For a another view on the CO2 issue, please see also the guest post by Tom Vonk: CO2 heats the atmosphere…a counter view -Anthony
Guest Post by Ferdinand Engelbeen
There have been hundreds of reactions to the previous post by Willis Eschenbach as he is convinced that humans are the cause of the past 150 years increase of CO2 in the atmosphere. For the (C)AGW theory, that is one of the cornerstones. If that fails, the whole theory fails.
This may be the main reason that many skeptics don’t like the idea that humans are the cause of the increase and try to demolish the connection between human emissions and the measured increase in the atmosphere with all means, some more scientific than others.
After several years of discussion on different discussion lists, skeptic and warmist alike, I have made a comprehensive web page where all arguments are put together: indeed near the full increase of CO2 in the atmosphere is caused by the human emissions. Only a small part might have been added by the (ocean) warming since the LIA. That doesn’t mean that the increase has a tremendous effect on the warming of the earth’s surface, as that is a completely different discussion. But of course, if the CO2 increase was mainly/completely natural, the discussion of the “A” in AGW wouldn’t be necessary. But it isn’t natural, as the mass balance proves beyond doubt and all other observations agree with. And all alternative explanations fail one or more observations. In the next parts I will touch other items like the process characteristics, the 13C and 14C/12C ratio, etc. Finally, I will touch some misconceptions about decay time of extra CO2, ice cores, historical CO2 measurements and stomata data.
The mass balance:
As the laws of conservation of mass rules: no carbon can be destroyed or generated. As there are no processes in the atmosphere which convert CO2 to something else, the law also holds for CO2, as long as it stays in the atmosphere. This means that the mass balance should be obeyed for all situations. In this case, the increase/decrease of the CO2 level in the atmosphere after a year (which only shows the end result of all exchanges, including the seasonal exchanges) must be:
dCO2(atm) = CO2(in1 + in2 + in3 +…) + CO2(em) – CO2(out1 + out2 + out3 +…)
The difference in the atmosphere after a year is the sum of all inflows, no matter how large they are, or how they changed over the years, plus the human emissions, minus the sum of all outflows, no matter how large they are, wherever they take place. Some rough indication of the flows involved is here in Figure 1 from NASA:
From all those flows very few are known to any accuracy. What is known with reasonable accuracy are the emissions, which are based on inventories of fossil fuel use by the finance departments (taxes!) of different countries and the very accurate measurements of the increase of CO2 in the atmosphere on a lot of places on earth, including Mauna Loa.
Thus in the above CO2 mass balance, we can replace some of the items with the real amounts (CO2 amounts expressed in gigaton carbon):
4 GtC = CO2(in1 + in2 + in3 +…) + 8 GtC – CO2(out1 + out2 + out3 +…)
Or rearranged:
CO2(in1 + in2 + in3 +…) – CO2(out1 + out2 + out3 +…) = – 4 GtC
Without any knowledge of any natural flow in or out of the atmosphere or changes in such flows, we know that the sum of all natural outflows is 4 GtC larger than the sum of all natural inflows. In other words, the net increase of the atmospheric CO2 content caused by all natural CO2 ins and outs together is negative. There is no net natural contribution to the observed increase, nature as a whole acts as a sink for CO2. Of course, a lot of CO2 is exchanged over the seasons, but at the end of the year, that doesn’t add anything to the total CO2 mass in the atmosphere. That only adds to the exchange rate of individual molecules: some 20% per year of all CO2 in the atmosphere is refreshed by the seasonal exchanges between atmosphere and oceans/vegetation. That can be seen in the above scheme: about 210 GtC CO2 is exchanged, but not all of that reaches the bulk of the atmosphere. Best guess (based on 13C/12C and oxygen exchanges) is that some 60 GtC is exchanged back and forth over the seasons between the atmosphere and vegetation and some 90 GtC is exchanged between the atmosphere and the oceans. These flows are countercurrent: warmer oceans release more CO2 in summer, while vegetation has its largest uptake in summer. In the NH, vegetation wins (more land), in the SH there is hardly any seasonal influence (more ocean). There is more influence near ground than at altitude and there is a NH-SH lag (which points to a NH source). See figure 2:
The net result of all these exchanges is some 4 GtC sink rate of the natural flows, which is variable: the variability of the natural sink capacity is mostly related to (ocean) temperature changes, but that has little influence on the trend itself, as most of the variability averages out over the years. Only a more permanent temperature increase/decrease should show a more permanent change in CO2 level. The Vostok ice core record shows that a temperature change of about 1°C gives a change in CO2 level of about 8 ppmv over very long term. That indicates an about 8 ppmv increase for the warming since the LIA, less than 10% of the observed increase.
As one can see in Fig. 3 below, there is a variability of +/- 1 ppmv (2 GtC) around the trend over the past 50 years, while the trend itself is about 55% of the emissions, currently around 2 ppmv (4 GtC) per year (land use changes not included, as these are far more uncertain, in that case the trend is about 45% of the emissions + land use changes).
We could end the whole discussion here, as humans have added about twice the amount of CO2 to the atmosphere as the observed increase over the past 150 years, the difference is absorbed by the oceans and/or vegetation. That is sufficient proof for the human origin of the increase, but there is more that points to the human cause… as will be shown in the following parts.
Please note that the RULES FOR THE DISCUSSION OF ATTRIBUTION OF THE CO2 RISE still apply!
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There is another, equally useful discussion on this issue at:
http://www.barrettbellamyclimate.com/page20.htm
It has the merit to my mind of explaining how challenging AGW orthodoxy emphatically means endorsing mainstream physics.
Many of us who are scientifically more or less literate but are neither physicists not climatologists find the “slam dunk” (lovely phrase) arguments that have been resurfacing recently in the sceptic blogosphere confusing to put it mildly and not very helpful.
The premise that humans have caused most of the recent CO2 increases rests on a very strong empirical base and I for one will need some persuading that it fails. I’ve yet to see it.
So, looking forward to Pt II.
Bill Yarber says:
August 5, 2010 at 8:19 am
I think you have seriously underestimated the impact on the oceans outguessing CO2 as they warm! Look at the ice core data
No I haven’t underestimated the impact of the oceans: over very long term (Vostok ice core) that is about 8 ppmv/C, the same for the MWP-LIA cooling (only visible in the high resolution Law Dome ice core). Currently the short term influence of temperature is about 4 ppmv/C around the trend, but the trend itself is largely from the emissions…
Questions for Ferdinand Engelbeen:
a) What is the NATURAL base line atmospheric ppmv of CO2 to be for planet earth ???
b) Is the natural atmospheric CO2 level dependant on temperature ???
c) What is the optimal atmospheric CO2 level for life on earth ???
d) What is a dangeruosly low atmospheric level of CO2 for life on earth ??
e) If we don’t have answers to the above questions how could we possibly engineer an atmospheric CO2 level that is correct for planet earth as proposed by the IPCC ???
Robert of Ottawa says:
August 5, 2010 at 8:28 am
I missed something here. Where did the 4GT/year come from?
The only accurate way would be to estimate it from the 2 ppm increase per year.
The 4 GtC is calculated as the increase in carbon mass of the atmosphere, while the 2 ppmv is CO2 in measured as volume procent of the atmosphere. These two are equivalent.
My only objection to the statement the CO2 cannot be created or destroyed (law of mass conservation) is that neither the Carbon or the Oxygen can be destroyed. CO2 can be formed or released during a combustion process. However, both had to exist either separately or together before being placed in the atmosphere. We’ve been taught during photosynthesis that CO2 is changed so that C is stored and O2 is released. Both still exist but not as a CO2 molecule.
I understand this is trivialized in the explanation, but the trivialization looses a lot of technical importance.
I was expecting that this counter point would have been relating to how CO2 increases Earth’s temperature. I think everyone agrees that CO2 has been increasing faster because of mankind, burning fossil fuels, building more towns etc. I doubt anyone can debate that it hasn’t been increasing
The point that’s up for debate is whether this will cause any warming. The previous article was talking about how more CO2 will not change the temperature since the same energy transfers occur, which he said to be none. So i was expecting a counter point being someone’s research saying that it will, though i don’t know if there is any studies that say that
Too many unmeasured exogenous intercorrelated variables and then there is the causality issue.
Malaga View says:
August 5, 2010 at 8:49 am
Malaga View says:
August 5, 2010 at 8:49 am
Basic logic error! The formula is:
dCO2(atm) = CO2(in1 + in2 + in3 + in4…) – CO2(out1 + out2 + out3 + out4…)
Where: in1, in2, in3, in4… ALL vary over time
The number of inputs may not have been fully defined
out1, out2, out3, out4… ALL vary over time
Yes, but if humans add 8 GtC per year as CO2 a year and we see only an increase of 4 GtC per year in the atmosphere, then all other flows together, whatever their variation within or over the years, must remove the difference. The variability of the natural removal rate is quite low: +/- 1 ppmv/year (or +/-2 GtC/year, about half the current emissions in year-by-year spread).
Response to: Why the CO2 increase is man made (part 1)
The linear increase of CO2 is your problem, or what is equilibrium, part II.
I object to some of the straight lines in fig. 3 In 1960 the annual increase of CO2 was around 1 ppm/y and the total amount of CO2 in the atmosphere was 315 ppm. Presently the increase is 2 ppm/y. Now, a total of 390 ppm CO2 is in the atmosphere, corresponding to 1000 Gigaton of Carbon. Presently, approx. 10 GtC fossil fuel are burned, which corresponds to 4.5 ppm/y when distributed fully into the atmosphere. In 1960 approx. 2 GtC of fossile fuel had been produced and burned, corresponding to roughly 1 ppm/y: This means, at that time basically all the CO2 remained in the atmosphere. Obviously, at that time, basically none of the CO2 has been sequestered elsewhere.
There is a very simple reason for that: the pre-industrial value of CO2 in the atmosphere had been 280 ppm. At that time, atmosphere and oceans have been in equilibrium concerning CO2 concentrations. (In the ice age with its lower temperatures, the equilibrium atmospheric concentration had been 200 ppm).
Around 1900, mankind started to burn fossile fuels in larger quantities. Atmospheric CO2 concentrations started to increase and to deviate from the equilibrium value. The simplest way to treat the deviation from equilibrium is to assume that the sequestering rate per year (into the oceans) is proportionate to the deviation from equilibrium in the atmosphere.
Now you can set up rate equations. With the simplifying assumption that the oceans, which contain a total of 40000 GtC of CO2, can take up eventually all extra CO2, you end up with a simple 1. order differential equation. You get the following results: Sequestering starts quadratically, not linearly, with deviation from equilibrium (as seen in the data). More importantly, eventually all emitted CO2 will be sequestered. This means that the atmospheric CO2 content gets saturated. Simple estimates give a saturation limit of approx. 450 to 480 ppm.
This can be seen quite easily: presently we have approx. 100 ppm excess CO2, and half of the presently emitted CO2 gets sequestered. with 200 ppm excess CO2, all of the then emitted CO2 gets sequestered. So the saturation limit is 280 + 200 = 480 ppm.
In this simplest of all models there is CO2 saturation in the atmosphere, there is no linear increase of CO2. IPCC keeps assuming a linear increase forever, models use 600 to 800 ppm CO2 for calculating warming in 2100. However, nobody bothers to argue why that simple model should fail.
A thought and questions –
What has changed in, say, the past thousand years? Look at human population, and we say, “Certainly! It’s Up!” Look at sea live, and we say, “Down Big Time?”
During a Glacial we have a rise in sea life and decline in land animals and plant types. During an Interglacial we have a decline in sea life and a rise in land mammals and vegetation? Has all this been adequately factored in to the math on CO2? Is the term Anthroprogenic appropriate, or is it better to say Zoologic (with a big chunk of manmade)?
jorgekafkazar says:
August 5, 2010 at 9:51 am
Peter says: “What I still don’t understand is that if the natural outflow is 4GT greater than the natural inflow, then how come atmospheric CO2 levels didn’t drop to virtually nothing after all the thousands of years before man started burning fossil fuels?”
They did, and they are.
Life forms have a nasty habit of being carbon based… they also have a nasty habit of dying and being buried in the ground… so overall biology can be seen as a carbon sink that accumulates in the ground.
CO2 levels have being dropping as life has evolved on earth… and they have been dropping towards dangerous levels in recent geologic times… luckily we have volcanoes, tectonic movements, natural gas, oil seeps and the WEATHER to naturally erode and re-cycle all that buried carbon… but best of all we have great big SUVs and AIRPLANES to so we can have fun while we help replenish the atmospheric CO2 levels which greens our planet and improves our harvests.
So adjust your lifestyle to address our CARBON challenged environment:
a) Get a bigger car and drive more.
b) Take more holidays abroad (and don’t forget to hire a car)
c) Rip out the central heating and put in a coal fire or wood burner.
d) Change you will to make sure you are cremated (so you don’t put your carbon in the ground)
ENJOY OUR GREENING PLANET – IT’S THE ONLY ONE WE’VE GOT!
It is indeed the case that some people still do not accept that the rise in atmospheric CO2 in recent times has been caused by human actions. The following (slightly edited) is a reply I made earlier this year to some such person after one of Christopher Booker’s articles in the UK Daily Telegraph:
“If you want to know how much humans have contributed to the increase in atmospheric CO2 you need to ask, “what would atmospheric CO2 levels be now in the absence of any influence from humans?” and compare that with present actual levels. Of course, we cannot be absolutely sure what the “natural” level would now be – the best we can do is to look at CO2 levels in the centuries and millennia before 1750 when human contributions were very small and extrapolate the graph to the present. Here, the evidence from ice cores shows that there was very little change in CO2 for several hundred years before the industrial revolution – the graph is flat. See, for example:
http://upload.wikimedia.org/wikipedia/commons/1/1c/Carbon_Dioxide_400kyr.png
Thus CO2 levels have not changed by more than a few ppmv of CO2 for several hundred years prior to 1750, and had not increased by as much as 20ppmv above the 1750 level of 280ppmv (ie exceeded 300ppmv) for at least 800,000 years. There is absolutely no reason to believe that levels should have suddenly shot upwards in recent times for any other reason than human action. Thus, from that reasoning, human activities can be safely said to account for all (or very nearly all) of the increase from 280ppmv in 1750 to 390ppmv now.
But, secondly, there is another way of understanding this claim:
If you wish to know if there has been any NET natural contribution to the increase in atmospheric CO2 levels, all you need to do is measure
1. the amount humans have ADDED to the atmosphere, and
2. the increase in CO2 in the atmosphere over the same period.
It is that simple.
The figures for the atmosphere from 1850-2000 are as follows:
1. Total human caused emissions of CO2: 1620 billion tons CO2
2. Increase in atmospheric CO2: 640 billion tons
Thus, the amount of CO2 humans have added to the atmosphere greatly exceeds the observed increase in CO2 in the atmosphere. Thus, the human contribution is more than able to account for the entire increase (most of the CO2 emitted by humans has been absorbed into the oceans and the terrestrial environment). The net flow has been from the atmosphere to the oceans, NOT from the oceans to the atmosphere.
Of course, the interesting question is for how much longer the oceans are going to behave as a net sink for CO2.
[If you want to check the figures go to the Carbon Dioxide Information Analysis Centre: http://cdiac.ornl.gov/faq.html#Q4 ]
Doug Proctor says:
August 5, 2010 at 8:50 am
The Barrow and the Mauna Loa CO2 concentrations drop between June and October, but do not in Antarctica. Is this reflecting the growing season in both a northern temperate forest and the oceanic phytoplancton?
Yes it is: the oceans have a larger capacity for changing the CO2 levels either way, but are relative slow emitters/absorbers, compared to the burst of greening in spring/summer of the mid-latitudes. That is a lot less in the SH, as there is less land and the ITCZ hinders the transport of air masses (including CO2, SO2, dust,…) between the NH and the SH.
That will be further explained in other parts…
Bill Toland says:
August 5, 2010 at 8:52 am
Why are the figures for the natural sinks so variable from year to year?
Mainly caused by temperature variations: some 4 ppmv/C (ocean) on short term. increasing to about 8 ppmv/C over long term. Several contributions here on WUWT have calculated the good correlation between temperature and the rate of increase (not the same as the cause of the increase itself!). From the “warmer” side, a good description is by Pieter Tans, who included precipitation in the equation:
http://esrl.noaa.gov/gmd/co2conference/pdfs/tans.pdf starts about half way the presentation.
Hi Ferdinand 🙂 Good to see you again in the debate!
1) In this little writing
http://hidethedecline.eu/pages/posts/co2-carbon-dioxide-concentration-history-of-71.php
– I have summarized some of the better pieces of evedence pointing to the “fact” that CO2 concentrations has fluctuated strongly earlier in the 20´ieth centure as well as in the stonage etc. This does not really support the idea that only humans can cause periods with larger CO2 concentrations?
2) Earlier i showed that Co2 concentration increase/year is smaller and smaller compared with global temperatures:
http://wattsupwiththat.com/2008/12/17/the-co2-temperature-link/
So even if humans did indeed cause significant contributions to CO2 concentrations, it appears that “something” (the biosphere) is rapidly on the way to omit the human effect.
As I remember in the debate we had back then, you said that the facts could be interpreted in both your and my way. Thus i think you should be open to my viewpoint as a real possibility.
3) Finally, with just a simple trend through CO2 measurements of the ocean, it appears that the CO2 content in upper layers of oceans are indeed not rising in the latest decade. yes, not many people mentions this, but i think its rather relevant to be aware in this contexts as in contradicts the great dominating human effect to some degree. Humans are still emitting CO2, but the big ocean buffer does not show increase of CO2 anymore…
http://hidethedecline.eu/pages/posts/co2-carbon-dioxide-concentration-in-the-oceans-72.php
– how does this affect your thoughts?
Again: good to see you again in the debate 🙂
K.R. Frank Lansner
I have always had in the back of my mind from way back (40+ years) that the levels of atmospheric CO2 show a dramatic decline at about the same time trees started to evolve and became a major part of the land environment. Both these events happened about 400-350 million years ago. Possibly co-incidence of course. Since then trees have been slowly killing themselves by sequestrating CO2, or at least reaching some sort of equilibrium with atmospheric CO2. Or was my biology teacher way off the mark?
So with de-forestation atmospheric CO2 can recover somewhat.
Ferdinand Engelbeen says:
August 5, 2010 at 10:25 am
Yes, but if humans add 8 GtC per year as CO2 a year and we see only an increase of 4 GtC per year in the atmosphere, then all other flows together, whatever their variation within or over the years, must remove the difference.
NO – you are not correct.
You have no idea what caused the observed increase and you have no idea whether your observed increase is correct.
Lets assume your formula is correct and your Carbon Cycle graphic is vaguely realistic
So the 5.5 “fossil fuels and cement production” (EM) in the graphic equals 8GtC.
Therefore, the ocean outgassing (OO) of 90 in the graphic equals roughly 131.
So lets retry your equation for ocean outgassing:
4 GtC = CO2(in1 + in2 + in3 +…) + 131 GtC – CO2(out1 + out2 + out3 +…)
See your problem?
CO2(in1 + in2 + in3 +…) – CO2(out1 + out2 + out3 +…) = -127
In fact it is a big problem for you!
Like I said:
Basic logic error!
The formula is:
dCO2(atm) = CO2(in1 + in2 + in3 + in4…) – CO2(out1 + out2 + out3 + out4…)
Peter says:
August 5, 2010 at 8:57 am
What I still don’t understand is that if the natural outflow is 4GT greater than the natural inflow, then how come atmospheric CO2 levels didn’t drop to virtually nothing after all the thousands of years before man started burning fossil fuels?
The simple answer is: if we stop all emissions today, next year the CO2 levels in the atmosphere indeed would drop with about 4 GtC (2 ppmv). But as the level in the oceans didn’t drop as fast, the pressure difference of CO2 in the atmosphere and the ocean surface drops a little, so that the second year, the drop isn’t 4 GtC but only 3.8 GtC,… and so on until we are back to around 300 ppmv in the atmosphere, which is the level which corresponds more or less with the current (ocean) temperature.
Reality is far more complicated, but in general, that is the trend…
Jim G says:
August 5, 2010 at 9:22 am
Models vs measurement again. This is a large planet and lord knows what CO2 might be spewing out in the 67% that is covered by water and I did not see any measurement devices in the plumes when Pinatubo or Mt St Helens went off.
No model at all in this case: fossil fuel sales inventory vs. measured CO2 increase in the atmosphere. Simple straight-forward calculation. And the Pinatubo emitted some more CO2, but also cooled the oceans by reflecting sunlight away, which caused more CO2 absorption and thus less CO2 increase than in warmer years…
Ferdinand Engelbeen says:
August 5, 2010 at 10:14 am
Robert of Ottawa says:
August 5, 2010 at 8:28 am
“I missed something here. Where did the 4GT/year come from?
The only accurate way would be to estimate it from the 2 ppm increase per year.
The 4 GtC is calculated as the increase in carbon mass of the atmosphere, while the 2 ppmv is CO2 in measured as volume procent of the atmosphere. These two are equivalent.”
Ok, so mass balance, I buy that. The 4GtC = 2ppmv I buy that. 2ppmv is the average increase/yr. I buy that. We know man’s emissions to a fairly accurate degree.(Even though I’m unclear about how we count agriculture and things of that nature and fauna breathing.) Even still, (and I hope you address this later) we know atmospheric CO2 with or without man’s emissions is not constant. For expedience, and since I’m not aware of anyone doubting the validity of such statements, http://en.wikipedia.org/wiki/File:Phanerozoic_Carbon_Dioxide.png .
Your equation 4 GtC = CO2(in1 + in2 + in3 +…) + 8 GtC – CO2(out1 + out2 + out3 +…) and correct me if I’m wrong. 8GtC is man’s emissions. So, without man’s emissions, as you stated, CO2(in1 + in2 + in3 +…) – CO2(out1 + out2 + out3 +…) = – 4 GtC
Doesn’t this eventually get us to a near zero ppmv atmospheric CO2. Is there any evidence that has ever happened? Doesn’t this indicate another mechanism in play? If I missed something in your presentation, feel free to point it out, if you’re going to present the answers later, feel free to ignore.
Thanks
richard says:
August 5, 2010 at 9:37 am
Ferdinand,
To take a (silly) example to make my point, imagine if 100% of human emission were from burning wood or, better, grass. This carbon would have been a natural outflow via decay except for the fact that we are burning it. In other words, one of the inflow terms decreased by our human emissions. In that situation, you cannot attribute the CO2 rise to our emissions.
In the case of burning more or less fast renewable sources of carbon, that doesn’t count as emissions, as that (as all human and animal food) was captured a few months to a few years before from the atmosphere. The impact of this on current CO2 levels is negligible. If you burn fossil fuels, burried in an atmosphere of many millions of years ago (at much higher CO2 levels), that makes a difference in the current atmosphere.
The border between “renewable” and not is not that clear: If you burn a 1,000 year old oak, that is assumed “renewable”, while burning peat of the same average age is “not renewable”…
If the increase is Anthropogenic and correct, has the biosphere already responded all it can to digest the extra C02?
One way in which man has made a lasting impact is with his paving/concreting to remove land from the biosphere’s growth balance. What percentage of land has been impacted by urban land smothering?
So, between the extra C02 calcualted to have been placed into the food chain and the land smothered by asphalt/concrete/buildings, have we increased or decreased the biosphere’s throughput?
indeed near the full increase of CO2 in the atmosphere is caused by the human emissions. Only a small part might have been added by the (ocean) warming since the LIA.
People need to study this:
Volcanic Gases and Their Effects
http://volcanoes.usgs.gov/hazards/
gas/index.php
The numbers and volume of eruptions have increased a lot since 1998, you can type in the years and look for yourself. Eruption volume has gone up and down throughout history.
http://www.volcano.si.edu/world/find_eruptions.cfm
Eyjafjallajökull was recently pumping out the equivalent weight of 100+ to 200, 2,000 lb F-150 pickup trucks a second in eruption volume for a very long time.
I see you answered part of my questions with a response to another person. Thanks, but if…………………… “The simple answer is: if we stop all emissions today, next year the CO2 levels in the atmosphere indeed would drop with about 4 GtC (2 ppmv). But as the level in the oceans didn’t drop as fast, the pressure difference of CO2 in the atmosphere and the ocean surface drops a little, so that the second year, the drop isn’t 4 GtC but only 3.8 GtC,… and so on until we are back to around 300 ppmv in the atmosphere, which is the level which corresponds more or less with the current (ocean) temperature.”…..is true then how did we get to 2000 ppmv CO2 100 million years ago?
One factor missing from figure 1 ( by NASA,) is volcanic activity. As Ian Plimer points out in his book Heaven and Earth, 80% of volcanic activity on Earth occurs on ocean floors, at mid-oceanic ridges and subduction zones. The CO2 released by this under water volcanic activity will be absorbed by cold water ( 4C) which is under pressure, so can hold a LOT of CO2. The “conveyor belt” system of ocean currents will eventually
( decades? centuries?) later bring this CO2 rich water to the surface, where, as it warms and the pressure decreases, it will release CO2 into the atmosphere. Is there any way to differentiate this CO2 from that produced by humans burning fossil fuels? For a dramatic example of cold, CO2 rich water suddenly deffervescing, do a Google search on Lake Nyos.