One of the few things that BOTH sides of the Carbon Dioxide and AGW debate seem to be able to agree on is the belief that CO2, as a trace gas, is “well-mixed” in the atmosphere. Keeling’s measurements at Mauna Loa and other locations worldwide rely on this being true, so that “hotspots” aren’t being inadvertently measured.
As support for this, if you do some Google searches for these phrases, you’ll get hundreds of results of the usage together:
“carbon dioxide” + “well mixed”
You’ll find complete opposites using the same “well mixed” phrase, for example:
Gavin Schmidt of Real Climate writes in comment # 162 of this thread on Realclimate.org
“A full doubling of CO2 is 3.7 W/m2, and so by looking at all well-mixed GHGs you get about 70% of the way to a doubling.”
Roger Pielke Sr. writes in April 2008:
“…and thus are not providing quantitatively realistic estimates of how the climate system responds to the increase in atmospheric well mixed greenhouse gases in terms of the water vapor feedback.”
You’ll also find the phrase in use in titles of scientific papers, for example this one published in the AGU:
New Estimates of Radiative Forcing Due to Well Mixed Greenhouse Gases
And you’ll find the phrase used in popular media, such as this article from the BBC:
Carbon dioxide continues its rise
In describing the emasurements of CO2 at Mauna Loa Observatory: “The thin Pacific air is ideal for this research since it is “well-mixed”, meaning that there is no obvious nearby source of pollution, such as a heavy industry, or a natural “sink”, such as forest which would absorb CO2.”
Hmm, “no obvious nearby source of pollution” I suppose the volcanic outgassing nearby doesn’t count as “pollution” since it is natural in origin.
So it seems clear that there is a broad agreement on the use of the term. I suppose you’d call that “scientific consensus”.
So it was with some surprise that I viewed this image from NASA JPL, a global CO2 distribution as measured by satellite:
Note the variations throughout the globe, ranging from highs of 382 PPM to lows around 365 PPM. There is a whole range of data and imagery like this above available here
My question is: how does this global variance translate into the phrase “well-mixed” when used to describe global CO2 distribution? It would seem that if it were truly “well-mixed”, we’d see only minor variances on the order of a couple of PPM. Yet clearly we have significant regional and hemispheric variance.
NASA JPL provides this caption to help understand it:
Although originally designed to measure atmospheric water vapor and temperature profiles for weather forecasting, data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua spacecraft are now also being used by scientists to observe atmospheric carbon dioxide. Scientists from NASA; the National Oceanic and Atmospheric Administration; the European Center for Medium-Range Weather Forecasts; the University of Maryland, Baltimore County; Princeton University, Princeton, New Jersey; and the California Institute of Technology (Caltech), Pasadena, Calif., are using several different methods to measure the concentration of carbon dioxide in the mid-troposphere (about eight kilometers, or five miles, above the surface). The global map of mid-troposphere carbon dioxide above, produced by AIRS Team Leader Dr. Moustafa Chahine at JPL, shows that despite the high degree of mixing that occurs with carbon dioxide, the regional patterns of atmospheric sources and sinks are still apparent in mid-troposphere carbon dioxide concentrations. “This pattern of high carbon dioxide in the Northern Hemisphere (North America, Atlantic Ocean, and Central Asia) is consistent with model predictions,” said Chahine. Climate modelers, such as Dr. Qinbin Li at JPL, and Dr. Yuk Yung at Caltech, are currently using the AIRS data to study the global distribution and transport of carbon dioxide and to improve their models.
As we’ve found with surface based temperature measurement, it seems the more we look at satellite data, the more we learn that our earth bound assumptions based on surface measurement don’t always hold true.
When measuring the planet, looking at the whole planet at one time seems a better idea than trying to measure thousands of data points at the surface, sorting out noise, doing adjustments to “fix” what is perceived as bias, and assuming the result is accurately representatiive of the globe.
UPDATE: 7/31/08 I got a response from the AIRS team on satellite CO2 measuremenst, see this new posting
We won’t have to rely on ground based CO2 measurements much longer.
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peer reviewer (19:43:52) :
I could not find a description of the plots in your link. I am on a dial up slow link at the moment and cannot really search.
The point is that the global map in the beginning of this thread speaks volumes. They say a picture is worth a thousand word, I would say a graduated map is worth a thousand histograms.
And it is funny that AIRS only managed to have one map out of all the data, from July 2003, miss labelled in another link as January 2003.
There is a funny character in modern greek folklore/shadow theater called Karagiosis. He tells a riddle to his friend:
“what am I holding here”
“a bird cage?”
“Ah, you found it.”
“And what is the sardine doing in the birdcage?”
“I just put it there to confuse you.”
The distribution of CO2 can be explained by distribution of rain/clouds versus clear sunny skies at that time of year (July), with possibly some effect from altitude.
Rain washes CO2 from the atmosphere and makes plants grow.
I don’t see any relationship with human activity. Look at India and southern China, the most densely populated regions on the planet.
So yes, this graphic shows anthropogenic CO2 is well mixed. Although I’d also like to see the January image.
Glenn, I mostly agree with Hansen in your quote. I am writing something on methane, ‘the other GHG’, which if I ever finish it, I will send to Anthony to see if he will publish.
Thanks Anthony for a fascinating query.
The term “well mixed” follows from the physics of gas diffusion. So as a concept it’s about 200 or so years old. Where CO2 is being generated from the spout of a laboratory retort, CO2 will be more concentrated near the spout than generally in the lab. At least it will be more concentrated in spots until the CO2 has diffused into the air in the room. Turn off the gas generator and the CO2 will eventually become well mixed (diffused).
If the CO2 is being generated continuosly, a snapshot will show spots of concentration near where the CO2 is being generated. Possibly, the lab has a tank full of a solution that absorbs CO2. With a really big tank to absorb CO2, we will get variations above and below the level in the lab next door. With continuous generation and absorption, CO2 concentration will never reach equilibrium.
If the rates of generation and absorption were both low, and we had a fan going, so that the variation was within plus or minus 5 per cent, we might say that the air was well mixed.
Whether or not the gases in the lab air become well mixed depends on the rate of CO2 generation and absorption. If I recall my lab work correctly, we used solutions of sodium hydroxide (NaOH) or calcium hydroxide (CaOH / limewater) to absorb CO2. Of course the Earth has clouds, plants and oceans instead of NaOH and limewater.
(The concentrations shown in the satellite image are for an elevation of 8,000 meters / about 27,000 feet. There may or may not be much water vapor or cloud at this elevation. This is important, but I am ignoring it for this discussion. There are jet streams at or near this elevation and interzonal / latitutinal movements of air, which I also ignore.)
In the satellite image, the concentration observed at the center of the range (372 ppm) might be that for fully mixed CO2 at this altitude. If so, we have to account for absorption of CO2 in the lower part of the range (360-372 ppm). Alternatively, the range is so small that perhaps the concentration of fully-mixed CO2 is at or close to the bottom end of the range and CO2 above the minimum concentration (360-385) is not yet fully diffused. Perhaps equilibrium has not been reached because of continuous CO2 generation, but most likely we are looking at generation above the mid-point of the range and absorption below the mid-point.
We may be looking at effects caused by processes occurring at a distance. The generation and absorption of CO2 may be occurring elsewhere, at different latitudes and longitudes and different elevations from what appears in the image. For this discussion let’s ignore this possibility.
This image shows for the whole atmosphere a plus or minus 5 per cent geographic variation. However interesting this may be, 5 per cent is not a big variation. What would interest me more would be a theory that explains how these small variations point to important atmospheric processes.
We would start by observing the pattern of geographic variability as some of the posters have done. An examination of the southern hemisphere allows us to formulate an approach based on latitude and the size of landmasses relative to ocean masses, recognizing some anomalies. The southern hemisphere has less in the way of continuous land masses, dense populations and CO2 emitters compared with the northern hemisphere. (The biggest and densest populations are in Brazil and Indonesia.)
Polar and equatorial latitudes seem to have depressed CO2 concentration: between the equator and 20 degrees and between 40 degrees to the pole, CO2 concentration is depressed. There is a band of elevated CO2 between about latitude 20 to 40 degrees.
There is an anomaly in the tropics north of Australia near the western Pacific “warm pool” that extends eastwards across the Pacific.
In the northern hemisphere, some CO2 “hotspots” we see might seem to be “downwind of industrialized areas”. But given the prevailing westerly winds, we would have to explain why CO2 concentration is so high over the western part of North America and the southern part of Europe extending across the Middle East. These are not areas with dense populations and industry.
So the idea that we have a correlation with densely populated industrial areas may result from biased perception. The same perception bias might arise concerning densely populated agricultural areas in the tropics. However few observers in the “North” are familiar with the pattern of CO2 emission in these regions.
The location of CO2 hotspots in North America and Eurasia correlate with latitude and land masses as in the southern hemisphere. There is an anomaly over the Himalayan Mountains. There is another anomaly in the western Atlantic between Florida and Newfoundland extending across to Gibraltar.
Land cover may be a factor: note the reduced concentration of CO2 over forested areas and over ice. Note increased CO2 concentration over areas with sparse vegetation and warm oceans, except the Atlantic between Brazil and the Congo.
These considerations indicate the possibility that at this altitude the processes underlying the variation in CO2 are natural. In any event, our null hypothesis should assume that the underlying process is natural. But I suspect that many will begin with a null hypothesis that assumes the variation is caused by man.
Finally, we could focus on the lower part of the range and try to explain why some regions have lower CO2 concentration. But to make sense of these images, we ought to look also at the images for higher and lower altitudes.
As a research topic this one should be good for a Masters thesis and maybe a PhD.
I fear political parties across the world have invested too much time, policies and resources into the cataclysmic aspects of AGW to afford to go back on it or even to moderate their stance to something less Oppenheimer-esque (I am destroyer of worlds). Their opposition parties would chew them up and spit them out for years and years to come. I fear that (to paraphrase former Australian Prime Minister Paul Keating) Anthropogenic Global Warming is ‘L.A.W. law’ not T.R.U.T.H. truth.
Phillip, Hansen said “The growth rate of non-CO2 GHGs has declined in the past decade.” Methane sure didn’t, and isn’t “declining”:
http://www.noaanews.noaa.gov/stories2008/images/methanetrend.jpg
http://commons.wikimedia.org/wiki/Image:Methane-global-average-2006.jpg
As to your comment “So yes, this graphic shows anthropogenic CO2 is well mixed.” I suggest a new pair of glasses.
“When the facts change, I change my mind. What do you do, sir?”
John Maynard Keynes
“Western politicians of all colours are corrupt cowards. It’s in their nature.”
Perry
Glenn, The growth rate of methane has declined for at least the last 2 decades (see link, which is also your 2nd link). Atmospheric methane stopped rising in 1997. Recently methane levels have again started rising, which may be a new upward trend or just natural variability. It’s to early to tell. Otherwise, you seem to be confusing growth rate and atmospheric concentration.
And on the CO2 graphic. Look to the north of India that sharp boundary between low and high CO2 is the limit of the monsoon in July. So yes without the effect from rain and clouds, I’d say CO2 is very well mixed. I don’t see any correlation with sources of human emissions.
http://en.wikipedia.org/wiki/Image:Methane-global-average-2006.jpg
Since there is no apparent correlation between concentration of CO2 producing industry (or population), the CO2 becomes “well mixed”?
A strange way of explaining no correlation?
Apart from a few hot/cold spots, the range of concentration on the map is about the same as the peaks of the normal annual variation around that time:
http://www.woodfortrees.org/plot/esrl-co2/from:2002/to:2004
So isn’t this simply local seasonal variation? Which I assume is due to variations in plant/algae growth rates, ocean temperatures (outgassing), etc.?
Also, the fact that the global median from the map is very close to the Mauna Loa figure for 2003.5 surely means it is well mixed over inter-annual timescales.
I’ve been looking for historical atmospheric CO2 data, going back 100 years or so. The older data obviously would use different methods of measurement than are employed today. Can anybody help me?
The year after Mt Pinetubo erupted very few of my tomatos ripened. I assumed the reason was that volcanic ash made it cooler and made the sunshine weaker.
I wonder if this means my tomatoes consumed less CO2.
Perhaps the post-Pinetubo spike in CO2 levels, in certain parts of the world, was caused by plants consuming less, and had nothing to do with CO2 the volcano actually vented.
Just a thought.
The more we learn, the more my sense of wonder grows.
The biggest wonder of all is that there are actually people who think they’ve got everything figured out, and that there is nothing to wonder about any more.
The more data the better.
Are the lower C02 concentrations over the poles, particularly the south, just due to the cold oceans absorbing it faster?
The bands seem to run east-west. At 5 miles up, I would expect the jet streams to have more of an effect. They don’t all run e-w. How else would soot from Asian power plants make it’s way to the Arctic?
Philip, the Hansen quote was from 2001, so if methane stopped rising in 1997 as you say, then why are you arguing with me about disagreeing with Hansen? And you just implied that a short period of time is too early to tell a trend. But 4 years is, to you? Look, Hansen said the growth rate had declined in the past decade. That’s 1991 to 2001. Look on the reference you provided, either the top or bottom graph. On the top graph the increase only appears to level during the last year or two at best. The bottom graph shows little decrease overall, from 1991 to 2001. And he was talking about a rate of increase, decreasing, basing that on a couple years.
But go with the understanding that 1991 to 2001 growth was slightly less of an increase than 1981 to 1991. From the chart below, you have a .15C increase from 1981 to 1991, and a .20C increase from 1991 to 2001. Shall we invoke natural variability here, since methane growth rate decreased in those two decades?
I also said that methane isn’t declining, and it isn’t. The last couple years on that graph show a definite increase. A real increase, and not too early to tell. I didn’t say methane was on an increasing rate.
As well, the graph shows a level of 1786 at the start of 2008. From Wiki on “Methane”: “The abundance of methane in the Earth’s atmosphere in 1998 was 1745 parts per billion.” Thats a 41ppb increase in 10 years, and that is about the same as the increase between 1991 to 2001, when we were supposedly heating up. Natural variability the answer here as well for the last 10 years of flat temps?
As to the CO2 graphic, I’d say that, well, a well mixed picture would be, like all one color. Your mileage seems to vary.
I find it interesting that most of the stations appear to be in areas with the highest CO2 concentration.
If CO2 does have an impact on temperature, then wouldn’t one expect the highest temperatures to be in areas with the highest CO2 concentrations?
When can we expect Dr. Hansen to issue a new correction for the raw data?
I would be very surprised to find CO2 to be “well mixed”.
Beck reports on the expeditions of Wattenberg crossing the Atlantic Ocean at various latitudes while performing volumetric CO2 determinations between 1925 and 1927.
Forgive me for being naive, but is the data available through FOIA, or do they stonewall that too?
Pops (03:17:14) :
Maybe this will help. Some of the comments below the article have links that are pretty helpful regarding historical vs current CO2 measuring methodologies and how closely they compare: click
Anna
the plots are really simple Giss mapping output. they are a few years old. you should be able to do them yourself at the giss mapping site, if it has not changed http://data.giss.nasa.gov/gistemp/maps/
the data is land and sea data 1880 to 2006, plotted by anomaly by latitude for each season. As you can see the largest anomalies are over the poles and only significant in the winter. the data set is the entire giss data and the comparison set is 1880 to 1950. This comparison was chosen as to be unbiased : pre co2 measurement and post c02 measurement, or pre industrial growth and post industrial growth or pre major population change and post major population change
a 3% variation across the whole planet seems fairly “well mixed” to me
“In describing the measurements of CO2 at Mauna Loa Observatory: “The thin Pacific air is ideal for this research since it is “well-mixed”, meaning that there is no obvious nearby source of pollution, such as a heavy industry, or a natural “sink”, such as forest which would absorb CO2.”
No, except for the Pacific Ocean. I can understand why someone on Mauna Loa would overlook that.
“The oceans represent a significant sink for atmospheric carbon dioxide. Variability in the strength of this sink occurs on interannual timescales, as a result of regional and basin-scale changes in the physical and biological parameters that control the flux of this greenhouse gas into and out of the surface mixed layer. Here we analyse a 13-year time series of oceanic carbon dioxide measurements from station ALOHA in the subtropical North Pacific Ocean near Hawaii, and find a significant decrease in the strength of the carbon dioxide sink over the period 1989–2001. We show that much of this reduction in sink strength can be attributed to an increase in the partial pressure of surface ocean carbon dioxide caused by excess evaporation and the accompanying concentration of solutes in the water mass. Our results suggest that carbon dioxide uptake by ocean waters can be strongly influenced by changes in regional precipitation and evaporation patterns brought on by climate variability.”
http://www.nature.com/nature/journal/v424/n6950/full/nature01885.html
From a 1994 article:
“The role of the ocean as a sink for anthropogenic carbon dioxide is a subject of intensive investigation and debate. Interest in this process is driven by the need to predict the rate of future increase of atmospheric carbon dioxide and subsequent global climatic change. Although estimates of the magnitude of the oceanic sink for carbon dioxide appear to be converging on a value of ∼2 (Gt) C yr−1 for the 1980s, a detailed understanding of the temporal and spatial variability in the rate of exchange of carbon dioxide between the ocean and the atmosphere is not available. For example, recent modeling work and direct measurements of air-sea carbon dioxide flux produce very different estimates of the air-sea flux in the northern hemisphere. As a consequence, it has been suggested that a large unidentified oceanic carbon dioxide sink may exist in the North Pacific. As a part of our time series observations in the North Pacific Subtropical Gyre, we have measured dissolved inorganic carbon and titration alkalinity over a four-year period. These measurements constitute the most extensive set of observations of carbon system parameters in the surface waters of the central Pacific Ocean. Our results show that the ocean in the vicinity of the time series site is a sink for atmospheric carbon dioxide. On the basis of these observations, we present a mechanism by which the North Pacific Subtropical Gyre can be a potential sink for ∼0.2 Gt C yr−1 of atmospheric carbon dioxide. Although our observations indicate that the North Pacific Subtropical Gyre is a sink for atmospheric carbon dioxide, the magnitude of this oceanic sink is relatively small. Our data and interpretations are therefore consistent with the argument for a relatively large sink during the 1980s in northern hemisphere terrestrial biomass. Another possibility is that the net release of carbon dioxide to the atmosphere owing to land use activities in tropical regions has been overestimated. ”
http://www.agu.org/pubs/crossref/1994/94GB00387.shtml
I take “interannual timescales” to be events over periods of more than a year, not seasonal changes. Perhaps that is wrong, but many conditions such as PDO are not seasonal and do affect CO2 sinks. Seems to me CO2 levels affected locally would not be reflected in measurements taken at different points on the globe for periods lasting over years.
An article reporting on the 2003 Nature abstract posted above:
“Increased salinity accounts for about 40 percent of the decrease in carbon dioxide absorption over the 13-year period, says Karl. He and his colleagues haven’t identified the cause of the rest of the absorption slowdown, but some candidates are changes in biological productivity and fluctuations in ocean-surface mixing. The dip in carbon sequestration doesn’t seem to be related to sea-surface temperature, however, because annual averages at the site haven’t changed over the period.The researchers report their findings in the Aug. 14 Nature.”
“Station ALOHA is located in the North Pacific subtropical gyre, a swirl nearly the width of the Pacific that typically has little biological activity near the sea’s surface. Such gyres account for 40 percent of Earth’s ocean area, says Karl.”
http://www.sciencenews.org/view/generic/id/4156/title/Saltier_Water_Climate_change_can_slow_oceans_absorption_of_carbon_dioxide_gas
Sounds like a significant decrease in CO2 ocean sink, in a sizeable chunk of the North Pacific, over a 13 year period, where non-changing surface ocean temps are not involved. I don’t recall whether IPCC models predicted drought over the North Pacific during this time, or have even seriously understood and considered the effects of the changing North Pacific subtropical gyre. This may have played an important part in the recent Arctic melt as well.
Glenn,
Increasing Salinity?? I thought the IPCC was telling us all the melting of glaciers and sea ice was decreasing salinity??
OOOOPS!!
Sadly they have poor justification for their CO2 balance data. Recently we had a paper telling us that MUCH more CO2 was being destroyed over the oceans than had been suspected. Where did that CO2 come from?? They aren’t even sure where the CO2 they KNOW about is sourced!!
joe, the minimum co2 is about 310 to 330 in the southern latitudes. the co2 in the artic is varied enormously by the season, but reaches close to 400 ppm ( vostek from Nasa)
the entire range of c02 from mauna loa is about 320 to 380.
so the variation over the planet is greater than the entire change in co2 from mauna loa in all the years it has been recorded.
this is not well mixed, if the natural variation is greater than the observed change. And it is this observed change which is the “cause” of all the disharmony over man’s destruction of the world
here is the Mauna loa data
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Annual Annual-Fit
1958 -99.99 -99.99 315.71 317.45 317.50 -99.99 315.86 314.93 313.19 -99.99 313.34 314.67 -99.99 -99.99
1959 315.58 316.47 316.65 317.71 318.29 318.16 316.55 314.80 313.84 313.34 314.81 315.59 315.98 316.00
1960 316.43 316.97 317.58 319.03 320.03 319.59 318.18 315.91 314.16 313.83 315.00 316.19 316.91 316.91
1961 316.89 317.70 318.54 319.48 320.58 319.78 318.58 316.79 314.99 315.31 316.10 317.01 317.65 317.63
1962 317.94 318.56 319.69 320.58 321.01 320.61 319.61 317.40 316.26 315.42 316.69 317.69 318.45 318.46
1963 318.74 319.08 319.86 321.39 322.24 321.47 319.74 317.77 316.21 315.99 317.07 318.36 318.99 319.02
1964 319.57 -99.99 -99.99 -99.99 322.23 321.89 320.44 318.70 316.70 316.87 317.68 318.71 -99.99 319.52
1965 319.44 320.44 320.89 322.13 322.16 321.87 321.21 318.87 317.81 317.30 318.87 319.42 320.03 320.09
1966 320.62 321.59 322.39 323.70 324.07 323.75 322.40 320.37 318.64 318.10 319.79 321.03 321.37 321.34
1967 322.33 322.50 323.04 324.42 325.00 324.09 322.55 320.92 319.26 319.39 320.72 321.96 322.18 322.13
1968 322.57 323.15 323.89 325.02 325.57 325.36 324.14 322.11 320.33 320.25 321.32 322.90 323.05 323.11
1969 324.00 324.42 325.64 326.66 327.38 326.70 325.89 323.67 322.38 321.78 322.85 324.12 324.62 324.60
1970 325.06 325.98 326.93 328.13 328.07 327.66 326.35 324.69 323.10 323.07 324.01 325.13 325.68 325.65
1971 326.17 326.68 327.18 327.78 328.92 328.57 327.37 325.43 323.36 323.56 324.80 326.01 326.32 326.32
1972 326.77 327.63 327.75 329.72 330.07 329.09 328.05 326.32 324.84 325.20 326.50 327.55 327.46 327.52
1973 328.54 329.56 330.30 331.50 332.48 332.07 330.87 329.31 327.51 327.18 328.16 328.64 329.68 329.61
1974 329.35 330.71 331.48 332.65 333.09 332.25 331.18 329.40 327.44 327.37 328.46 329.58 330.25 330.29
1975 330.40 331.41 332.04 333.31 333.96 333.59 331.91 330.06 328.56 328.34 329.49 330.76 331.15 331.16
1976 331.74 332.56 333.50 334.58 334.87 334.34 333.05 330.94 329.30 328.94 330.31 331.68 332.15 332.18
1977 332.92 333.42 334.70 336.07 336.74 336.27 334.93 332.75 331.58 331.16 332.40 333.85 333.90 333.88
1978 334.97 335.39 336.64 337.76 338.01 337.89 336.54 334.68 332.76 332.54 333.92 334.95 335.50 335.52
1979 336.23 336.76 337.96 338.89 339.47 339.29 337.73 336.09 333.91 333.86 335.29 336.73 336.85 336.89
1980 338.01 338.36 340.08 340.77 341.46 341.17 339.56 337.60 335.88 336.01 337.10 338.21 338.69 338.67
1981 339.23 340.47 341.38 342.51 342.91 342.25 340.49 338.43 336.69 336.85 338.36 339.61 339.93 339.95
1982 340.75 341.61 342.70 343.56 344.13 343.35 342.06 339.82 337.97 337.86 339.26 340.49 341.13 341.09
1983 341.37 342.52 343.10 344.94 345.75 345.32 343.99 342.39 339.86 339.99 341.16 342.99 342.78 342.75
1984 343.70 344.51 345.28 347.08 347.43 346.79 345.40 343.28 341.07 341.35 342.98 344.22 344.42 344.44
1985 344.97 346.00 347.43 348.35 348.93 348.25 346.56 344.69 343.09 342.80 344.24 345.56 345.90 345.86
1986 346.29 346.96 347.86 349.55 350.21 349.54 347.94 345.91 344.86 344.17 345.66 346.90 347.15 347.14
1987 348.02 348.47 349.42 350.99 351.84 351.25 349.52 348.10 346.44 346.36 347.81 348.96 348.93 348.99
1988 350.43 351.72 352.22 353.59 354.22 353.79 352.39 350.44 348.72 348.88 350.07 351.34 351.48 351.44
1989 352.76 353.07 353.68 355.42 355.67 355.13 353.90 351.67 349.80 349.99 351.30 352.53 352.91 352.94
1990 353.66 354.70 355.39 356.20 357.16 356.22 354.82 352.91 350.96 351.18 352.83 354.21 354.19 354.19
1991 354.72 355.75 357.16 358.60 359.34 358.24 356.17 354.03 352.16 352.21 353.75 354.99 355.59 355.62
1992 355.98 356.72 357.81 359.15 359.66 359.25 357.03 355.00 353.01 353.31 354.16 355.40 356.37 356.36
1993 356.70 357.16 358.38 359.46 360.28 359.60 357.57 355.52 353.70 353.98 355.33 356.80 357.04 357.10
1994 358.36 358.91 359.97 361.26 361.68 360.95 359.55 357.49 355.84 355.99 357.58 359.04 358.88 358.86
1995 359.96 361.00 361.64 363.45 363.79 363.26 361.90 359.46 358.06 357.75 359.56 360.70 360.88 360.90
1996 362.05 363.25 364.03 364.72 365.41 364.97 363.65 361.49 359.46 359.60 360.76 362.33 362.64 362.58
1997 363.18 364.00 364.57 366.35 366.79 365.62 364.47 362.51 360.19 360.77 362.43 364.28 363.76 363.84
1998 365.32 366.15 367.31 368.61 369.29 368.87 367.64 365.77 363.90 364.23 365.46 366.97 366.63 366.58
1999 368.15 368.87 369.59 371.14 371.00 370.35 369.27 366.94 364.63 365.12 366.67 368.01 368.31 368.30
2000 369.14 369.46 370.52 371.66 371.82 371.70 370.12 368.12 366.62 366.73 368.29 369.53 369.48 369.47
2001 370.28 371.50 372.12 372.87 374.02 373.30 371.62 369.55 367.96 368.09 369.68 371.24 371.02 371.04
2002 372.43 373.09 373.52 374.86 375.55 375.40 374.02 371.49 370.71 370.24 372.08 373.78 373.10 373.08
2003 374.68 375.63 376.11 377.65 378.35 378.13 376.62 374.50 372.99 373.00 374.35 375.70 375.64 375.61
2004 376.79 377.37 378.41 380.52 380.63 379.57 377.79 375.86 374.06 374.24 375.86 377.48 377.38 377.43
Monthly values are expressed in parts per million (ppm) and reported in the 2003A SIO manometric mole
fraction scale. The monthly values have been adjusted to the 15th of each month. Missing values are
denoted by -99.99. The “annual” average is the arithmetic mean of the twelve monthly values. In years
with one or two missing monthly values, annual values were calculated by substituting a fit value
(4-harmonics with gain factor and spline) for that month and then averaging the twelve monthly values.