The problem was spotted only recently, but the technology and knowledge used in identifying the problem are also quite recent; so is it possible the hole has been there for centuries, or even millenia, and all we’ve done is make it worse? or… better? maybe it was really huge a century ago and after a period of reducing size (because of our chemicals in the atmosphere) now it’s increasing (because we’ve reduced the chemicals that were reducing it)?
Probably not, but I’m just wonderin…
Well for a start the holes in the ozone layer aren’t permanent. A hole opens up every summer over the Antarctic, and a smaller one opens up over the Arctic.
Secondly, they were measuring ozone levels before the hole opened up. So its not possible the hole was there before, because we would have detected it.
Hmm. Possibly not. Examiners of satelite data, according to the page linked, may have treat earlier depletion of the ozone (earlier than 1985) as “bad data”, and therefore it was discounted.
However, I do think relatively recent use of chemicals in industrial use, such as CFCs, have contributed to the rapidity of the growth of the hole.
Well, mooka, how about before that? Man has been on earth about what? 20,000 to 50,000 years? A blip in the 4 or 5 billion years since the earth existed. Since the earth has undergone a couple of Ice Ages we know about and likely a bunch we don’t, who’s to say the ozone layer doesn’t naturally wax and wane over a hundred thousand years?
We actually don’t know much at all about the ozone layer. We observed it and believed it was being affected by our activity. We got rid of some stuff we believe depletes it (hydroflourocarbons, freon), but we don’t really know why it comes and goes as it does. Observing it for 30 years out of 4 billion is like looking at an infant and deciding if she’ll be good at penmanship.
It would be more like determining the origin of the universe based on a couple thousand years of observation.
Man, I can’t believe we broke the sky. Who knew?
“Believe” doesn’t come into it. It’s a fact of chemistry. All is open for debate is the how much of the hole is the result of our production of these chemicals. There is no doubt that they deplete ozone.
I have never understood the CFC arguement.
These are incredibly stable molecules which are much heavier than air, and yet they manage get from ground level in the northern hemisphere to the ionosphere over the antarctic, and then the chlorine magically comes out somehow.
The last figures I saw (admitedly over 10 years ago) attributed somewhere between 2 and 4 percent of atmospheric chlorine to manmade sources, and CFC’s were a small portion of that.
Swimming pools are a much larger source.
It is of course possible that the ozone layer waxes and wanes over thousands of years. We’ve only be observing it for a few decades. The levels aren’t waning though - they’re crashing down very quickly, to zero in some places. The only reasonable explanation scientists can think of for this are certain specific chemicals that we’ve been releasing into the atmosphere.
We actually know quite a lot about the ozone layer. We know how ozone forms (and thus why there is an ozone layer) and we know how various gases can destroy it. Naturally occuring gases like carbon dioxide also destroy ozone. The difference is that CFCs destroy ozone, but aren’t themselves destroyed in the process. One molecule of CFC can destroy hundreds of molecules of ozone.
So basically we have a theory for why ozone levels are depleting. We have evidence that backs up that theory. We don’t have any other theories that can explain the evidence. Why don’t you believe that theory?
Ice Wolf: If you go onto the second page of that site they have a graph showing ozone levels from around 1960 to around 1990. The levels stay around the same until about 1970 when they start rapidly falling. So it looks like we were measuring ozone levels before they started falling.
But the stability of the CFC allows it to exist for extended period of time. The atmosphere churns it all up (otherwise we’d all be dead from CO2 poisoning) and it gets into the stratosphere. Now you get photo dissociation, and all the chlorine can muck things up. Better details here http://www.epa.gov/ozone/science/q_a.html
Now you’re pool analogy doesn’t really work because the chlorine you’re talking about lack the stability to reach the upper atmosphere.
Also I believe the hole was getting smaller following the Montreal protocols.
Mario Molina won the Nobel prize for his work on ozone chemisty.
From the linked site…
Okay, Grey, now you’re confusing me.
I still don’t understand how Freon-12 from my refrigerator winds up at altitude over Antarctica. Also, “photo-dissociation” as a stand-alone explanation doesn’t really cut it either. It takes a whack of a lot of energy to get the chlorine out of a CFC, and that level of incident radiation would tend to produce a lot more ozone as well.
Chlorine gassing off from swimming pools is “unstable?” That makes no sense. What in hell happens to it, nuclear decay?
As I said before, while chlorine is the culprit, well over 90% of it comes from natural sources.
Exgineer - take a look at the link Ice Wolf provided above. Here it is again:
http://www.atm.ch.cam.ac.uk/tour/part1.html
It explains the whole process of ozone formation and the way in which CFCs destroy ozone as well.
Have a look at this link for why chlorine from swimming pools etc doesn’t effect the ozone layer:
http://www.renewingindia.org/cliozone.html
From that link:
"Chlorine from swimming pools, industrial plants, sea salt, and volcanoes does not reach the stratosphere. Chlorine compounds from these sources readily combine with water and repeated measurements show that they rain out of the troposphere very quickly. In contrast, CFCs are very stable and do not dissolve in rain. "
and
"Large fires and certain types of marine life produce one stable form of chlorine that does reach the stratosphere. However, numerous experiments have shown that CFCs and other widely-used chemicals produce roughly 85% of the chlorine in the stratosphere, while natural sources contribute only 15%. "
Well CFC’s were used for a lot more than just refrigerants. Aerosol propellants were also based on CFCs.
The CFC is a stable molecule right? 100 years or some such. That means there is a huge amount of time for the damn thing to go anywhere. The fact is, the atmosphere is continually churning about. Your point of CFC being heavy and sinking would apply to CO2 sinking and not being present above a certain level. That doesn’t happen. (http://www.ifh.uni-karlsruhe.de/ifh/studneu/envflu_I/Downloads/course_script/ed2/ch6.PDF is a paper I found on mixing. Note that 3d models are crude.) So let us agree that if there are stable molecules at sea level they will make it up to the troposphere/stratosphere boundary. The longer the molecule is stable the higher the probability that it will reach this boundary. As a quick aside this is why HCFCs are allowed, they last about 5-10 years. Once there, some will move across. Now you are in a region with energetic ultraviolet photons. Energetic enough to snip a chlorine atom off the CFC molecule. You now have free chlorine running around a region were O3 is present. Now O3 exists as a result of UV photons mucking up O2. The newly arrived chlorine atom starts reacting with O3 reducing its presence. From my previous cite a single chlorine atom can react with 100 000 O3 molecules before falling out of the reaction chain.
You seem to be partly right about pool chlorine making it into the atmosphere but the reaction rate of chlorine is higher and it has the chance of being washed out by rain. My unstable comment was meant to convey a sense of how short lived pool type chlorine is compared to CFCs.
How’s that?
That’s much better, but I’m still sceptical.
Why didn’t the hole form over the arctic? Most CFCs were released in the northern hemisphere, and that’s a much shorter trip. There should be many times more atmospheric CFCs in the north than the south.
I have the same question about the mixing, but if we say it takes a couple of years to reach the upper troposphere that gives plenty of time to diffuse across the globe. I’d bet you’re right for concentrations at lower levels but they get smeared out as you go higher.
The holes are really regions where there is a lower concentration of ozone, not an absence. My wild guess would be that the since the average elevation of Antarctica is 2.5 km and the artic is sea level, ice crystal can more easily reach the upper atmosphere. Perhaps, if this guess is right, the excessive amount of ice crystals intrudes into the chlorine/ozone reaction and speeds it up. That’s my WAG/hand waving argument. I’ll now go see if I’m right.
See the Ozone Depletion FAQs for info on dispersion, why the Antarctic hole is much larger, etc.
One thing to note: NASA has directly measured CFC density in the atmosphere. It’s uniform all the way up to the ozone layer. That tells you that a) CFCs do mix in the atmosphere and b) something peculiar is happening when they hit the ozone layer, i.e, there’s a chemical reaction going on.
Basically, it’s because the extremely cold air over Antarctica in the winter (much colder than over the Arctic, due to the fact that its a continent rather than ocean) produces special conditions that promote the critical reactions.
ftg’s link provides much more detail.