RealClimate logo

CO2 equivalents

Filed under: — gavin @ 11 October 2007

There was a minor kerfuffle in recent days over claims by Tim Flannery (author of “The Weather Makers”) that new information from the upcoming IPCC synthesis report will show that we have reached 455 ppmv CO2_equivalent 10 years ahead of schedule, with predictable implications. This is confused and incorrect, but the definitions of CO2_e, why one would use it and what the relevant level is, are all highly uncertain in many peoples’ minds. So here is a quick rundown.

Definition: The CO2_equivalent level is the amount of CO2 that would be required to give the same global mean radiative forcing as the sum of a basket of other forcings. This is a way to include the effects of CH4 and N2O etc. in a simple way, particularly for people doing future impacts or cost-benefit analysis. The equivalent amount is calculated using the IPCC formula for CO2 forcing:

Total Forcing = 5.35 log(CO2_e/CO2_orig)

where CO2_orig is the 1750 concentration (278 ppmv).

Usage: There are two main ways it is used. Firstly, it is often used to group together all the forcings from the Kyoto greenhouse gases (CO2, CH4, N2O and CFCs), and secondly to group together all forcings (including ozone, sulphate aerosols, black carbon etc.). The first is simply a convenience, but the second is what matters to the planet. Many stabilisation scenarios, such as are being discussed in UNFCCC negotiations are based on stabilising total CO2_e at 450, 550 or 750 ppmv.

Magnitude The values of CO2_e (Kyoto) and CO2_e (Total) can be calculated from Figure 2.21 and Table 2.12 in the IPCC WG1 Chapter 2. The forcing for CO2, CH4 (including indirect effects), N2O and CFCs is 1.66+0.48+0.07+0.16+0.34=2.71 W/m2 (with around 0.3 W/m2 uncertainty). Using the formula above, that gives CO2_e (Kyoto) = 460 ppmv. However, including all the forcings (some of which are negative), you get a net forcing of around 1.6 W/m2, and a CO2_e (Total) of 375 ppmv with quite a wide error bar. This is, coincidently, close to the actual CO2 level.

Implications The important number is CO2_e (Total) which is around 375 ppmv. Stabilisation scenarios of 450 ppmv or 550 ppmv are therefore still within reach. Claims that we have passed the first target are simply incorrect, however, that is not to say they are easily achievable. It is even more of a stretch to state that we have all of a sudden gone past the ‘dangerous’ level. It is still not clear what that level is, but if you take a conventional 450 ppmv CO2_e value (which will lead to a net equilibrium warming of ~ 2 deg C above pre-industrial levels), we are still a number of years from that, and we have (probably) not yet committed ourselves to reaching it.

Finally, the IPCC synthesis report is simply a concise summary of the three separate reports that have already come out. It therefore can’t be significantly different from what is already available. But this is another example where people are quoting from draft reports that they have neither properly read nor understood and for which better informed opinion is not immediately available. I wish journalists and editors would resist the temptation to jump on leaks like this (though I know it’s hard). The situation is confusing enough without adding to it unintentionally.

193 Responses to “CO2 equivalents”

  1. 151
    catman306 says:

    #147 David Benson, I’m not trying to be argumentative here, but burning wood and biomass derive their energy from photosynthesis, wind and hydro energy come directly from solar energy.
    Out of the solar radiation loop: nuclear, tidal, geothermal, but tidal and geothermal get at least part of their energy from solar gravitational energy.

  2. 152
    James says:

    Re #149: [At its crudest evaluation (yes or no), 50 degrees latitude seems to be the line: any afforestation beyond is quite strongly warming, anything nearer to the equater slowly becomes cooling…]

    I’ll atmit that most of my experience of forests are of those below 50 degrees. However, I’d argue that most of the area that could be reforested (or revegetated, such as prairie grasslands) does lie below 50 degrees.

  3. 153
    David B. Benson says:

    catman306 (151) — Geothermal obtains at most an insignificant fraction from anything but the internal (nuclear derived) heat inside the earth.

    I would of said that tidal derives its energy by slowing the earth’s rotation a tiny bit.

  4. 154
    Ray Ladbury says:

    David B. Benson,
    In addition to the radiogenic energy, the inner regions of Earth also derive a significant amount of energy from condensation of the liquid outer core onto the solid inner core. This energy is very important in generating the geomagnetic field. Not sure how it relates to the geothermal energy flux at the surface.

  5. 155
    podwalker says:

    Since trees absorb carbon dioxide and give off oxygen, they are essential for combating the global warming effect being created by excess carbon dioxide generation. Since they retain water in the soil and transpire moisture into the air, they are—in part—responsible for the ongoing existence of many springs, the even flow of rivers, and the formation of rain clouds. Since their innumerable roots hold soil in place and their bodies block wind, they are the best of all means for stopping erosion. Indeed, since they continually pull nutrients from the subsoils and drop organic matter to the earth, they are unparalleled soil builders as well.

    But that isn’t all. Consider that:
    A single mature tree absorbs around 13 pounds of carbon dioxide a year, while a younger, actively growing tree may absorb up to 26 pounds of CO 2 , per year—approximately five tons per acre of trees.

    Whether as a family project or an individual one, the point is to plant!

    About half of the weight of any tree is carbon. To maximize the amount of carbon dioxide absorbed, trees should be planted that gain weight the fastest. Depending on the trees’ densities, these may or may not be the same ones that gain diameter the fastest. Some common trees that “bulk up” quickly (in various parts of the country) include river birch, sycamore, tulip poplar, willow oak, red maple (commercial varieties), green ash, and black gum. In the South, try lobolly pine; in the West, Douglas fir; and in the Deep South and the tropics, leucaena. If in doubt, plant any native species that generally do well locally.

    Reducing atmospheric CO 2 , through tree planting costs about 0.3 ¢ to 1.3 ¢ per pound. Doing the same thing, by improving the energy efficiency of appliances costs about 2.5 ¢ for each pound of CO 2 ; and by improving electrical supply efficiency, about 10 ¢ per pound. While tree planting can make a significant contribution to reducing CO 2 buildup, it won’t solve the problem, not unless we all turn into Johnny Appleseeds. For it to do so, we would have to replant all the planet’s deforested areas—or double the growth rate of existing forests—to compensate for humanity’s excess carbon dioxide production. It’s been estimated that a typical family of four would need to plant six acres of trees to offset its CO 2 generation.

    In many locations, the cooling effects of trees can be more important than their ability to absorb carbon. Using landscape trees to shade buildings (and thus decrease the need for air-conditioning) results in CO 2 , emission reductions that are 15 times as great as the amount of the trees alone can absorb. Indeed, shade trees on the south and west sides of a house can lower its air-conditioning bills by up to half.

    Cities are particularly important locales for new tree-planting efforts. All that concrete and asphalt creates a “heat island” that makes cities 5° to 9° warmer than surrounding areas, so the cooling effects of trees can be especially helpful. The American Forestry Association estimates that there are 100 million tree-planting sites available. Planting them all would reduce carbon dioxide emissions from energy production by about 18 million tons per year and save consumers $4 billion each year in energy costs. (
    Perhaps you should all start thinking on a different branch?
    Posted by : the ignored one

  6. 156
    James says:

    Re #155: […trees should be planted that gain weight the fastest.]

    I’d disagree slightly with that, and a couple of other points. I spent this past weekend taking down several of the cottonwood trees planted by a previous owner. They’re a fast-growing tree (some of the annual growth rings are nearly an inch across), but use lots of water. They grow fast, but often die fast, as these did. Slower-growing, less water-hungry species would have been a better choice.

    I’d also suggest broadening the selection of species simply to avoid the problems that come with monocultures.

    I concur with the benefits re A/C and heating. In a climate (east side of the Sierra Nevada mountains) where hot summers are common, a combination of deciduous shade trees and good insulation has meant that I’ve never needed air conditioning, unlike most of my neighbors.

  7. 157
    Rod B says:

    podwalker (155) says, “…A single mature tree absorbs around 13 pounds of carbon dioxide a year… actively growing tree… up to 26 pounds of CO2 a year… ”

    While the thought is good, the problem is that tree absorption is piddly. One gallon of gasoline driving somebody ~20 miles puts out a little less than 20 lbs of CO2, That’s somebody’s short RT commute for one day.

    Others: I fail to see how the reduced albedo from the trees growing in the Arctic is hardly measurable, let alone a problem. A small percentage of the reflecting surface may be going away, but the solar radiation is coming in at a big obtuse angle, and we’re talking about 30watts/m^2 reflecting off the entire surface to begin with. So the reduced Arctic albedo is going to cut it to what, 29.99watts?? That’s magnitudes outside the error of measurement of albedo.

    Which reminds me, I still can’t fathom why a little global warming warms the poles greatly and cools the tropics. Makes no sense, if you omit the Rube Goldberg school of climatology. But I’m working on it.

  8. 158
    James says:

    Re #155: [A single mature tree absorbs around 13 pounds of carbon dioxide a year, while a younger, actively growing tree may absorb up to 26 pounds of CO2…]

    I would think it would have to be quite a bit more than that. For instance, a quick back-of-the-envelope calculation on the ones I had to take down: about 3 ft at the base, roughly 100 ft tall, which gives about 500 cubic ft per tree (remember that the root system is about the same size as the above-ground part). Figure the dry wood is a little less dense than water, say 50 lbs/cubic foot, or 12.5 tons per tree. Wood’s mostly cellulose, C6H10O5, so about 40% of that is carbon, about 5 tons. Since the trees are about 40 years old, that gives about 250 lbs of carbon per tree per year.

    Feel free to check my math, of course :-) Then remember there’s the annual crop of leaves that get raked up and turned to compost…

  9. 159

    Rod B. posts:

    [[I still can’t fathom why a little global warming warms the poles greatly and cools the tropics]]

    It doesn’t cool the tropics. It just warms them less than the poles.

  10. 160
    Ray Ladbury says:

    Rod B., I hope you have read the discussion of polar amplification here:

    Remember our discussions of thermal radiation. If radiation is not absorbed by the surface, it is reflected back out into space as visible light, to which the atmosphere is transparent/inert. It is only when the light is absorbed and goes into heating the surface that energy is changed into IR and greenhouse mechanisms are accelerated.
    The energy budget in polar regions is so impoverished, that small changes make a big difference. I would imagine that the lower temperatures at the pole decrease energy transport as latent heat and so increase the importance of radiation as a transport mechanism. Somebody pleas correct me if I’m wrong.

  11. 161
    Rod B says:

    James, here’s a post [edited] from an earlier Friday Roundup thread (I don’t know how to just show the link…).

    Rod B Says:
    16 September 2007 at 5:10 PM
    re 230: Forest Guardians (in the offset business) say the average tree weighs less than a ton at maturity, which they take as 100 years, so has sequestered 1/2ton (300-350kg to use their exact calculus) of carbon over 100 years, though their math seems a bit funny in places.
    [ ]

    [INSERT: that would put the average mature tree at one to 1-1/2 tons total weight. Other sources say about the same thing. That makes your estimate 10x too much. But even at that, the rest of your calculations would put absorbtion of carbon at 25 lbs/yr, or about 100 lbs of CO2 — still piddly though.]

    Makes Ike’s point even more pronounced.

    But something doesn’t seem right. One acre of corn (~10,000 plants) will sequester about 2500kg of carbon in one year, which is ~8 times what the average tree will sequester in 100 years. Seems funny. Any comments or insights?

  12. 162
    James says:

    Re 161: [Forest Guardians (in the offset business) say the average tree weighs less than a ton at maturity, which they take as 100 years…]

    I admit that I’ve never weighed a tree, but I have cut, hauled, and stacked a lot of firewood in my time. If they think an average tree weighs less than a ton, they must have included a lot of bonsai in their calculations :-)

    Likewise with the period to maturity for cottonwoods: I know the previous owner bought this house about 1965, and planted the trees sometime thereafter, which gives about 40 years (and a rough count of growth rings matches) to attain 3+ ft diameter. It’s true that these are cottonwoods, which are among the fastest-growing trees in temperate areas, but still…

  13. 163

    I though CO2 reached 380 ppm in 2005 and has been rising ~2 ppm annually. This would suggest about 385 now.

  14. 164
    Rick Brown says:
    Looks as though current CO2 level is about 384 ppm

  15. 165
    podwalker says: :
    “Photosynthesis accounts for 98% of the world’s atmospheric oxygen, while the breakup of water molecules by ultraviolet radiation composes the other 1-2%.
    The sources of atmospheric oxygen through photosynthesis are cyanobacteria and plankton in the ocean, and trees on land. The amount of atmospheric oxygen that each source contributes is under debate: some scientists suggest that over half of the world’s atmospheric oxygen comes from oceans, for example, while others put the number at closer to one third…”

    So – the carbon absorbed by trees is ‘piddly’?(157 Rod B). Is the oxygen they release for us to breathe also ‘piddly’? Or don’t we need that either? Am I missing something here? Am I merely an ignorant treehugger muttering nonsense? If there was 24% forest earth coverage that is now down to 6% – are you telling me this has made no difference, whatsoever to the amount of CO2 in the atmosphere? Is that what you are saying? Please, I would really like to know.
    Have a look at :

  16. 166
    podwalker says:

    And more : from :

    How can trees help fight air pollution?

    * Vegetation purifies the air by removing gaseous pollutants by absorbing them through pores in the leaf surface.
    * Particulate pollution is trapped and filtered by leaves, stems and twigs, and is washed to the ground by rainfall.
    * Trees absorb carbon dioxide – the main greenhouse gas. One acre of trees can absorb as much as 4 tons of carbon dioxide a year, the same amount as a car driven 26,000 miles.
    * Trees save energy. Shade trees reduce air-conditioning needs up to 50%. Reduced energy use means reduced energy production and associated pollution.
    * Trees store carbon dioxide and produce enough oxygen from one acre for 18 people every day. “”

    Are all these people lying ??

    Or are all the scientists ignoring these facts because it too easy a solution??

  17. 167
    Hank Roberts says:

    No, those people aren’t lying, though without cites I can’t say their numbers are right and neither can you. But you can look them up.

    No, all the scientists are not ignoring this.
    No, the scientists are not ignoring ths.
    No, it is not too easy a solution.

    Look, you can be as wrong as a treehugger as you can be as a coalburner. It’s not what you love, it’s how well you do math and read cites and understand footnotes that will advance what you know.

    Have you had a college ecology course? (It’d be an advanced level biology course as an undergrad). Have you had the intro geology course?

    If so you’ve got a basis for reading up on biogeochemical cycling; if you can’t find the text online post back and ask, or ask your local reference librarian.

    Short answer — don’t believe me, look into this. You can look at the total amount of coal, versus the total amount of vegetation, and the amount of CO2 in the atmosphere before the carboniferous period. You can’t plant enough trees to soak up all that carbon if it’s burned, unless you also have a way to put the trees back into deep sediments and make them back into coal.

    Yes it’s very important to reforest, revegetate, restore ecosystems. Topsoil loss exceeds tree loss overall, and may hold more carbon longer if we can get it restored.

    I’m working on restoring a mountain site that had a foot of topsoil a century and more ago. Before it was first logged. Before the big fires after the logging. Before the late 1800s when sheep grazing ate back everything that lived on the topsoil and it started seriously washing away. The river below this site has thirty feet of debris in its bed. All that came off the surrounding mountains. This is nothing unusual. The Midwest lost far more, down to the Gulf of Mexico, and it’s still happening everywhere.

    Plenty of work to do in this regard. Nobody’s ignoring it.

  18. 168
    Ray Ladbury says:

    Podwalker, I don’t think that people are against growing trees, but they are emphasizing that it is at best a partial solution. Yes, trees store carbon, but they either grow fairly slowly (e.g. hardwoods) or they have relatively short lifetimes. Moreover, they do give off ghgs–some with a higher potential for warming than CO2–when they decay and at night when they consume rather than store energy. Moreover, the prospect of having to grow gigatons of trees indefinitely is not sustainable.
    As H. L. Mencken said: “Explanations exist: they have existed for all times, for there is always an easy solution to every problem — neat, plausible and wrong.”
    In this case, I would substitute “partial” for “wrong”. Don’t get me wrong, I believe in planting trees. I’ve planted hundreds in the past few years.

    BTW, where in Africa are you from. I spent a couple of years in Togo.

  19. 169
    Rod B says:

    I can’t verify any of my figures; I was just quoting mostly Forest Guardians who, being in the carbon credit business, you wouldn’t seem would underestimate the carbon that trees absorb. Though, as I said, the numbers seem screwy, especially compared to what corn is estimated to absorb. On the other hand, piddly being a relative term, post #166 was not impressive from this regard: one acre of trees takes care of two average-mileaged cars’ CO2 per year, at your assumed absorption rate (which I can’t refute). This means that a little less than 25% of the US land area needs to be in trees just to absorb the CO2 from passanger vehicles (cars, SUVs, PUs, etc.) Though I’m kinda with you — it just doesn’t sound right.

    I have nothing against trees. Most of your points on their benefits are right on. But, as they say here: math is math and science is science.

  20. 170
    podwalker says:

    Thank you for explanations. By the way – they are not my figures or calculations – these refs are from the quoted websites. I am truly an ignorant, concerned treehugger – I am not being facetious or sarcastic in my questions. Now I know – trees cannot be the only solution. Thanks again.

  21. 171
    Rick Brown says:

    Podwalker, I’ve worked to conserve forests my whole adult life, think that trees are very fine things indeed and there are lots of reasons to plant more of them. However, they do not provide the oxygen we breathe. Someone can correct me on the fine details, but it goes something like this: The 20% of the atmosphere that is O2 is the result of many millions of years of accumulation of photosynthetic products in sediments and ultimately in geologic formations, mostly as diffuse kerogen, less as fossil fuels. Trees provided some of that photosynthetic product, but aquatic microorganisms provided much more. Relative to the large pool of O2 in the atmosphere, the annual fluxes between the biosphere and atmosphere are tiny and essentially in balance, i.e., as much organic matter is oxidized as is produced. The amount of photosynthate that goes to the sediments is tinier still and it is only the slow accumulation of this material that adds oxygen to the atmosphere. Photosynthesis would have to be shut down for a very, very long time before any reduction in atmospheric O2 could be detected. (See, for instance,

    Rod B, the best estimates I’ve seen are that for the period from about 1952 to 1992, forests in the U.S. sequestered an amount of carbon equal to about 20-25% of U.S. fossil-fuel emissions for that period. Because emissions increased and forest dynamics changed (primarily maturation of forests that began growing on abandoned farms starting in the 1930s), by 2000 the off-set was probably more like 10% and estimates going forward to 2050 are that it will be about 15%. Not nearly enough to solve our problems, but not trivial either. (I think some of this is available online at and I can come up with additional cites if folks want them.)

    Hope this helps.

  22. 172
    Rod B says:

    Thanks, Rick. In the context you describe I would agree it is not trivial; nor is it stupendous. But from the context of much ballyhoo like, “Plant a tree and save the planet!” it is much over-hyped.

  23. 173
    podwalker says:

    Thanks again. My concern is that no-one is going to do anything really significant about cutting emissions. Not Mr Citizen, not governments, not industry. My thoughts were if this is the case, perhaps we could do something positively significant to counteract the emissions, even in a small way. I guess not….

  24. 174
    Ray Ladbury says:

    There is a low we can do–and planting trees is probably a part of the equation–just not all of it. At a minimum, trees sequester carbon for a finite time, and buying time may be essential to developing other solutions. I suspect there is no “answer” to our current predicament. It will take effort on a lot of fronts to create a truly sustainable economy.

  25. 175
    Hank Roberts says:

    Podwalker, you’re talking nonsense. Someone’s fed you discouragement and it’s bogus.

    You can look this stuff up.

    If you’ve believed someone who tells you there’s no hope, most likely you’re reading the PR sites funded by the fossil fuel industry. _They_ leaped from “no proof” to “no problem” to “no hope” without an intervening period of giving a damn about making any effort. That’s advertising puffery public relations.

    Seriously, make an effort. Let me just suggest a few pointers, and you can certainly find more with a minimum of effort. And you can visit any public library, talk to the reference librarian and ask for help finding more.

    From the library:
    Dodging a Warming Bullet — Berardelli 2007 (305): 1 — ScienceNOW
    Dodging a Warming Bullet. By Phil Berardelli ScienceNOW Daily News … 191 countries to curb CFC emissions from sources such as refrigeration, dry cleaning, …

  26. 176
    Chuck Booth says:

    Re # 171 Rick Brown: Trees and photosynthesis

    I think you need to go back and re-read the reference you cited. At the risk of introducting my own errors, let me try to clarify some of your points:

    1. “The 20% of the atmosphere that is O2 is the result of many millions of years of accumulation of photosynthetic products in sediments and ultimately in geologic formations, mostly as diffuse kerogen, less as fossil fuels.”
    Ummm…no. The “accumulation of photosynthetic products” represents the sequestration of phytoplankton biomass in the deep sea sediments. This chemically-bound oxygen is removed from the biogeochemical oxygen cycle. The oxygen gas (O2) in the atmosphere and dissolved in the ocean was produced by early photosynthetic cyanobacteria, starting around 2.4 billion years ago (the so-called the Great Oxidation Event) – oxygen levels rose quickly, until organisms carrying out aerobic cell respiration became abundant, around 1.9 billion years ago.

    2. “Trees provided some of that photosynthetic product, but aquatic microorganisms provided much more. ”
    Mmm…no again. According to the most recent figures I’ve seen (admittedly 10 years old: Field et al. 1998, Science 281: 237-240., trees provide nearly half of the annual terrestrial net primary productivity – i.e., adding oxgen to the atmosphere – with rain forest trees performing the bulk of that; grasslands and cultivated regions provide most of the remainder. Oceanic primary productivity is somewhat less than 50% of the total global net primary production (~ 40-45%), most of that carried out by phytoplankton, primarily cyanobacteria.

    3.”Relative to the large pool of O2 in the atmosphere, the annual fluxes between the biosphere and atmosphere are tiny and essentially in balance, i.e., as much organic matter is oxidized as is produced.”

    I don’t have any data to contradict that, but I think your point is better made by stating that the photosynthetic production of oxygen is essentially in balance with the metabolic consumption of oxygen by aerobic respiration (geochemical oxidation-reduction processes play a minor role in adding or removing oxygen from the ocean-atmosphere pool).

    4. “the amount of photosynthate that goes to the sediments is tinier still and it is only the slow accumulation of this material that adds oxygen to the atmosphere.”
    Again, this process does not add oxygen to the atmosphere – it removes chemically- bound oxygen from the biogeochemical cycle. You need to differentiate between photosynthetic biomass (consisting of carbohydrates, proteins, lipids, etc, all of which contain bound oxygen) and photosynthetic oxygen production (= O2 gas released to the environment).

    5. “Photosynthesis would have to be shut down for a very, very long time before any reduction in atmospheric O2 could be detected.”
    Assume that net primary production adds 105 petagrams of oxygen to the atmosphere each year, and respiration and other oxygen-consuming processes extract an equal quantity of oxygen each year. The pool of oxygen in the atmosphere is about 37,000 petagrams, with another 0.4 petagrams of dissolved oxygen in the atmosphere (according to the web site you cited). Eliminating photosynthesis but keeping respiration rates constant means that the 37,000.4 petagrams of available oxygen would last about 352 years; the enormous quantities of chemically-bound sequestered in sedimentary rocks would likely not change. That is not a particularly long time.

    If I have made some incorrect assumpions, or math errors, please correct me.

  27. 177
    Hank Roberts says:

    > Eliminating photosynthesis but keeping respiration rates constant
    > … available oxygen would last about 352 years …

    See Peter Ward’s “Under a Green Sky” — he’s describing work with sediments across the several ‘great extinction’ periods in terms of changes in the location of downwelling ocean circulation — resulting in changing the temperature, and so the oxygen content, of the deep ocean.

    One abstract here,

    If you’re in New York:
    Monday, November 19, 2007, 7:30 PM Rose Center for Earth and Space

  28. 178
    Timothy Chase says:

    Hank Roberts (#177) wrote:

    See Peter Ward’s “Under a Green Sky” …

    If you’re in New York:
    Monday, November 19, 2007, 7:30 PM Rose Center for Earth and Space

    I can’t get to New York, but maybe he will give something like that in Seattle at some point…

  29. 179

    All this talk about trees, reminds me of what one of our leaders had to say about trees several decades ago. Remember this one “trees cause more pollution than automobiles do.”- Ronald Reagan, August 1980-

    Maybe that’s what Dubya was talking about when he said Saddam had WMD. Anyhow, Reagan’s statement emphasizes that the most important thing we can do come next November,regarding AGW is to choose our leadership carefully. We don’t need people at the top who make a mockery of this very serious issue and potential looming crisis.

  30. 180
    Chuck Booth says:

    Re # 176 My comment about (hypothetically) eliminating photosynthesis:

    In the absence of photsynthetic oxygen production the rates of oxygen consumption by respiration would almost certainly decline exponentially as available oxygen declined, and so oxygen might last for much longer than 352 years. On the other hand, by the time environmental oxygen levels are reduced by ~50% of normal, many aerobic organisms will be suffering,and some will die off. I think the major point here is life on earth depends on the plants, algae, and bacteria carrying out photosynthesis, and we should take great pains to assure their survival.

  31. 181
    Hank Roberts says:

    Timothy, Dr. Ward is at UW and you’ve missed a handful of his presentations locally; I’m sure there will be others. Google …

  32. 182
    Hank Roberts says:

    Chuck wrote
    > rates of oxygen consumption by respiration would almost
    > certainly decline

    This is the mistake that caused Biosphere II to fail. They were in a hurry, so they didn’t take time to build up proper soil profiles by bringing in first mineral soil, then topsoil, then duff and leaf litter.

    They went out and hauled in truckloads of topsoil and filled their entire soil profiles with topsoil that was mostly live, respiring microorganisms.

    Those died. Result, lots and lots of oxygen lost to carbon dioxide as the dying soil organisms oxidized. Level of CO2 went, well, not through the roof since the roof was airtight — it got quite bad.

    This mistake about topsoil came out quite late during the period it was inhabited I recall. Someone wasn’t thinking who ran the dumptrucks and skiploaders.

    So, no, oxygen demand doesn’t go down when life starts to die off.
    Not right away, anyhow.

  33. 183

    Chuck —

    It’s true that photosynthesis is the main source of oxygen in Earth’s atmosphere, but it has been allowed to accumulate only because organic matter was constantly being buried. It’s the burial of carbon, not oxygen, that is at issue. Otherwise the oxygen would have combined with the organic matter at its death and there would be no net gain. This is pretty standard geochemistry, I believe, going back to the 1950s at least. I remember it being discussed in Dole’s book, “Habitable Planets for Man,” in 1964, and I think Rubey explored it in 1952.

  34. 184
    Chuck Booth says:

    Re # 182 Hank R. and # 183 Barton P.L.

    I see now that I misinterpreted Rick Brown’s (# 171) comments – I took literally his comments that “The 20% of the atmosphere that is O2 is the result of many millions of years of accumulation of photosynthetic products in sediments” and “The amount of photosynthate that goes to the sediments is tinier still and it is only the slow accumulation of this material that adds oxygen to the atmosphere.” What he meant, I now see, is that because those organisms did not decay, O2 stayed in the atmosphere (instead of being consumed by bacteria and other decomposers).

    Re: Hank’s comment that “oxygen demand doesn’t go down when life starts to die off. Not right away, anyhow.”
    What I wrote (or meant, at least) is that when oxygen levels decline (due to all forms of aerobic respiration, including aerobic decomposition, without replenishment of that oxygen by photosynthesis), rates of oxygen consumption also decline due to the reduced oxygen partial pressure gradient that drives the diffusion of oxygen into the cells – simple physiology (Fick’s Law of Diffusion).

    Re: Hank’s comment that “…lots and lots of oxygen lost to carbon dioxide as the dying soil organisms oxidized…” and Barton’s comment that “Otherwise the oxygen would have combined with the organic matter at its death” – I would point out that during aerobic decomposition the oxygen combines with electrons to form water, not CO2 – the CO2 comes from the removal of carbon from organic substrates in the citric acid (Krebs) cycle – standard biochemistry, complicated a bit, to be sure, by anaerobic decomposition and abiotic redox reactions.

    Anyway, thanks for your clarifications.

  35. 185
    podwalker says:

    Hank Roberts(175). I’m not talking nonsense… I know there is a lot of talk, a lot of articles, a lot of research, a lot of speculation. But is anyone, any govt, any industry, actually REALLY doing anything positive (apart from ‘piddly’ carbon buy backs and sniffles of cutting by 2020 – too late… Perhaps you could enlighten me if there are more positive actions by govts and industry?) Your web refs : Biofuels -the ever-increasing population will starve (because of climate change crop failure and because of using agriculture for fuel) and more forests will be cut down – (my humble opinion); it was encouraging to see graph of reduction in ozone depleting chemicals; could not get into science mag without being a paying subscriber – but did find this – (not encouraging)
    Here, where I live they are about to build more huge power stations which will use dirty coal. China – building the same on a massive scale – vehicles on their roads are increasing daily. India – the same. These are enormous population countries – only just starting on their pollution journey. Air travel increasing daily – Russia buying new fleets of planes.
    Northwest Passage now open for shipping – govts delighted about this – gives them access to oil fields previously icebound and easy transportation of this same oil. Etc, etc, etc. North arctic region melting away this past summer.
    I don’t think I’m talking nonsense. It is very depressing, and I honestly don’t see any hope. And most Mr/s Citizen remark – “well nothing can be done, economies cannot be changed from their reliance on transportation and industry – we don’t want to change our lifestyle…..”

  36. 186
    Mary C says:

    Re 185. I find that I fluctuate between hope and despair on the subject of AGW. I think probably most people who understand the arguments at all do so to some degree. Of course, some people spend more time on the hope side of the swing and others on the despair.

    When I despair, it’s not because I don’t think we can find the fixes that would make a difference or that not enough citizens (worldwide) could be brought on board to change things. Where I despair is, first, the fear that it’s too late, that we have already passed some tipping point of the physical processes that will make any efforts on our part useless. The second fear is that the forces arrayed against doing anything meaningful, not the ordinary people, but the politicians and the corporations who control so much and whose voices ring loudest in the media will manage to block both awareness and action until it is too late.

    But, most of the time, I dwell in hope and even some excitement at the possibilities that could open up out of this crisis.

  37. 187
    David B. Benson says:

    podwalker (185) — Follow Biopact daily to discover some of the actions being taken by researchers, companies and many govenments.

  38. 188
    Hank Roberts says:

    > people are quoting from draft reports that they have
    > neither properly read nor understood and for which
    > better informed opinion is not immediately available.

    Any more on what’s going on with that?

    In other news:
    PNAS finally out today with this one:
    Josep G. Canadell, Corinne Le Quéré, Michael R. Raupach, Christopher B. Field, Erik T. Buitenhuis, Philippe Ciais, Thomas J. Conway, Nathan P. Gillett, R. A. Houghton, and Gregg Marland
    Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks
    PNAS published October 25, 2007, 10.1073/pnas.0702737104 ( Sustainability_Science ) [Abstract] [PDF] OPEN ACCESS ARTICLE discussing Science (vol 318, p 582)

  39. 189
    Bruce Tabor says:

    Tim Flannery is an expert mammologist and palaeontologist with a big heart who recently won Australian of the Year. He is not a climatologist. He is a brilliant populariser of science with a commitment to the environment, similar to Al Gore, with a similar level of understanding of the issues.

    We are in the middle of an election campaign here and climate-skeptic Prime Minister John Howard is doing badly in the polls. I suspect Tim’s public statements, which I saw live, were an expression of genuine (if slightly mistaken) concern and were intended to make climate change an issue in the campaign, especially to force the opposition to lift its game. It has worked. The government is now internally divided about how to respond.

    I don’t think Flannery intended to mislead, but to admit he made an error now would have the right wing Newscorp press howling “I told you so.” His credibility would become the issue, not climate change. Any subtlety in the issue would be utterly lost and the public would be confused. His technical error has got little air in Australia except among the right wing press, who few believe on this issue anymore.

    The government and much of the press and in Australia have spent years denying climate change or trivialising its significance. The usual staid, measured scientific statements have been easily dismissed and climate change researchers in public organisations have been censored. It takes science popularisers like Flannery to cut through this oppression.

  40. 190
    Chris Squire says:

    It would be helpful [and it is anyway good practice] to show the units of ‘forcing’ [ W/m2] in its definition as the concept is still a new one to some who read this most useful web site.

  41. 191
    Alice says:

    Hello, I have just read your original comment about CO2 equivalent, and find the explanation useful. However, my understanding is that although a 375ppmv figure includes carbon black, aerosols etc., it still omits aviation-induced contrails, NOx from transport (particularly aviation), and contrail-induced cirrus clouds. Is this true, and do you know what else it omits? Presumably it is important to include all additional non-greenhouse gas warming and cooling contributions to get to a true figure. My feeling is that we are some way off being able to quantify this, and may never be able to do so, given the very different nature of some of these emissions (e.g. contrails, ship tracks etc). Any thoughts?

  42. 192
    Anil Tandon says: is India’s 1st Carpool/Rideshare Classifieds. Indimoto’s aim is to enable commuters from over 130 Indian cities to form carpools and reduce harmful CO2 emissions which are increasingly making India into one of the fastest growing contributers to Global Warming. If you are from India, do your bit and try out a carpool. Use of the site is free ofcourse and by carpooling you save money too.

  43. 193
    Bruce Marshall says:

    Gavin meant “ln” not “log” in ∆F=5.35 log (C02_e/C02_orig).
    Cf TAR, The Scientific Basis, p.358.
    I.e., he should have written ∆F=5.35 ln(C02_e/C02_orig).