About carbon isotopes and oxygen use…
1. The different carbon isotopes in nature.
The carbon of CO2 is composed of different isotopes. Most is of the lighter type: 12C, which has 6 protons and 6 neutrons in its nucleus. About 1.1% is the heavier 13C which has 6 protons and 7 neutrons in the nucleus. There also is a tiny amount of 14C which has 6 protons and 8 neutrons in the nucleus. 14C is continuously formed in the upper stratosphere from the collisions of nitrogen with cosmic rays particles. This type of carbon (also formed by above-ground atomic bomb experiments in the 1950’s) is radio-active and can be used to determine the age of fossils up to about 60,000 years.
One can measure the 13C/12C ratio and compare it to a standard. The standard was some type of carbonate rock, called Pee Dee Belemnite (PDB). When the standard rock was exhausted, this was replaced by a zero definition in a Vienna conference, therefore the new standard is called the VPDB (Vienna PDB). Every carbon containing part of any subject can be measured for its 13C/12C ratio. The comparison with the standard is expressed as d13C in per thousand (the term mostly used is per mil):
(13C/12C)sampled – (13C/12C)standard
————————————————————— x 1.000
(13C/12C)standard
Where the standard is defined as 0.0112372 part of 13C to 1 part of total carbon. Thus positive values have more 13C, negative values have less 13C. Now, the interesting point is that vegetation growth in general uses by preference 12C, thus if you measure d13C in vegetation, you will see that it has quite low d13C values. As fossil fuels were formed from vegetation (or methanogenic bacteria, with similar preferences), these have low d13C values too. Most other carbon sources (oceans, carbonate rock wearing, volcanic degassing,…) have higher d13C values. For a nice introduction of the isotope cycle in nature, see the web page of Anton Uriarte Cantolla ( http://homepage.mac.com/uriarte/carbon13.html ).
This is an interesting feature, as we can determine whether changes of CO2 levels in the atmosphere (observed to be currently -8 per mil VPDB) were caused by vegetation decay or fossil fuel burning (both about -24 per mil) or by ocean degassing (0 to +4 per mil).
2. Trends in carbon isotope ratios, the 13C/12C ratio.
From different CO2 baseline stations, we not only have CO2 measurements, but also d13C measurements. Although only over a period of about 25 years, the trend is clear and indicates an extra source of low d13C in the atmosphere.
Recent trends in d13C from direct measurements of ambient air at different baseline stations.
Data from http://cdiac.ornl.gov/trends/co2/contents.htm
ALT=Alert; BAR=Barrow; LJO=La Jolla; MLO=Mauna Loa; CUM=Cape Kumukahi; CHR=Christmas Island; SAM=Samoa; KER=Kermadec Island; NZD=New Zealand (Baring Head); SPO=South Pole.
Again, we see a lag in the trends with altitude and NH/SH border transfer and less variability in the SH. Again, this points to a source in the NH. If that is from vegetation decay (more present in the NH than in the SH) and/or from fossil fuel burning (90% in the NH) is solved in the investigation of Battle ea. http://www.sciencemag.org/cgi/reprint/287/5462/2467.pdf
More up-to-date (Bender e.a.) and not behind a paywall:
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/BenderGBC2005.pdf
Where it is shown that there is less oxygen used than can be calculated from fossil fuel burning. Vegetation thus produces O2, by incorporating more CO2 than is formed by decaying vegetation (which uses oxygen). This means that more 12C is incorporated, and thus more 13C is left behind in the atmosphere. Vegetation is thus a source of 13C and is not the cause of decreasing d13C ratios.
And we have several other, older measurements of d13C in the atmosphere: ice cores and firn (not completely closed air bubbles in the snow/ice). These align smoothly with the recent air measurements. There is a similar line of measurements from coralline sponges and sediments in the upper oceans. Coralline sponges grow in shallow waters and their skeleton is built from CO2 in the upper ocean waters, without altering the 13C/12C ratio in seawater at the time of building. The combination of atmospheric/firn/ice and ocean measurements gives a nice history of d13C changes over the past 600 years:
Figure from http://www.agu.org/pubs/crossref/2002/2001GC000264.shtml gives a comparison of upper ocean water and atmospheric d13C changes.
What we can see, is that the d13C levels as well as in the atmosphere as in the upper oceans start to decrease from 1850 on, that is at the start of the industrial revolution. In the 400 years before, there is only a small variation, probably caused by the temperature drop in the Little Ice Age.
In comparison, over the whole Holocene, the variation of d13C was only 0.4 per mil:
http://www.nature.com/nature/journal/v461/n7263/full/nature08393.html
And the change in d13C from the coldest part of the last glacial to the warm Holocene Optimum was only 0.7 per mil, slightly over the recent d13C change:
http://epic.awi.de/Publications/Khl2004e.pdf
The decrease of d13C in the atmosphere cannot be caused by some extra outgassing from the oceans, as that would INcrease the d13C ratios of the atmosphere (even including the fractionation at the ocean-air border), while we see a DEcrease both in the oceans and the atmosphere. This effectively excludes the oceans as the main cause of the increase.
3. The 14C/12C ratio
14C is a carbon isotope that is produced in the atmosphere by the impact of cosmic rays. It is an unstable (radioactive) isotope and breaks down with a half-life time of less than 6,000 years. 14C is used for radiocarbon dating of not too old fossils (maximum 60,000 years). The amount of 14C in the atmosphere is variable (depends of the sun’s activity), but despite that, it allows for a reasonable good dating method. Until humans started to burn fossil fuels…
The amounts of 14C in the atmosphere and in vegetation is more or less in equilibrium (as is the case for 13C: a slight depletion, due to 12C preference of the biological reactions). But about half of it returns to the atmosphere within a year, by the decay of leaves. Other parts need more time, but a lot goes back into the atmosphere within a few decades. For the oceans, the lag between 14C going into the oceans (at the North Atlantic sink place of the great conveyor belt) is 500-1500 years, which gives a slight depletion of 14C, together with some very old carbonate going into solution which is completely 14C depleted. In pre-industrial times, there was an equilibrium between cosmogenic 14C production and oceanic depletion.
Fossil fuels at the moment of formation (either wood for coal or plankton for oil) incorporated some 14C, but as these are millions of years old, there is virtually no 14C anymore left. Just as is the case for 13C, the amount of CO2 released from fossil fuel burning dilutes the 14C content of the atmosphere. This caused problems for carbon dating from about 1890 on. Therefore a correction table is used to correct samples after 1890.
In the 1950’s another human intervention caused trouble for carbon dating: nuclear bomb testing induced a lot of radiation, which nearly doubled the atmospheric 14C content. Since then, the amount is fast decreasing, as the oceans replace it with “normal” 14C levels. The half life time of the excess 14C caused by this refresh rate is about 5 years.
This adds to the evidence that fossil fuel burning is the main cause of the increase of CO2 in the atmosphere…
T4. Trends in oxygen use.
To burn fossil fuels, you need oxygen. As for every type of fuel the ratio of oxygen use to fuel use is known, it is possible to calculate the total amount of oxygen which is used by fossil fuel burning. At the other hand, the real amount of oxygen which is used can be measured in the atmosphere. This is quite a challenging problem, as the change in atmospheric O2 from year to year is quite low, compared to the total amount of O2 (a few ppmv in over 200,000 ppmv). Moreover, as good as for CO2 as for oxygen, there is the seasonal to year-by-year influence of vegetation growth and decay. Only since the 1990’s, oxygen measurements with sufficient resolution are available. These revealed that there was less oxygen used than was calculated from fossil fuel use. This points to vegetation growth as source of extra O2, thus vegetation is a sink of CO2, at least since 1990.
This effectively excludes vegetation as the main cause of the recent increase.
The combination of O2 and d13C measurements allowed Battle e.a. to calculate how much CO2 was absorbed by vegetation and how much by the oceans (see the references above). The trends of O2 and CO2 in the period 1990-2000 can be combined in this nice diagram:
O2-CO2 trends 1990-2000, figure from the IPCC TAR
http://www.grida.no/climate/IPCC_tar/wg1/pdf/TAR-03.PDF
This doesn’t directly prove that all the CO2 increase in the atmosphere is from fossil fuel burning, but as both the oceans and vegetation are not the cause, and even show a net uptake, and other sources are much slower and/or smaller (rock weathering, volcanic outgassing,…), there is only one fast possible source: fossil fuel burning.
Engelbeen on why he thinks the CO2 increase is man made (part 3)
About carbon isotopes and oxygen use…
-
The different carbon isotopes in nature.
The carbon of CO2 is composed of different isotopes. Most is of the lighter type: 12C, which has 6 protons and 6 neutrons in its nucleus. About 1.1% is the heavier 13C which has 6 protons and 7 neutrons in the nucleus. There also is a tiny amount of 14C which has 6 protons and 8 neutrons in the nucleus. 14C is continuously formed in the upper stratosphere from the collisions of nitrogen with cosmic rays particles. This type of carbon (also formed by above-ground atomic bomb experiments in the 1950’s) is radio-active and can be used to determine the age of fossils up to about 60,000 years.
One can measure the 13C/12C ratio and compare it to a standard. The standard was some type of carbonate rock, called Pee Dee Belemnite (PDB). When the standard rock was exhausted, this was replaced by a zero definition in a Vienna conference, therefore the new standard is called the VPDB (Vienna PDB). Every carbon containing part of any subject can be measured for its 13C/12C ratio. The comparison with the standard is expressed as d13C in per thousand (the term mostly used is per mil):
(13C/12C)sampled – (13C/12C)standard
————————————————————— x 1.000
(13C/12C)standard
Where the standard is defined as 0.0112372 part of 13C to 1 part of total carbon. Thus positive values have more 13C, negative values have less 13C. Now, the interesting point is that vegetation growth in general uses by preference 12C, thus if you measure d13C in vegetation, you will see that it has quite low d13C values. As fossil fuels were formed from vegetation (or methanogenic bacteria, with similar preferences), these have low d13C values too. Most other carbon sources (oceans, carbonate rock wearing, volcanic degassing,…) have higher d13C values. For a nice introduction of the isotope cycle in nature, see the web page of Anton Uriarte Cantolla ( http://homepage.mac.com/uriarte/carbon13.html ).
This is an interesting feature, as we can determine whether changes of CO2 levels in the atmosphere (observed to be currently -8 per mil VPDB) were caused by vegetation decay or fossil fuel burning (both about -24 per mil) or by ocean degassing (0 to +4 per mil).
-
Trends in carbon isotope ratios, the 13C/12C ratio.
From different CO2 baseline stations, we not only have CO2 measurements, but also d13C measurements. Although only over a period of about 25 years, the trend is clear and indicates an extra source of low d13C in the atmosphere.
Recent trends in d13C from direct measurements of ambient air at different baseline stations.
Data from http://cdiac.ornl.gov/trends/co2/contents.htm
ALT=Alert; BAR=Barrow; LJO=La Jolla; MLO=Mauna Loa; CUM=Cape Kumukahi; CHR=Christmas Island; SAM=Samoa; KER=Kermadec Island; NZD=New Zealand (Baring Head); SPO=South Pole.
Again, we see a lag in the trends with altitude and NH/SH border transfer and less variability in the SH. Again, this points to a source in the NH. If that is from vegetation decay (more present in the NH than in the SH) and/or from fossil fuel burning (90% in the NH) is solved in the investigation of Battle ea. http://www.sciencemag.org/cgi/reprint/287/5462/2467.pdf
More up-to-date (Bender e.a.) and not behind a paywall:
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/BenderGBC2005.pdf
Where it is shown that there is less oxygen used than can be calculated from fossil fuel burning. Vegetation thus produces O2, by incorporating more CO2 than is formed by decaying vegetation (which uses oxygen). This means that more 12C is incorporated, and thus more 13C is left behind in the atmosphere. Vegetation is thus a source of 13C and is not the cause of decreasing d13C ratios.
And we have several other, older measurements of d13C in the atmosphere: ice cores and firn (not completely closed air bubbles in the snow/ice). These align smoothly with the recent air measurements. There is a similar line of measurements from coralline sponges and sediments in the upper oceans. Coralline sponges grow in shallow waters and their skeleton is built from CO2 in the upper ocean waters, without altering the 13C/12C ratio in seawater at the time of building. The combination of atmospheric/firn/ice and ocean measurements gives a nice history of d13C changes over the past 600 years:
Figure from http://www.agu.org/pubs/crossref/2002/2001GC000264.shtml gives a comparison of upper ocean water and atmospheric d13C changes.
What we can see, is that the d13C levels as well as in the atmosphere as in the upper oceans start to decrease from 1850 on, that is at the start of the industrial revolution. In the 400 years before, there is only a small variation, probably caused by the temperature drop in the Little Ice Age.
In comparison, over the whole Holocene, the variation of d13C was only 0.4 per mil:
http://www.nature.com/nature/journal/v461/n7263/full/nature08393.html
And the change in d13C from the coldest part of the last glacial to the warm Holocene Optimum was only 0.7 per mil, slightly over the recent d13C change:
http://epic.awi.de/Publications/Khl2004e.pdf
The decrease of d13C in the atmosphere cannot be caused by some extra outgassing from the oceans, as that would INcrease the d13C ratios of the atmosphere (even including the fractionation at the ocean-air border), while we see a DEcrease both in the oceans and the atmosphere. This effectively excludes the oceans as the main cause of the increase.
-
The 14C/12C ratio
14C is a carbon isotope that is produced in the atmosphere by the impact of cosmic rays. It is an unstable (radioactive) isotope and breaks down with a half-life time of less than 6,000 years. 14C is used for radiocarbon dating of not too old fossils (maximum 60,000 years). The amount of 14C in the atmosphere is variable (depends of the sun’s activity), but despite that, it allows for a reasonable good dating method. Until humans started to burn fossil fuels…
The amounts of 14C in the atmosphere and in vegetation is more or less in equilibrium (as is the case for 13C: a slight depletion, due to 12C preference of the biological reactions). But about half of it returns to the atmosphere within a year, by the decay of leaves. Other parts need more time, but a lot goes back into the atmosphere within a few decades. For the oceans, the lag between 14C going into the oceans (at the North Atlantic sink place of the great conveyor belt) is 500-1500 years, which gives a slight depletion of 14C, together with some very old carbonate going into solution which is completely 14C depleted. In pre-industrial times, there was an equilibrium between cosmogenic 14C production and oceanic depletion.
Fossil fuels at the moment of formation (either wood for coal or plankton for oil) incorporated some 14C, but as these are millions of years old, there is virtually no 14C anymore left. Just as is the case for 13C, the amount of CO2 released from fossil fuel burning dilutes the 14C content of the atmosphere. This caused problems for carbon dating from about 1890 on. Therefore a correction table is used to correct samples after 1890.
In the 1950’s another human intervention caused trouble for carbon dating: nuclear bomb testing induced a lot of radiation, which nearly doubled the atmospheric 14C content. Since then, the amount is fast decreasing, as the oceans replace it with “normal” 14C levels. The half life time of the excess 14C caused by this refresh rate is about 5 years.
This adds to the evidence that fossil fuel burning is the main cause of the increase of CO2 in the atmosphere…
4
-
Trends in oxygen use.
To burn fossil fuels, you need oxygen. As for every type of fuel the ratio of oxygen use to fuel use is known, it is possible to calculate the total amount of oxygen which is used by fossil fuel burning. At the other hand, the real amount of oxygen which is used can be measured in the atmosphere. This is quite a challenging problem, as the change in atmospheric O2 from year to year is quite low, compared to the total amount of O2 (a few ppmv in over 200,000 ppmv). Moreover, as good as for CO2 as for oxygen, there is the seasonal to year-by-year influence of vegetation growth and decay. Only since the 1990’s, oxygen measurements with sufficient resolution are available. These revealed that there was less oxygen used than was calculated from fossil fuel use. This points to vegetation growth as source of extra O2, thus vegetation is a sink of CO2, at least since 1990.
This effectively excludes vegetation as the main cause of the recent increase.
The combination of O2 and d13C measurements allowed Battle e.a. to calculate how much CO2 was absorbed by vegetation and how much by the oceans (see the references above). The trends of O2 and CO2 in the period 1990-2000 can be combined in this nice diagram:
O2-CO2 trends 1990-2000, figure from the IPCC TAR
http://www.grida.no/climate/IPCC_tar/wg1/pdf/TAR-03.PDF
This doesn’t directly prove that all the CO2 increase in the atmosphere is from fossil fuel burning, but as both the oceans and vegetation are not the cause, and even show a net uptake, and other sources are much slower and/or smaller (rock weathering, volcanic outgassing,…), there is only one fast possible source: fossil fuel burning.
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Steven mosher says:
September 16, 2010 at 4:33 pm
D. Patterson:
“Burning fossil fuels may or may not result in lower CO2 concentrations in the atmosphere, but it is not inconceivable for fossil fuels to stimulate enough new plant growth to generally maintain concentrations or lower them in some other circumstances.”
You missed the point. Absent any evidence that burning Fossil fuels causes a net decrease, absent ANY argument, I think the reasonable alternative is the obvious.
I understood your point quite clearly. You are plainly suggesting the uncontroversial fact that the burning of fossil fuels obviously emits carbon dioxide as a product of the combustion process and must therefore cause a net increase in atmospheric concentrations of carbon dioxide. Such an argument is invalid, because it wrongly assumes the addition of of carbon dioxide to the atmosphere can only and must only result in continuing net increases of carbon dioxide concentrations in the atmosphere. The real world evidence demonstrates such an assumption is not true and is, in fact, contrary to experience.
The biosphere is responsible for taking Earth’s earlier atmosphere that was more than a hundred times more massive than today and composed of nearly all carbon dioxide, removed nearly all of that carbon dioxide from the atmosphere, and deposited the carbon dioxide in the lithosphere, hydrosphere, and biosphere. The only reason there is any more than a trace amount of carbon dioxide in the atmosphere today is the continued geological emissions and the inability of the biosphere to reduce the carbon dioxide beyond equilibrium levels without suffering extinction upon the cessation of photosynthesis. In other words, the biosphere has demonstrated an unquestionable capacity to reduce mega-atmospheric concentrations of carbon dioxide to the minimum equilibrium levels achievable by the biosphere over a sufficient time period.
The only questions we need to have answered about the carbon dioxide added to the atmosphere by the burning of fossil fuels is just how long of a time period the biosphere will require to reduce the additions to the equilibrium levels and what those equilibrium levels are in a particular time period and circumstance. Until and unless the biosphere becomes extinct or virtually extinct due to <180ppm levels of carbon dioxide and or ice age events, the biosphere will always remove added carbon dioxide from fossil fuels or any other source until the atmospheric concentrations reach the equilibrium levels. So, it is not a question of if there is an ultimate net decrease after burning fossil fuels, but it is a question of how soon or when the net decrease to equilibrium levels occurs.
Given the biosphere's past achievement of reducing more than 100 present Earth atmospheres with something like 988,000 parts per million of carbon dioxide to only 280-390 parts per million in an atmosphere with less than 100th the mass, someone is going to have a lot of mighty mighty fancy explaining to do as to why the biosphere can no longer capable of handling one or a few percentage points of anthropogenic carbon dioxide emissions to the latest trace ~280-390 parts per million or less. Furthermore…
What are the past equilibrium levels?
Are the anthropogenic sources of carbon dioxide: 1. net additions in the short term, 2. net decreases in the short term, or 3. no significant changes in the short term?
What constitutes a significant change in carbon dioxide levels when past equilibrium levels of carbon dioxide were 1,000ppm, 2,500ppm, and greater to more than 7,000ppm?
D. Patterson says:
September 21, 2010 at 2:42 am
Furthermore…
What are the past equilibrium levels?
Are the anthropogenic sources of carbon dioxide: 1. net additions in the short term, 2. net decreases in the short term, or 3. no significant changes in the short term?
What constitutes a significant change in carbon dioxide levels when past equilibrium levels of carbon dioxide were 1,000ppm, 2,500ppm, and greater to more than 7,000ppm?
Most of these amounts of the (far) past are buried in relative stable carbonate and/or fossil fuel layers. For the current geological distribution of the continents, the 180-300 ppmv CO2 levels found in ice cores may be the most relevant levels, as these show a remarkable linear ratio between CO2 levels (lagging) and temperature of about 8 ppmv/°C, sustained over 800,000 years.
Based on that ratio, the current temperature would give some 290 ppmv for CO2, which did go up together with the emissions since the start of the industrial revolution till nowadays 390 ppmv. The decay rate of this excess CO2 may be around 40 years, see: http://www.john-daly.com/carbon.htm
I note there has been a report of a massive decline in phytoplankton over the last 100 years as the oceans appear to be becoming more transparent. If true, could this also be a cause of more CO2 in the atmosphere?
http://dalnews.dal.ca/2010/07/28/photoplank.html
http://wattsupwiththat.com/2010/07/30/now-its-phytoplankton-panic/
Spector says:
September 22, 2010 at 2:41 am
I note there has been a report of a massive decline in phytoplankton over the last 100 years as the oceans appear to be becoming more transparent. If true, could this also be a cause of more CO2 in the atmosphere?
http://dalnews.dal.ca/2010/07/28/photoplank.html
http://wattsupwiththat.com/2010/07/30/now-its-phytoplankton-panic/
Plankton indeed is a part of the carbon cycle which removes CO2 from the atmosphere by depositing calcite (shells) and organic carbon out of the upper ocean mixed layer into the deep oceans. That would influence the sink rate of the oceans and thus indirectly increase the increase rate in the atmosphere. But the increase rate in the atmosphere shows a more steady state in recent years.