatures have caused the appearance of so-called mini ozone holes, small areas of ozone depleted air similar to the Antarctic ozone hole, but of a much smaller size.
More general note:
Although international steps have been taken to address the possible depletion of the ozone layer, addressing the concerns of global warming is much more difficult. In the ozone depletion story, the science behind the ozone hole was good, and large companies like Du Pont, who saw a future in producing alternate ‘ozone friendly’ chemicals, agreed with the science that CFC’s could potentially destroy large amounts of ozone. However, in the case of global warming, the science is much more complicated, and the economic interests are much larger, and could mean the end of an era of energy producing companies. Thus, the story of ozone depletion, although far from over, seems headed for some time of happy ending, while global warming is just heating up, pardon the pun. It therefore seems particular important that we pass on the ozone depletion story to today’s students, so they can refer to this experience when making the difficult decisions that will be needed to deal with global warming.
Ozone module prepared by Eugene C. Cordero

13. What are the consequences of an ozone depleted world?
With ozone depletion, there will be higher rates of UV radiation.
More UV radiation rates mean
Higher rates of skin cancer
Higher amounts of cataracts
Possible danger to plant and animal life
Recall: Without the ozone layer, life on the Earth’s surface would not exist!!!
When the international community first realized that there was potential for large scale ozone depletion the consequences spurred rapid action. A lowering of global ozone levels by 10% could have a catastrophic impact on biological life on earth. Not only would human cases of skin cancer soar, but animal and plant life would be severely impacted.
Ozone module prepared by Eugene C. Cordero

14. Summary
The international community has a plan to phase out CFC’s in the atmosphere. So far, it looks like it’s working!
Current predictions indicate that ozone will recover in next years.
Learning activity 4 is designed to go along with the section on skin cancer. The goal of this lesson and the learning activity is to dispel the misconception that ozone depletion is responsible for Australia’s high rate of skin cancer.
Ozone module prepared by Eugene C. Cordero