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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. 1
    Coby says:

    Can you please provide some indication of the degree of ocean acidity increase that these numbers involve? For example, what pH changes would arise from 500Gt C staying in the air.

    Have any of the stabilisation studies addressed the impact on marine life? ie. stabilised at 450ppm is a common idea (though that ship may have already sailed), what would that mean for ocean acidification?

    [Response:I wrote a post on ocean acidification here, but it won’t really answer your question about how bad it would be, if pCO2 were stabilized at some level. I guess I feel that ocean acidification is analogous to ozone depletion, in that it seems like a fairly frightening, fundamental change to a component of the Earth system, but it’s difficult to point to who exactly would suffer and how much. For ozone depletion, one could get a comparable increase in UV by moving a few hundred kilometers closer to the equator, and yet it seemed a serious enough problem to ban freons, a decision I agree with. Would ocean acidification lead to some sort of biological collapse in the ocean, or extinctions, or would the biological effects even be measurable? It’s hard to know. David]

  2. 2
    Mark J. Fiore says:

    RealClimate does an excellent job on reporting the facts about global warming. This piece on co2 emissions is one of the best, realistic, fact driven summary of the current state of affairs.Realclimate should be required reading for every member of the House and Senate.I believe that worldwide co2 emission levels should be immediately reduced by 80%, right now, for us to have any viable chance at reducing the negative impacts of the global warming trends already in the pipeline.The latest conference. in Nairobi, of the parties to the UNFCCC must extend Kyoto beyond 2012 and implement much greater restricions that those currently in effect.Once again, thanks to RealClimate for all the work that you do.

  3. 3

    Could a 500Gton “emission slug” reasonably called safe given other likely impact besides atmospheric ones the kinds of consequences of ocean acidification that some studies (e.g. The Royal Society, June 2005) point to?

  4. 4
    Andrew Alcorn says:

    Given the environmental changes we are already seeing with less than 1C warming, the idea of 2C being “safe” may need some clarification. Is 2C the point at which some irreversible “tipping” points are thought to occur (meridional overturning current disruption; clathrate release; ice-sheet loss; forest die-off; …)? Putting it another way, can we expect the climate and environment around us to be familiar and reasonably livable still at 2C, for the long term?

    [Response:Replying at once to this comment and the last (#3). The word “safe” seems a little weird to me in this context also. A smaller CO2 slug would definitely be better. I think Hansen takes 1 degree C as his “safety limit”. I guess they’re also referred to as “danger limits”. Maybe that’s a bit better word.

    And in response to just #4, it’s not as clear cut as that to predict when any sort of tipping point might be reached and what it might be that tips. Who knows? We can’t even figure out past tips, let alone predict future ones.


  5. 5

    It is silly to say that a rise of up to 2C in global temperatures is not dangerous.

    A global increase of 2C means will mean an increase of at least 4C on the continents, because they heat much more than the oceans which provide 70% of the surface. Moreover, with polar amplification you will get 8C in mid latitude continental areas such as the USA and Europe, and up 20C in polar regions. That will means a rapid thaw of the Greenland ice sheet, which is already starting to melt, and so the flooding of New York, London, and nearly every other port in the world.

    Here I am emphasising the effects on the developed nations, not out of chauvism but because there is a myth that it is the developing nations who will suffer and we in the west will get off scot free.

    It is obvious to me that with a 33% increase in CO2 above preindustrial levels, we have already reached the limit of a safe increase. The scientific commitment to higher temperatures from the one third increase will lead not only to sea levels that will flood our cities, but also to an increased number of hurricanes, drought and floods that we are already seeing. OTOH, the record wild fires that the USA has experienced this year can not continue to increase, since eventually the lack of unburnt forests will set a limit!

    But unless the scientists come down out of their dreaming spires, join the political debate, and tell the politicians it is time to stop, we will continue to sleep walk towards the precipice, and eventually step over the edge. We do not know the cause of rapid climate change, so we are running forward like a man wearing a blindfolded. What could be more insane than that?

    When are you scientists going to admit that you do not know all the facts? When are you going to have the courage to admit that you are wrong, and that your hubris has led the world to the brink of disaster?

    [Response:I apologize, I guess I used the wrong word, as I responded to the last comment. I’m just thinking of a boundary in the continuum of the climate impacts. Greater than 2 degrees C is clearly dangerous, is what I meant to say. Just to have a number, to talk about. The best would be to not change climate at all, I absolutely agree with you. David. ]

  6. 6
    Hank Roberts says:

    Some earlier discussion in response to:
    Comment by dave – 3 Jul 2005 @ 9:39 pm
    (Click the timestamp to see the original)

    [Response:The ratio of dissolved CO2 to CO32- is about 1:10 preanthropogenic in tropical surface waters. The two will remain about inversely proportionate as CO2 rises. So double CO2, and you halve CO32-. I’d never thought about this in this way, but it sounds like the ratio of the two would reach 1:1 when CO2 reached about three times preanthropogenic, at which point the buffer is getting pretty weak. We should note that there are huge uncertainties with regard to changes in the circulation and biology of the ocean. David. ]

  7. 7
    Karen Street says:

    The Stern report focused on carbon dioxide equivalent, at least the portion I’ve read, citing current atmospheric levels of GHG of 430 ppm carbon dioxide equivalent and discussing stabilizing at 550 ppm or lower.

    How would you rewrite this article if the question were, “How much GHG emission is too much?”

    [Response:I hadn’t thought of the other greenhouse gases. Putting them into the mix would definitely make the not-quite-as-dangerous CO2 level go down. I’m not sure we know what methane is going to do in the future (see my other recent scholary work, “Rasslin’ swamp gas”). More like to go up than down, though, I expect. David]

  8. 8
    Almuth Ernsting says:

    I’ve heard a few people say that we are really at 420 or 430 ppm CO2 equivalent already, once the increase in other greenhouse gases is taken into account. What is the figure for CO2 equivalent at present or where can I find it? Thanks!

    [Response:I just calculated an equivalent CO2 of 465 ppm. I assumed a radiative forcing of 3.4 W/m2 for doubling CO2, and that CO2 accounts for 60% of the total greenhouse gas forcing (no aerosols or anything like that). And that the real pCO2 is now 380 ppm. David]

    [Response: 430 ppm CO2e comes from just taking the 6 Kyoto gases (CO2+CH4+N2O+SF6+HFCs+PFCs). That doesn’t include CFCs, nor O3, nor aerosols, nor land use etc. The argument was made in Stern that the uncertainties in the other components don’t lead to them being easily incorporated into this definition (which is true), and that CFCs (which are quite well known) are not likely to increase further given the Montreal Protocol and subsequent amendments. Our ‘best’ estimate of the net effect of all known anthropogenic forcings is around 380ppm (i.e. most everything else apart from CO2 cancels). PS. the most usual estimate for the adjusted forcing due to 2xCO2 is 3.7 (not 3.4) W/m2. – gavin]

  9. 9
    Hank Roberts says:

    Dang, bad link
    The link to the July 2005 9:39 pm question and response should lead to:
    2 Jul 2005
    The Acid Ocean � the Other Problem with CO2 Emission

  10. 10
    pete best says:

    Once again it comes down to what the politicians can do in this regard whilst maintaining economic prosperity (seems to be a prerequisite for politicians all over the world apparantly). I still cannot see humankind reducing the CO2 levels by the amount required because we will burn all of the available natural GAS and Oil whilst continuing to burn coal through it all because even if we had an alternatibe to Oil/GAS/Coal it nould take 50 years for a worldwide rollout anyways which will still give us potentially dangerous warming because levels of CO2 burning are going to rise worldwide by 50% by 2040.

    Its a nasty situation by all accounts.

  11. 11
    Andrew Alcorn says:

    Re #7. How do you get to 465 CO2equivalent exactly? Sorry, I couldn’t follow the arithmetic. Its seems an important number many should understand…

    [Response:Gavin is an atmospheric modeler, I’m a water guy, so I defer on 3.7. For what it’s worth here’s how I did it.

    Doublings = ln (380/280) / ln (2)

    CO2WattsPerM2 = 3.7 * Doublings

    GHGWattsPerM2 = CO2WattsPerM2 / 60%

    CO2EquivalentDoublings = GHGWattsPerM2 / 3.7

    CO2EquivalentPPM = 280 * 2^(CO2EquivalentDoublings)

    corrections welcome. David]

  12. 12
    ninin says:

    The problem with emission cuts is that we won’t be able to see the science get validated. That would be a real shame.

    [Response:The Montreal Protocol is a bummer for ocean thermocline tracer types. David]

  13. 13
    Paul Duignan says:

    “A warming of 2° C could be accomplished by raising CO2 to 420 ppm and waiting a century or so, assuming a climate sensitivity of 3.5°C for doubling CO2, a typical value from models and diagnosed from paleo-data.”

    Does this warming estimate include the effect of the current earth energy imbalance which means that there is considerable heat stored in the sea which will come out over the coming decades regardless of CO2 concentration in the atmosphere?

    [Response:Yes, the climate sensitivity parameter is defined as the equilibrium response, after the ocean has had a chance to warm up. David]

  14. 14
    Niko Jaakkola says:

    I regard and the work you guys do very highly. However, I feel that this post oversteps the boundaries of what the blog should be about — communicating and commenting on climate _science_.

    If we consider improvements in human welfare to be our ultimate goal, judgements on what constitutes a ‘dangerous’ or ‘safe’ level of climate change should be based on careful economic analysis, itself ultimately based on a consistent system of values (or a number of alternative value systems, if we find it difficult to agree on a common one). Mitigation of climate change does carry costs, so the question is not trivial!

    The analysis should, obviously, be as complete as possible, in the sense of considering uncertainties and insuring sufficiently for them, considering potential extreme outcomes, considering the effects the inequal global income distribution has on the analysis, and so on. However, ultimately, the question of what is a ‘dangerous’ level of climate change is not a scientific question, but an economic and ethical one!

    I feel would be stronger for sticking to its chosen mission and recognizing its limitations. Maybe you should encourage a bunch of climate change economists to start a ‘twin’ blog focusing on the economic / ethical issues?

    [Response: Well, this post was mainly about what the carbon cycle implies for policy decisions – and that is clearly a scientific issue that those designing such policy need to account for. That is a very different thing than saying that we are in a position to decide what aim policy makers should have or what the cost-benefit analysis shows. David picked some numbers here (I assume) on the ‘dangerous’ limits because they are prevalent in discussions, not becuase we think that they are necessarily right. Another blog run by RealEconomists would be great though! – gavin]

  15. 15
    joel Hammer says:


    Our young climate scientists not only claim to understand global climate, a very debatable claim, but they also claim to be able to forecast the evolution of technology and the human condition 100 years from now.

    [Response: Your point being that no efforts to deal with horse-related pollution should have occured because they didn’t forsee the motor car? Good one…… -gavin]

  16. 16
    Blair Dowden says:

    I would like to point out that some of the figures presented in this article are rather different than those given by James Hansen (eg. in this summary).

    David says fossil fuel emissions are “5 Gton C per year from fossil fuel combustion, with a further 2 Gton C per year from deforestation,” while Hansen states that annual emissions are now 7.5 Gigatons. The 2 Gt/yr for deforestation seems rather high, even if you count forest fires.

    David says “the natural world is absorbing CO2 at a rate of about 2 Gton C per year into the land biosphere and into the oceans, for a total of about 4 Gton C per year,” whereas Hansen says “The ocean is thought to take up about 20-35%, leaving 5-20% as the net sink in vegetation and soil.” While a little uncertain, it suggests the ocean takes up quite a bit more than the land.

    David assumes a climate sensitivity of 3.5 degrees C for doubling CO2, while Hansen works with 2.7 degrees C.

    Finally, David says “The models tend to predict a maximum atmospheric CO2 inventory of about 50-70% of the total fossil fuel emission slug.” Given that about 60% of CO2 is being absorbed now, with little change in trend over the past few decades, what is going to change to reduce that amount substantially?

    [Response:The range of climate sensitivity from IPCC is 1.5 to 4.5 degrees C. Hansen also assumes 1 degree as a danger limit, if I remember correctly. According to him, we’re already over the line (1 degree is the equilibrium warming to the CO2 already in the atmosphere. Sabine et al (Science 305: 367, 2004) estimates that the ocean contains 118 Gton C of the fossil fuel carbon, while the atmosphere contains about 200 Gton excess C. David. ]

  17. 17
    Tom Fiddaman says:

    Re 14

    I think the post actually could have gone much further toward policy without leaving the domain of science – there’s an awful lot of science required to determine the impacts of a given level of CO2/warming on the biosphere etc. before getting to the economics. Too many economic impact assessments start with the assumption that welfare=consumption and the global distribution of agriculture and capital is in equilibrium with climate, and neglect the physical world.

  18. 18
    Jim Baerg says:

    The figure of reducing CO2 emmisions down to about 10% of current emmisions answers half of a question I’ve had about AGW.

    The other half is beyond the scope of this blog, but can anyone point me to a discussion of how much fossil fuel is used for various applications? With current technology any stationary uses of energy can be done with a mix of nuclear, hydroelectric etc., but small mobile machinery like cars, bulldozers & farm tractors are hard to run on anything but fossil fuels.

    I’ve seen energy use broken down into categories like transportation etc, but we need more detail to determine how low emmisions can go with current tech, since railways can be electrified & large ships can run on nuclear.

    Also, any practical cuts would have to be a few % a year continued over decades, as old equipment is replaced with non-fossil or more efficient equipment. How does such a gradual decline in emmisions affect the calculated climate effects?

  19. 19
    Hank Roberts says:

    Worth reading:

    Conclusion: Acting Under Uncertainty

    The Montreal Protocol was by no means inevitable. Knowledgeable observers had long believed it would be impossible to achieve. The ozone negotiators confronted formidable political, economic, and psychological obstacles. The dangers of ozone depletion could touch every nation and all life on earth over periods far beyond politicians’ normal time horizons. But although the potential consequences were grave, they could neither be measured nor predicted with certitude when the diplomats began their work.

    In the realm of international relations there will always be resistance to change, and there will always be uncertainties. Faced with global environmental threats, governments may need to act while some major questions remain unresolved. In achieving the Montreal accord, consensus was forged and decisions were made on a balancing of probabilities — and the risks of waiting for more complete evidence were finally deemed to be too great.

    “Politics,” stated Lord Kennet during ozone debates in the House of Lords, “is the art of taking good decisions on insufficient evidence.”14 The success of the Montreal Protocol stands as a beacon of how science can help decision makers to overcome conflicting political and economic interests and reach solutions. The ozone history demonstrates that even in the real world of ambiguity and imperfect knowledge, the international community, with the assistance of science, is capable of undertaking difficult and far-reaching actions for the common good.


    Latest Information
    October 20, 2006
    2006 was a record-breaking year. The area of 29 million square kilometers (11.4 million square miles) on September 24 tied the largest value (on September 9, 2000) and the value of 85 Dobson Units on October 8 was the second lowest ever recorded by satellite measurements. The year also saw the second largest sustained ozone hole. In September and October, temperatures in the middle stratosphere set many record lows.

  20. 20

    The carbon flux numbers are quite dated. It’s now over 8Gt per year from fossil fuels, and rising very fast.

    See this link for a graph through 2004.

    (that’s emissions data from ORNL through 2002, extrapolated by BP fuel production data after that).

    Global coal production is increasing by 5-7% annually from 2001-2005 (see the numbers at

    It’s extremely hard to see how we can stabilize the climate change under 2 deg C on this trajectory, and yet 2 deg C itself seems a dangerously high goal (given Eemian sea level 5m or so higher than present and the present lack of quantitative understanding of how fast the ice sheets will equilibriate to give that sea level).

    There’s also a Science paper this week arguing that maintaining concentration below 450 ppm (which they take to be the threshold for 2 deg C) would require in the near future reaching an annual 3.2% reduction in carbon emissions.

  21. 21
    Timothy says:

    Re: Gavin’s response to #8. “…most everything else apart from CO2 cancels

    …but, if aerosols are a net negative and given that they have an atmospheric residence time of ~days-weeks compared to ~centuries-millenia for CO2, CFCs, then it’s a bit non-useful to cancel out some of the other non-CO2 forcings with aerosols.

    From a scientific point of view [rather than a political/economic point of view] I’m really worried that the 500-550 ppm CO2-eq stabilisation level takes us far too close to the edge. There are a lot of thresholds at around that ballpark level: Greenland, permafrost melt; soil carbon feedback.

    It would seem to me that an emissions pathway that took us to 550 ppm, could easily end up being a lot higher [750+?] if we were “unlucky”.

    From a politics/economics point of view, I still don’t see any sign of concrete policies being proposed that would limit CO2 emissions at all, let alone stabilise them at any level <1000 ppm. You simply have to look at where the investment money is going [or not going] in terms of the oil majors, etc, to see that the captain hasn’t given the order to turn the supertanker around yet.

    It does seem bizarre that still nothing is really changing on the ground.

  22. 22
    Aaron says:

    Sorry if this comment is only incidentally related to this posting, but I am surprised to see that RealClimate has so far let Christopher Monckton’s attack on the Stern report, the IPCC, Mann’s hockeystick, James Hansen, etc. go unaddressed. I wouldn’t have mentioned it, except that it received front page attention at Slashdot and a surprising number of links at, which suggests to me that the denialists are really latching onto this piece. Is there a refutation in the works at RealClimate? It could probably just be a series of links, since most of the arguments made by Monckton have already been refuted here.

    [Response: It’s a neat tactic to package so much mis-information into one article that it requires substantial effort to debunk – effort that most of us can’t afford to spend (what with having actual jobs and such). Maybe we need to think about new ways to combine efforts to do this though… WikiDebunk perhaps? But watch this space. -gavin]

  23. 23
    llewelly says:

    Two questions:

    … 2C seems 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) I recall that Greenland’s ice sheet is 6m sea level rise equivalent, while WAIS is 7m sea level rise equivalent, for a total of 13m. That implies 2C rise is enough to melt GIS, WAIS, and a bit of EAIS. That’s a big reduction in surface area covered by ice, and therefor, a big reduction in albedo, right? (Unless it is counterbalanced by more clouds?)

    … assuming a climate sensitivity of 3.5C …

    (b) Why 3.5C rather than 3.0C ?

  24. 24
    Phil Atack says:

    I am not a mathemetician or a scientist. I have a layman’s question.

    Assume that some wake up call achieves a revolutionary shift in political priorities re GHG emissions. A year of anarchy perhaps in which gas guzzlers and Beoings are destroyed on the tarmac by an uprising of concerned citizens round the world. Assume that this is enough to make world politicians realise that they should start worrying about their granchildren instead of their own careers.

    Assume that this year of anarchy occurs in 2008 and as an immediate result GHG emissions were held constant at end 2007 levels through 2008.

    Following this, the world political community realise that radical global change has to occur in order to return order to the streets.

    After 2008, by some miracle of honest and fair implementation, global regulation perhaps, that global GHG emissions reduce by 5% per year until end of 2024 (straight line attrition) and that in 2025 fossil fuel use flattens out at 20% of the 2008 level of GHG emissions. Assume that sanctions on the burning of fossil fuels allows innovation to deliver substitute renewable energy sources to sustainably replace all attrition in fossil fuel exploitation.

    Would this scenario be enough to hold the world temperature increase within the “Stern” 2 degree C target in the longer term? Best Case/Worst Case.

    Could the GHG emission reduction strategy be less severe than this?

    Anybody prepared to have a go at this calculation?

    Phil – A concerned Grandad.

    [Response:I think to a first approximation you can just add up the total emissions through time of whatever scenario you’re envisioning, and if it comes to less than 200 Gton C, you’re probably staying within the 2 degrees C. David]

  25. 25
    Nigel Williams says:

    RE 21, Timothy wonders why nothing is really being seen on the ground. If there is sufficient ice hung up above sea level to give us say 20 metres of sea level rise, then I wonder if the thing that is holding it all together at the moment is the input of the anthropogenic forcings into the latent heat of fusion being absorbed by all that ice. It’s a huge sink.

    I’ve noticed that if you put a pair of ice cubes in a box, then they both hold up until they are both ice at zero C, then they both melt with a rush when the trigger Joule is absorbed. If the same thing holds at a global scale, then when it starts to happen we will definitely be living in “interesting times”!

    I guess a measure of that issue would be the proportion of global ice that is currently at zero C. Do we have any idea of that?

  26. 26
    Katherine Cinq-Mars says:

    You mention a climate sensitivity of 3.5 C for a doubling of CO2 and say that it’s a typical value. I was under the impression (or wishful thinking) that 3.5 C was more towards the high end of the range for climate sensitivity. Are there any estimates of the likelihood of different climate sensitivities? What range for climate sensitivity is the IPCC working on? Thank you.

    [Response:The range from IPCC was 1.5 – 4.5 degrees C. I don’t know if the real climate sensitivity is higher or lower than 3.5 degrees C, I just chose a number for discussion. David. ]

  27. 27
    Christopher Sargent says:

    I was wondering if anyone was going to take on Steven Milloy’s latest challenge:
    Challenge issued to environmental journalists and advocates of catastrophic AGW (Anthropogenic Global Warming):

    He says, “We believe climate models are programmed with excessive climate sensitivity based on a flawed understanding of past ice ages. Moreover, climate models wrongly magnify potential warming to accommodate positive feedback mechanisms while comparison with empirical measure shows negative feedback dominates, reducing warming experienced to about half theoretical values.

    The challenge is for you to actually check the numbers — see for yourselves whether we are wrong or not. Look up Stefan’s Constant or just use 5.67 x 10-8 (close enough for our purpose but look it up to be sure). Now use it to check the assertion: “Global climate forcing was about 6 1/2 Wm2 less than in the current interglacial period. This forcing maintains a global temperature difference of 5 °C, implying a climate sensitivity of 3/4 ± 1/4 °C per Wm2.” Either consult your texts for Earth’s temperature in Kelvin and any other numbers you need or see the numbers we’ve used here. Off you go — we’ll wait.

    Back so soon — how did you go, prove us wrong yet? Well, we’re waiting. All you need to do is show us where we’ve messed up the calculations and we’ll publicly retract and correct. We’ve left you plenty of opportunities in our analysis of models and climate sensitivity. While you are about it, see how the “smoking gun for global warming” turned out to be nothing but a clown gun, just another failure of “global warming proof” that didn’t make it into mainstream media coverage. Why is that?

    If it’s proving too hard following a moderately complex document, try this simple one where we find significant heating does not trigger self-perpetuating enhanced greenhouse from the most prolific and important greenhouse gas — water vapor. Same deal — show us where we’re wrong and we’ll retract and correct.

    We believe estimations of “dangerous climate interference” are based on seriously flawed models producing patently ridiculous “projections.” We find no evidence the world is conforming to the models and therefore conclude it is the models that are wrong (aren’t we terrible?).

    We see no evidence carbon constraint will have any measurable effect on global temperatures and conclude desperate measures to transform energy supply have vastly greater potential for harm than for good.

    We place our calculations online where scrutiny is invited and expected.

    The only question now is whether reporters still follow the science or simply follow the faith.”

    Thank you

    [Response: He’s a funny guy…. We’ve dealt with the reasons why climate sensitivity is considered to be around 3 deg C for 2xCo2 in many pieces, and Milloy’s arithmetical sleight-of-hand doesn’t impact any of that. (Clue: dividing any temperature by any energy flux one can get something in the same units as climate sensitivity, but it won’t be the same thing). I note that Monckton’s recent piece tries to pull the same trick. We may take this on for a bit of target practice…. – gavin]

  28. 28
    L. David Cooke says:

    RE: David’s Post

    I have a few simple layman’s questions. Rather then the data that David lays out we consider the data presented on the Oak Ridge Nat. Lab. that the Global Carbon Cycle Balance on an average year between 1997 and 2002 or even the NOAA data for 2004 we get very different numbers from what I think I read in this article.

    In the later two examples we have values of between 205 and 210 CT C that goes into the atmosphere and between 207 to 212 that comes out of the atmosphere. Also from these sites we get an average direct anthropogenic contribution to the atmosphere of between 5 and 6.5 GT C where some tables indicate a value as greate as 7.5 GT C (It must be the difference in contribution from deforestation or forest fires).

    Given this the total anthropogenic contribution to the atmosphere on an annual basis is approximately 3%, if I read things correctly. Though David is likely correct that a reduction of 3-4 GT C would likely allow things to return to a balanced level, it means we must halve the current contribution across the globe to get close to the correct balance.

    It really does not matter if you recharge your vehicle at the wall socket (Though under nuclear sources this is not true.) or run a methane/ethane/biodiesel converted fossil fuel engine or feed and water your burro your “engine” will still emit high amounts of CO2 with any of these systems. The time necessary to move to a Carbon free energy system is likely a min. of 30 years away.

    Which is the the preferred manner in which to deal with the problem now? Do you start today to cut back 1/2 of the energy you use every day? Do you only drive 1/2 of the distance to work or school and walk the balance? (I would love to see the average worker in DC drive only 30 miles and attempt to walk the balance in 8 hours there and 8 hours back.) Do you only light or heat your house and warm the water on average for 4 hours every day? (Even with R-40 insulation throughout you would average 1/2 the equilibrium between the daily high and low within 8 hours. What do you do if the high is less then 68 degrees?) Do you not buy anything made of or covered by plastic? Do we reduce the population of the globe by 1/2 in the next 5 years? (Even if you halfed the population of the US you only get back 10% of it’s contrabution to GW, that leaves the other 80% to be dealt with.)

    It simply makes much more sense to boost the natural processes 1.5% to sequester the 3 GT C that it currently is not. Would it not make more sense to start the process of dealing with the immediate problem while working on the other issues. It almost appears that the issues will not get dealt with in a timely manner, so why do we we have to endure the “knawing of the bone” Ad Nauseum.

    Apparently, if it truly was a big deal you would think a few scientists could put together a fully funded NSF research project that involved a research ship to be chartered to dump several tons of Ironite mixed with sargasso weed for 6 months for less then a million dollars per year. If each of the major industialized countries did the same you would be at a balance in next to no time, wouldn’t you?

    Dave Cooke

    [Response:There have been iron fertilization experiments in the ocean, many of them, and there’s no evidence from the field or from models that this technique could make much of a dent in the rising atmospheric CO2 concentration. The reason is the long equilibration time between the atmosphere and the ocean; if we could keep it up for 500 years, we might make some progress, but on shorter timescales, walking to work is more practical. I do it every day. David. ]

  29. 29
    Lynn Vincentnathan says:

    Again, an excellent post. We certainly do need to think beyond 100 years, since we are the ones causing the problem for hundreds of years to come, perhaps millennia.

    As for economic tipping points, I keep thinking about how the stock market nearly crashed in the 80s bec of a computer glitch (nothing to do with productivity). So, I’d say the economic tipping point (the point at which economic problems, increasing economic inequalities, econ & polit fears, frustrations, fighting, wars, social chaos throw us into a really bad state) is probably well before the 2 degrees warming. Look at Katrina, and scientists tell us that wasn’t caused by AGW (or they are unable to tell us), so what’ll be like in 5-10 years when AGW harms greater than Katrina really start kicking in.

    Also, another problem w/ neoclassical econ is that it mainly measures the monetization of the economy, not actual productivity, and certainly not quality of life. (For instance they might find a severe hurricane year to be just great, due to all the rebuilding.) And they reduce everything to (or equate everything with) money. While diamonds may be more valuable than bread, we just can’t eat them. Cost/benefit analyses are pretty useless when you’re standed on a desert island. At least paper money can be used as toilet paper, though. I would suggest another measure, “LIFE-YEARS,” over money. So how many life-years is my driving to the coast going to cost re earlier death for people due to GW harms.

    What we need is a holistic view, including the hard sciences and the social (economic, political, etc), cultural (beliefs, values, ideologies), and psychological (craziness factor) dimensions of the human/world system to fully understand climate change, its causes & consequences.

    In anthro and sociol they have revitalization (or social) movement theory: people fairly suddenly change and construct a better culture/society. I think that’s our only hope. The problem is large numbers of people have to sense something is really wrong, have some acurate assessment of it, come up with technical and structural solutions, and implement things. I know we have the technical solutions (see, we just need to have a social movement to implement them. And it seems no matter how alarmist environmentalists become, people aren’t connecting the problems to their lives or those of their children, and they certainly aren’t connecting the causes to their actions.

  30. 30
    Lynn Vincentnathan says:

    Forgot to add, “life-years” (measured in earlier death of people) for as long as the GHGs one emits today are doing harm & causing death, part of which could be in the atmosphere for millennia (as David pointed out in a previous article here re life time of CO2 in the atmosphere).

    And we need to consider all the indirect effects (not just heat deaths), such as crop & potable water loss & destruction of the web of life from AGW, AND wars & fighting due to harms due to AGW. The suicides of drought-stricken farmers in India, etc.

  31. 31
    Katherine Cinq-Mars says:

    In response to comment 19, I think it’s important to recognise that the Montreal Protocol on substances depleting the ozone layer largely became possible when a substitute was found for CFCs in most applications. Essentially, pressure from consummers and the threat of a ban forced CFC companies to invest in R&D of a substitute. When one was found, all of a sudden the lobby groups for these industries started recognising the scientific evidence that CFCs were depleting the ozone and the Montreal conference was held in a matter of months. Finding a substitute dramatically reduced the losses that the CFC industries would suffer from a ban on CFCs (and thus, the political costs), not to mention that it also meant that the practical uses of CFCs would not have to be given up.

    Unfortunately, the ozone and climate change cases are so different that there really is no basis for hope for climate change based on the success of the Montreal Protocol. In the ozone case, the ban is of one group of chemicals used in fairly limited applications and by just a few major companies. The boycot of aerosols didn’t require big sacrifices on the part of consummers. The same couldn’t be said of a boycot of cars or heating! Also, everybody and all sectors of the economy emit GHGs, not just a handful of companies as in the ozone case.

    I think it’s very important that further research into the science and economics of climate change help reduce the uncertainty on these issues, but I don’t think that uncertainty is the main obstacle to decisive action. Many policy decisions involving huge investments of public money are made on the basis of far less information than what we have on climate change. If policy makers were told that there was a 30% chance that there would be a terrorist attack on a major city, do you think they would delay action until they knew how many people were likely to be killed? or until studies showed whether the economic disruptions of the attack would be worth the investments in increased precautionary security measures?
    Changes in the status quo happen when it becomes possible to minimize the losses of the projected losers from a change in policy (or when there are bombs falling on your head). So, the best contribution scientists can do is not to join the political debate, as suggested in comment 5, but to work on technological solutions that will provide 1) low-carbon alternatives to consummers (so they can afford to put commercial pressure on companies to go low-carbon) and 2) technologies such as carbon-capture storage that will minimise the losses of the major GHG emitters who are also major economic actors and as such have significant political influence.

  32. 32
    Hank Roberts says:

    “There was an old lady who swallowed a fly ….” Know that cautionary song?

    You’re putting too much water, too fast, into the bathtub and it’s going to overflow, because the drain’s not designed to remove that much water that fast. What’s your best response? Figure out how to turn down the taps? Or try to enlarge the drain?

    You can look this stuff up, to find out if anyone has ever thought of it before. Google is your friend.

    “… some researchers and entrepreneurs have proposed boosting phytoplankton growth by “fertilizing” oceans with iron, a nutrient essential to the organism’s growth. Preliminary tests in the equatorial Pacific Ocean and Southern Ocean since 1995 have shown that seeding seawater with iron does increase phytoplankton populationsâ��in the short run.

    “But the prospect horrifies some ecologists. They say the approach could backfire, increasing atmospheric carbon dioxide levels by spurring the growth of the marine bacteria that feed on dead diatoms. “I could see significant warming happening even faster than anyone’s imagined,” says Kay Bidle, a marine biologist at the Rutgers marine institute and an expert on diatom ecology. Beyond that, Bidle and others say no one can predict how dumping iron into the ocean would affect marine life in the long run.”

    This may happen anyway, if we see a whole lot of desert dust blown into the oceans from China and the Sahara — whether we want it to happen or not.

  33. 33
    Richard LaRosa says:

    I wonder if everybody understands that the concentration of greenhouse gases in the atmosphere determines the excess of solar input compared to the longwave IR radiation to space. This determiones the RATE of temperature rise. If the GHG concentration does not change, the temperature will keep rising.

    [Response: Only until equilibirum when the OLR will again match the INC SW. – gavin]

  34. 34
    James Annan says:

    From David’s response to comment #5:

    The best would be to not change climate at all

    Perhaps it was just a throwaway comment that I’m reading too much into, but I have to ask whether this assertion is simply axiomatic, or based on some scientific and/or moral judgement.

    [Response:Interesting philosophical question, thank you for raising it. I guess I look at climate change as an unintended consequence of our energy pursuits. If it’s unintended, I think of it as something to be absolutely minimized, just almost by definition. If one wants to talk about intentional climate change, that’s another thing. In that discussion, I feel that it would be unwise to undertake so momentous, irreversible, and unpredictable project as changing the climate, without at least talking about it first, beyond “oh well, maybe it won’t be so bad”, or “well, but we’re addicted”. Is changing climate something we would do even if it weren’t our link to cheap energy? I think in our current circumstances, the ideal, the best, would be to not change climate at all. David]

  35. 35
    Hank Roberts says:

    Perhaps David’s thinking of precautionary folk wisdom, as in “don’t make waves, don’t rock the boat”?

    “While abrupt climate changes have occurred throughout the Earth’s history, human civilization arose during a period of relative climate stability.”

    Image from A. V. Fedorov et al. Science 312, 1485 (2006):

    where the authors write: “During the early Pliocene, 5 to 3 million years ago, globally averaged temperatures were substantially higher than they are today, even though the external factors that determine climate were essentially the same. In the tropics, El Niño was continual (or “permanent”) rather than intermittent……”

  36. 36
    joel Hammer says:

    [Response: Your point being that no efforts to deal with horse-related pollution should have occured because they didn’t forsee the motor car? Good one…… -gavin]

    No. You missed my point.

    The problem of horse pollution was solved by technological advances, not by limiting the growth of cities, limiting economic growth, or putting arteficial caps on horse manure production.

    Nobody foresaw that the problem of horse pollution would be solved by the automobile.

    In like manner, the pessimists of an earlier day saw the end of civilization because the supply of whales was running out and where would the oils come from which were used to light the cities of the day. Whale oil was crucial as a source of kerosene. That black stuff oozing out of the ground in Pennsylvannia provided the answer. Then, when it looked like the oil industry was doomed by the invention of the light bulb (who needed all that kerosene now) the automobile came along.

    My point is that technological innovation is still going on. Projecting our current technology 100 years into the future is just not realistic.

    [Response:Strawman argument. First off, no-one has ever said that technological developement is forseeable 100 years ahead – that’s one of the reasons why the scenarios have such a large diveregence. Secondly, the reason horses were phased out as quickly as they were was because the costs associated with using horses (maunre, dead carcasses, stabling etc.) were bourne by the same entities that benefited from their services (i.e. cities and businesses). Thus as soon as technology with larger benefits and smaller costs came in, they were adopted. This was very simple. If you want to take a lesson from that, it is that the costs associated with GHG emissions should be bourne by the producers of those emissions such that no new technology is handicapped by effective subsidies to fossil fuel users. Right now, the benefits accrue to the producers, and the costs are likely to be bourne by others. -gavin]

  37. 37
    Andrew Dodds says:

    Re: 34, James..

    Certainly an interesting point – and unless you put an absolute premium on non-interference in nature, there is no specific moral reason. After all – to play the cynic – Nature ‘had’ the planet for 4.55 billion years before humans and will presumably ‘have’ the planet for several billion years after humans [go extinct]/[migrate into space]/[undergo technological transendance]/[insert future here].

    But from a purely practical/economic point of view.. our agriculture is build around a constant climate and any change will be bad because a farmer needs to know the likely weather to know what to plant. Our cities need fresh water; if climate changes and rivers stop flowing then many cities will be written off; and the effect of sea level rises on the large percentage of the world’s population that lives on the coast goes without saying.

    So.. it’s not an axiom, but there are two angles – if we completely screw up the environment then it’s going to take longer than human timescales to recover even if we clean up our act later, and it’s almost certainly going to hurt us economically by more than the avoidance cost.

  38. 38

    Re #33 It is obvious from Gavins’s reply that he is not aware that the level of carbon dioxide determines the rate of increase in temperature. However, the temperature does not keep rising, because higher tempertures mean more water vapour and clouds which reflect more of the incoming solar energy away, and a balance is reached.

  39. 39

    Re #34 I can’t speak for David, but there is a logical reason why we should not change the climate. Modern society has tuned itself to exist on the planet as it is. Agriculture is arranged to match the local climate, and buildings are designed for the climate in which they were built. For instance, in Europe the slope of roofs is set to match the winter snowfall. In a warming world, here in Britain the central heating boilers will need to be replaced with air conditioning units, and the wall to wall carpets with tiled floors. Any change in climate will involve vast costs of adaption.

    More serious is the desertification of the Mid West of the USA, already under way, and the subsequent reduction in global grain supplies.

    But a warming world will also mean that the Greenland ice sheet melts. A 20 foot rise in sea level, which now seems inevitable, will have few advantages. Travelling through the streets of London and New York by gondola, are the only one I can think of!

  40. 40

    Re #22 Here is a rebuttal of Christopher Monkton’s piece that I wrote earlier.

    Here are replies to his ten propositions. You can see that I accept none of his conclusions. He is just a charlatan holding out false promises.

    Proposition – Conclusion
    1. That the debate is over and all credible climate scientists are agreed. – False

    Wrong! All credible scientists do agree that global warming is mainly caused by greenhouse gases. However, the debate is not over anymore than the debate over evolution is over. Creationists and their fellow travellers will ensure that!

    2. That temperature has risen above millennial variability and is exceptional. – Very unlikely

    Wrong! From all the available evidence points to the current global temperature being higher than at any time during the last 1000 years. However, that is unimportant since it is the temperature rise in the future that will do the damage. At present we are surviving fail well, except in New Orleans.

    3. That changes in solar irradiance are an insignificant forcing mechanism. – False

    Wrong! The main source of warmth on the Earth is solar flux. However, there has been little change over the last 100 years, and especially the last ten when temperatures have been at record levels.

    4. That the last century’s increases in temperature are correctly measured. – Unlikely

    Wrong! Extreme measures have been taken in order to correct any errors that may have occurred in temperature readings in order to ensure their accuracy. Examples are the corrections for the urban heat island effect, and for the adiabatic temperature difference in water temperature caused by the height of deck of the ship when taking sea surface temperatures.

    5. That greenhouse-gas increase is the main forcing agent of temperature. – Not proven

    Wrong! The 1000 page IPCC report is enough evidence for me that greenhouse gas increase is the main cause of global warming. What proof would all Mr Monckton accept?

    6. That temperature will rise far enough to do more harm than good. – Very unlikely

    Wrong! Humans have tuned their agriculture and housing to the climate as it is now. Any alteration in climate will have severe costs, and the benefits such as gondolas in the streets of London will be trivial.

    7. That continuing greenhouse-gas emissions will be very harmful to life. – Unlikely

    Wrong! The Paleocene-Eocene extinction and the Permian-Triassic mass extinction are both thought to have been caused by release of methane hydrates. This could happen in the future if ocean temperatures rise too much. Only last night on BBC’s Planet Earth it showed that the polar bears are threatened, and will be doomed if we do nothing to stop the Arctic ice melting.

    8. That proposed carbon-emission limits would make a definite difference. – Very unlikely

    Wrong! The Kyoto limits would not make much of a difference but the were only intended as a pilot experiment. The full limits cutting CO2 emissions to 40% of today’s levels would have an effect.

    9. That the environmental benefits of remediation will be cost-effective. – Very unlikely

    Wrong! If you do not ignore or downplay the costs of global warming, which should include a rise in sea level of 7 meters, drowning London and all other British ports, then the costs of doing nothing soon escalate.

    10. That taking precautions, just in case, would be the responsible course. – False

    Wrong! Who does not take out house insurance against fire, flood etc. against the full value of their home? If you were to consider the odds of it burning down then it is only one in a hundred, so why not only insure for 1% of its value. That is the false reasoning of the self proclaimed Monckton of Brenchley!

    If he has a serious scientific contribution to make why does he not write to Nature or Science where his ideas can be properly accessed? I would attack the Telegraph as a Tory rag, but in fact even they printed a rebuttal of Professor Lindzen by their weather correspondent, a qualified meteorologist. See

    Here is a more sensible article from the Telegraph So you can see that in fact, as Sargent Frazer in Dad’s Army used to say “Waur doomed!”

  41. 41
    Fernando Magyar says:

    Would some of the climate scientists here care to comment on this article in today’s New York Times:

  42. 42
    Pascal says:

    Is it possible to get the good amounts of fossil fuel CO2 and deforestation or land-use CO2?
    When I look at NASA-GISS, I don’t find David’s amounts.

    [Response:Sabine et al (Science 305: 367, 2004) estimate 118 Gton of fossil fuel C in the oceans, and that the land is near zero net (deforestation + “greening” or whatever the high-latitude sink is). The atmosphere contains about 200 Gton of fossil fuel C (100 ppm * 2 Gton C / ppm). So I get about 300 for the total anthropogenic carbon emission. David]

  43. 43

    Re #27 and “If it’s proving too hard following a moderately complex document, try this simple one where we find significant heating does not trigger self-perpetuating enhanced greenhouse from the most prolific and important greenhouse gas — water vapor. Same deal — show us where we’re wrong and we’ll retract and correct.”

    Do a Google search for “Clausius-Clapeyron Law.”

  44. 44
    L. David Cooke says:

    RE: #32

    (Prenote: If my laymans ignorance is showing my humble apologies.)

    Hey Hank;

    Is it not time to defrock ecologists, not that they do not have a point in that it is a good idea to reduce the anthropogenic footprint. We are simply talking a slight boost of 3% total oceanic population of phytoplankton in one year, while humans do the same on the land. (Believe me, I am well aware of alternatives, I have been studying them since 1967. Your ecologists seem to forget that in the case of failure all that is being returned to the atmosphere is the very same CO2 that the phytoplankton were supposedly reducing. Meaning if the experiment fails, the contribution is net zero, except for some a couple million dollars, some ships oil, a little iron re-disposition and a little shading of the GS from the redistribution of a little Sargasso.)

    As to your tub issues, it depends, which can you do most economically, turn down the taps or make the drain larger? If it takes thirty years to turn down the taps 3%, costing 4 trillion dollars and only takes one year to cut out a 3% larger drain costing 3 million dollars, which do you think is the likely action?

    In the presence of the constant bombardment of de-empowering rhetoric coming out of the scientific community, action appears to be taking the reciprocal. Is this true desire, to de-empower the people to the point that the only solution is political? Why can’t a simple green funded test take place. Certainly someone realizes if you distributed the iron contribution widely, the issue of anoxia should not be an issue. (Anoxia is likely to happen only if the “Ironite” contribution is concentrated in one place; if you distributed the iron over a large area where there is likely to be phytoplankton, you would likely reduce the tendency of anoxia from forming. Anchoring the research ship in the middle of the GS and simply taking advantage of the GS for distribution would even save the use of ships oil. For that matter, simply anchoring out a few rusting old hulks in the GS may do the same.)

    In the meantime, government can address the increase towards the possible 15% anthropogenic contribution in 30 years. (Note: You are unlikely to make the drain 15% larger.) The result is you can economically deal with your current issues and set in motion a economically responsible movement towards a solution with a deadline in the future. (Of course if ecologists keep pushing as hard as they are now without taking action themselves the general attitude of the population at large is likely to rebound in the opposite direction, (as was the apparent case in 1980, when economics ruled and the environment returned to the pre-1976 condition for 20 years.).

    Dave Cooke

  45. 45
    yartrebo says:

    Re #25:

    “I’ve noticed that if you put a pair of ice cubes in a box, then they both hold up until they are both ice at zero C, then they both melt with a rush when the trigger Joule is absorbed. If the same thing holds at a global scale, then when it starts to happen we will definitely be living in “interesting times”!”

    There is no such thing as a ‘trigger joule.’ It takes an enormous amount of energy to melt ice from a 0C solid to a 0C liquid (roughly enough energy to heat that liquid to 80C). Try it – take an ice cube that’s at 0C and put it in a small glass of lukewarm water. See if the water is still warm after the ice is melted (it should be just as warm if ice melts as you so describe).

    PS: If ice did melt in this way, one could easily fashion a perpetual motion machine that also generates free cold as follows:
    1 – Take a piston and fill it with water at 0C.
    2 – Have the water spontaneously freeze by removing 1 joule of heat to push it over the edge (pushing against the piston will further cool the ice, pushing it somewhat below 0C) (the joule can be removed just by tugging on the piston a bit – decompressing a solid does cool it down by some tiny amount).
    3 – Melt the ice using heat from the outside.
    4 – Go to step 2.

    And voila, perpetual motion.

  46. 46
    Tom Fiddaman says:

    Re 36

    See the Marland and Houghton datasets at CDIAC.

  47. 47
    Angi says:

    Another view on CO2 emissions can be found on You can find there a nice graph about the emissions of CO2 in 1990, ordered by states. Also, there are some elements highlighted regarding the impact that the ocean and naval war has on climate change.

  48. 48
    Julian Flood says:

    Looking at the CO2 graph mentioned above, it looks as if we produced around 5Gt in 1980, 8Gt in 2000. Very round figures.

    The Mauna Loa graphs suggest that if I cut my CO2 production next year to 1980 levels, the increase in atmospheric CO2 will still be around 1.5/1.7ppm, the same as this year, the same as 1980.

    What am I missing here?

    [incidentally, for the site admin: clicking on comment policy after you’ve typed but not sent a comment leaves no way back and the post is lost. Unless, of course, you know different and you are reading my question twice.]

  49. 49
    Hank Roberts says:

    David Cooke — I can’t come up with sensible responses to your postings, sorry. They don’t make sense to me, from what I know of the science. It seems to me you’re making up fanciful speculation about what might be the case with both CO2 absorbtion and primary production/ecology and saying “why can’t this be true.” Look to nature for your basic facts before you speculate about how nature ought to or might most conveniently work.

  50. 50
    David Lea says:

    Re: original post, #16, #20. 5 Gt of fossil fuel emission is not correct. According to the EIA (DOE), world carbon dioxide emissions from fossil fuels in 2004 was 27,044 Mt CO2 or 7.4 Gt C. The data is available here: