Global Warming, The Carbon Cycle, and Fish Poop.

When we talk about the role of fossil fuels in climate chance, what we're really talking about is the carbon cycle. That's the term that scientists use to describe the different forms that carbon is stored in on the earth, and the different ways that it can move from form to form. Understanding the carbon cycle is one of the keys to understanding both the effect of burning carbon-based fuels and the issues involved in trying to take carbon dioxide out of the atmosphere. According to a paper in the latest edition of Science, there may still be some pretty significant gaps in our knowledge of the carbon cycle. In particular, it looks like our understanding of the way carbon moves through the oceans may have been suffering because we didn't know poop about fish poop.

Before we get down to the gritty details and talk about what poop has to do with anything, it might be good to start with a quick review of the carbon cycle. Actually, it might be even better to start with a quick review of one of those concepts that we all learn in third-grade physics, but don't think about much in our day to day world: the law of conservation of mass/matter.

Matter is not created or destroyed. Therefore the amount of mass in a closed system will remain constant no matter what happens.

Like most things in science, that might be a bit of a simplification, but when we're looking at something the size of the Earth, it's good enough. Relativity, quantum mechanics, and space dust might all complicate things a bit, but not enough to matter. For our purposes, we can reasonably assume that all the carbon that we're putting into the atmosphere in the form of carbon dioxide has been here since the earth was formed, and that if we want to take the carbon dioxide back out of the atmosphere, we're going to have to find somewhere on this planet to store the carbon.

With that in mind, let's look at the some of the more important ways that carbon can move through the crust, oceans, and biosphere, and atmosphere.

Carbon Cycle-Cute Diagram.Jpeg

Source: NASA via Wikimedia.

Carbon can be found in the atmosphere in a few forms, the most important of which is carbon dioxide. It can be found on land and in the crust in any number of forms, both as organic compounds in living organisms and their remains (including the range of fossil fuels) and in rocks and soils as inorganic minerals like calcium carbonate. It can be found in the oceans as dissolved carbon dioxide, dissolved minerals, and in organisms that live in the oceans.

Carbon can be released into the atmosphere in a number of different ways. Carbonate rocks, for example, can produce carbon dioxide through natural weathering processes, and volcanoes can release carbon dioxide from magmas. At this point in the history of the earth, though, we know what the biggest cause of carbon dioxide entering the atmosphere is - and he is us.

It's possible that our entire success as a species has been the result of our learning how to use a particular chemical reaction:

Organic carbon + Oxygen = Carbon Dioxide + Water + Energy

For most of human history, we were mostly burning plant matter in relatively small quantities, so this wasn't a huge deal. The organic carbon in question had mostly come from photosynthesis, and most of it would have been released as carbon dioxide anyway - we use, along with lots of other living things, use that same chemical reaction when we produce our own energy.

The Industrial Revolution changed that. We started to burn fossil fuels - coal, petroleum products, and natural gas. The carbon that's in the fossil fuels comes from the remains of plants that pulled it out of the atmosphere and fixed it as organic compounds. Most plants, when they die, decompose and their carbon is released back into the atmosphere. The same thing happens to most animals. But not all. Some living things get fossilized after they die.

The thing is, we don't have lots of fossil fuel because lots of things get turned into fossils all the time. We have lots of fossil fuel because there's been a lot of time for things to get turned into fossil fuels. These are deposits of carbon that were formed very slowly, over tens and hundreds of millions of years. Left to themselves, these deposits would have been released back into the atmosphere through weathering and other natural processes over similarly long periods of time. We're taking these deposits that were formed over intervals of tens and hundreds of millions of years, and we're burning them over periods of tens to hundreds of years.

If you think that we're not pumping fossil-fuel derived carbon dioxide into the atmosphere millions of times faster than it would get there on its own, I'd suggest that you go back and look at the two bits of boldfaced text earlier in this article.

The increase in carbon dioxide in the atmosphere is leading to an increase in the amount of heat that we're retaining from the sun because carbon dioxide is a greenhouse gas - it traps energy that would otherwise have radiated out into space.

Now that we've figured out that this is a real problem - the odd conservative ideologue notwithstanding - we've started to try and find ways to fix the problem, while still producing enough energy to drive our modern world. A wide variety of solutions have been proposed, many of which involve continuing to burn fossil fuels, but trapping and storing the carbon dioxide that's produced. In fact, there's a coal plant in Germany that's started doing just that.

The German plant is storing (or at least planing to store) the carbon dioxide by injecting it into a depleted oil field, but another storage site that's frequently proposed is the deep ocean. At depth, the ocean is undersaturated with respect to carbon dioxide, which is a fancy way of saying that it can hold more than it currently does. That means, it's been suggested, that we can take the carbon dioxide from fossil fuel combustion and pump it down into the deep ocean through really long pipes.

And this, finally, brings us to the gut of the matter. And to fish poop.

The I haven't talked about it much yet, but the ocean is involved in the carbon cycle. Things like the depth at which the ocean is no longer carbon-dioxide saturated are determined by the chemistry of the ocean, and by the way carbon moves through the seas. An article that was just published in the journal Science by Wilson et al. suggests that we may not have known as much about the oceanic carbon cycle as we thought we did.

In particular, we might not have considered the impact that billions of fish can have, just by living, drinking, and pooping.

You see, the internal environment of a fish contains a higher concentration of water (and lower concentration of salt) than the ocean does. As we all learned at some point in school, this means that water is going to tend to move from the fish back into the ocean. This is the same process that's in play when salt is poured on a slug, and even in the ocean the effects would be similar if the fish weren't able to somehow counteract it.

Fish counteract the tendency of water to leave their body by actively pulling more water in. Fish drink like fish. But, because they're drinking saltwater, they need to do something to pull out the salts. In the case of the calcium and magnesium, they precipitate it out in their guts by forming inorganic calcium and magnesium carbonate crystals. What happens to these "piscine carbonates" is entirely predictable, as Wilson et al. point out:

Carbonate precipitates formed in the gut are excreted either within discrete mucus-coated tubes or pellets, or incorporated with feces when fish are feeding. The organic mucus-matrix is rapidly degraded in natural seawater, leaving only inorganic crystals of CaCO3 with high magnesium content (Mg:Ca ratio ranging from 10 to 33 mol %)

[endnotes omitted]

The importance of this effect is a bit less obvious. There's a lot less fish than plankton, after all, so how important is it really likely to be? The answer is a bit surprising. The authors did a range of calculations based on a number of different estimates of both fish biomass and the rate of production of "piscine carbonates":

To calculate the teleostean contribution to oceanic carbonate budgets requires knowledge of global marine fish biomass. We used two entirely independent models to describe the size composition and abundance of marine fish across the global oceans, one by using a size-based macro-ecological approach and the other by using Ecopath software. The fish biomass estimates generated for each size-class and the relevant average local sea temperatures were then combined with individual fish carbonate excretion rates to predict global fish CaCO3 production ranging from 3.2 x 1012 to 8.9 x 1012 mol year-1 (0.04 to 0.11 Pg of CaCO3-C year-1). This range accounts for 2.7 to 15.4% of estimates for total global new CaCO3 production in the surface oceans.

[endnotes omitted]

In simple terms, the authors of the paper have just informed us that we may not have noticed a process that's responsible for a substantial amount of the carbon movement in the oceans. That's kind of a big deal (which would explain the Science article).

The effect that climate change is going to have on this particular form of carbon movement is not entirely clear (at least to me), nor is the effect that this might have on climate change. "Not none" is probably a reasonable guess, and I'm sure that we'll learn more in the future.

What is clear is that this shows us something that we would be advised to remember when we start to talk about things like pumping a gajillion tons of CO2 into the oceans:

Do we really want to take chances messing around with things that we might not know piscine carbonates about?


R. W. Wilson, F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, M. Grosell (2009). Contribution of Fish to the Marine Inorganic Carbon Cycle Science, 323 (5912), 359-362 DOI: 10.1126/science.1157972

23 responses so far

  • Fischer says:

    I wonder how the carbonate compensation depth comes into this. From a chemist's point of view, carbon sequestration in the abyssal will lower the CCD considerably, thus facilitate deposition of carbonates that would otherwise remain dissolved.
    Any thoughts on this?

  • Mike says:

    Is there any scientific evidence, other then Pogo, that the increase CO2 in the atmosphere is primarily anthropogenic?

  • bigTom says:

    The article (or at least the sciencedaily review) seemed to claim that this would reduce the acidification process (because the carbonates were expected to dissolve). Now my uneducated reaction is, there is no net effect, seawater in, seawater out( after the calcium poop dissolves). Am I missing something? Is there such a thing as conservation of acidity/alkalinity (it may be a figment of my imagination)? If the carbonates sank into the deep ocean or to the sea floor, carbon would be sequestered in deep water or sediments, but this was NOT what the article claimed.
    As for your bottom line about not messing with the ocean. Your graphic shows the current deepocean inventory as an order of magnitude greater than the total carbon available via fossil fuels. If we pumped all this carbon into the deepsea it would raise the total by ten percent. That doesn't sound like a big change to me. Especially, if we restrict fossil fuel consumption to a small fraction of its potential, or only use deepsea sequestration for a small percentage of fossil carbon burnt. Of course that assumes the anthropogenic stuff is well mixed.

  • Mark says:

    Information on Carbon Sequestration from Geotimes in March of 2003.

  • Bob Burk says:

    When will NASA's James Hansen release the code for GISS for peer review?

  • James says:

    Mike (#2): There's lots of scientific evidence. The complicated stuff uses things like isotope ratios. You can look it up if you're interested. However, there's a really simple way that just takes a bit of web searching, plus some basic math and elementary chemistry. What you do is a search on the amount of coal & oil produced each year (references like the CIA Factbook have this). Use simple chemistry to figure out how much CO2 is produced by burning the coal & oil, then math will tell you how much the atmospheric concentration would increase. Compare that number to the measured increase, and see how well they match.
    And match they do: in fact, the amount of CO2 produced is rather more than enough, because some gets dissolved in the oceans. But when you have an observed CO2 increase of X amount, and humans burn fossil fuels enough to emit that amount, it takes a special kind of mind to suggest that there's no connection.

  • Lee says:

    Q: "Is there any scientific evidence, other then Pogo, that the increase CO2 in the atmosphere is primarily anthropogenic?
    Posted by: Mike | January 16, 2009 2:23 PM "
    A: Yes.

  • Mike says:

    >Mike (#2): There's lots of scientific evidence. The complicated stuff uses things like isotope ratios. You can look it up if you're interested. However, there's a really simple way that just takes a bit of web searching, plus some basic math and elementary chemistry.
    Thanks Mike#2. here's what I found on the web:
    Atmospheric CO2 Increase Varies by 100% Year to Year
    If natural CO2 emissions and sinks were in balance, then the increase in atmospheric concentrations should be more in line with emmisions. This does not seem to be the case.

  • Mrs. W says:

    I've always found this site useful in talking to climate change skeptic. It covers most of the major arguments presented to disprove climate change and debunks them: How to talk to a climate change skeptic: a guide

  • Kelly says:

    I'm wondering if the collapse of so many commercial fisheries figures into this process. Do other less tasty species (jellies?) exploit the gaps we're creating leaving no net impact or are we disabling a natural carbon process that will be another positive feedback?

  • Outeast says:

    Mike, just a hint: taking your data from cdesign proponentsists website is unlikely to win you anything other than troll status on science blogs.

  • Charles S says:

    I'm not sure what point you think you are making. Why do you think that natural sinks and sources for CO2 should be in static balance? Consider what happens during a season of massive forest fires, or during the eruption of a volcano. Both of these are natural sources for CO2, so we should expect to see the non-anthropogenic CO2 concentration increase. We would then expect that increased CO2 to gradually get pulled out of the atmosphere. Likewise, the ENSO cycle (specifically mentioned in the caption to the chart you were looking at) involves multi-year cycles of increasing and decreasing phytoplankton blooms. During a massive bloom of phytoplankton all along the Chilean coast, large quantities of CO2 get bound as organic carbon, some substantial portion of which gets settled out to the sea floor or bound up in increased fish biomass. This causes a drop in the non-anthropogenic CO2 concentration, followed by a gradual increase as organic matter decays and releases CO2.
    The non-anthropogenic CO2 concentration is not perfectly stable, and there is no reason to think that it would be. That is not an argument against the fact that humans are producing massive amounts of CO2 on top of the existing non-anthropogenic CO2 cycle (no one disputes this point, right? you aren't in denial on what happens when you burn coal or gasoline, right?), and that the non-anthropogenic CO2 cycle is not capable of absorbing all of that additional CO2 as quickly as we are generating it (as shown by the fact that CO2 levels are rising). The graph you pointed to is evidence that we are producing CO2 and that that additional CO2 is causing global CO2 levels to rise. In order to deny that anthropogenic CO2 is causing the rising CO2 levels, you would have to claim that something is absorbing all of the anthropogenic CO2, while something entirely unrelated is emitting non-anthropogenic CO2 at a rate that happens to mimic the anthropogenic CO2 contribution. The burden of proof falls to anyone who wishes to support such a dubious claim, not to those of us who doubt it. There is no evidence for the coincidence theory that I know of, so we are left with the anthropogenic CO2 drives CO2 increase theory, for which there is plenty of evidence.

  • Al Gore has predicted that global warming will result in the northern polar ice cap being gone in five years. View the vid, tell your friends, and don't let anyone forget. Gore has started his credibility countdown timer ticking and he must be forced to admit he was wrong once the time has passed.
    Click on the pic of Big Al holding up five fingers.

  • Hugo F. Franzen says:

    From some of the comments it seems to me that there are many who do not understand that we currently produce 28 billion metric tons of carbon dioxide through the worldwide combustion of fossil fuels (e.g. ignoring other sources such as CaO production) while the Keeling curve shows that the rate at which carbon dioxide is increasiong in the atmosphere, including all sources and sinks, is 13.6 billion metric tons. That is, the rate of production of carbon dioxide by humans is moethan twice the rate of increase of carbon dioxide in the atmosphere and there is therefore not the shadow of a doubt that athropogenic carbon dioxide is causing the observed ppm increase.

  • pmont says:

    Hahaha. People who understand science discuss chemistry and physics and other scientific explanations of the human impact on the carbon cycle and global warming, and people who don't understand science reference the Hooterville Gazette. Hahaha.

  • Mike says:

    >Mike, just a hint: taking your data from cdesign proponentsists website is unlikely to win you anything other than troll status on science blogs.
    Does this mean that questioning assumptions and open debate are not acceptable on science blogs?

  • trent142 says:

    At December's U.N. Global Warming conference in Poznan, Poland, 650 of the world's top climatologists stood up and said man-made global warming is a media generated myth without basis. Said climatologist Dr. David Gee, Chairman of the International Geological Congress, "For how many years must the planet cool before we begin to understand that the planet is not warming?"
    I asked myself, why would such obviously smart guy say such a ridiculous thing? But it turns out he's right.
    The earth's temperature peaked in 1998. It's been falling ever since; it dropped dramatically in 2007 and got worse in 2008, when temperatures touched 1980 levels.
    Meanwhile, the University of Illinois' Arctic Climate Research Center released conclusive satellite photos showing that Arctic ice is back to 1979 levels. What's more, measurements of Antarctic ice now show that its accumulation is up 5 percent since 1980.
    In other words, during what was supposed to be massive global warming, the biggest chunks of ice on earth grew larger.

  • Tony S. says:

    Dr. Kunihiko, Chancellor of Japan's Institute of Science and Technology said this: "CO2 emissions make absolutely no difference one way or the other ... every scientist knows this, but it doesn't pay to say so." Now why would a learned man say such a crazy thing?
    This is where the looney left gets lost. Their mantra is atmospheric CO2 levels are escalating and this is unquestionably causing earth's temperature rise. But ask yourself -- if global temperatures are experiencing the biggest sustained drop in decades, while CO2 levels continue to rise -- how can it be true?
    Ironically, in spite of being shown false, we must now pray for it. Because a massive study, just released by the Russian Government, contains overwhelming evidence that earth is on the verge of another Ice Age.
    Based on core samples from Russia's Vostok Station in Antarctica, we now know earth's atmosphere and temperature for the last 420,000 years. This evidence suggests that the 12,000 years of warmth we call the Holocene period is over.
    Apparently, we're headed into an ice age of about 100,000 years -- give or take. As for CO2 levels, core samples show conclusively they follow the earth's temperature rise, not lead it.
    It turns out CO2 fluctuations follow the change in sea temperature. As water temperatures rise, oceans release additional dissolved CO2 -- like opening a warm brewsky.

  • B Bouwhuis says:

    Hm. So here is the question the rest of us have to ask ourselves: are trent142 and Tony S. the same person, none other than John Tomlinson (the original author of the material posted by both trent142 and Tony S.); or are trent142 and Tony S. simply copying the work of Mr. Tomlinson?

  • B Bouwhuis says:

    I forgot to include this: a rebuttal to the Tomlinson/trent142/Tony S. responses above, the author of which is at least as credible as Mr. Tomlinson on this subject.

  • Bryan says:

    I'd just like to point out that the diagram is clearly biased. It has the burning of fossil fuels as an example of CO2 emission into the atmosphere when a much more representative illustration would be a volcano, for example. Fossil fuels are a marginal source of atmospheric CO2 compared to volcanoes.
    Also, isn't the term "science blog" a bit of an oxymoron?

  • Michael Ralston says:

    Mike: Questioning assumptions is acceptable.
    Citing known, deliberate, and repeated liars is not.
    Uncommon Descent are the latter. Citing them absolutely destroys your credibility here. Either you didn't know they were liars, in which case you've clearly not done much research, or you yourself are a liar - in which case we have no reason to listen to you.
    As for actual fact-based rebuttals, Hugo and Charles already covered that, so I'll just point out that there's really no rebuttal I can even envision to what they said.

  • Wow. Hi Mike Dunford... I came to your blog because I was looking for more on Wilson's research, and was amazed to see your comment thread. There is a serious problem with basic science literacy when anything related to climate is mentioned; people can't resist adding all kinds of nonsense.
    Just to correct one in the flood: Bryan, at #21, you have it backwards. The carbon from volcanoes is negligible by comparison with fossil fuel use. You've been listening to Plimer or some other such nut.
    See this USGS page on volcanoes and their emissions
    The annual CO2 emission from volcanoes is listed there are from 130-230 million tonnes CO2. That would be about 0.04 Gt carbon; not enough to even show up on the diagram used in this blog, and less than 1% of what you get from fossil fuel emissions.
    I'm late to the party, Mike Dunford, but I saw this and decided it was worth leaving a correction. Keep up the good work.