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How much CO2 emission is too much?

Filed under: — david @ 6 November 2006 - (Slovenčina)

This week, representatives from around the world will gather in Nairobi, Kenya for the latest Conference of Parties (COP) meeting of the Framework Convention of Climate Change (FCCC) which brought us the Kyoto Protocol. The Kyoto Protocol expires in 2012, and the task facing the current delegates is to negotiate a further 5-year extension. This is a gradual, negotiated, no doubt frustrating process. By way of getting our bearings, a reader asks the question, what should the ultimate goal be? How much CO2 emissions cutting would it take to truly avoid “dangerous human interference in the climate system”?

On the short term of the next few decades, the line between success and excess can be diagnosed from carbon fluxes on Earth today. Humankind is releasing CO2 at a rate of about 7 Gton C per year from fossil fuel combustion, with a further 2 Gton C per year from deforestation. Because the atmospheric CO2 concentration is higher than normal, the natural world is absorbing CO2 at a rate of about 2 or 2.5 Gton C per year into the land biosphere and into the oceans, for a total of about 5 Gton C per year. The CO2 concentration of the atmosphere is rising because of the 4 Gton C imbalance. If we were to cut emissions by about half, from a total of 9 down to about 4 Gton C per year, the CO2 concentration of the atmosphere would stop rising for awhile. That would be a stunning success, but the emission cuts contemplated by Kyoto were only a small step in this direction.

Eventually, the chemistry of the ocean would equilibrate with this new atmospheric pCO2 concentration of about 380 ppm (the current concentration), and its absorption of new CO2 would tail off. Presumably the land biosphere would also inhale its fill and stop absorbing more. How long can we expect to be able to continue our lessened emissions of 4 Gton C per year? The answer can be diagnosed from carbon cycle models. A range of carbon cycle models have been run for longer than the single-century timescale that is the focus of the IPCC and the FCCC negotiation process. The models include an ocean and often a terrestrial biosphere to absorb CO2, and sometimes chemical weathering (dissolution of rocks) on land and deposition of sediments in the ocean. The models tend to predict a maximum atmospheric CO2 inventory of about 50-70% of the total fossil fuel emission slug. Let’s call this quantity the peak airborne fraction, and assume it to be 60%.

The next piece of the equation is to define “dangerous climate change”. This is a bit of a guessing game, but 2°C has been proposed as a reasonable danger limit. This would be decidedly warmer than the Earth has been in millions of years, and warm enough to eventually raise sea level by tens of meters. A warming of 2° C could be accomplished by raising CO2 to 450 ppm and waiting a century or so, assuming a climate sensitivity of 3 °C for doubling CO2, a typical value from models and diagnosed from paleo-data. Of the 450 ppm, 170 ppm would be from fossil fuels (given an original natural pCO2 of 280 ppm). 170 ppm equals 340 Gton C, which divided by the peak airborne fraction of 60% yields a total emission slug of about 570 Gton C.

How much is 570 Gton C? We have already released about 300 Gton C, and the business-as-usual scenario projects 1600 Gton C total release by the year 2100. Avoiding dangerous climate change requires very deep cuts in CO2 emissions in the long term, something like 85% of business-as-usual averaged over the coming century. Put it this way and it sounds impossible. Another way to look at it, which doesn’t seem quite as intractable, is to say that the 200 Gton C that can still be “safely” emitted is roughly equivalent to the remaining traditional reserves of oil and natural gas. We could burn those until they’re gone, but declare an immediate moratorium on coal, and that would be OK, according to our defined danger limit of 2°C. A third perspective is that if we could limit emissions to 5 Gton C per year starting now, we could continue doing that for 250/5 = 50 years.

One final note: most of the climate change community, steered by Kyoto and IPCC, limit the scope of their consideration to the year 2100. By setting up the problem in this way, the calculation of a safe CO2 emission goes up by about 40%, because it takes about a century for the climate to fully respond to rising CO2. If CO2 emission continues up to the year 2100, then the warming in the year 2100 would only be about 60% of the “committed warming” from the CO2 concentration in 2100. This calculation seems rather callous, almost sneaky, given the inevitability of warming once the CO2 is released. I suspect that many in the community are not aware of this sneaky implication of restricting our attention to a relatively short time horizon.

Note: responding to suggestions in the comments, some of the numbers in the text above have been revised. November 7, 2:31 pm. David


232 Responses to “How much CO2 emission is too much?”

  1. 151
    Steve Hemphill says:

    Seems to be a lot of threshold attributions here – brain size is not a necessity for succesful agriculture. How do we know there wasn’t any agriculture in the Eemian? For a good discussion on that, with respect to linear vs. parallel thought, check out “The Edison Gene” by Thom Hartmann. Linear thought leads to Tower of Babel disfunction.

    As far as a threshold level on CO2 for agriculture, that seems anthropocentric as well. CO2 (aka the base of the food chain) helps flora overcome other stresses – particularly water. All locations are different with respect to limiting factors. Therefore, it not only can be said that 200 ppm starves flora, but so does 380 ppm. Commercial greenhouse gardeners use 800 to 1000 ppm. That should tell us something.

  2. 152
    James Davey says:

    Onar : If it is proven that significant damage to individuals is caused when releasing more than some amount of CO2 into the atmosphere per year, then CO2 emissions must be considered a limited resource like any other resource and a system of private property for it developed. Property rights should be designated on previous emissions e.g. in the last 20 years. That is, if you emitted 1 ton per year for the past 20 years you own emission rights of 1 ton per year. You can do whatever you want with these emission rights, including selling them.

    I just *love* economists. I mean, this is great. Onar lectures us that restricting CO2 production will damage the 1st world economy, which will in turn damage the 3rd world economy yada yada yada. And now this.

    Just in case you missed it Onar, the ‘solution’ to CO2 pollution you point out above would cripple the economic growth of the 2nd and 3rd world, while maintaining the economic supremacy of the West. You are actually advocating a solution whereby an American should own 100 times more CO2 credits than a Kenyan, because the American has emitted more.

    Aside from the fact that the Chinese and Indians would laugh you out of the room when you proposed this ‘solution’ you’d be condeming the developing world to stay exactly where they were, while giving the main culprits a free ride.

    How about this as an alternative solution? We introduce a GLOBAL carbon tax, set at an appropriate level (I think analysis suggests around $40 per tonne CO2 produced). This money is invested by governments, private companies or Multilateral bodies (World Bank, IMF, other UN fund) in a number of ways. A portion offsets other forms of taxation, a portion goes to R&D, a portion goes to local adaptation, a portion to tech. transfer to the third world and a portion to third world adaptation.

    Obviously there are many subtleties, such as companies using CDM or JI to offset their emissions, difficult negotiations to agree exact how much money flows from the developed to developing world, who controls the spending, who audits it etc.

    But it is a possible solution.

    And guess what? ‘Our’ economists predict that this system would result in world GDP higher than the business as usual scenario by 2100.

  3. 153
    James says:

    Re #152: “… you’d be condeming the developing world to stay exactly where they were…”

    Err… Why is this, exactly? Current technology provides alternatives for many CO2 emitters; different (though still prosperous) lifestyles reduce the need for others. Why shouldn’t the developing world just bypass the late-19th/early 20th century fossil-fuel technology currently in use?

    A lot of the objections to CO2 reductions in the developed world seem to be from vested interests, and in a sense you can’t really blame them. If I had millions invested in a coal-fired power plant or oil refinery, I might be reluctant to shut them down, too :-) The developing world doesn’t have these vested interests, so for instance Brazil can develop an ethanol economy, cell phones can be used instead of land lines, etc.

  4. 154
    James Davey says:

    And who is going to pay for the (more expensive) low carbon technology in the developing world?

    You are absolutely right to say that low carbon development in the third world is VITAL if we are to stabilise CO2 at a level currently considered ‘safe’ (or at least less dangerous)

    However, the proposal mooted by Onar (to allow exisiting emmiters the rights to continue to do so) is ridiculous for two reasons

    1 – You would never get agreement on the issue.

    2 – How would the 3rd world develop?

    Any sensible proposal would be based on a ‘polluter pays’ principle. Anyone can pollute. They just pay. You can avoid paying by instead investing in clean development in the developing world.

    The EU ETS basically works on this principle. So long as credits are expensive enough under the EU ETS (and in the first phase, they ain’t) you get a move from high carbon to low carbon technology.

    We need either a global carbon market, or a global carbon tax, if we are ever to reduce GHG emissions.

  5. 155
    Onar Ã?m says:

    Re #152, 154.

    James,

    first the moral aspects of it: who discovered oil? who invented the technology for utilizing it? Who developed a market for creating values from it? It was the West. Kenyans have no moral claims on this technology or its utilization just because they’re poor. So IF this in your words “cripple their economic growth” it was not a growth rightfully theirs for the taking.

    Second, does a farmer owning the land he has cultivated cripple the growth of non-farmers? Does a radio station owning the frequency he transmits at cripple the growth of non-radio owners? No, because they sell the fruits of their property to others in exchange for value. Farmers sell produce and radio stations sell radio programs (indirectly in the form of commercials). Therefore other people benefit from their property. That’s obviously what would happen in the case of CO2 emissions as well. If there is a fixed limit on how much CO2 emissions the world can take there will blossom a market for creating sinks and alternative fuels.

    The point with a property right based on previous CO2 emissions is to ensure a *fair* and *just* distribution. And the fairest distribution is obtained when those who produce something own their own product.

    You say that China and India would laugh me out of the room with this solution. If so it is only because China and India somehow believe that they have a right to own other people’s property. And why wouldn’t people in the west laugh at “solutions” that involve putting all the costs on the West?

  6. 156
    Christian King says:

    On the 2 degree change in temperature…It is my understanding from the literature I have read on the subject (such as Jeremy Leggets- Half Gone, and the Scientific American etc), that many scientists insist anything above 400ppm is very dangerous and could lead to a chain reaction heating effect that can’t be stopped once started. Judging by our current C02 levels within 10yrs we will have run out of time if we don’t do something serious about warming today, and failing a significant reduction in CO2 by then, the temperatures rises will be inevitable.

    As alarmist as this sounds, I have also not seen other large scale risk factors added to any CO2 model; the effect of extinctions of Biomass in the tropical rainforests of the world (such as the amazon which looks terribly sick); the amount of methane being naturally released into the atmosphere as the permafrost melts, the impact and the likelihood of a volcanic eruption in the near future..just to name a few other large scale greenhouse impacts. Is there any large factor that might actually reduce global warming in the next hundred years or is the potential risk of other large scale greenhouse events over the next century likely to cause a chain reaction? I think this would be an interesting area to explore..

    Another interesting comparison I stumbled across on the wiki (yeah I know, but it’s got some ok stuff on global warming). These 3 graphs: CO2 levels, temperature and biodiversity..do seem to roughly correlate quite well (given that the measurements may not be THAT accurate). http://en.wikipedia.org/wiki/Image:Phanerozoic_Carbon_Dioxide.png http://en.wikipedia.org/wiki/Image:Phanerozoic_Biodiversity.png
    http://en.wikipedia.org/wiki/Image:Phanerozoic_Climate_Change.png

    The most interesting thing about this correlation is when man came into the picture (if you believe your evolutionary history). The earliest primates recorded appeared 60 million years ago, at the time when CO2 had fallen to 800-900ppm and temperatures had cooled and biodiversity had exploded. Since mankind has existed on the planet 200,000 years ago we can be fairly certain that CO2 has never risen anywhere near 500ppm. I found this a useful way to take in the whole cycle of the planet’s biodiversity as being influenced by temp and CO2. It also puts the argument that the planet did have larger CO2 emissions in the past in perspective. Sure it was higher, but look at the lack of biodiversity that existed!

    I realize that there is a complicated relationship here, but looking at general trends it seems clear that Biodiversity will plummet to a level of mass extinction if we do hit the 2 degree barrier, or 400-500ppm CO2, which now seems quite inevitable.

    Which brings me to my attitude on the topic. Even an undergrad like me without years of training can see the writing on the wall. I find it frustratingly difficult conversing with people on this topic when all anyone seems to be concerned about is the economic impact. The economy is a fictitious make believe concept created by humans in order to control each other. While I am making plans to ditch my western lifestyle, move to a place less effected by climate change and commence a sustainable life without cars, tv sets or the requirement of “money”, everyone is worried they are going to be worse off financially!! How are you going to survive in a 2 degree hotter world?

    If the planet hits 2 degrees you won’t be buying food from your local supermarket anymore, there will be an economic depression, there will be bloodshed, our cities will be abandoned. The world’s population will collapse since the planet will not be able to support us all. It’s simple science really, how arrogant of humanity to think that boom and bust doesn’t apply to us? How much longer until the conversation changes from what will happen and what we should do to stop climate change and habitat destruction, to climate change is coming and how can we best prepare to survive it?

  7. 157

    Lendel Zed wonders why no-one devises a chimney box that captures CO2 as solid carbon. It can be captured as a solid, without putting back more energy than was yielded in its formation, as the supposed chimney-box would need.

    Every puff from a tailpipe spreads around the world in, I don’t recall exactly, a few years. This means CO2 sequestration doesn’t have to be done at the top of thousands of flues or the ends of a billion tailpipes; it can be done in large central installations, and these can be anywhere in the world. The carbon dioxide will come to them. This is the most practical way to sequester CO2, and in my opinion it is the most practical way to ease the atmosphere’s CO2 level back down to where it was in 1900.

    That is to say, gross CO2 emissions from tailpipes and stacks do not need to decline. They can increase rapidly for many years — not that I want them to, but they can — and the net emissions can easily enough be made negative by an industry of anywhere-on-Earth CO2 capture regions, with total area equal to that of a circle no more than ~120 km in diameter, funded as public works.

    [Response:There's a guy at Columbia named Klaus Lackner who advocates this, also. The difficulty is that it does energy to unix the CO2 from the atmosphere. It's thermodynamics, no way around it. For the same reason, IGCC (gasification) coal plants, which produce pure CO2 stream, would be preferable to burning coal in air, so that you'd have to unmix it from the N2. David]

  8. 158
    Matthew Kennel says:

    The most well known example of sequestered CO2 as solid carbon is called a “coal mine”.

    The easiest way to sequester CO2 to avoid desequestering it.

    If we can’t completely ban coal mining and burning now (and we are very far away from this—coal’s burning is increasing, and will get worse as oil gets expensive) then there’s no possible way that we will do the more thermodynamically difficult solution.

  9. 159
    Matthew Kennel says:

    Regarding agriculture: in almost all areas the limiting factor is H2O, not CO2, and climate disruption that screws up rainfall and especially snowfall (as icemelt is released conveniently slowly) may hurt agricultural productivity much worse than the increased CO2 could benefit it.

    Consider that current planting and irrigation patterns and infrastructure correspond to optimization for the past climate.

    An irrigated greenhouse is not relevant for global agricultural production.

  10. 160
    yartrebo says:

    Re #157:

    There is no way to convert CO2 back into solid carbon for less energy than you get from burning it in the first place. Here’s a quick disproof by construction of a perpetual motion machine:

    1 – Assume that CO2 can be converted into solid carbon using less energy than is released in its combustion.
    2 – Build a power plant.
    3 – Give it an initial supply of carbon and oxygen, then seal it off from the outside world to make a closed system.
    4 – Use some of the energy from the power plant to take the CO2 generated and turn it back into carbon and oxygen.
    5 – Feed the carbon and oxygen back into the furnace of the power plant.
    6 – Use the left over energy (which will exist because less energy was needed than the carbon released upon being burnt) for whatever purpose you desire.

    Since perpetual motion machines cannot exist, the assumption must be false and carbon must need at least as much energy to reduce back to elemental carbon as is released in its combustion.

  11. 161

    If we can’t completely ban coal mining and burning now (and we are very far away from this—coal’s burning is increasing, and will get worse as oil gets expensive) then there’s no possible way that we will do the more thermodynamically difficult solution.

    That doesn’t follow. Thermodynamically more difficult can be logistically easier. Politically easier, too, because fossil fuels are heavily taxed.

  12. 162
    Matthew Kennel says:

    Thermodynamically more difficult can be logistically easier.

    I think it’s logical to put the burden of proof on those who wish to assert that we’ll be able to swim up entropy river, and make it back up over the waterfall in reverse.

    From the thermodynamics you can get decent orders-of-magnitude immutable lower bounds on the amount of additional energy necessary—and it must be a few times the energy released in the combustion. This is really really really big.

    And if you start producing that power at the enormous quantities necessary (presumably by a titanic scale-up of nuclear plants) then certainly the first economically feasible use would be to sell electricity for primary consumption before using it to fix CO2.

    Only until power-grid electricity is literally too cheap to meter (i.e. never) would this start to be sensible.

  13. 163
    Lendel Zed says:

    Re: 162(?), 160, 157, 140, 137:

    Thankyou for your replies. As I said I am a layman (not an inventor, businessman, etc I am just trying to get a handle on options – I have to vote on policies directly related to GW one day soon I think).

    Before I let it rest, can I qualify something. I understand it takes energy to turn CO2 into O2 and C-anything else. I was alluding to solar, wind, etc energy being put to use for this purpose (of ‘scrubbing’ CO2 from the air). I didn’t mean the process that produces the CO2 also somehow produces the energy to undo its production.

    #162, maybe you answered this… are you saying it takes so much energy to separate the O2 from CO2 that ‘clean’ sources cannot do it, or if they could produce that much energy we’d be better off using it to replace a traditional method before using it to scrub CO2? I am guessing so.

    I’m out of my depth here and probably this may not be an appropriate forum. Apologies for boring you guys, I just don’t know where else to ask. I see (from the link in #157) that these things are being persued. That’s all I was really trying to find out.

    Thankyou for your time and replies.

  14. 164
    James Davey says:

    Onar – “who discovered oil? who invented the technology for utilizing it? Who developed a market for creating values from it?”

    You didn’t. Nor did I. In fact, I think you’ll find fossil fuel use origninated in Roman times. How, precisely, does that fact mean that Mr America of Montana, who drives a Humvee and emits more CO2 than Mr Africa of Kenya ‘owns’ the right to emit the CO2?

    Anyway, your point is utterly, utterly pointless. To reduce global emissions of CO2, you need a global agreement. To get a global agreement you need to enter into negotiations. And to enter into negotiations with the Chinese and Indians, you need sensible proposals. Your proposal is unacceptable to them. you may say “Fine” and walk away from negotiations, but ultimately we will all (or at least, the younger ones of us) pay for that failure.

    “If there is a fixed limit on how much CO2 emissions the world can take there will blossom a market for creating sinks and alternative fuels.”

    I agree. Where we differ is the those who currently emit CO2 don’t own the right to do so in future.

    “You say that China and India would laugh me out of the room with this solution. If so it is only because China and India somehow believe that they have a right to own other people’s property.”

    Where’s the property? This isn’t like your farmer or your radio station. There is no scarcity of atmosphere in which one can emit.

    YOU believe that YOU have the right to emit 20 tonnes of carbon a year, because YOU CAN.

    China believe that when THEY CAN (and believe me, in 30 years, they’ll be able to) emit 20 tonnes of carbon per person by year, the have that right.

    Who are you to tell them what they can or cannot do? And (assuming that we can agree that CO2 is a problem) how are you going to stop them emitting?

    Invade?

    Or negotiate?

  15. 165
    James Davey says:

    Christian, #156

    “Which brings me to my attitude on the topic. Even an undergrad like me without years of training can see the writing on the wall. I find it frustratingly difficult conversing with people on this topic when all anyone seems to be concerned about is the economic impact. The economy is a fictitious make believe concept created by humans in order to control each other. While I am making plans to ditch my western lifestyle, move to a place less effected by climate change and commence a sustainable life without cars, tv sets or the requirement of “money”, everyone is worried they are going to be worse off financially!! How are you going to survive in a 2 degree hotter world?”

    1 – While I agree that a 2 degree rise in global mean temperature may be a bad thing, and should (but won’t) be avoided, it isn’t going to bring the downfall of civilisation as we know if, particularly in Europe and the US.

    2 – The reason economic arguements are important are twofold

    i : There are a lot of people who say it’s too expensive to deal with climate change. You can persuade them they are wrong with economic arguements

    ii : For people in the 3rd world, development IS life. And development, the complicated beast that it is, is related to the world economy. A global recession will make it harder for the developing world to bring themselves that little bit closer to development.

  16. 166
    Hank Roberts says:

    > the downfall of civilisation as we know if, particularly in Europe and the US …

    While this is reminiscent of

    “what is perhaps the most famous of Gandhi stories. On a visit to London in 1931, for a conference on determining Indiaâ��s political future, Gandhi was asked by a British journalist what he thought of Western civilization. â��I think it would be a good idea,â�� he replied.”

    http://www.mkgandhi.org/articles/abusing_gandhi.htm

    The author goes on to tell a story rather poignant in the current climate debate.

    “… a little-known story that has, to my knowledge, never found its way into the Gandhi anthologies and Gandhi biographies.

    “….. an Indian, Yusuf Meherally,… a freedom fighter, founding-member of the Congress Socialist Party, and sometime Mayor of Bombay…..

    “In 1946, Yusuf Meherally was in the United States. He was dying of tuberculosis, and had come to rest from his labours in India. His past ten years had been spent mostly in prison…..
    ….
    “… this time around, he was even willing to offer the British some praise. …. asked for an explanation. ‘

    “‘They are leaving,’ answered Meherally. ‘Any day now, we will be free. Gandhiji says that now that they are going, we must remember the best of British civilization the rule of law, their sense of fair play, and so on. Remember it, and keep it.’”

    Does the West have a sense of fair play? I hope so, in the climate context.

  17. 167
    James Davey says:

    Lendel Zed, re #163 : Actually, there’s already a widely available, cheap, efficient, self-healing technology for turning CO2 into O2 and C-something. This is, of course, the plant.

    There is absolutely no point trying to develop land-based carbon scrubbers seeing as we have trees. Sure, we could probably develop a more efficient scrubber than the tree, but the cost, energy required to run it etc. would be prohibtive. And the CO2 is only present at 400ppm or so, which means you have to process a phenomenal amount of air to remove any significant volume of CO2 (I’m not saying anything about chemical methods to reduce ocean CO2, but this would probably be likewise impractical, because CO2 in VERY dilute in sea water)

    What we should do is this

    Stop deforestation and invest in reforestation.

    Use market forces to get clean energy supplies. (It’s much more sensible to invest in ways to reduce emissions, rather than in ways reduce atmospheric CO2. Treat the cause, not the symptom)

    Invest in adaptation.

  18. 168
    olle w says:

    Our life is much more linked to our standard of living and economy than the potential climate changes. Environmentalists simply donâ??t have a clue on what makes this world tick. There for itâ??s dangerous when they come with drastic soviet like â??solutionsâ?? that would cripple the economy and send it in to a huge depression. Then there will be no recourses available to do any meaningful about the potential problem. New technology and adoption to the real climate change when it happens is the only way forward. Today we can use bio fuels with existing technology, in the near future we have hybrids, electric , fuel cells, coal fired power plants can deposit CO2 in to the oceans and so on. With in 50 years fusion power will most likely have solved all our energy problem any way.

  19. 169

    Re “With in 50 years fusion power will most likely have solved all our energy problem any way.”

    Fusion is going to be economical no more than 5-15 years from now. Unfortunately, that’s been true for more than 50 years. ;)

  20. 170
    Dan says:

    re: 166. “Environmentalists simply don’t have a clue on what makes this world tick. There for it’s dangerous when they come with drastic soviet like “solutions” that would cripple the economy and send it in to a huge depression.”

    Oh really? That is a red herring that comes straight from industry PR with no basis in reality. For just one example (there are many more and in other areas worldwide), in the US, prior to passage of the Clean Air Act Amendments of 1990, industries and certain politicians far and wide loudly cried wolf about the devastation it would bring to the economy. Which was promptly followed by some of the strongest economic growth in the nation’s history during the Clinton Administration.

  21. 171
    Grant says:

    Re: #163

    You’re very welcome. But don’t feel that it’s “trouble” for us to provide useful information on the issue; that’s one of the reasons this site exists.

  22. 172
    James says:

    Re #167: “Actually, there’s already a widely available, cheap, efficient, self-healing technology for turning CO2 into O2 and C-something. This is, of course, the plant.”

    I wonder if anyone has ever tried to work out some actual numbers on this? There are large areas of the world – the Sahel, much of Australia, parts of the western US – that have been partially or totally devegetated by human activity. Suppose the world could overcome the political difficulties, and re-vegetate these areas? (I say re-vegetate because much of the area was originally grassland rather than forest.) How much CO2 would that sequester?

    And re #168: You say “…in the near future we have hybrids…”. Sorry, but the future snuck up while you weren’t looking, as there’s a hybrid sitting in my driveway now :-) As for the economic disaster that CO2-mitigation programs are supposedly going to cause, consider this: At the present time, goverments extract a certain percentage of your income in taxes. In the US it’s mostly a federal tax on income and a state-level tax on sales.

    Now suppose part or all of those taxes are replaced by CO2 taxes on gasoline, electricity from fossil fuel plants, etc. The government is extracting the same dollar amount. Some things will cost more, if making them produces a lot of CO2, other things will cost less, but the total will remain the same. How does this cause an economic disaster?

    In addition, the makers of CO2 intensive stuff will (if they are sensible) work to reduce the amount of CO2 they use, in order to better compete in the marketplace. This means that they are producing their goods more efficiently, thus causing a _gain_ in productivity, and that’s good for the economy, isn’t it?

  23. 173

    From comment 162,

    From the thermodynamics you can get decent orders-of-magnitude immutable lower bounds on the amount of additional energy necessary—and it must be a few times the energy released in the combustion. This is really really really big.

    That is false, but it would be true if what were being discussed were capture of carbon as the pure element, and not as a carbonate.

    Burning a mole of elemental carbon yields 393 kJ; in fossil fuels, attached hydrogen typically raises the yield above 600 kJ per mole C. Extracting a mole of CO2 from air in which it has diluted itself to mole fraction 0.0004 takes at least -RT ln 0.0004, at 300 K that’s at least 19.5 kJ. Later on, as the mole fraction got back towards the preindustrial 0.00028, the minimum work of extracting each of the last moles above that level rises to 20.5 kJ.

    Quicklime uses rather more than 20 kJ to yank down CO2, and thus will do so rather roughly, even from much greater dilution than nature provides. That, I think, is why the area that must be quicklime-covered is such a small fraction of the Earth’s surface, no larger than a three-gigawatt biofuel plantation, even if everyone in India and China insists on getting around in a Hummer fuelled with coal-derived gasoline.

    The subsequent extraction of pure CO2 from the produced lime takes 178 kJ of mere heat, not electricity. So in fact the heat needed is a manageably small fraction of the heat the CO2′s production yielded.

    Certainly it’s better not to burn the fossil fuels in the first place, but if they are burned as everyone on a public payroll seems to wish, the atmosphere can still be put back the way it was, with respect to CO2 anyway.

    From comment 164,

    I understand it takes energy to turn CO2 into O2 and C-anything else. I was alluding to solar, wind, etc energy being put to use for this purpose (of ‘scrubbing’ CO2 from the air). I didn’t mean the process that produces the CO2 also somehow produces the energy to undo its production.

    Right. It can be scrubbed out without ceasing to be CO2. Limestone is CO2 that is solid because it is combined with CaO.

  24. 174
    Matthew Kennel says:

    Reforestation and increasing the biomass doens’t sequester CO2 on a long timescale unless the dead plants do not decay and release it back into the atmosphere.

    Sequestration means “in the ground” for a long time as in making new fossil fuel.

    This is extremely slow and difficult—it’s so much better to just avoid extracting existing fossil fuels and burning them, as we are doing at hundreds to thousands of times the rate that they were deposited.

    Possibly biomass in the oceans which sinks down to the depths can stay there for orders of thousands of years, otherwise I don’t feel that reforestation is a potential major solution.

    I see no feasible option except radically lower use of fossil fuels and very large scale substitutions with something else. In that something else I think only nuclear fission can be scaled up to sufficient magnitude with any current of engineering certainty. In reality, of course pursuing all forms of non-greenhouse substitutes is essential as the critical logistical bottlenecks may not all be the same.

  25. 175
    Dan Hughes says:

    #172. In the US the collection of taxes is not uniformly distributed across all income levels, nor are individuals responsible for all taxes collected. I think that something like the top 20% of the population of individual tax payers pay about 70% of the taxes collected from individuals. Those people better be responsible for production of a lot of CO2.

  26. 176
    Hank Roberts says:

    Consider the costs of producing quicklime:

    “Quicklime production is thought to result in about 800kg of carbon dioxide per tonne”

    http://www.ghgonline.org/co2industry.htm

  27. 177
    Hank Roberts says:

    Note the chemistry involved in quicklime production; replacing fossil fuel with solar heating doesn’t change the fact that turning limestone to quicklime releases as much CO2 as the quicklime can then absorb.

    http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000127000003000386000001&idtype=cvips&gifs=yes

  28. 178
    Dick Veldkamp says:

    Re: #172, #174 Sequestration of CO2 by trees

    I looked into the matter some time ago, and here are some numbers.

    Current world CO2-output is 2.4e13 kg/year = 6.5e12 kgC/year (multiply by 12/44). Wood produced by trees: 4000 kg/ha/year = 4e5 kg/km2/year. Wood is about 50% C, so the area you need to offset world CO2 emission is

    A = 6.4e12 / 4e5 / 0.50 = 3e7 km2 = 30 million km2. That is about 1/4 of the world’s land area. For comparison, Russia is 17 milliom km2, the US 9 million km2.

    IPCC (I think it is in the TAR) thinks that 7 million km2 could be used in the short term (the area of Australia) for forestation.

    While I agree that this is no permanent solution (eventually wood will be turned into CO2 again), the numbers seem to suggest that planting trees is not entirely unfeasible, and that we could buy ourselves some valuable time (say a few decades). Also there is a lot to be said for at least stopping DEforestation.

    If anybody has better numbers, feel free to correct me.

  29. 179
    Jeffrey Davis says:

    I’m trying to understand the quicklime/CO2 absorption gag.

    It seems to me that if it were a genuine option, there wouldn’t any quicklime to use, that it would already have absorbed ambient CO2 of which there is no dearth and have turned into something else. What’s to stop it? And yet, I remember having bags of quicklime around from the days when I lived in a cabin without plumbing. It wasn’t outback playing magic with CO2 to any important degree.

  30. 180
    Gareth says:

    Re #172, #178

    I don’t think anyone suggests that planting trees can be a total solution to global CO2 emissions, but they can certainly make a huge difference, both locally and globally. Replacing a forest that has been chopped down, or planting trees where none have grown in recent history, will lock up a reasonable amount of carbon for the lifetime of the forest. The key word is lifetime. Provided that the forest is not removed at some future date – ie, it is sustainably managed – the long term effect will be that a constant amount of carbon will have been removed from the system. In effect, each “new” forest buys us some time to get emissions under control.

    Forest management can also have a large impact on local emissions. In NZ, the Dept of Conservation has done some work that indicates that an enlarged programme of pest control (removing possums, goats and deer – all invasive introduced species) in the forests they manage would allow enough regrowth and therefore carbon uptake to meet all of NZ’s commitment under Kyoto1. As the NZ PM has recently indicated she wants to work towards making NZ carbon-neutral, this strikes me as an excellent contribution.

  31. 181

    Hank Roberts says,

    … turning limestone to quicklime releases as much CO2 as the quicklime can then absorb…

    I would rephrase this as follows: turning limestone to quicklime releases as much pure, sequesterable CO2 as the quicklime can then absorb of the dilute CO2 in air. As earlier said, one stationary, large-scale installation can do this anywhere on Earth, compensating for many small CO2 releasers each of which can be in any region on Earth, continuing to yield the fossil fuel tax revenue to which many in that region are accustomed.

    Roberts’ version makes it sound pointless. But consider the perplexity expressed earlier — “It does seem bizarre that still nothing is really changing on the ground”. Billions of dollars a day in oil and gas money, to people who don’t think of themselves as “the oil interests”, but absolutely are, makes this, to me, quite unperplexing.

    – and a way of preventing atmospheric CO2 concentration from hitting 500 ppm that doesn’t require us to roll over these people, or indeed, require them to conscientiously roll over themselves, seems extremely pointful to me.

  32. 182
    SecularAnimist says:

    Matthew Kennel wrote in #174: “I see no feasible option except radically lower use of fossil fuels and very large scale substitutions with something else. In that something else I think only nuclear fission can be scaled up to sufficient magnitude with any current of engineering certainty.”

    Nuclear fission cannot possibly be “scaled up” to replace enough of the energy produced from burning fossil fuels to reduce CO2 emissions by the amounts that are needed.

    Nuclear fission cannot realistically even be scaled up to replace enough of the fossil fuels used only to generate electricity — which is the only use of fossil fuels where nuclear fission is a “direct replacement” — to have a significant impact on CO2 emissions in anything like the time scale (less than a decade) in which this must be done to avert catastrophic climate change.

    As far as non-fossil-fuel methods of generating electricity, wind power and photovoltaics can both be scaled up — and are in fact being scaled up already — much faster than nuclear fission could possibly be. And both are more appropriate solutions to the growing demand for electricity in the developing world than is nuclear fission. And neither presents the extremely serious drawbacks of toxic waste, nuclear weapons proliferation and vulnerability to terrorist attacks that nuclear fission does.

    But by far the fastest, cheapest and most effective way to “replace” the use of fossil fuels is to reduce waste and increase efficiency, especially in the developed world, and most especially in the USA, which is a flagrant and egregious waster of energy.

  33. 183
    Hank Roberts says:

    Okay, what’s the difference between these two approaches?

    1) Building new coal fired generators that produce pure CO2 and collect it to be sequestered in the first place — at the source.

    2) Building another half century’s worth of old type coal generators, emitting the CO2 etc., and using some of the power to heat limestone to produce quicklime in plants that sequester the CO2 using the same technology not being used by the coal plants

    You might consider recommending

    3) Build the quicklime plant next to the closed cycle new type coal generating plant, use waste heat from the coal generation plants to heat the limestone, and sequester the CO2 from both the coal plant and from the quicklime plant.

  34. 184
    Hank Roberts says:

    Some numbers, found here:
    http://www.powells.com/biblio?show=HARDCOVER:NEW:0618319409:25.95&page=excerpt#page

    “… Most of us have no idea how central coal is to our everyday lives or what our relationship with this black rock really costs us…. The average American consumes about twenty pounds of it a day.

    “… the United States is a big advocate for coal because it has the geological good luck of having more than 25 percent of the worldâ��s recoverable coal reservesâ��about 270 billion tonsâ��buried within its borders…. enough coal to fuel America at the current rate of consumption for about 250 years.
    … western Europe has only 36 billion tons of recoverable coal.
    China has … 126 billion tons.
    India and Australia … have even less than China.
    … Russia,… 176 billion tons,… in remote regions and difficult to mine.”

  35. 185
    yartrebo says:

    Re #163:

    “Before I let it rest, can I qualify something. I understand it takes energy to turn CO2 into O2 and C-anything else.”

    Not exactly. Fluorine can oxidize oxygen via the reaction: 2 F2 + CO2 -> O2 + CF4, which is exothermic. Too bad that fluorine is not only quite hard to produce in its pure form, but CF4 is a very potent greenhouse gas in its own right. Fluorine also has a nasty habit of eating glass among many other things, making its storage and usage very problematic.

    Chlorine and a few other substances might also be able to generate O2 via reactions of the form 2Cl2 + 2CO2 -> O2 + 2COCl2, though I’m guessing the activation energy would be prohibitively high even if the reactions are exothermic considering how stable CFCs are. COCl2 is also a potent greenhouse gas that also does a number on the ozone layer.

  36. 186
    James Davey says:

    “Reforestation and increasing the biomass doens’t sequester CO2 on a long timescale unless the dead plants do not decay and release it back into the atmosphere.”

    Actually, this is not quite correct. If we reforest a deforested area, then the mass of carbon stored in the living forest is removed from the atmosphere. Furthermore, a forest increases soil carbon, though I assume this reaches an equilibrium value over some timescale.

    Of course, one can also do all sorts of clever things, like using plants as biofuel (to replace fossil fuels), or even using plants as carbon pumps. The carbon pump idea works as follows

    1 – Take a coal plant and attach a CCS unit to it
    2 – To captured CO2 in depleted gas reserves etc.
    3 – Produce sustainable biofuel
    4 – Use a coal/biofuel mix or pure biofuel in the plant

    In this manner, plants can be used to reduce atmospheric CO2

    Of course, this is not a pratical solution to the whole problem but it could contribute. Ultimately we must :

    STOP deforestation

    Reduce fossil fuel use

    Invest in CCS

  37. 187
    L. David Cooke says:

    RE: #174, 183

    Hank and Mr. Kennel;

    Curious the discussions regarding the use of lime is not unlike discussions I had back in 1970. The proposal was fine except for the sequesting of the CO2 whether from the reduction in a limewater bath or extraction in a algae pool did not seem to matter. The CO2 would quickly be returned to the atmosphere as the Carbon from the reaction was not a precipitant. However, that the algae could be piped back into the Oil Well and the hydrocarbon in essence recycled for future usage seemed to be a possible benefit.

    The idea being converting fossil fuels to a renewable resource was very appealing. Funny thing though is that we have not seen any discussions remotely resembling this technique. I wonder why?

    Dave Cooke

  38. 188
    Phillip Shaw says:

    This thread has been sort of a blog fruitcake . . . a tasty matrix with nuts and fruits mixed in. :-) Some of the posts have been a bit off-topic but I feel that there is a real value in having an occasional ‘free-range’ topic. It helps me better understand the misinformation and disinformation circulating among us laypeople. We can’t counter what we don’t hear about.

    Re 186: It seems to me that biofuel is close to being a carbon-neutral fuel source for vehicles and power generation. The carbon removed from the air by growing the biomass (minus the fuel burned to grow it) is roughly equal to the carbon released when the biofuel is burned. Much of the remainder is the carbon in the ash and waste which can be sequestered. Growing the next year’s biomass again removes the same amount of carbon from the atmosphere. If biofuel generation can be improved to the point where it is carbon neutral it would appear to be a truly sustainable approach.

    Am I missing something?

  39. 189
    Dick Veldkamp says:

    Re #188 Biofuel

    Philip,

    Basically you are right about CO2-neutrality of biofuel.

    However in reality production of biofuel also takes energy (sowing, harvesting, further processing to fuel that can be used), which takes ‘CO2 efficiency’ down from 100% (= nett emission zero) to a lower number. I have read different figures, but you seem to end up with 25-50% of the CO2 you would have emitted if you’d started with oil.

    Another problem is the area you need (competition with food crops). Did anybody do the math on this? Which area do we need if we want to produce alcohol for the world’s 500 million cars or so?

    James Davey (#186) is right that the first thing to do is save fuel, rather than try different production methods.

  40. 190
    John L. McCormick says:

    Are biofuels advocates victims of disinformation, misinformation or simple failure to think comprehensively?

    There has been some attention – not enough – on the RealClimate pages to the melt back of the Arctic ice, deforestation in the Amazon and jet stream shift towards the poles with expansion of the subtropical zones N and S of the equator.

    Now, I can hardly put all of that together myself but a climate scientist might postulate that greater reliance upon Western North American topsoil to offset US addiction to fossil fuels is a risky proposition given some of the recent research on the above-mentioned topics.

    Maybe the ethanol enthusiasts have it all figured out but they cannot augment recharge of the Ogallala aquifer.

    I know these are pesky details but circumstantial evidence usually is pesky. Nonetheless, failure to factor prospect and consequences of those massive climate-driven dynamics means the US could be building an ethanol industry in a box canyon at taxpayer and consumer (even — dare I mention environmental) expense.

    Park the enthusiasm for biofuels long enough to think through the total implications of a biofuels future. You may not really want what you wish for.

  41. 191
    Phillip Shaw says:

    Re #189:

    Dick, thank you for your comments. I understand that growing biofuel takes energy, but I don’t understand why you say that reduces the carbon efficiency. If I had a biofuel farm, and was using some of my product to run my tractors and processing plant, all I would be doing is reducing the net (saleable) output per acre. Most of the carbon in my fuel still came from the air and will return there when it is burned.

    I agree wholeheartedly that the first priority is to save fuel. But the reality is is that most american cities and suburbs were designed and built for an auto-centered lifestyle. Where I live in Austin, Tx, it is four miles to the nearest market, and that’s not atypical. I drive a 60 mpg Insight, but I still drive about 1,000 miles each month. Rather than bemoan the fact that cars will be a fact of life for the foreseeable future, I’d rather we foster innovations like biofueled diesel/electric hybrids. A carbon-neutral car makes a lot more sense to me than a fossil fuel powered vehicle, whether the fossil fuel is burned in the engine or a distant coal-fired power plant.

    I wish that commentors to RC would refrain from criticizing ‘grass-roots’ efforts for conservation, renewable energy, and sustainable development. These efforts are not a panacea, but they are a step in the right direction and they serve to educate and persuade a lot of people who will never visit this site or read a technical study of the issue.

  42. 192

    From comment 183,

    what’s the difference between these two approaches?

    1) Building new coal fired generators that produce pure CO2 and collect it to be sequestered in the first place — at the source.

    2) Building another half century’s worth of old type coal generators, emitting the CO2 etc., and using some of the power to heat limestone to produce quicklime in plants that sequester the CO2 using the same technology not being used by the coal plants …

    Approach 1 is more thermodynamically efficient.

    Approach (2) is more pragmatic: it partly or wholly solves the CO2 problem without requiring the cooperation of two billion would-be, very likely will-be motorists in Asia, nor that of the builders of “old type” coal-fired generators (which type includes every one of the however many hundred coal-fired plants being built as I write).

    One detail of approach 2 seem strawmannish to me: “using some of the power”, apparently meaning the power produced by the coal-fired plants built by non-cooperators, to heat limestone. That would be electrical power, bought at full market rates, lossily transmitted, and then … converted to heat. No.

    No, the faraway atmospheric trash-collectors could be, and I think would be, farther away than electricity can usefully be transmitted, and would generate their own thermal power for the calciners. Perhaps with fairly ordinary fission reactors that would transfer it to them in short four-metre-diameter liquid lead conduits in which the metal would flow at 10 m/s, being alternately heated and cooled between maybe 1,300 K and 1,600 K. Low pressure at the top, low pressure plus four bar of hydrostatic pressure, maybe that should be “plumbostatic”, at the bottom.

    Although their operating temperature would be high, such reactors’ thermal output would not have access to heat engines that could convert it to any transmissible, saleable form, and as mentioned they’d be far enough off the beaten path that while CO2 could get to them, power demand could not, even if they were connected to heat engines and dynamos.

    So they would excite little or no controversy; they’d get the same pass that small reactors operating barely above room temperature, and therefore intrinsically unable to drive efficient heat engines, have traditionally received.

  43. 193
    Dick Veldkamp says:

    Re #191 Biofuel

    Philip, you are right of course. You could produce even more biofuel to cover the energy cost of the biofuel production itself. You would just need more land.

    I am all for grass roots efforts, as Al Gore says in his movie “These things add up”. On the other hand it is not wrong to do some careful accounting to check feasibility before you start promoting a certain line of action.

    If I may be permitted a somewhat simplistic utopian remark: what we need is a heavy tax on energy (gas, oil, electricity, coal). Just imagine, it would automatically become unattractive to drive big cars, to buy kiwis from New-Zealand, to use equipment with stand by and so on. Also every product requiring much energy in production (like plastic bags) would skyrocket in price and be replaced by better alternatives. Not to mention a surge in wind and solar power. That’s it: one tax and the rest follows.

    (Before you say it: yes I know there’s a lot of details to work out, people who are dependent on cars etc.)

  44. 194
    Gareth says:

    Just imagine, it would automatically become unattractive to drive big cars, to buy kiwis from New-Zealand…

    Kiwis ship their fruit by ship, not air. And if ships are a problem, we’ll reinvent the old wool clippers and send them by sail.

  45. 195
    Hank Roberts says:

    > reinvent the … clipper … by sail

    good news: it’s already being done. Combining keels and parasails looks very good.

    http://www.kiteship.com/images/banner07.jpg
    http://www.kiteship.com/images/banner_marine.jpg

  46. 196
    L. David Cooke says:

    RE: 193

    Dick;

    The problem is that the plastics made from petroleum products were the alternative. The original products such as paper used in paper bags was becoming expensive and uneconomical as the resource was insufficient as we clear cut the last of the unprotected forests in the lower 48. Plastics and specifically plastic grocery bags were the cost effective alternative. What happens if you get rid of plastic or tax it out of circulation?

    There is not sufficient paper to replace them so what do your use then, cloth bags. Most cloth today is originally a polymer fiber or plastic in orgin. So if you remove this resource what do you use, natural fibers? Are there sufficient natural fibers to meet the global requirement, not only no; but even if all the ariable resources were put to use for the generation of biofuels and fibers it would at best meet 10% of the worlds requirements. (Do we go back to animal skins, amphora vessels (pottery) and stone caves, along with oxen/horses and wooden sail boats?)

    Even the simple energy required to light and heat/cool the home is not going to be easy. How do you meet the requirements to sustain the human population of the planet? I certainly haven’t a clue. For immediate needs there is little question that Photo-Volatic can at least reduce the demand; however, the use of solar panels in association with Nuclear generation to make up the difference in demand or to meet demand when the sun doesn’t shine is not a good pairing of technologies. The reason is that Nuclear can not react to demand fast enough.

    So if you couple Solar with an on-site storage system seems to make sense; however, it will require the ability to do so for 48 to 72 hours to allow the nuclear plant to ramp up. When you couple the cost with the requirement to store nearly three days of energy on site really begins to make your tax idea not very attractive.

    Are you sure you guys have thought this through enough?

    Dave Cooke

  47. 197
    David B. Benson says:

    I just learned of one idea that won’t work: grow lots of poplar trees. Seems good as the grow fast. However, these trees emit lots of an organic which is an ozone promoter.

  48. 198
    C. W. Magee says:

    Dear Boron Burner:
    You can’t use quicklime to capture CO2 because quicklime (CaO) is produced by decomposing calcium carbonate in the reaction CaCO3 + heat -> CaO + CO2. If you then scrub the atmosphere with the reaction CaO + CO2 -> CaCO3, then you only get back where you started.

    Producing CaO on an industrial scale from any other source is very difficult and energy-intensive.

    However, over hundreds of thousands of years, the silicate weathering cycle will do this for you, with the reaction CaSiO3 + CO2 -> CaCO3 + SiO2. The timescale for that process is too long to significantly effect the anthropogenic CO2 spike.

  49. 199
    Dick Veldkamp says:

    Re #194

    Kiwis from New Zealand shipped to Europe were just an example (and yes, I know that the travel by ship, not air). I have nothing against kiwis (or New Zealand for that matter). The point is that if energy were more expensive all energy (and hence CO2) intensive activities would automatically be less attractive and CO2-emissions reduced.

  50. 200
    Dick Veldkamp says:

    Re: #196 High energy tax?

    Dave, you raise a lot of questions that all deserve a detailed discussion. Let me just say a few general things.

    1. Yes, providing for the world’s energy needs is not a trivial problem. However if energy were more expensive, there would be a big incentive to make an effort and use all creativity to reduce energy use. Lots of interesting business opportunities too: “Save the planet and get rich”. For example, a recent study in the Netherlands showed that even with current technology energy use in homes could be cut by 80% and in the industry by 50%. But at present there is no money in it!

    2. Paper or plastic bags. In the US it seems to be customary to pack your groceries in paper bags , while in the UK plastic is apparently favoured. In the Netherlands it is quite common to take your own bag or crate if you go shopping – so you don’t need any paper or plastic at all. By the way, paper recycling is now 80% over here – so the need to chop down trees for paper is reduced by a factor 5.

    3. Need for storage of solar energy. Often people do not realise that a. most of us are connected to a big electrical grid b. there always is, and has been, a mismatch between supply and demand (that is, there would be if we didn’t do something about it). The situation is NOT (yet) made much worse by hooking up solar panels or wind turbines as production units. At present storage is not necessary: for example the energy of the solar panels on my roof goes straight back into the grid (and is not stored).

    There is much more to be said about this (in fact the other week I attended a two day workshop dedicated to just this: integration of renewables into the grid) but the bottom line is:
    - we have to be clever to be able to put great amounts of wind and solar electricty into the grid
    - but we are far from having exhausted the possibilities.

    In summary then, a high energy tax would not solve everything, but provide a powerful stimulus to take steps in the right direction, and cut CO2 emissions.


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