Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


The Global Carbon Cycle by David Archer—a review

Posted on 15 February 2011 by Andy Skuce

"The climate system is an angry beast and we are poking it with sticks" - Wallace Broecker

The belly of Broecker’s climate beast is surely the global carbon cycle. Currently, the beast is digesting about half of our fossil-fuel CO2 emissions, acting as a major stabilizing influence on the climate, a negative feedback. But as Professor David Archer warns us in his latest book, The Global Carbon Cycle, the carbon cycle behaves unpredictably in different circumstances and over different timescales. For example, during the Paleocene-Eocene Thermal Maximum (PETM), it acted to bring things back to the then hothouse normal after a massive belch of carbon into the atmosphere.  At other times, it amplified small temperature perturbations into climate events that changed the face of the planet, as it did in the ice age cycles, the period we are still currently in.  Humans are administering a perhaps PETM-scale dose of carbon into the atmosphere during a time when the global carbon cycle has acted as an amplifier rather than a damper. Ominously, Archer tells us, the planet’s reservoirs of carbon in the form of peat, gas hydrates and rain-forest carbon are now probably as charged up as they can be. That's some beast; some stick.

A continuing negative feedback carbon cycle response, in conjunction with restraint on human emissions, plus some luck with experiencing the lower ranges of climate sensitivity, could lead to climate change of, let’s say, 2°C. A future strong positive feedback from the carbon cycle, on the other hand, could add as much CO2 to the atmosphere as humans have, leading to temperature increases well beyond the International Panel on Climate Change’s (IPCC) upper limits. (The models used in the IPCC projections don’t generally deal with slow feedbacks from the carbon cycle— they are considered too uncertain to quantify.) Therefore, subject both to our own choices and equally to the whims of the global carbon cycle, the effect of climate change on our civilization could range from merely disruptive to unendurable.  Quite obviously, biogeochemistry is a subject we should pay attention to.

The Primer

Archer’s book is the first of eight planned books in the Princeton Primers in Climate series.  These short books are aimed at “students, researchers and scientifically minded general readers”.  The publisher offers a free download of the first chapter of The Global Carbon Cycle here

David Archer is one of the best writers on climate science. His introductory textbook Global Warming: Understanding the Forecast is a lucid introduction to the physics and chemistry of climate science.  His subsequent book The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate—it covers some of the same ground as The Global Carbon Cycle—was written with the general reader in mind and is probably the best book of the three to start with for those new to the subject. Archer writes clearly, using quirky metaphors and a lively style that is entertaining as well as instructive.  

The Global Carbon Cycle contains some twenty-two “Boxes” that delve more deeply into specific background topics. Some of these boxes are more than six pages long and tend to disrupt the flow of the main text. They are essential reading, however.  Many of the boxes explain aspects of the complicated chemistry of the carbon cycle. For those of us whose last chemistry lesson is but a dim memory and whose knowledge of pH systems and redox reactions is, well, basic and rusty, fully understanding all of this can be a struggle. The box on "The Carbon Cycle Orrery" is particularly helpful, providing an imagined physical model of vessels and interconnecting tubes that helps the learner visualize how the moving parts of the the marine carbon cycle work together.

The main shortcoming of the book is in the quantity and quality of most of the graphics. Many are taken directly from other publications and have inadequate captions or explanations in the accompanying text (an exception is Figure 10, an artist's conception of the carbon cycle orrery). For example, his Figure 7 is taken from a Nature Geoscience paper by Le Quere (2009)—more correctly, Le Quéré et al. (2009)—in which Figure 7A  shows indistinguishable lines relating to IPCC scenarios and Figure 7B refers to “Annex-B” and “non-Annex B” emissions histories, which, Google tells us, is a Kyoto Protocol definition. There are also some minor errors in the labelling of the y-axes in Figure 3, which, incidentally, is the same graph shown in Figure 12 in The Long Thaw, where it is correctly labelled. 

One of the best features of the book is that Archer is very straightforward in detailing many of the unsolved scientific problems relating to the carbon cycle.  I offer brief summaries of some of them below.

Unsolved mysteries

It’s astonishing to step back and contemplate how much has been learned about the Earth’s past. There are some detailed pages of information that have been meticulously reconstructed after having passed through the cross-cut shredder of geological history: the information from ice cores and the deep sea sediment cores are obvious examples. Yet, there are important chapters missing and many pages are only partly legible. Mysteries remain and here’s a sketch of Archer’s account of some of them.

  • The source of the PETM carbon “burp”. We know that the carbon was isotopically light, meaning that it came from an organic source rather than from calcium carbonate. The usual prime suspect is methane hydrate, released from deep ocean sediments. However, the biogenic methane in the hydrates is very isotopically light, meaning that the amount needed to explain the lightening of the carbon in the atmosphere would have been too little to have caused the inferred temperature change of 5°C. So, we have insufficient evidence to pin this event on hydrates, unless they had an accomplice, perhaps in the form of much higher climate sensitivity in the early Eocene hothouse than today.
  • The carbon feedbacks of the unstable ice age cycles. We know that the triggers for the glacial events were the orbital variations known as Milankovitch cycles, which caused small variations in temperatures in high, northern latitudes. The temperature changes which were then amplified by the carbon cycle, with more CO2 released from the atmosphere during the warming phase and more removed as things cooled. The isotope record shows that the biosphere contains less carbon during the cold times than during the hot times, thus the biosphere acted as negative feedback during the ice age cycles, an innocent bystander. Those of us who have observed that a warm beer loses more of its fizz than a cold one may be tempted to believe that the CO2/water temperature/solubility relationship is sufficient to explain the glacial era feedbacks. However, the physical chemistry is well enough understood that this effect only explains about one third of the feedback mystery.  Among the many additional suspects is the “biological pump”, whereby chemically fertilized plankton bloom, die and their carbon sinks to the ocean bottom.  It seems that the ice-age feedbacks were not caused by an agent acting alone but were instead the result of a conspiracy of multiple actors.
  • The missing sink.  Since 1935, the terrestrial biosphere has been taking up carbon at a rate of more than 1Gton per year: see the figure below from Tans (2009). But we don’t know for sure where all this carbon has gone. To give us a feel for what this large number means, Archer tells us that the (literal) mass of humanity (everything, not just our carbon) is about 0.5Gton. So, every year, Mother Nature is burying the equivalent an awful lot of bodies somewhere, most likely in the high northern latitudes.  The probable mechanisms include: increased plant growth in the tundra due to the warming climate; reforestation; and fertilisation by increased CO2 in the air or the nitrate in acid rain.

This is a brief and partial outline of just some of the topics covered in The Global Carbon Cycle.  Read the book to get a complete account.

Tans (2009)

Spoiler alert

Even though David Archer has written a book full of mysteries, there is, alas, no final scene where a Miss Marple figure assembles all the suspects in the drawing room, dispatches all the red herrings and finally unmasks the perpetrator: It was you, Professor Milankovitch, on the Continental Slope, with the Clathrate Gun!  So, I can safely quote the last chapter in full without spoiling the story.

"It is premature even to attempt to guess how strong the overall carbon cycle feedback on climate change might be, but my hunch is that, in the worst case scenario, the carbon cycle feedback might eventually release as much CO2 as humans do, a sort of “matching funds” arrangement. If the carbon cycle feedbacks in general were much stronger than that, the climate system would be so unstable it would have melted down in the geologic past more frequently than it apparently has. But Earth’s biosphere and carbon cycle are vastly more creative than human imagination is able to anticipate, so don’t take my word for any of this. We’ll have to wait and see." 

0 0

Printable Version  |  Link to this page


Comments 1 to 10:

  1. I am reading this book at the moment, the main problem I have with it is that the boxes (which house various digression) are rather distracting (works well in a magazine with large pages, but no so well in a standard paperback). The content is excellent though, I'd certainly recommend it to anyone wanting to know a bit more about the carbon cycle.
    0 0
  2. Nice review, Andy. I will second the book recommendation. I often think that organizing a high-school or first-year university science curriculum around a parallel track studying the carbon cycle (and maybe other biogeochemical cycles) would be an effective teaching tool, because the latter inevitably intersects with biochemistry, paleontology, geology, fossil fuels, marine chemistry, and on and on. In that vein, I also rather liked Tyler Volk's "CO2 Rising" and Eric Roston's "The Carbon Age". Regarding the mystery of the terrestrial biosphere's "missing sink". You might enjoy this recent video of a seminar at Stanford with Stephen Pacala. Specifically the first 3:40 and then from 8:20 to 34:50. He references upcoming work from Oliver Phillips, Stefan Gerber and others, which seems to suggest that much of the missing sink may have been identified: it/has been in the tropical forests, and CO2 fertilization is the key driver. (Interestingly, he makes the point that tropical forests are not limited by nitrogen fixation to the same degree as temperate and boreal forests so that would at least help explain why would see the CO2 fertilization effects in some forests but not others.) If this is true, then, in a way, that would be an interesting and encouraging result. If CO2 fertilization were the driver, it would have the potential to scale up with atmospheric concentrations, whereas if the "missing sink" were due to things like secondary forest regrowth it would just be one-time bumps. But if one then considers the 2005 and 2010 droughts in the Amazon, it is somewhat disconcerting, because this sink could quickly reverse! Of course, these are new - and therefore, preliminary results - which circles back to Archer's point of how much more there is to learn. But it's fascinating watching the carbon cycle mysteries as they are being investigated and resolved.
    0 0
  3. I also liked Archer's book quite a bit, although, like others here, I wasn't thrilled with the illos or the long sidebars (those boxed pieces of text). There's no excuse for the former, but the latter is really tough to get around because of the nature of the material. Sequester that material (pun intended) into appendices, for example, and few people will read it. Leave it in place and you wind up with the problem of forcing the reader to make a lot of side-trips in his or her journey through the book. On the issue of the PETM burp, I have to wonder if we're approaching a realization that aerosols have a higher cooling effect than expected. Notice in the current IPCC report that the error bars on aerosol cooling are quite large. Low aerosols in the PETM (no one was burning coal) means more warming from a given CO2 content. For us, here in bright and shiny 2011, that's exceedingly bad news because one area where we seem to be making progress on the environmental front is reducing those aerosol emissions from coal plants in the US, EU, and China. If we wind up exposing a lot more warming effect than expected, the "aerosol whiplash" effect could be a very nasty surprise.
    0 0
  4. I recently finished viewing his class lectures (23) from PHSC 13400, Global Warming for non-science majors, Fall, 2009. Its a good primer for understanding Earth's heat balance and how the planet is warming as well as the acidification of the oceans. The lectures can be found here.
    0 0
  5. I am concerned that his final summary, "Wait and see" sounds too much like exactly what the 'deniers' want us to do: rather than act on reducing carbon, they want us to "wait and see" if the carbon cycle can automagically recover from the shock we are giving it.
    0 0
  6. RickG@4 I second that recommendation, I've only seen the first four so far, but they were well worth watching - definitely time well spent.
    0 0
  7. MattJ@5 That's a good point. It's easy to become fatalistic about the response of the carbon cycle to global warming. After all, we can't refrigerate the permafrost and we don't have a control knob to regulate rainfall patterns in the tropics. We can, however, do some things like stopping deforestation and draining wetlands (see here). Most of all, we can, of course, reduce the chances and the severity of future carbon cycle feedbacks by limiting our CO2 emissions now. It should be remembered that David Archer's final paragraph is a description of what is not what should be. He wrote a science book. But the uncertainty that is so thoroughly described within it shouldn't provide comfort for anybody. As The Economist wrote about a year ago: Action on climate is justified, not because the science is certain, but precisely because it is not.
    0 0
  8. Andy S @ 7, What actions are feasible and effective? Not broad strokes, but please be more specific. Thanks
    0 0
  9. Marvin Gardens@8 I assume that you mean actions to avert climate change, since I just said that our options to directly prevent major carbon cycle feedbacks are limited. I'm no policy wonk, and this is off topic, but here goes anyway: I would start with an escalating revenue-neutral carbon tax, see here. But I don't think that's sufficient, just a good start. I believe that there will also have to be state subsidies to improve electricity grids, as well as to support alternative energy sources such as nuclear power and mitigation strategies such as carbon capture and storage, controversial and problematic though both of those approaches are. I think that we should start negotiating international protocols on the possible use of geo-engineering technologies should the very worst outcomes start to unfold. To be sure, all those actions are politically very difficult to implement and their effectiveness is uncertain. Somebody once said that lost causes are the only ones worth fighting for. Perhaps we should continue discussion of this on another thread; maybe our diligent moderators could suggest a suitable one.
    0 0
  10. "We’ll have to wait and see.", like "youll see what happens when youre dead."
    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us