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
“Steve Fitzpatrick says:
June 5, 2010 at 8:47 am
Hi Willis,
Having been through this argument several times on different threads, I have concluded that it may be impossible to make progress on this subject with many who comment; they seem immune to influence by data or reasoned analysis. ”
It’s such a waste of energy to engage them. I was glad you added this. They seem to forget the fundamentals. Everybody should know this
“The only CO2 concentration that matters in terms of radiative forcing is the concentration high in the atmosphere. CO2 concentration near sea level makes no difference, since the lower atmosphere is essentially opaque to infrared at the wavelength where CO2 absorbs.”
re: RobGM
I don’t have time to debunk all the incorrect statements a number of people have responded to Willis article with, but this one needs to be straightened out. The problem is that there are two major portions of the ocean, the mixed surface layer and the deeper bulk of the Ocean. The mixing between the two is rather slow, on the order of several decades to many centuries. The deep ocean is where the great bulk of CO2 is stored, the amount in the mixed surface layer is not much larger than the amount in the atmosphere. One diagram I keep handy, though it’s a bit old, shows the atmosphere with 775 GtC while the surface waters have 1020 GtC. This means that roughly half of the CO2 added to the atmosphere by human burning, etc. will end up in the ocean within a few years. This isn’t precisely the same as noting that the increase in the atmospheric concentration of CO2 each year is about half of what is emitted as the time scales are different (annual vs roughly decadal) but depending on the rate of increase in human production of CO2 it may account for much of the decrease in amount in the atmosphere vs amount produced anthropicly.
Now, yes over centuries of time the human-produced CO2 will be transported into the deep ocean, but over the time period 1950-2010 the amount of transport is rather small.
Thanks Willis for an excellent article. The use of only CO2 data from Mauna Loa Observatory has always bothered me and was one of the things I was going to dig into. Your article has answered most of my questions. Actually the only question I have left is – could the rise in CO2 be caused by the MWP and the 800 to 1200 year lag in CO2 to temperature? It has been 1000 years since the MWP and fits well with the lag time in CO2 rise.
I was wondering if you have any thoughts on this?
Again, excellent article!
Pamela,
Were you looking for this one?
http://wattsupwiththat.com/2009/11/10/bombshell-from-bristol-is-the-airborne-fraction-of-anthropogenic-co2-emissions-increasing-study-says-no/
Steve Fitzpatrick:
At June 5, 2010 at 8:47 am you assert:
“There are so many legitimate scientific issues in the CAGW story which are ripe targets for skeptics that it is difficult for me to understand why some insist on spending time arguing about the cause for increasing atmospheric CO2, when it is one of the very few issues which is pretty much rock solid from a scientific POV.”
Your assertions are complete rubbish!
Firstly, some of us “sceptics” are scientists so we do not have any “targets”: we merely want to discern the truth.
Secondly, we “insist” on attempting to determine “the cause for increasing atmospheric CO2” because that cause is not known and – at present – it cannot be known. Please see my above post at June 5, 2010 at 3:34 am for an explanation of why it cannot be known. I say there:
“But the above findings demonstrate that there is no data that only fits either an anthropogenic or a natural cause of the recent rise in atmospheric CO2 concentration. Hence, the only factual statements that can be made on the true cause of the recent rise in atmospheric CO2 concentration are
(a) the recent rise in atmospheric CO2 concentration may have an anthropogenic cause, or a natural cause, or some combination of anthropogenic and natural causes,
but
(b) there is no evidence that the recent rise in atmospheric CO2 concentration has a mostly anthropogenic cause or a mostly natural cause. ”
Thirdly, if you think “the cause for increasing atmospheric CO2” is known and “is pretty much rock solid from a scientific POV” then please state the evidence which support this POV. I and many others want to know it.
Additionally, “the cause for increasing atmospheric CO2” is not merely of academic interest. The hypothesis of anthropogenic global warming (AGW) is being used as justification for amending energy, industrial and acaemic policies world-wide. But that hypothesis is founded on three assumptions: viz
(1) It is assumed that the anthropogenic CO2 emission is the major cause of the increasing atmospheric CO2 concentration
and
(2) It is assumed that the increasing atmospheric CO2 concentration is significantly increasing radiative forcing
and
(3) It is assumed that the increasing radiative forcing will significantly increase mean global temperature.
There are reasons to doubt each of these assumptions. But if any one of them were known to be false then the entire AGW hypothesis would be known to be false.
Richard
fredJ says:
June 5, 2010 at 12:34 am
The reasons for the variation is unknown at this point. There are basically three camps, one of which says “plants”, one says “sea temperatures” and the other says “sea ice melt and freeze”.
Bart says:
June 5, 2010 at 1:26 am
As far as I know, they are some of the very few climate science records that have not been adjusted at all.
“The reasons for the (seasonal) variation is unknown at this point. There are basically three camps, one of which says “plants”, one says “sea temperatures” and the other says “sea ice melt and freeze”.
I would suggest changing insolation into the oceans as the main cloud banks (the mid latitude jets and the ITCZ) move poleward and equatorward as part of normal seasonal variation.
The longer term background trend (currently upwards) being due to similar such changes beyond normal seasonal variation over longer periods of time.
Dave Dardinger:
At June 5, 2010 at 9:57 am yu assert:
“Now, yes over centuries of time the human-produced CO2 will be transported into the deep ocean, but over the time period 1950-2010 the amount of transport is rather small.”
Really? I would be interested to learn how you can know the transport “is rather small”.
You admit that much of the CO2 emission is absorbed in the ocean surface layer.
Please explain how you can quantify the change (increase ?) to biota in the surface layer which results from this absorbtion.
And please explain how you can quantify the change (increase ?) to carbon tansferred to deep ocean as dead biota that results from the altered amount and/or type(s) of biota in the surface layer.
There is far too much arm-waving and assumption stated as though it is fact in this subject. The truth is that we know little about the details of the carbon cycle and, therefore, we cannot determine the cause(s) of recent increase to atmospheric CO2 concentration.
Proclamations of improbable assumptions as fact hinder work to determine the cause(s) of recent increase to atmospheric CO2 concentration.
Richard
Richard S Courtney says:
June 5, 2010 at 3:34 am
John Finn:
At June 5, 2010 at 1:30 am you assert:
“We need to accept that CO2 levels are increasing and that fossil fuel burning is almost certainly responsible for most of those increases.”
No!!
Please note how trivial the anthropogenic emission is to the total CO2 flowing around the carbon cycle.
I’ve noted how trivial the anthropogenic emissions are, Richard, and I’ve also noted that there is a consisetendnt annula increase which is equivalent to ~45% of the human contribution. There is only variability seems to be due to fluctiuations in ocean temperature. You’re probably aware that I have great respect for your opinion on many climate-related issues but on this, I’m afraid, we disagree.
Steve Fitzpatrick says:
June 5, 2010 at 8:47 am
Spot on. The “science is settled” on this issue and those sceptics that continually allude to it are diverting attention from areas where there is genuine debate.
Richard S Courtney says:
June 5, 2010 at 3:13 am
Jerry says:
June 5, 2010 at 7:44 am
Gail Combs, you picked up on the real deal here. I am an analytical chemist, so instead of taking Willis’ synopsis as rote, I went to the Mauna Loa site itself. There are serious problems with the methodology, especially since it is on an active volcano that became more active, building and leading to a crescendo.
For those faint of heart in chemistry, here is a verbatim reprint from the site. My problem places are in bold:
“At Mauna Loa we use the following data selection criteria:
1. The standard deviation of minute averages should be less than 0.30 ppm within a given hour. A standard deviation larger than 0.30 ppm is indicated by a “V” flag in the hourly data file, and by the red color in Figure 2.
2. The hourly average should differ from the preceding hour by less than 0.25 ppm. A larger hour-to-hour change is indicated by a “D” flag in the hourly data file, and by the green color in Figure 2.
3. There is often a diurnal wind flow pattern on Mauna Loa driven by warming of the surface during the day and cooling during the night. During the day warm air flows up the slope, typically reaching the observatory at 9 am local time (19 UTC) or later. The upslope air may have CO2 that has been lowered by plants removing CO2 through photosynthesis at lower elevations on the island, although the CO2 decrease arrives later than the change in wind direction, because the observatory is surrounded by miles of bare lava. In Figure 2 the downslope wind changed to upslope during hour 18. Upslope winds can persist through ~7 pm local time (5 UTC, next day, or hour 29 in Figure 2). Hours that are likely affected by local photosynthesis are indicated by a “U” flag in the hourly data file, and by the blue color in Figure 2. The selection to minimize this potential non-background bias takes place as part of step 4. At night the flow is often downslope, bringing background air. However, that air is sometimes contaminated by CO2 emissions from the crater of Mauna Loa. As the air meanders down the slope that situation is characterized by high variability of the CO2 mole fraction. In Figure 2, downslope winds resumed in hour 28. Hour 33 in Figure 2 is the first of an episode of high variability lasting 7 hours.
4. In keeping with the requirement that CO2 in background air should be steady, we apply a general “outlier rejection” step, in which we fit a curve to the preliminary daily means for each day calculated from the hours surviving step 1 and 2, and not including times with upslope winds. All hourly averages that are further than two standard deviations, calculated for every day, away from the fitted curve (“outliers”) are rejected. This step is iterated until no more rejections occur. These hours are indicated by an “A” flag in the hourly data file, and by the purple color in Figure 2, also indicated as “spline” in the legend. Spline is a curve fitting technique. Rejected hours occurring during times with upslope winds are given a “U” character in the data file.”
Willis does a good job, but leaves out some worrisome problems as I highlighted above. There are other troublesome issues if you read the whole method.
1) The upslope and downslope winds are prevailing. But we see above that is usually not the case for any specific time. There is swirling and irregular mixing.
2) CO2 is twice as heavy as air. Regardless of miscibility, this is different from mixing, and there is molecular mass enrichment towards lower levels. Most non-experts confuse miscibility and mixing. Mixing requires turbulence. Puffs of gas from the volcano, heated, will rise; the resultant cloud will overwhelm the minute concentrations we have in “background” or ambient air. Instead of mixing, as a chemist, I must assume non-mixing! As we remember from Lake Nyos in Africa, where almost 2000 people were killed by CO2 outgassing of the lake, it takes time to mix.
3) In accordance with 2), all Mauna Loa measurements must be higher than ambient. All statistics must be heteroskedastic, not homoskedastic, meaning the error bars favor the high rather than the low error.
4) Plants – at night plants give off O2 in favor of CO2 (i.e., “abnormal” respiration). During the day, this ratio exists to favor CO2 production. This depends on the cloud cover, or the existence of rains.
5) Willis, you are right. No data is thrown away. I never throw papers away, I either put them in a circular file or shred them. They still exist. Most of the data is rejected, as admitted by the site!
6) As with most analytical methods, the measurement itself is usually highly precise and accurate. It is the sampling errors, usually followed by the statistical methods that are problematic.
7) As a paranoiac, I also see areas in which ulterior motives could sway results. Who takes the log? Is he a grad student? Is she a grantee from government or quango? Who wrote the algorithms for rejection criteria?
Why didn’t they set up on Mt. Washington, or in the Peruvian Andes where we have great telescopes and not an active volcano? Especially Mauna Loa that has increased in activity in the last 50 years (coincidentally, a period when the CO2 slopes have increased)?
My conclusion: If there is systematic error at Mauna Loa, it is heteroskedastic and could only lead to a high result, never a low one. We are only talking about less than 10% increases in CO2 in the last few decades. If it were 20 or 30%, the inaccuracy would be still there, but less important. If we were dealing with parts per thousand, then, no big problem. But parts per million?? It doesn’t matter of the trend compares to other sites favorably. We have to look at these as separate issues that probably have their own systematic biases, all to the upside, I’ll wager!
Anyhow, higher CO2, I’ll concede would be a very good thing for the planet. I am not convinced it has risen in the last century from my vantage point, however.
Re: John Finn says:
June 5, 2010 at 10:23 am
My last post was actually written in English but it seems to have been translated into some as yet undiscovered language.
Translation:
consisetendnt annula = consistent annual
There is only variability seems to be due to fluctiuations = The only variability seems to be due to fluctuations
I’m late for the discussion and I haven’t bothered to read all the posts, so it could be what I’m going to state has already been stated.
First, let me say, I don’t really care about our CO2 levels. I don’t consider them meaningful. Secondly, Willis, while I rarely disagree with you, Keeling chose a bad location. Why? Because of the 5 reasons you felt compelled to list before having the discussion. Why pick a spot that must come with a list of explanations and disclaimers first? And any number of them, while you articulated quit reasonably, would have “flies in the ointment”. And, I’d be very surprised if a few of these posts didn’t point them out. Why not pick a spot that’s not by a volcano and eliminate a couple of the arguments? Heck, why not use multiple locations. I know there are others, but they’re hardly mentioned in any studies. Once we have a good cross section, then we can do some proper comparisons. It wouldn’t be that difficult, but then I don’t think the world really wants to know. If it did, we’d have plenty of sites to compare. We don’t. Personally, given that CO2 is heavier than O2, I don’t believe CO2 concentrations can be uniform at any given elevation, location at a specific point in time. Certainly not while using one location as the arbiter of our CO2 levels. I believe it is ridiculous for anyone to make that assertion. All one has to do is look at the uniformity of the graphs that emanate from Mauna to know it belies the seemingly chaotic events that occur daily world wide. (Ocean absorption and release, winds, heating and cooling, currents…ect.) No way CO2 levels a Mauna are that uniform to reflect properly how much(not to mention where) CO2 exists in the different levels of our atmosphere. If I cared enough about CO2 levels, I’d destroy the credibility of Mauna’s measurements in a day.
Tenuc says:
June 5, 2010 at 1:29 am
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.
Good question, I discount Jaworoski so I didn’t think of it but it is a common question. I’ll update the head post to include your question, much appreciated.
DennisA says:
June 5, 2010 at 1:36 am
Not that I know of. Do you have a citation?
See above for my comments on Jaworowski. (AFAIK, he criticized ice cores in general, not Law Dome.) I see no problem with using all the different possible ways to measure a variable, as long as they are not “spliced” as in the Mann-made hokeystick.
True. People don’t generally get excited when the concentration of a trace atmospheric gas goes from 0.03% to 0.04% …
Willis,
You mention ‘sea-ice melt and freeze’ as a possible component in annual atmospheric CO2 variation. I am now having a boggle-moment;
Do you say that when water freezes, the CO2 comes out of solution? So how come the ice-cores contain CO2? Is it a gradient thing, in which case CO2 concentrations in icecores must be a function of core temperature history as well as atmospheric concentration at the time.
What about when rain turns to snow? Is there a big burst of local CO2 concentration when it snows? Does Henry’s law stop at freezing point?
Does CO2 adsorb onto snow and ice surfaces? If so, does it do it at high altitude? (where the CO2 is supposed to do the warming?)
And so on. Answers please.
John Finn says:
June 5, 2010 at 1:38 am
“Diffusion”, as I understand it, is the tendency for the CO2 to dissolve into the ice itself. As a result, the ice core data would give a low answer for the historical CO2.
While this is possible, one would assume that this would be a slow, time-dependent process. As a result, if it were happening in a significant way, we would see a trend with the older CO2 values being lower than the modern values. I don’t see that.
So as a result, I generally trust the ice core CO2 data. There is enough of it now, from enough different ice cores, processed by enough different investigators, to convince me that it is a valid measurement. Are all the details exact and correct to the last significant figure? Likely not, but it seems to be correct in the main.
Steven mosher says:
June 5, 2010 at 9:44 am
“It’s such a waste of energy to engage them. I was glad you added this. They seem to forget the fundamentals.”
Yes, it is, and yes, they do (or never knew them!). See several other replies to my first comment for clear examples. Wills has a lot more fortitude for this sort of thing than I do; I won’t waste any more time on it.
anna v says:
June 5, 2010 at 2:22 am
Say what? I’ve explained why Mauna Loa is a good place to measure background CO2. That does not mean that it is a good place to measure the temperature, or the effect of gamma rays on man-in-th-moon marigolds, for that matter … so?
Not sure what you mean by that.
As I said, the volcanic CO2 is held in by the temperature inversion. Plus the fact that the air is generally descending all over the island, which slows the ground level CO2 from mixing upwards.
As long as I had a reliable way to distinguish water with oil from water without oil, sure. And they have such a method, that’s the point. From their description:
That doesn’t happen if the sample is polluted with volcanic CO2.
Wow! What a read! Thank you Willis and Anthony and some fantastic instructive comments.
One small niggle, I still haven’t learned how atmospheric CO2 can increase radiative forcing.
Bill Yarber says:
June 5, 2010 at 6:14 am
A previous poster on this site suggested quite a while ago that and experiment should be conducted to verify that the CO2 concentrations found in ice core data is indeed representative of atmospheric concentrations at that time. Has anyone actually done such an experiment (freeze water in the presence of a know concentration of CO2, store it at freezing conditions and then test portions over various time periods) to verify that:
1) the concentrations actually match
And
2) there is no degradation in CO2 concentrations over time.
This is far more important than whether CO2 measurement at Mona Loa are precisely accurate. Even if there is a bias due to contamination from the volcanoes emissions, they should be a relative consistent error and thus are irrelevant.
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That has been done in part see: http://www.warwickhughes.com/icecore/
Unfortunately it is not quite as simple an experiment as we could want.
1. Gases migrate. Leave a plastic soda bottle on the shelf for a couple of years and the soda will be FLAT. That is based on the two year old bottle of Dr. Pepper I just opened.
Snow and ice will also allow CO2 to migrate, especially since cold water absorbs CO2
2. Due to the enormous pressure at the bottom of the glaciers the gases change into the solid clathrates, which are tiny crystals formed by interaction of gas with water molecules.
3.Cracking of the ice. Tiny fractures can form in the ice as well as large fractures like cravasses.
4. The results of the ice cores are on the ragged edge of plant extinction. If CO2 is much under 200 PPM you are going to have a change from trees to grassland. Just google CO2 plants and starvation.
5. Microbes confound results: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC384798/
CO2 solubility vs sea temperature graph from real life: http://hockeyschtick.blogspot.com/2010/01/co2-levels-in-atmosphere-are-damped-by.html
Ernst Beck says:
June 5, 2010 at 2:44 am
Outstanding, sir. I look forward to your new paper. I also find your proposed method of adjusting ground measurements to extract the background level to be interesting. As you point out, the thousands of historical chemical analyses of CO2 which you have collected are a huge resource which has been overlooked to date. There is always more to learn.
Keep fighting the good fight, my best to you,
w.
You da man Willis! I applaud your efforts.
Slioch says:
June 5, 2010 at 3:44 am
There has been more than enough CO2 emitted from human burning of fossil fuels to account for all the increase in atmospheric CO2 in recent centuries.”
Why do people think this constitutes evidence that the CO2 increase is man-made? It’s like a coroner proclaiming a victim of a heart attack to have died by drowning, because the output of all the rivers of the world is more than enough to fill the lungs of every person on Earth.
Geoff Sherrington says:
June 5, 2010 at 2:53 am
Don’t know … the start was 1958, however.
CO2 is generally considered to be a “well-mixed gas”. However, as you point out, at any given point on the ground there is likely to be a different concentration than found up in the troposphere.
I don’t know how much this matters, however … but then I don’t think that CO2 matters much, so my opinion may not matter much.
Pass. Methane is a different question, with different parameters. I’d rather keep this thread on CO2.