I've been googling to try and answer this but can find no easily digested answers. A lot seems to be made of measurements captured at Mauna Loa, the worlds largest volcano in Hawaii. Is this truly representative? I'd have thought concentrations would vary according to height, biomass, proximity to industry, northern vs southern hemispheres (I assume the air does not mix between the two?), time of year atc.
northern vs southern hemispheres (I assume the air does not mix between the two?)
Air does mix between the two. I'm told there is a delay between northern and southern hemisphere observations because most anthropogenic CO2 is emitted in the northern hemisphere (certainly the values from 2004 seem to be a bit lower for the southern hemisphere stations).
The Mauna Loa graph that is reproduced quite a lot shows a wobble that I assume is related to the seasons.
Originally posted by Steve_M: The following webpage links to 8 sites:
cdiac.esd.ornl.gov/trends/co2/sio-keel.htm
Thanks Steve, and are these "THE" measurement stations from which we deduce the mean global concentration? Seems like a very narrow line of longitude to site the stations?
I don't know. I assume so. These sites should be reasonably trusted because they are in the middle of the Pacific or upwind of likely sorts of nearby pollution. I think there would be more concern if they were at the same latitude, as winds/weather, and therefore mixing of air, tend to go west to east rather than north to south.
I've seen studies of sulphur dioxide from volcanoes going off, and it tends to mix quickly along the same latitude, but doesn't go north or south quite so quickly.
Originally posted by Steve_M: I don't know. I assume so. These sites should be reasonably trusted because they are in the middle of the Pacific or upwind of likely sorts of nearby pollution. I think there would be more concern if they were at the same latitude, as winds/weather, and therefore mixing of air, tend to go west to east rather than north to south.
I've seen studies of sulphur dioxide from volcanoes going off, and it tends to mix quickly along the same latitude, but doesn't go north or south quite so quickly.
Makes some kind of sense but I'm intrigued to know why they don't take readings from the various major zones around tyhe world such as desert, industrialised, rain forest, grass lands etc etc. The Global Dimming horizon program I refered to elsewhere showed very marked differences in air quality in a relatively small area around the Maldives. So my guess is CO2 concentrations vary enormously from place to place.
Makes some kind of sense but I'm intrigued to know why they don't take readings from the various major zones around tyhe world such as desert, industrialised, rain forest, grass lands etc etc. The Global Dimming horizon program I refered to elsewhere showed very marked differences in air quality in a relatively small area around the Maldives. So my guess is CO2 concentrations vary enormously from place to place.
If I were designing an experiment to measure CO2 concentrations I would want both a measure of the global trend (which is what the stations do). But I'd also want local measures plus measures in the upper atmosphere.
I've read that CO2 is mixed reasonably uniform in the atmosphere, so I assume vertical measurements have been done. I've also read of studies making careful measurements of CO2 in and around forests etc. So I guess there is some understanding of this too. Once I was happy that in general CO2 is reasonably well mixed and that measurements elsewhere tended to match those at the stations though, I would be happy that the trend from these stable observation sites are good enough for modelling studies. Furthermore, CO2 increases quite slowly (0.5% per year) so a mild inaccuracy in the absolute value of CO2 in models is not important as long as the trend is correct.
On the other hand, the short lifetime of chemicals such as sulphates in the atmosphere, and the fact that they can be produced in large bursts (eg. volcanoes) or from localised sources (eg Beijing) mean that it is important to know their distribution in space and time. So modelling of sulphates etc. is therefore much more complicated than modelling of CO2.
