For the last time, increasing atmospheric CO2 is coming from fossil fuels, and not from volcanoes.
The concentration
of CO2 in the atmosphere is rising rapidly.
Before widespread burning of coal, circa 1750, atmospheric CO2 was about
280 parts per million (ppm). By 1955, global
CO2 concentration had risen to 314 ppm. Average
global CO2 levels are now about 412 ppm, and are still rising at about 3 ppm
per year.
Industrial
processes are able to change the composition of the earth’s atmosphere because
there really isn’t very much atmosphere, and there isn’t very much CO2. The atmosphere thins rapidly with altitude,
so that about half of the atmosphere is less than 3 miles above the earth, and breathable atmosphere extends only about 6 miles above the earth. Further, there isn’t very much CO2 in the
atmosphere – about 400 ppm, or 0.04%.
Nevertheless, that small amount of CO2 is very effective at blocking
thermal infrared radiation, which is why changing the CO2 concentration of the
atmosphere has already had a significant impact on global climate.
Figure 1. There isn’t very much atmosphere, and there really isn't very much CO2. The pie-slice of CO2 in the second figure is exaggerated three-fold for visibility.
A common myth
that circulates on social media is that rising CO2 in the atmosphere is coming from
volcanoes. It isn't. I already wrote one
blog post about the origin of atmospheric CO2.
(https://dougrobbins.blogspot.com/2017/06/volcanic-co2-emissions.html).
This blog post will
present additional evidence that rising CO2 is of human origin. The evidence is:
- Declining oxygen concentration of the atmosphere
- The quantity of missing oxygen
- The location of declining oxygen concentration by hemisphere
- Volumetric data for fossil fuel emissions, deforestation, and volcanism, compared to volumes of CO2 appearing in the atmosphere
- The location of rising CO2 by hemisphere
- Changing carbon isotopic composition of the atmosphere
- The location of the declining carbon isotope measure (del C13) by hemisphere
- The steady rise of atmospheric CO2, whereas volcanic eruptions are intermittent (although slow emissions from non-eruptive events, mid-ocean ridges and rifts also occur).
Atmospheric CO2
is now also monitored by two orbiting carbon observatories (OCO), which
directly measure CO2 concentrations in the atmosphere and connect rising atmospheric
CO2 with points of origin.
The myth that volcanoes
are responsible for human-caused atmospheric disruption has been propagated since
the 1990s. The book “Merchants of Doubt”
provides a history of claims that volcanoes were responsible for destruction of
stratospheric ozone, or for acid rain in the US and Canada. Those claims were thoroughly debunked long
ago. Nevertheless, articles attributing
rising CO2 to volcanoes still appear on climate-change denying websites, (e.g.
James Edward Kamis’ 2018 post on ClimateChangeDispatch).
Let’s look at the
evidence.
Fossil-Fuel
Combustion
When fossil fuels
are burned, atmospheric oxygen is converted to CO2.
Consequently, the oxygen concentration in the atmosphere falls. If we quantify oxygen depletion in the
atmosphere, we find that it validates the volumes of fossil fuel consumption reported
by inventory methods (BP Statistical Review, CDIAC, EIA, etc.). The volumes of CO2 determined by either method are approximately twice what is necessary to account for the observed rise in atmospheric CO2. The
remaining CO2 is dispersed into CO2 reservoirs in the oceans and biosphere. A full accounting of the CO2 flows on earth can be
found in the Global Carbon Project or Berkeley Earth websites.
Simply stated, the
depletion of atmospheric oxygen quantifies CO2 emissions from fossil fuels. This volume of CO2 emssions more than accounts
for the rise in atmospheric CO2. There isn’t
any room for a significant contribution from volcanoes without somehow getting
rid of the CO2 from the combustion of fossil fuels in some as-of-yet
unidentified carbon sink (which is unlikely to exist).
Depletion
of Atmospheric Oxygen
The amount of
oxygen in the atmosphere is falling (although not enough to cause trouble for
breathing). Atmospheric oxygen is
falling because oxygen is consumed by burning fossil fuels. This would not occur if the source of rising CO2
was from volcanoes (Figure 2). As seen
in the bulk CO2 and Del C13 charts, there is a strong seasonal signal in the
concentration of atmospheric oxygen, related to the growing season in each
hemisphere. The amplitude of the
seasonal cycle is somewhat stronger in the Northern Hemisphere, due to the
preponderance of temperate land-mass and agriculture.
Figure 2. The concentration of atmospheric oxygen is
falling, due to combustion of fossil fuels.
The Per Meg (del O2/N2) can be roughly converted to ppm by multiplying
by 0.2095, the fractional concentration of oxygen in the atmosphere. A discussion of the Per Meg (del O2/N2) measure
can be found on the Scripps Institute CO2 website FAQs. The loss of 700 ppm of oxygen is a relatively
small change because of the greater abundance of oxygen in the atmosphere as
compared to CO2. The percentage of
oxygen in the atmosphere is about 20.95%; the percentage of CO2 in the
atmosphere is about 0.04%.
Oxygen
Depletion by Hemisphere
Falling oxygen
concentrations in the Northern Hemisphere lead falling oxygen in the Southern
Hemisphere (Figure 3). This is because
90% of fossil fuels are being burned in the Northern Hemisphere, consuming
oxygen in the Northern Hemisphere.
Atmospheric mixing works to equilibrate oxygen concentrations, but
continuing combustion of fossil fuels in the Northern Hemisphere keeps oxygen
lower than in the Southern Hemisphere.
Oxygen –
Carbon Stoichiometry
The number of
molecules of oxygen disappearing from the atmosphere is a very close match to
the number of carbon atoms burned in fossil fuels and deforestation (Figure 4). There is a quantitative match, showing that for
each atom of carbon burned, one molecule of oxygen disappears from the
atmosphere, as C + 02 -> CO2. The
depletion of atmospheric oxygen, in stochiometric balance with human carbon
combustion, validates the volume of CO2 released into the atmosphere by burning
fossil fuels.
Figure 4. Moles of carbon burned by fossil fuels and
deforestation annually, compared to atmospheric oxygen depletion in moles. The close match confirms that volumes of CO2
released from fossil fuels and deforestation are responsible for rising
atmospheric CO2.
Moles of oxygen
depletion can be calculated by converting “per meg” to ppm (oxygen/atmosphere)
and assuming an initial volume of the total atmosphere of 1.81E+20 moles (various
Internet sources). Notes on the calculation
are given in the Appendix, following References.
Volumetric
Evidence
CO2 emissions
from gas, oil, coal, cement, flaring, and deforestation are now about 40 gt per
year, and forecast to go higher. Estimates
and measurements of volcanic CO2 emissions are far smaller than known volumes
of CO2 from fossil fuels and deforestation (Figure 5). Estimated volumes of volcanic CO2 include
deep carbon emissions, and passive emissions from continental rifts and
mid-ocean ridges. Volcanic CO2 emissions
are only about 1.8% of human CO2 emissions by volume.
Fraction of
CO2 Emissions Which Remain in the Atmosphere
Only about 44% of
human CO2 emissions remain in the atmosphere; the rest of the CO2 is absorbed
by the oceans or taken up by plants.
Human CO2 emissions are more than twice what is necessary to account for
rising atmospheric CO2. Since volcanic
CO2 emissions represent only 1.8% of human CO2 emissions, it is impossible for
volcanoes to account for the large volume of CO2 now appearing in the
atmosphere. (Figure 6).
Difference
in CO2 between Northern and Southern Hemispheres, and
Comparison to Net CO2 Emissions from the Northern Hemisphere
Comparison to Net CO2 Emissions from the Northern Hemisphere
About 90% of humans
live in the northern hemisphere, and 90% of human CO2 emissions originate in
the northern hemisphere. Atmospheric CO2
concentrations in the northern hemisphere are consistently higher than CO2
concentrations in the southern hemisphere.
The amount of the difference is
very close to the net CO2 emissions from fossil fuels in the northern
hemisphere (Figure 7). The close
correspondence of net Northern Hemisphere CO2 emissions and the difference
between Northern and Southern CO2 concentration is partly a coincidence between
the mixing rate between the hemispheres and the reporting period for CO2
emissions. However, the consistent fit
is a clear proof that fossil fuel emissions in the Northern Hemisphere are
principally responsible for rising CO2. The
largest volcanic eruptions of the past 60 years have been in the Southern
Hemisphere, but these have made no impact on the record of atmospheric CO2.
Carbon
Isotope Ratios in Atmospheric CO2
Natural carbon
mostly occurs in two isotopes: C12 and C13.
Plants and all fossil fuels (which derive from plants) are enriched in
C12 by biological processes, giving fossil fuel emissions and deforestation a
“lighter” isotopic signature (more C12) than the atmosphere. The measure of carbon isotopic ratios is d C13/C12, typically called “del C13”. Samples which are relatively enriched in
“light” C12 have a negative del C13, while samples that are enriched in “heavy”
C13 have a positive del C13. A technical
definition of del C13 is given at the bottom of the article, below the
references.
In the 1950s, the
atmosphere had a del C13 value of about -7.5, reflecting a higher concentration
of C12 than the oceans, which has a del C13 of about zero. As mentioned above, fossil fuels are enriched
in C12 with typical values in the range of -20 to -30. Biogenic natural gas has been fractionated
twice, and may have del C13 values ranging from -40 to -70. Volcanic emissions have a heavier isotopic
signature than the atmosphere, with a del C13 value of about -1 to -4.
The isotopic
composition of the atmosphere is steadily becoming lighter as CO2 concentrations
rise. This is only possible if the
additional CO2 is from a source isotopically lighter than the atmosphere, not
heavier. Thus, fossil fuels, and not
volcanoes or the oceans, are the source of rising CO2 (Figure 8).
After filtering
the seasonal cycle, we see that the Northern Hemisphere leads the Southern
Hemisphere in falling Del C13 isotope ratio (Figure 10). This is because 90% of fossil fuel emissions occur
in the Northern Hemisphere. The remaining wavy signal in the Del C13 record
correlates to El Nino cycles (Figure 9), with a rapidly falling Del C13 ratio
during El Nino events, and a slightly rising Del C13 ratio during La Nina
events. It is unclear whether the El
Nino signal in the data is due to fractionation between atmosphere and ocean,
changes in the uptake of carbon in the ocean, or related climate events.
https://dougrobbins.blogspot.com/2013/11/carbon-isotopes-in-atmosphere-part-ii.html ]
Rate of Increase in Global Atmospheric CO2
Atmospheric CO2 is steadily rising around the globe. Volcanic eruptions are intermittent; the largest eruption (Mt. Pinatubo) and the third-largest eruption (Mt. Hudson) of the past century both occurred in 1991, but there is no perceptible change in the rate of rising atmospheric CO2 (Figure 10). Likewise, other large volcanic eruptions produced no perceptible impact over the period of detailed CO2 observations [Mount Agung (1963), Mt. St. Helens (1980), El Chichon (1982). Puyehue-Cordón Caulle (2011)]. Slow, *quiet*, emissions of CO2 also occur from non-eruptive events, mid-ocean ridges and onshore rifts, but these have been well quantified over the past 20 years, and do not contribute significant volumes of CO2 to the atmosphere.
Orbiting
Carbon Observatories and NASA CO2 Modeling
Two new NASA
satellites, OCO2 & OCO3, now provide worldwide continuous CO2
monitoring. Data gathered by these
satellites will provide a detailed identification of the specific sources of
CO2 across the entire globe.
NASA also
prepared a supercomputer simulation of atmospheric CO2, based on ground-based
and aerial CO2 observations. A video of
the simulation can be seen on YouTube:
The simulation
highlights major CO2 sources, in the eastern US, eastern China, industrial
centers of central & eastern Europe, oilfields of western Siberia, and
wildfires in the Amazon rainforests (Figures 11A and 11B).
Conclusion
Rising CO2
concentrations are unquestionably from human sources, as a result of combustion
of fossil fuels and deforestation. There
is volumetric, temporal, isotopic, geographic, stoichiometric evidence
supporting human sources of rising atmospheric CO2. There is no evidence that volcanoes make a significant
contribution to rising CO2.
References:
Previous Posts on
Volcanic and Atmospheric CO2
Posts on Twitter on Volcanic CO2
External References:
Scripps Institute CO2 Home
Scripps Institute O2 Program
Boden, et al, 2013, Global and National Fossil-fuel CO2
Emissions, in Global Carbon Atlas
http://www.globalcarbonatlas.org/en/content/fossil-fuel-emissions
http://www.globalcarbonatlas.org/docs/Public_Presentation_of_the_GCA_Paris_EN.pdf
Burton et al, 2013, Deep Carbon Emissions from
Volcanoes
Discussion of CO2 flux from subaerial volcanic eruptions on
page 332.
Total CO2 flux from volcanic sources: 637 mT per year,
p. 341, table 6.
The eruption of Mt. Pinatubo in 1991 was the largest
volcanic eruption since 1912. That eruption produced ~50 Mt of CO2
(Gerlach et al. 2011). Individual eruptions are dwarfed by the
time-averaged continuous CO2 emissions from global volcanism. The
eruption of Mt. Pinatubo was equivalent to only 5 weeks of global subaerial
volcanic emissions.
The average volume of eruptive CO2 emissions over the past
300 years was only 0.1 cubic kilometers, which suggests an annual rate of about
1 million tonnes of CO2 annually (Crisp, 1984, cited in Burton).
CO2 consumption from continental silicate weathering was 515
Mt/yr, (Gaillardet et al., 1999, cited in Burton).
Metamorphism accounts for the release of about 300 million
tonnes of CO2 annually. (Mörner and Etiope, 2002, Carbon degassing from
the lithosphere. Global Planet Change 33:185-203, cited in Burton).
Lee et al, 2016, Massive and prolonged deep carbon emissions
associated with continental rifting, Nature Geoscience Letters, Jan.18,
2016.
Paper accounts for additional CO2 emissions from East
African Rift, potentially bringing natural world CO2 emissions to 708 mT, an
increase of 11% from previous estimates.
Houghton, R.A. 2008. Carbon Flux to the Atmosphere from
Land-Use Changes: 1850-2005. In TRENDS: A Compendium of Data on Global Change.
Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S.
Department of Energy, Oak Ridge, Tenn., U.S.A.
Marland, G., T.A. Boden, and R.J. Andres. 2008. Global,
Regional, and National Fossil Fuel CO2 Emissions. In Trends: A Compendium of
Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge
National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.
Erik Klemetti, 2015, Volcanic versus Anthropogenic Carbon
Dioxide: An Addendum, WIRED website.
Pre-industrial atmospheric del C13 was about -6.5, and declined
following industrialization, in correlation with rising atmospheric CO2.
Individual Volcanic Eruptions
Judy Fierstein, USGS, in Forbes, Ethan Siegel, "How Much CO2 Does a Single Volcano Emit?"
Del C13: -4.9 to -6.3
Del C13: Currently -0.9 to -1.4; 1970s and 1980s ~ -4
Del C13: -6 to -10. N.B.: These are samples of soil gases in a rift zone with known petroleum generation, and may be contaminated by thermogenic or biogenic CO2 deriving from petroleum sources.
Faure, 1984, Principles of Isotope Geochemistry
Del C13: -2 to -6.
Del C13: -2 to -6.
Volcanoes and CO2
A good discussion of former and current estimates of CO2
emissions from volcanoes and fossil fuels.
Also, a good recap of errors made by certain commentators in creating
and propagating the volcanic CO2 myth.
Naomi Oreskes and Erik Conway, 2010, Merchants of Doubt.
A deeply researched book about right-wing scientists, funded
by industry, working outside of their fields of expertise, tried to throw doubt
on science that might result in regulations in the interest of public health or
environmental protection. The scientists
involved were generally retired, had worked in military science and were given
compensation or recognition in return for their efforts. Among the false narratives they created was
the idea that volcanoes were responsible for chlorine damage to stratospheric ozone,
and that volcanoes were responsible for acid rain in the US and Canada. Neither idea is correct. The idea of blaming volcanoes for man-made
atmospheric disruption has now been extended to CO2 and climate change.
Which emits more carbon dioxide: volcanoes or human
activities? Climate.gov.
The following are examples of deliberately misleading
media articles about atmospheric CO2.
Volcano eruption WARNING: Intense volcanic CO2 activity
'drives GLOBAL EXTINCTION'
Article omits mention of fossil fuels entirely.
J.E. Kamis, 2018, Discovery Of Massive Volcanic CO2
Emissions Puts Damper On Global Warming Theory
This article contains false claims. Notably, the article claims that:
“Natural volcanic and man-made CO2 emissions have the exact
same and very distinctive carbon isotopic fingerprint. It is therefore scientifically impossible to
distinguish the difference between volcanic CO2 and human-induced CO2 from the
burning of fossil fuels (see here).”
The reference provided (https://skepticalscience.com/anthrocarbon-brief.html)
directly contradicts the claim! “In fact
the global C13/C12 ratio has declined, which is very strong evidence the source
of the CO2 increase has was C12 enriched, ie, derived from photosynthesis. Therefore it is very strong evidence that it
comes from the biosphere or fossil fuels, rather than from volcanoes or oceanic
outgassing.”
Stoichiometry Calculations
Annual fossil fuel emissions are reported in tonnes of CO2 by CDIAC, the BP Annual Statistical Review of World Energy, and the EIA. One tonnes of CO2 (1000 kg) contains 22,722 moles of CO2.
Annual fossil fuel emissions are reported in tonnes of CO2 by CDIAC, the BP Annual Statistical Review of World Energy, and the EIA. One tonnes of CO2 (1000 kg) contains 22,722 moles of CO2.
Calculation Notes for atmosphere stoichiometry. The Scripps pages on units and FAQs are
helpful in understanding the use of the “per meg” unit, and conversion to
ppm.
“Per meg” units of oxygen reported by Scripps can be
converted to ppm (oxygen/atmosphere) over small ranges by multiplying by 20.95%,
the current oxygen fraction in air. Parts
per million (ppm) of oxygen can then be converted to moles by multiplying by
the number of moles in the atmosphere (1.81E+20), from various Internet sources.
https://www.theweatherprediction.com/habyhints3/976/
A Few Words about CO2 Carbon
Isotopes
There are two stable isotopes of
carbon, C13 and C12. C12 is the more
abundant isotope; the natural ratio of C12 to C13 is about 99 to 1. The
standard measure of carbon isotopes compares the C12/C13 isotope ratio of the
sample in question to the C13/C12 ratio of a standard limestone, according to
the expression:
d C13/C12 = ((C13/C12
sample/C13/C12 standard) – 1)*1000.
This expression, commonly termed
“del 13”, amplifies small but meaningful differences in the isotopes, which are
diagnostic of certain processes and occurrences of carbon. The standard
is a uniform Cretaceous limestone with a d 13 value defined as zero. Positive values
indicate a heavier composition, i.e., a greater concentration of C13 than the
standard. Negative values indicate a lighter composition, i.e., a smaller
concentration of C13 than the standard.
Plants fractionate carbon, favoring
the lighter isotope C12. Anything derived from plants, including oil,
gas, and coal (and algae, animals and people) carries a light (negative) d C13/C12 signature.
Limestone carries a d C13/C12
ratio near zero. The atmosphere, in 1977, had a d C13/C12 ratio of about -7.5;
it is currently about -8.3, reflecting the influence of fossil fuels.
Oceans have a slightly positive d C13/C12 ratio of dissolved inorganic carbon, although
Northern Hemisphere waters show a negative ratio due to the greater use of
fossil fuels in the Northern Hemisphere. Fossil fuel CO2 emissions
and CO2 emissions from deforestation carry a very light d C13/C12, often in the range
of -25 to -28 (although biogenic natural gas, which is fractionated twice, can
have del 13 value in the range of -40 to -70). The distinctive isotopic signature
of CO2 from fossil fuels and deforestation is useful in
tracking the movement of carbon through the atmosphere and oceans.
