Practice what you preach, as they say. So I have decided to do some reflective learning and blog about my experience with our Climate Change MOOC. It’s been great this week, seeing so much engagement with the course material on the discussion threads. But it left me looking for one place where I could respond to some of the issues that were catching fire, without having to repeat myself. Hopefully this will be it. So here goes with this week’s favourite topic – ozone…
Yes, we threw a curveball in the very first question on the course. A lot of people were surprised to hear that ozone (chemical formula O3) is a greenhouse gas, especially knowing that we have been trying to protect the ozone layer for the last twenty years. So, let’s tackle that one head on.
The first point to grasp is that ozone is present in two layers of our atmosphere – the well-mixed bottom layer that we breathe, known as the ‘troposphere’ – and the next layer up, known as the ‘stratosphere’ (because it is vertically stratified, i.e. layered).
It is in the stratosphere that the ozone layer forms, and it is the absorption of high energy (UV) sunlight by the ozone layer that heats up the stratosphere and gives it its stratification (with temperature increasing as a function of height).
Down in the troposphere ozone is a short-lived gas, concentrated near the surface, and produced as a by-product of chemical reactions acting on a range of mostly human pollutant gases, including oxides of nitrogen, carbon monoxide, methane, and other ‘volatile organic carbon’ species.
In both atmospheric layers, ozone functions as a ‘blanket gas’ absorbing heat radiation coming off the Earth and thus helping warm the surface. However, the warming associated with the stratospheric ozone layer is natural, and the ozone layer is doing a wonderful service shielding us from ultraviolet radiation, which we couldn’t live without. The ozone in the troposphere on the other hand has been increased in concentration by human activities, thus contributing to climate change – and it has some other nasty effects, like inhibiting plant productivity.
The depletion of the stratospheric ozone layer that was caused by human-produced chlorofluorocarbons (CFCs) did, as would be expected, tend to cool the planet, but only by a small amount when globally averaged. That cooling was more than outweighed by warming due to the CFCs themselves, which are potent ‘blanket gases’. And both effects are small compared to the contribution of carbon dioxide (CO2) to recent warming.
Interestingly, the creation of the ozone hole, as well as letting more UV radiation down to the Earth’s surface, has affected the climate regionally in Antarctica and the Southern Ocean, tending to keep things cool there, and leading to a strengthening of the winds encircling the planet above the Southern Ocean. Those strengthening winds have in turn tended to blow more sea-ice away from the areas where it is made around Antarctica, causing the surprising increase in area of Antarctic sea-ice that is so beloved of climate sceptics.
Hopefully that gives some glimpse of the beautiful, interconnected complexity of the climate system. Happily the stratospheric ozone layer is on the mend, but unfortunately the compounds we replaced CFCs with (the HCFCs) are still potent ‘blanket gases’. One day we’ll learn…
Professor Tim
Yes, I take your point re: CFCs etc but we don’t know for how long there has been a hole in the ozone layer or whether it has always been there. It may be a necessary requirement of the Earth for ‘respiration’ purposes. It may have been in existence for millions of years or it may only have evolved since and because of the industrial revolution. It is only relatively recently that we have been able to measure the size and depletion/accretion rates etc of the hole because the necessary instruments were not available several million years ago or, indeed, during the industrial revolution. Whereas the ozone hole may well have been created and exacerbated by CFCs a blanket statement that anthropogenic activity caused the hole relies on only a few years real-time data and a great deal of extrapolation.
Thanks for clearing that up. I know I’m not the only one who was thrown by you including ozone (O3) as one of the greenhouse gases (GHGs)/ blanket gases (‘BeeGees’?)*, but not chlorofluorocarbons (CFCs) — especially when the NASA page you linked to did the reverse! Want to keep us on our toes, eh? I guess we on the MOOC should expect more ‘curve balls’ like that 🙂
A friend of mine over at Wit’s End is my guru when it comes to ozone in the troposphere. Over the last few years, she has amassed a wealth of information about the effects of our poisonous, polluting way of life upon the trees.
[…] but unfortunately the compounds we replaced CFCs with (the HCFCs) are still potent ‘blanket gases’. One day we’ll learn…
I doubt that, very much, which is why I’m on a campaign to try to get our species renamed from ‘homo sapiens sapiens’ (‘the wise, thinking man’) to ‘homo fatuus brutus’ (‘the foolish, stupid man’) — on the grounds that only once we accept that we’re not as smart as we like to think we are will we learn to change our ways.
* Concerning the attempt at the beginning of week 1 to try to redefine ‘greenhouse effect’ as ‘blanket effect’ (and thus ‘greenhouse gas’ as ‘blanket gas’): there’s already quite enough confusion in the minds of the man (and woman) in the street when it comes to global warming/ climate change. Attempting to change a name that has been in use since at least 1896 that I know of (Arrhenius) and that is plastered all through the common literature on the subject is, I believe, a mistake.
As Hernan Nadal pointed out in the MOOC discussion thread on the Future Learn site: “the gases are called greenhouse gases, so it could generate more confusion among non experts.”
There was one course student’s website (no link, to protect the innocent!) I visited recently where the author waxed lyrical about the ‘new discovery’ of the blanket effect :/
Thought I would cut and paste this in from another MOOC (Sustainability) This includes a link to my Flickr page, a photo of the Dobson Spectrometer. This is the actual instrument used by Joe Farman, Brian Gardener and Jonathan Shanklin when they discovered the hole in the ozone layer. It is still used for daily readings of ozone above the British Antarctic Survey’s Halley Base on the Brunt Ice Shelf in Antarctca. I was privileged to use this iconic machine last year and thrilled to be able to contribute to the long-running data set that this instrument is providing…..magnificent!
http://www.flickr.com/41780809@N08/11984536416/
I hope to get back there this year!
Dear Professor,
I have some few queries if you could, reply me. What kind of effects do the CFCs have on troposphere ozone layer? Since I’m an agriculture graduate I would like to read more on those nasty effects.
You have referred to “the surprising increase in area of Antarctic sea-ice”. Do you have the most recent figures for the change in Arctic sea ice, and what the over all sea ice extent is at both poles combined?
Thanks – these review videos are excellent. Truly does feel like interactive learning. Your explanation in particular of the various and contradicting ways volcanoes impact our climate was timely. I can’t recommend this course highly enough.
Hi Tim
Not all the ozone in the stratosphere is natural. High flying aircraft emit NOx which forms ozone
Martin
There is a lot of calcium carbonate on land and in the sea. When carbonic acid falls on chalk and limestone CO2 must be released? Does this not negate some of the silicate weathering?