Guest Post by Willis Eschenbach
In 2006, I lived for a year in Waimea, on the Big Island of Hawaii. From my house I could see the Mauna Loa Observatory (MLO). This observatory is the home of the longest continuous series of CO2 measurements we have. The recording station was set up by Dave Keeling in 1959, and has operated continuously ever since.
Figure 1. Mauna Loa Observatory ( 19.536337°N, 155.576248°W)
Here’s a view of the observatory:
Every time the subject of CO2 measurements comes up, people raise all kinds of objections to the Mauna Loa measurements. So I thought I’d start a thread where we can discuss those objections, and perhaps dispose of some of them.
Here are the objections that I hear the most:
1. The Mauna Loa results don’t measure the background CO2 levels.
2. You can’t get accurate CO2 measurements from samples taken on the side of an active volcano that is outgassing CO2.
3. The measurements from Mauna Loa are not representative of the rest of the world.
4. What about the Beck data, doesn’t it contradict the MLO data?
5. Keeling chose a bad location.
Before we get into those issues, let’s start by looking at the local meteorological conditions at the site. Mauna Loa is at an elevation of 3397 metres (11,140 ft) on the side of a 4,170 metre (13,680 ft) volcano way out in the middle of the Pacific Ocean. Because it is on an island, it gets the “sea breeze” in the daytime, and the “land breeze” in the nighttime.
These winds are caused by the differential heating of the land and the sea. Land heats up much faster than the ocean. So during the day, the warmer land heats the air, which rises. This rising air is replaced by air moving in from the surrounding ocean, creating the “sea breeze”.
At night, the situation is reversed. The land is cooler than the ocean. This cools the air. The cool air runs downhill along the slopes of the island and out to sea, creating the “land breeze”. Here’s a drawing of the situation:
Figure 2. Day and night breezes at Mauna Loa.
Now that we understand what is happening at Mauna Loa, let’s look at the objections.
1. The Mauna Loa results don’t measure the background CO2 levels. As you might imagine from Fig. 2, the CO2 measurements are taken only at night. Thus, they are measuring descending air that is coming from thousands of feet aloft. This air has traveled across half of the Pacific Ocean, so it is far from any man-made CO2 sources. And as a result, it is very representative of the global background CO2 levels. That’s why Keeling chose the site.
2. You can’t get accurate CO2 measurements from samples taken on the side of an active volcano that is outgassing CO2. This seems like an insuperable objection. I mean, Mauna Loa is in fact an active volcano that is outgassing CO2. How do they avoid that?
The answer lies in the fact that the volcanic gasses are very rich in CO2. At night, they are trapped in a thin layer near the ground by a temperature inversion.
To detect the difference between volcanic and background CO2, the measurements are taken simultaneously from tall towers and from near the ground, at intervals throughout the night. Background CO2 levels will be around 380 ppmv (these days), will be steady, and will be identical at the top and bottom of the towers. Volcanic gasses, on the other hand, will be well above 380 ppmv, will be variable, and will be greater near the ground than at the top of the towers.
This allows the scientists to distinguish reliably between volcanic and background CO2 levels. Here is a description of the process:
Air samples at Mauna Loa are collected continuously from air intakes at the top of four 7-m towers and one 27-m tower. Four air samples are collected each hour for the purpose of determining the CO2 concentration. Determinations of CO2 are made by using a Siemens Ultramat 3 nondispersive infrared gas analyzer with a water vapor freeze trap. This analyzer registers the concentration of CO2 in a stream of air flowing at ~0.5 L/min. Every 30 minutes, the flow is replaced by a stream of calibrating gas or “working reference gas”. In December 1983, CO2-in-N2 calibration gases were replaced with the currently used CO2-in-air calibration gases. These calibration gases and other reference gases are compared periodically to determine the instrument sensitivity and to check for possible contamination in the air-handling system. These reference gases are themselves calibrated against specific standard gases whose CO2 concentrations are determined manometrically. Greater details about the sampling methods at Mauna Loa are given in Keeling et al. (1982) and Keeling et al. (2002).
Hourly averages of atmospheric CO2 concentration, wind speed, and wind direction are plotted as a basis for selecting data for further processing. Data are selected for periods of steady hourly data to within ~0.5 parts per million by volume (ppmv); at least six consecutive hours of steady data are required to form a daily average. Greater details about the data selection criteria used at Mauna Loa are given in Bacastow et al. (1985). Data are in terms of the Scripps “03A” calibration scale.
There is a more detailed description of the measurement and selection process here.
As a result, the Mauna Loa record does accurately measure the background CO2 levels, despite the fact that it is on an active volcano. The samples that are identified as volcanic CO2 are not thrown away, however. They are used for analyses of the volcanic emission rates, such as this one (pdf).
3. The measurements from Mauna Loa are not representative of the rest of the world. Well, yes and no. The concentration of atmospheric CO2 varies by month, and also by latitude. Here is a “carpet diagram” of the changes by time and latitude.
Figure 3. A “carpet diagram” of CO2 distributions, by time and latitude.
Note that the swings are much greater in the Northern Hemisphere. Presumably, this is from the plants in the much larger land area of the Northern Hemisphere. However, the difference between the annual average of the Northern and Southern Hemispheres is small. In addition, there are smaller daily variations around the planet. An animation of these is visible here, with day by day variations available here.
Figure 4 shows is a typical day’s variations, picked at random:
Figure 4. Snapshot of the variations in tropospheric CO2. Note that the range is small, about ±1% of the average value.
In general, the different global records match quite closely. In addition to the Mauna Loa observatory, NOAA maintains CO2 measuring stations at Barrow, Alaska; American Samoa; and the South Pole. Here is a comparison of the four records (along with two methane records):
Figure 5. Comparison of the CO2 records from the four NOAA measuring sites.
As you can see, there is very little difference between the CO2 measurements at the four stations – two in the Northern Hemisphere, two in the Southern, two tropical, and two polar.
4. What about the Beck data, doesn’t it contradict the MLO data? In 2007, Ernst-Georg Beck published a paper called “180 Years Of Atmospheric CO2 Gas Analysis by Chemical Methods” (pdf). In it, he showed a variety of results from earlier analyses of the atmospheric CO2. In general, these were larger than either the ice core or the MLO data. So why don’t I believe them?
I do believe them … with a caveat. I think that the Beck data is accurate, but that it is not measuring the background CO2. CO2 measurements need to be done very carefully, in selected locations, to avoid contamination from a host of natural CO2 sources. These sources include industry, automobiles, fires, soil, plants, the list is long. To illustrate the problems, I have graphed the Beck data from his Figure 13, against the Law Dome ice core data and the MLO data.
Figure 6. CO2 data from a variety of sources. White crosses are MLO data. Three separate ice core records are shown. Photo is of Mauna Loa dusted with snow (yes, it snows in Hawaii.) PHOTO SOURCE
There are several things to note about this graph. First, there is good agreement between the Law Dome ice core data and the MLO data over the ~ two decade overlap. Second, there is good agreement between the three separate Law Dome ice core datasets. Third, both the ice cores and the MLO data do not vary much from year to year.
Now look at the various datasets cited by Beck. Many of them vary quite widely from one year to the next. The different datasets show very different values for either the same year or for nearby years. And they differ greatly from both the ice core and the MLO data.
Because of this, I conclude that the Beck data, while valuable for showing ground level CO2 variations at individual locations, do not reflect the background CO2 level of the planet. As such, they cannot be compared to the MLO data, to the ice core data, or to each other.
5. Keeling chose a bad location. I would say that Keeling picked a very good location. It not only allows us to measure the background CO2 in a very accurate manner, it provides invaluable information about the amount of CO2 coming from the volcano.
My conclusion? Most of the records in the field of climate science are short, spotty, and not very accurate. We have little global historical information on ocean temperatures, on land temperatures, on relative humidity, on atmospheric temperatures, on hurricane occurrence and strength, or on a host of other variables. By contrast, the Mauna Loa CO2 records are complete since 1959, are very accurate, and are verified by measurements in several other locations.
I’m about as skeptical as anyone I know. But I think that the Mauna Loa CO2 measurements are arguably the best dataset in the field of climate science. I wouldn’t waste time fighting to disprove them, there are lots of other datasets that deserve closer scrutiny.
[UPDATE] A reader below has added another question, viz:
6. What about Jaworoski’s claim that the ice core data has had its age “adjusted”?
Jaworoski argues that the age of the air in the ice cores has been “adjusted” to make it align with the modern data. He says, for example, that the Siple ice core data has been moved forwards exactly 83 years to make them match the Mauna Loa data.
Dating the ice core data is problematic. We can date the ice itself pretty accurately, through counting layers (like tree rings) and through studying various substances such as volcanic dust that is trapped in the ice. However, dating the air is harder.
The difficulty is that the air is not trapped in the ice immediately. The pores in the “firn”, the snow that falls annually on top of the ice are open. Air can flow in and out.
As more and more snow falls over the years, at some point the pores close off and the air is trapped. So how long does it take for the pores in the firn to seal off?
Unfortunately, as in so many areas of climate science, the answer is … “depends”. It depends inter alia on how much snow falls every year, how much of that snow sublimates (changes from a solid to a gas) every year, and even the shape and size of the individual snowflakes.
The end result of all of this is that we end up with two ages for any given thin slice of an ice core. These are the “ice age” (how old the ice itself is), and the “air age” (how old the air trapped in the ice is). The ice is always older than the air.
The main variable in that is thought to be the annual snowfall. Unfortunately, while we know the current rate of annual snowfall, we don’t know the historical rate, particularly tens of thousands of years ago. So we use the concentration of an isotope of oxygen called “d18O” to estimate the historical snowfall rate, and thence the firn closing rate, and from that the air age.
Sounds a bit sketchy? Well … it is, particularly as we go way back. However, for recent data, it is much more accurate.
So to bring this back to real data, in the ice core data I showed in Fig. 5, the air is calculated to be 30 years younger than the ice for cores DEO8 and DEO8-2, and 58 years younger for the DSS core. Is this correct? I don’t know, but I do know that there are sound scientific reasons for the “adjustment” that Jaworowski objects to .
Finally, the existence of a thirty to sixty year difference in air and ice age doesn’t make much difference in the pre-industrial levels of CO2. This is because prior to about 1800, the level is basically flat, so an error in the air age dating doesn’t change the CO2 values in any significant manner.
FURTHER INFORMATION:
Greenhouse Gas & Carbon Cycle Research Programs
Trends in Atmospheric Carbon Dioxide
How we measure background CO2 levels on Mauna Loa
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Thank you, Mr. Eschenbach, that answered many questions that I had about those CO2 measurements.
If it matters, I have no objection to the Mauna Loa CO2 observations. The thing is that I don’t think anyone has shown that increased CO2 has any detrimental impact on anything. So what if it is rising? Pine trees apparently love it. There is no evidence that it has had any significant climate impact to date as most of the temperature variation to day seems to be natural cyclical activity that goes on all the time.
The CO2 measurements are “interesting” but I wouldn’t worry all that much about them at this point. The additional CO2 is probably doing more good than harm.
Thanx Willis.
since so many people see skeptics as anti science it would be instructive to point out the science that is accepted by skeptics. So many people waste their time with silly misinformed arguments
What about CO2 measurements from ice core samples and the like? I have heard it argued that because ice is not a closed system, those historical measurements are far from accurate. The CO2 level in the past could have been much higher (or lower).
Mauna Loa is sporadically active. I never see out gassing unless it is active, less than once every 30 years or so. In that case, as the largest volcano on Earth, and largest active in the solar system, we all know when the shit has hit the fan and adjustments to the CO2 count can be made. Like shutting down the measures and getting out of Hilo.
It is, however down wind of a very active volcano, Kilauea Iki.
I suspect that much of the CO2 we now measure is because of oceanic out gassing, caused by global warmth. Whether this is really true is unknown and will not be known unless we see an unexplained decease in the same.
Your post clarified some of my own misconceptions and I thank you for that.
However, the Mauna Loa data shows seasonal CO2 variation. Why would that be so? Is it due to tempeature variation? Could it be due to sea temperature changes? Is there a temperature record for the sampling points and is there a corresponding ocean temperature record for the surrounding area?
Thank you Willis.
I was one who was once highly skeptical of the choice of this monotoring site.
Not just because of it being on “a volcano,” but rather an area of high volcanic activity also situated in the middle of warm waters.
That’s what so much of this is about. Knowing what data and observations we can be confident of, and building from that.
Very clear and informative presentation, Willis. I shall have to modify my previous thoughts on such matters.
/dr.bill
Having these objections about CO2 and MLO come up over and over again in various comment threads, the doubt they express sort of seeps into the whole thinking on this issue. Great to have them put to rest. Thanks Willis.
It would be interesting to contrast the sophisticated instrumentation, rigour of method, calibrations and accuracy of this set of measurements with some of the temperature measurements. For example we hear various things about the satellite measurements suffering instrument drift requiring correction. Are there weak points in some of these global measurements? And where are they?
There is a lovely Chinese proverb that says “Only he that has travelled the road knows where the holes are deep”. There is such a lot of time wasted by armchair travellers speculating about the location and size of ‘holes’ in climate data. We need to sure where the real holes are and ensure they are marked with a big ‘danger’ sign. Perhaps then the climate change road map can be shown to be so full of holes that it is not safe to travel.
Just a minor point. From my misspent (or I feel very well spent, but others differ) youth on tropical beaches, the breeze tends to go out until midday and then inland until some time in the night. I recall this well as we tended to wallow in the sea at the time the breeze stopped as the heat was too much.
We assumed from this that the land heats up during the day, and when it reaches the sea temperature the breeze stopped. It then reversed as the land became hotter than the sea. The reverse surely occurred at night, although we were not so aware as it was cooler (and we were probably less ‘observant’ for a number of reasons).
I am sure the same would happen here, so the explanation showing air flow down, and out to sea, in the evening is a tad simplistic and this would not occur until some time in the night. I suspect this is taken into account, however.
And I was told I would never learn anything bumming around on tropical beaches heh?
Regarding the yearly variation in CO2 levels, a long time ago I noticed an interesting phenomenon. If you look at the Mauna Loa record, you will easily see that the yearly increment of CO2 is increasing, i.e. we are putting CO2 into the atmosphere more quickly now than in the 60’s. Everybody knows that, and the typical answer is “of course, we are emitting more”.
But we have increased our emissions roughly the same for all the months of the year, the industry doesn´t stop in the summer. We emmit about the same all year. However, if you look really carefully at the Mauna Loa data, you will see that the yearly increase has not happened in the same ammount for all the months of the year. Actually, only in (NH) winter do we see a difference compared to the 60’s. In the yearly oscillation, you will see that, on average, the reduction of atmospheric CO2 in the (NH) summer is the same that was happening in the 60’s, despite the fact that we emmit much more CO2 now in the summer than we did then. One would expect an everytime smaller reduction in CO2 levels according to our increasing emissions. However, it is only the winter increase that is getting bigger.
Many months ago I told this to Gavin Smith, as proof that the biosphere, the plants in the NH, are keeping up with our emissions. We emit more AND the plants are also able to absorb more, leading to the same summer reduction. But they can only do it in the growing seasons. However, Gavin told me that this was wrong, and the main reason was the bigger CO2 absorption in the southern oceans, especially in their winter (NH summer) when they are colder.
I couldn’t refute him, I really didn’t know which effect was more important. But now thanks to Willis I know that I WAS RIGHT. Because if the dominant effect was the absorption and release of CO2 by the souhtern oceans, then the yearly variations of CO2 should be bigger in the SH than in the NH. And in Willis’ graphs it is clearly understood that that’s not the case.
Thanks a lot, Willis.
Are the four records you show genuinely independent and unadulterated, or have they been adjusted in any way?
Thanks Willis, looks like the current measurements for CO2 levels are valid. However, I think the historic pre-industrial levels from the ice core data, quoted at 290ppmv, are open to argument as adjustments may have been made to ‘align’ them with the post 1959 Mauna Loa Observatory measurements (shades of the Briffa Tree Ring Data controversy perhaps?).
The following link to a statement by Prof. Zbigniew Jaworowski, (Chairman of Scientific Council of Central Laboratory for Radiological Protection, Warsaw, Poland) written for the hearing before the US Senate Committee on Commerce, Science, and Transportation has a good explanation of this potential issue, “Climate Change: Incorrect information on pre-industrial CO2 – March 2004”
http://www.warwickhughes.com/icecore/
I would be interested in your thoughts on this please.
This will make an excellent link. Too often the ‘sceptic’ side gets distracted by muddled arguments about CO2 concentrations. The Beck measurements come up repeatedly. We need to accept that CO2 levels are increasing and that fossil fuel burning is almost certainly responsible for most of those increases.
Willis, another valuable essay. Keep up the good work.
However I disagree with your conclusion of suitable placement.
My internal alarm goes off once I hear that it’s really ok becuase the scientists use readings [and probably algorithms and computers] to distinguish the volcanic CO2 from the atmospheric CO2 readings.
“……This allows the scientists to distinguish reliably between volcanic and background CO2 levels.”
Isn’t a tenet of sceptical argument that it’s often the ‘adjustments’ that are the problem.
Further I’d like to know how the sensors in the towers read the CO2. I’m concerned about freezing as opposed to drying. If the air has been sufficiently filtered is it possible for super cooled water vapour to remain in the sample as the water has nothing to freeze on to? How is the CO2 seperated from other IR absorbers in the sample like methane ? I can’t believe the towers are as sophisticated as the lab where these things are hopefully done.
Anyway as I say very stimulating and much appreciated.
cheers David
Willis ,
You say that MLO is complete since 1959. Wasn’t there a period when there were funding difficulties and perhaps the record had to be retro-fitted in the sixties?
Isn’t the homogenisation of Law Dome with MLO a little suspect? Aren’t we again looking at apples and kiwi fruit, CO2 trapped in ice cores compared with aerial measurement seems as illogical as mixing tree ring data and direct instrumental measurement for temperature records.
Do you dismiss Jaworowski and his criticism of Law Dome and ice cores in general, relating to CO2 measurement?
In your figure 5 chart it looks as if the “consensus” is achieved by all of them assessing the same data, that of Law Dome, in the same way that we get “consensus” in IPCC.
If Jaworowski is right then the consensus is wrong and more credence can be given to Beck.
Of course if it were not for the claims that CO2 is driving temperature upwards in contradiction of the cooling from the 40’s to the 80’s, when CO2 was increasing and a lack of warming currently, in the face of increasing CO2, then it would all be irrelevant.
A very welcome contribution which will help avoid needless distractions from the fundamental questions 🙂
Willis
Just one question. Do you have any comments on the reliability of ice core data and, in particular, the issue of ‘diffusion’.
Now can you ever imagine a post like this at RealClimate on say a paper By Steve McIntyre.
Just makes you think.
Thankyou for the information. does the above data mean ice-core data gives accurate historical records?
Rhoda R says:
June 4, 2010 at 11:38 pm
More than welcome, Rhoda. Always more to learn, for all of us, myself included. That’s why I hang out here at WUWT …
Thanks once again, Willis, and Anthony too. I had thought, from time to time, about the CO2 readings from the Moana Loa observatory in my usual sceptical but unstructured way – you have very neatly enunciated my doubts and laid them to rest. It is good to have you and WUWT as a source of stuff one can trust, unlike so much ‘out there’ that is contaminated by vested interests.
OT, but Leo Hickman of The Guardian seems to regard anyone who attended the recent Chicago conference as tainted by association with ‘the lunatic fringe’ (his term, not mine) which denies the link between smoking tobacco and cancer, HIV and AIDS, etc.
I thought The Guardian had a new policy of playing nice with sceptics who are rational and polite, but I am unsurprised that the same newspaper carries no word of the ‘peer reveiwed and published’ (which they claim is their criteria for publishing) the paper debunking the alarmist nonsense about Tuvalu being in danger of being swamped by rising oceans.
Well, Willis,
would you accept the same reasoning for temperature measurements?
I.e. go to the top of a mountain at night and call that the global temperature?
I think that there is no meaning in global CO2 as there is no meaning in global temperature.
You quote:
The answer lies in the fact that the volcanic gasses are very rich in CO2. At night, they are trapped in a thin layer near the ground by a temperature inversion.
To detect the difference between volcanic and background CO2, the measurements are taken simultaneously from tall towers and from near the ground, at intervals throughout the night. Background CO2 levels will be around 380 ppmv (these days), will be steady, and will be identical at the top and bottom of the towers. Volcanic gasses, on the other hand, will be well above 380 ppmv, will be variable, and will be greater near the ground than at the top of the towers.
!!!!
And what prevents run of the mill CO2 molecules to generally to lie low?
Does each molecule carry a passport that says: I am from the volcano, I am from the top atmosphere?
Think of the oil spill. Would you defend measuring the chemistry of clear water next to the oil spill ? And we are talking of a gas that is supposed to be a good mixer?
That last sentence is a non sequitur, John.
/dr.bill
Good summary, Willis.
However, if this single data series from a single evolving methodology is all that is underpinning the CO2/Climate change hypothesis … then it certainly cannot support the weight of AGW theorising and speculation, let alone the Carbon Tax concept.
The Mauna Loa graph is after all, an ‘average’ struck from incredibly noisy datapoints that have huge variations. And, the parallel with the problem of trying to establish an ‘average’ global temperature series, is striking.
And so, I have concerns about the processes, and the history of the processes.
a) Re the various changes and ‘improvements’ that have been made (such as changing the material of the pressure vessels, the cleaning of the cell windows, etc.,) and whether retrospective reanalyses/corrections and restatement of the time-graph were made. Is there a ‘history of the history’ so to speak?
b) Has the statistical methodology been published?
c) Has the record of all the raw data been made available, and has anyone done a completely independent analysis?
d) You mentioned the idea that only the night-time samples are used because that air will be downwelling. But, does that not mean that this air was yesterday’s upwelling? And given the local wind-vector data, could a proportion of the downwelling sample have emanated from local population-centres (… that have grown over time)
e) For example, in the case of a very low average airspeed, the site itself seems to have grown substantially since the ‘fifties, with huge amounts of concrete, generators, airconditioners, road traffic, cooking, permanent staff (all CO2 producers?). Has there been an attempt at a correlation with a graph of the history of local CO2 emissions?
Such a claimed instrumental sensitivity ought to show such growth in an analysis of the daytime data record. Does it?
f) The seasonal variations that are claimed to be observed in the data history, is remarkable, and is ascribed to photosynthesis. Do these ‘waves’ in terms of shape and rates of change, correspond with the actual seasonal photosysthesis cycle of northern hemisphere land plants. At what latitude? Or, is the data showing only the effect of oceanic photosynthesis? Or dare I say it, only the local pacific ocean insolation and surface temperature changes?
Then, there is the Beck data. As you say, these records show CO2 concentrations on a local, low-altitude basis. They were made at a time when the industrial revolution was in full swing. I haven’t checked, but I vaguely remember that some of these series spanned WWI, where Anthropic CO2 emissions must have peaked dramatically, and slumped just as dramatically in 1919/20 . Does this show-up?
But more seriously, if an ‘average’ can be teased out of the fuzz of the actual Mauna Loa data, why can’t it be teased out of the presumably equally fuzzy Beck data using the SAME statistical techniques ?
I know that this raises a possibly silly thought, but as the increase in background CO2
is claimed to affect the climate, surely a local increase in CO2 on a local level ought to affect local weather? By that I mean that as climate maps to weather in terms of area and time, as measured by average temperature and influenced by average CO2 concentrations , then why cannot local average temperature records and local average CO2 concetrations be used to study the linkage. After all, whilst the data would be very ‘noisy’.. the same statistical techniques used by Scripps for CO2 and Climatologists for temperature, ought to yield comparable results.
A related question is the comparison of the Scripps CO2 measurement technique versus the earlier chemical technique, in terms of fundamental accuracy and resolution . Assuming that the two techniques can be correlated … it would be obvious to have seen the two techniques being used together, and results co-recorded. As I have not heard of chemical records from Mauna Loa, I assume they are not. Could you or any readers comment?
This raises a further question. I understand that over the past decade or so, several instances of alternative methods of measuring atmospheric CO2 have been developed. What has happened to these instruments? Do they work? I’d have thought that such systems would have been trialled at the Mauna Loa site? Why not? Can anybody shed light on this mystery?