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Global Warming: Not Reversible, But Stoppable

Posted on 19 April 2013 by Andy Skuce

Let's start with two skill-testing questions:

1. If we stop greenhouse gas emissions, won't the climate naturally go back to the way it was before?
2. Isn't there "warming in the pipeline" that will continue to heat up the planet no matter what we do?

The correct answer to both questions is "no".

Global warming is not reversible but it is stoppable.

Many people incorrectly assume that once we stop making greenhouse gas emissions, the CO2 will be drawn out of the air, the old equilibrium will be re-established and the climate of the planet will go back to the way it used to be; just like the way the acid rain problem was solved once scrubbers were put on smoke stacks, or the way lead pollution disappeared once we changed to unleaded gasoline. This misinterpretation can lead to complacency about the need to act now. In fact, global warming is, on human timescales, here forever. The truth is that the damage we have done—and continue to do—to the climate system cannot be undone.

The second question reveals a different kind of misunderstanding: many mistakenly believe that the climate system is going to send more warming our way no matter what we choose to do. Taken to an extreme, that viewpoint can lead to a fatalistic approach, in which efforts to mitigate climate change by cutting emissions are seen as futile: we should instead begin planning for adaptation or, worse, start deliberately intervening through geoengineering. But this is wrong. The inertia is not in the physics of the climate system, but rather in the human economy.

This is explained in a recent paper in Science Magazine (2013, paywalled but freely accessible here, scroll down to "Publications, 2013") by Damon Matthews and Susan Solomon: Irreversible Does Not Mean Unavoidable

Since the Industrial Revolution, CO2 from our burning of fossil fuels has been building up in the atmosphere. The concentration of CO2 is now approaching 400 parts per million (ppm), up from 280 ppm prior to 1800. If we were to stop all emissions immediately, the CO2 concentration would also start to decline immediately, with some of the gas continuing to be absorbed into the oceans and smaller amounts being taken up by carbon sinks on land. According to the models of the carbon cycle, the level of CO2 (the red line in Figure 1A) would have dropped to about 340 ppm by 2300, approximately the same level as it was in 1980. In the next 300 years, therefore, nature will have recouped the last 30 years of our emissions.


Figure 1 CO2 concentrations (A); CO2 emissions (B) ; and temperature change (C). There are two scenarios: zero emissions after 2010 (red) and reduced emissions producing constant concentrations (blue). From a presentation by Damon Matthews, via Serendipity

So, does this mean that some of the climate change we have experienced so far would go into reverse, allowing, for example, the Arctic sea ice to freeze over again? Unfortunately, no. Today, because of the greenhouse gas build-up, there is more solar energy being trapped, which is warming the oceans, atmosphere, land and ice, a process that has been referred to as the Earth's energy imbalance. The energy flow will continue to be out of balance until the Earth warms up enough so that the amount of energy leaving the Earth matches the amount coming in. It takes time for the Earth to heat up, particularly the oceans, where approximately  90% of the thermal energy ends up. It just so happens that the delayed heating from this thermal inertia balances almost exactly with the drop in CO2 concentrations, meaning the temperature of the Earth would stay approximately constant from the minute we stopped adding more CO2, as shown in Figure 1C.

There is bad news and good news in this. The bad news is that, once we have caused some warming, we can’t go back, at least not without huge and probably unaffordable efforts to put the CO2 back into the ground, or by making risky interventions by scattering tons of sulphate particles into the upper atmosphere, to shade us from the Sun. The good news is that, once we stop emissions, further warming will immediately cease; we are not on an unstoppable path to oblivion. The future is not out of our hands. Global warming is stoppable, even if it is not reversible.

Warming in the pipeline

Bringing human emissions to a dead stop, as shown by the red lines in Figure 1, is not a realistic option. This would put the entire world, all seven billion of us, into a new dark age and the human suffering would be unimaginable. For this reason, most climate models don’t even consider it as a viable scenario and, if they run the model at all, it is as a "what-if".

Even cutting back emissions severely enough to stabilize CO2 concentrations at a fixed level, as shown in the blue lines in Figure 1, would still require massive and rapid reductions in fossil fuel use. But, even this reduction would not be enough to stop future warming. For example, holding concentration levels steady at 380 ppm would lead to temperatures rising an additional 0.5 degrees C over the next two hundred years. This effect is often referred to as “warming in the pipeline”: extra warming that we can’t do anything to avoid.

The most important distinction to grasp, though, is that the inertia is not inherent in the physics and chemistry of the planet’s climate system, but rather in our inability to change our behaviour rapidly enough.

Figure 2 shows the average lifetimes of the equipment and infrastructure that we rely upon in the modern world. Cars last us up to 20 years; pipelines up to 50; coal-fired plants 60; our buildings and urban infrastructure a century. It takes time to change our ways, unless we discard working vehicles, power plants and buildings and immediately replace them with, electric cars, renewable energy plants and new, energy-efficient buildings. 


Figure 2 Average expected lifetimes for equipment and infrastructure. 

“Warming in the pipeline” is not, therefore, a very good metaphor to describe the natural climate system, if we could stop emissions, the warming would stop. However, when it comes to the decisions we are making to build new, carbon-intensive infrastructure, such as the Keystone XL pipeline, the expression is quite literally true.


The Matthews and Solomon paper only deals with CO2. Short-lived greenhouse gases like methane are not considered in the study and nor are aerosols. Stopping fossil fuel burning, especially coal, would reduce aerosol (small particle) emissions, reducing their current shading effect and increasing warming. On the other hand, stopping fossil fuel consumption would decrease methane emissions and thus decrease warming even more than these authors have projected. It may turn out that these two effects balance out.

The other potential problem is that the carbon cycle model that Matthews and Solomon use may not be as well behaved as they predict. For example, MacDougall et al (2012) ran their own "industrial shutdown" experiments and found that future CO2 concentrations in their most likely climate sensitivity case remained steady, because emissions from the permafrost (see this SkS post, Figure 3) balanced the reductions from other carbon sinks. This means that a shutdown of human emissions could, in practice, look more like the blue lines in Figure 1.

The likelihood and severity of unexpected carbon-cycle feedbacks, including the way in which the ocean absorbs CO2,  will be larger when there has been more warming—due to more emissions or higher climate sensitivities, or both—but this only increases the need for prompt and substantial action in reducing emissions.

Takeaway points

  • The warming we have caused by our emissions of carbon cannot be undone. 
  • The additional future warming we will experience will be a result of our current and future emissions. 
  • The inertia in the climate system is not natural, but human.
  • Emissions avoided today mean less warming tomorrow, and forever.

The confusion that many of us have with answering the two questions posed at the beginning of the article is probably rooted in our mental models, one being that the climate change will naturally revert back to normal; the other that the changes in the climate system have unstoppable momentum. Neither view is correct and they both favour inaction; one by implying that we can wait to fix the problem, the other by implying that it is already too late.

Metaphors and mental models are essential to understanding the way complex systems work. But they can mislead as well as illuminate. Here are a couple of analogies that I have come up with, but they are not perfect either. Maybe readers can do better. 

  • We can't put toothpaste back in the tube once we have accidentally squeezed too much out, but we can prevent any further waste by stopping squeezing. 
  • Like a bull in a china shop, we can't unbreak what we have already broken, but once the rampaging stops, no more damage will be done. 

Other articles on the paper by Matthews and Solomon can be found at Climate Central (Andrew Freedman) and Serendipity (Steve Easterbrook).

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Comments 1 to 50 out of 117:

  1. Two things:

    1)The link to the PDF is broken. Please help!

    2) What about the "warming in the pipeline" caused not by the current global radiative imbalance, but by the masking of part of the greenhouse forcing by short-lived, man-made cooling aerosols(the so-called "global dimming")? They have masked nearly half of the CO2 forcing, and have very brief lifetimes, unlike CO2 and the other greehouse gases. 

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    Moderator Response:

    [AS] 1) Could you let me know which link is broken? 2) The aerosol issue was discussed briefly in the "Wrinkles" sub-section. I understand that Matthews has a paper "in the pipeline" addressing aerosols and non-CO2 GHGs, but I haven't seen it.

    [DB] The source paper PDF is here.

  2. Excellent article. Even people who have paid attention to the science often have trouble with these details, so it is good to have a clear summation. The only point I might have stressed more is that the bit about warming stopping when human CO2 emissions do is conditional on how high the temperature goes. Currently it is true. At some future higher temperature permafrost and/or methane hydrates may be releasing enough greenhouse gases that atmospheric levels and temperatures continue rising even without further human emissions. This is alluded to in the 'Wrinkles' section, but is one of the major reasons action is needed now. Otherwise, foolish people might reason that we can continue letting the temperature rise and 'just stop emitting when things get bad'. Even in the best case that would mean we'd be stuck with the 'bad' conditions for hundreds of years, but it could also put us past the point where carbon feedbacks kick in and things do keep getting worse no matter what we do.

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  3. Is it not possible to use biochar on an industrial scale to reduce C02 levels? If it were to take a hundred years to reabsorb the CO2 to preindustrial levels it would be worth the effort.

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  4. Thank you for this post!  I've been needing to point to something like this.

    Next we need a post that shows why the uncertainty about sensitivity is irrelevant to our need to take significant action immediately.  In a business as usual scenario:

    1. Here are five versions of graph C--one for each of the sensitivities 1.5, 2, 3, 4, 4.5.

    2. The consequent temperatures in each of those five graphs are sufficiently bad that it is far more cost effective to prevent than to purely adapt.

    I guess we first need a peer reviewed paper for item 1.

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  5. Tom @4 - sounds like you're asking for this post, no?

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  6. Hat tip?

    Excellent article clairifying the science. I think the key issue as in the linked article and your above post is to make certain that people understand warming is mostly stoppable, but not reversible.

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    Moderator Response:

    [AS] Thanks for the link to that article, which I hadn't previously seen. I made it clickable.

  7. Well, heck, you're right, Dana!  Maybe Andy could add a link to that post to his post?

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  8. Damon Matthew's figure 1c doesn't seem to resemble what I recall seeing with regard to the 1% to 2x CMIP3 ensemble.  IIRC the temperature deceleration after stabilzation is much quicker.  Given that the actual growth has been much slower than a 1% growth, the deceleration should be even flatter.  Shouldn't it?

    Regards, AJ 

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  9. @villalob#3, biochar would reduce or delay emittance for a 42 to 100 years. For USA only (based on 1999 figures) one would to torrefact 13,530,208,333 metric tons to replace the coal fired electricity. Pure biomass residues dry matter weight.

    Slightly more efficient approach is to do the torrefaction of the biomass and gassify an amount to produce high hydrogen containing syngas, helped by solar assisted steam generation (ISCC,IGCC combination). Capture the CO2 during cleaning of syngas and use in controlled (greenhouse) environment to boost plant productivity.

    Even capturing CO2 of coal would help right away and can be executed right away. Of course to use the CO2 in plantgrow stimulation not for enhanced oil recover methods.

    Anyway stop emitting of CO2

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  10. Andy,

    Are you sure the climate system doesn't have any inertia? This is a general feature of  system dynamics. Doesn't the ocean act as an accumulator, as a capacitor in a circuit? What, then, is the meaning of "at equilibrium"?

    After a pulse of CO2, "about 40 percent of the equilibrium response is obtained within five years. This quick response is due to the small effective inertia of continents, but warming over continents is limited by exchange of continental and marine air masses. Even after a century only 60 percent of the equilibrium response has been achieved. Nearly full response requires a millennium." (Hansen, 2008, Earth's Energy Imbalance and Implications). I don't think Hansen refers to the socioeconomic system... I may have some misunderstanding here-

    Could you please clarify this for me?

    Thank you


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  11. I can't believe people - everyone - gets this so wrong. Of course Climate Change is reversible. At least the process is. While some of th effects will be hard to reverse as bioregions change, if we act quickly enough that the bases of these zones are still intact, these will also revert. To the extent some changes are permanenet, adaptation will be possible.

    The key issue is how longit takes to start reversing and get back to pre-industrial levels of CO2. That will ultimately determine how much ecosystems are impacted before we can cool the planet. It should be obvious to all that returning GHGs to pre-industrial levels will, in fact, cause the planet to cool over time. The approximate 30-year lag is the largest obstacle. It would take, in the absolute best case, 20 years to draw down CO2 to preindustrial levels, but more realistically closer to 50 since, well, human beings are largely idiots. That means we're looking at roughly 20 to  75 years of additional warming before reaching a level where a relative cooling would take place, with relatively less heat retained a GHG levels fall.

    Far too many people still don't understand the full systemic nature of this. Even without AGW we still have to simplify society due to resource constraints and the instabilities that come with that and diminishing returns to complexity. (See J. Tainter.) Once a society has reached a level where the resource base has been overshot there are two essential options: deceiving itself into believing it can overcome Nature with technology and/or bigger mo‘ai and the magical thinking that comes from both. The fact our economy is based on mythology is what has basically gotten us to this point, being based in a non-mathematical realities that do not even consider physical limits. This cannot go on. A resource-based economy, steady-state is not only a good idea for management of resources, it's absolutley necessary to avoid a collapsed society. This is a choice that is unavoidable. (See J. Diamond.)

    Such an economy requires localization based on bio-regional management of resources. Natural systems and resources will become far more a part of the materials we use. Natural building, virtually no cars, mass transit for the far less movement we will be doing, etc. A huge change will be a natural system of localized food production using regenerative methods, which are based in natural organizational principles. (See permaculture, 30-year Rodale study, Alan Savory, etc.) And this is the first leg of our carbon draw down. According to the Rodale study, very large amounts of carbon can be sequestered in soils, which is where it needs to be anyway. This has addtional positive effects such as mitigating flooding, reducing run-off into water systems and eliminating chemical runoff which is the primary cause of eutrophication. We can even green desert regions with this methodolgy and potentially choose to shape the hydrological cycle.

    The second leg of this is reforestation and aforestation. 40% of the dry weight of trees is carbon. Rebuilding lost forest ecosystems alone will draw down huge amounts of carbon based on estimates from Hansen, et al. I don't recal lthe number, but it is a minimum of 50 ppm, potentially double that. Adding to this a key element to a localized and highly resilient food system, Food Forests, would have hte same, but accelerated, effect given Food Forests are actively managed and accumulate carbon faster than a natural process of getting to an apex forest system. Whereas a prairie to forest process can take centuries, or more, reforestation, aforestation and food forests can reach apex in mere decades, and be essentially established within 7 years, particularly a Food Forest.

    These processes alone can get us to negative accumulation with no changes to our economic system. Add in a full shift to a localized, largely de-industrialized economic and social system with "renewable" (renewables are dependent on FFs, so are not truly renewable, yet) energy and we mazimize this even more be reducing the load we are putting into the atmosphere by 80 - 90 percent.

    In other words, those who call AGW irreversible are bdly incorrect and it is extremely dangerous to keep repeating this defeatist mantra. While it is not intentionally defeatist, it may as well be. Designing sysems depends on initial conditions and a needs analysis. This must have a realistic understanding of the resource base. But if you are convinced we will be living in a radically different world because we cannot draws down carbon, your planning will be skewed to adaptation rather than mitigation and will allow massive amounts of current resources to be lost altogether or squandered on trying to survive an avoidable future.

    The only reason to believe AGW is irreversible is to believe only long, slow natural feedbacks will draw it down. This is blatantly incorrect and is somethiung we need to stop repeating. Fast feedback, human-engineered, natural systems can get us back to < 300 ppm CO2 in mere decades.

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    Moderator Response:

    [DB] Please provide proof citations for your claims, especially this one:

    Fast feedback, human-engineered, natural systems can get us back to < 300 ppm CO2 in mere decades.

    As that flies in the face of established oceanic chemistry.

  12. Agree with comment from CB@2.  As human inertia will not rapidly decline and temps will continue to rise, will not climate inertia pick up on its own with declining albedo and increasing defrosting of the perma frost.

    Thinking beyond zero human GHG emissions, might we also focus on planetary recovery, even in small gradual steps?  

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  13. @Killian #11:

    Please provide citations for the numerous claims that you have made. Thank you. 

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  14. I must admit that when I started reading this post my first reaction was 'WHAT!'.  After carefully reading through it 2 times my reaction was "Ok, that, guess, is technically right. But what a way to misstakenly try to accomplish the stated goal of trying to forestall inaction on the part of people because they have the wrong impressions about the answers to the 2 posed questions. 

    I think that a significant percentage of the readers (not even counting the Deniers,) on initial reading of the post, would come to the conclusion that all we have to do is wait until the rising levels of CO2 have resulted in conditions which are at our limits of tolerance and then we stop emmisions and all is going to be ok.  The Deniers of course would twist the language of the post towards their arguments with no trouble at all.

    In frank words, I think the way this post went about explaining the science completely misunderstands how most people comprehend what they sort of read and will result in exactly the opposite of what the authors intended.   They better hope that the general public is not reading this. 

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  15. Moderator, I stated clearly my awareness of the 30-year lag with regard to the climate system. What I have said flies in the face of nothing, you simply don't know of these exceedingly simple ways to return to pre-industrial levels of GHG's.

    As I said, it is yet a tiny percentage of people who look at the energy, resource and climate issues we have in a fully holistic manner, yet, no discussion of any of these issues is meaningful without discussing all of them. So long as we continue to attempt to discuss them seperately we will continue to fail to make meaningful changes in policies.

    People, seriously, if you think you understand what's going on yet look only at the climate science or tech-based solutions...  egad.

    You can start with Rodale, which is a study that looked at, though they don't use the term, applying permaculture design principles to farming. Basically what most of you might think of as no-till farming.

    Rodale Institute 30-year comparative Study of Farming Methods. 
    Tainter video (1 of 7, the rest are also available.) Diminishing Returns on Complexity 
    Jared Diamond on Choosing to Simplify 
    Hansen, et al. 
    An essay on Hansen's strategies 
    Willie Smits: Rebuild a Rainforest, Grow a Commmunity 
    Food Forest process 
    Seattle Food Forest 
    Yacouba: Stopping The Desert 
    Green deserts?

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    Moderator Response:

    [DB] And again, none of what you furnish for support deals with ocean acidification and the basic chemistry of seawater.  If humans manage to somehow initiate the drawdown of atmospheric CO2, the oceans will simply start spitting back out what they have under duress absorbed.  So your goal of returning atmospheric CO2 below 300 ppm target remains an elusive and unrealized goal.

    If you wish to explore that further, take it to the Physical Chemistry of Carbon Dioxide Absorption thread, and the followup Seawater Equilibria thread, where that is more appropriately discussed.

    Further, please note that Youtube videos, while useful, generally do not constitute scientifically reliable evidence in a science-based forum such as this.  Much more credence is given to the primary literature published in peer-reviewed, reputable journals.

  16. Sorry, here are the Seattle Food Forest links:

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  17. Wyoming wrote: "I think that a significant percentage of the readers (not even counting the Deniers,) on initial reading of the post, would come to the conclusion that all we have to do is wait until the rising levels of CO2 have resulted in conditions which are at our limits of tolerance and then we stop emmisions and all is going to be ok."

    Except that the point the article actually makes is that rather than 'everything being ok' in such a scenario, what it would actually mean is that "conditions which are at our limits of tolerance" would then persist for hundreds of years.

    Seems like a bad plan.

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  18. Killian,

    I think you have a misunderstanding regarding sustainable agriculture techniques and permaculture in particular. Some background, after I retired from my engineering career I owned and operated an organic farming operation for a number of years. I have spent a lot of time learning about farming, sustainable practices and such particular issues as permaculture and biodynamic practices.

    I have no issues with any of the attempts to develop sustainable farming practices and think it is a worthy goal. However, one has to keep in mind that these techniques are knowledge that we need people to develop and preserve for future needs as they have no fundamental ability to sustain our current population levels and complex civilization. Our extremely complex civilization and some 7 billion plus population is the direct result of our forebear's having obtained access to vast amounts of fossil fuels. One leads to the other and this has been well researched and documented.

    Almost all global food production, in percentage terms, is based upon heavy dependency on fossil fuels, be it from building the machinery used in farming and transporting food, storing food, making fertilizer, pesticides, fungicides and herbicides, etc. This reliance is not limited to 'industrial agriculture' but also applies to almost 100% of organic production as well. The amount of global food production from human/animal only labor food production is very small. And ramping up human/animal production to levels sufficient to support our current population/civilizational complexity is mathematically impossible. This is the dilemma of being in overshoot or past our global carrying capacity. If we continue BAU we will have a collapse due to climate change/fuel supply issues, if we don't continue BAU we have collapse because only BAU can supply the food requirements of 7 going on 9 billion people.

    Take some time to research permaculture production levels per human hour of labor. It will shock you. There is a good reason that before the introduction of industrial farming techniques and access to cheap fossil fuel some 98% of the population were farmers. When only human and animal labor is used it is very difficult for a farmer to reliably grow more food than he, his family and his animals (a plow horse is a tractor that runs on bio-fuel) need for their own use. There is no avoiding having some years when you produce less than you need to consume. This is why starvation was common in older times and is common in places where subsistence farming is still practiced. Now think about trying to supplant our current system of food production and supply for a city like Phoenix, Sao Paulo, Cairo, Moscow, Beijing, Hong Kong, Los Angeles, New York, etc. Pretty hard to solve that problem. And if you are planting vast acreages to forest like you mention it is wise to keep in mind that by definition you are covering arable land in forest that your sustainable farmers will need to be growing crops upon. You will need to be using every square inch of ground while you are trying to maintain the population levels if you are using sustainable techniques.

    There are a host of things we all must do to avert total disaster and there are no simple solutions. We absolutely have to cut GHG emissions, we must become much more efficient in our use of fuels, we must develop alternative energies, we must learn to live more simply and consume less, but most important of all things (and by far the hardest) is that we must find a way to dramatically reduce population levels as fast as possible. If we do not find a way to agree to cut population levels beyond the very slow decline in global growth rates( which indicate a maxing of population near 9 billion around mid-century) there is no possible solution to our above dilemma. We will just run into a brick wall.

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  19. CBD,

    I think we are in violent agreement as they say.  I say the general non-scientific reader will likely misunderstand the structure of the language used by the authors and reach the wrong conclusion.  You say that the " foolish people might reason that we can continue letting the temperature rise and 'just stop emitting when things get bad'."  I think we are talking about the same people, in a slightly different way, and coming to the same conclusion.

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  20. Paradigm changes can occur incredibly rapidly when they get going.  Look at our nearly smoke free indore environment and  the change from horses to cars.  However, to really change the world opinion on the use of fossil fuels to an extent that it will lead to action and will overcome vested interests, it will take a high impact disaster.  Sandy, the disappearance of the Arctic ice and such events are not enough.  We need, for instance, a complete failure of northern hemisphere crops due to a clear, demostrable lurch northward in the climate zones.  Unfortunately (or fortunately, depending on your point of view) it will be too late for many of us.  Massive starvations have occured again and again in the past but they have been localized.  Think Ireland, for instance.   We have had a little hint of  crop failure in Russia in 2010 and the USA in 2012 but they will only be seen as signs in hindsite.  If indeed the modern fertile crescent (Russia, Canada and the USA) fail, starvation will be global.  It will be too late for Most of us.  The following link is interesting.  Guy is pretty far out there but he gives a good list of possible tipping points.

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  21. Scenario #1 in Limits To Growth, the equivalent of the "no policy" of current MIT prof's, looked to the long-term consequences of "poisoning the planet" and the global population's decline from starvation due to those various poisons in our seas, soils, food water, air and us. Here in Puget Sound we are already seeing those consequences in our shellfish industries, salmon unable to spawn in their natal streams,&  first-born Orca dying from the toxins concentrated in their mother's milk. The continuing leak of radioactivity from the Fukushima Daiichi nuclear power plant crisis hasn't reached us in significant amounts yet, but prognosticaters report it is enroute. How many streams, lakes and rivers are uncontaminated? None around here or other parts of this continent. Folks who live in the Niger River delta have seen their life expectancy rates reduced from 65 to 45. Contaminated breast milk is being reported in subsistence cultures all over the world.  Without our pollution, yes, survival of the species 200 years from now might be possible.  Getting there seems unlikely - unless, of course, you have a mustard seed.

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  22. Ger @ 9, can you clarify what you mean by "torrefact"and "torrefaction"? Google suggests it is from the Spanish "torrefacto", which refers to the roasting of coffee beans. I presume torrefaction is a process for roasting or burning biomass, but I have never encountered the word before.

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  23. Wyoming @ 18, you said:

    If we continue BAU we will have a collapse due to climate change/fuel supply issues, if we don't continue BAU we have collapse because only BAU can supply the food requirements of 7 going on 9 billion people.

    I have never seen our dilemma so succinctly expressed. Everything comes back to the fact that there are simply too many of us.

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  24. Let's put some figures on Killian @11.

    Between 1850 and 2008, cumulative emissions due to Land Use Change represented 32.8% of all anthropogenic emissions.  Part of that comes from intensive animal husbandary and the expansion of rice paddies rather than deforestation, but we will ignore that.  If follows that complete reforestation to 1850 levels will draw down around 36 ppmv of CO2.  That could be approximately doubled by reforesting to, essentially, tenth century levels, ie, by returning Europe to the once verdant forest it was.

    That is the total of the draw down that could be managed by "sustainable" means.  Counting a switch to permaculture is not an additional draw down.  A permaculture garden stores substantially less carbon per acre than does a forest, so any acreage set aside for permaculture reduces that total draw down.  Never-the-less, it must be considered technically feasible to draw down CO2 as Killian suggests.  The total draw down would reduce the CO2 concentration to approx 310 ppmv, with equilbriation of the partial pressure of CO2 in the ocean over the next two centuries drawing that down further to abotu 285-290 ppmv.  Problem solved!


    What is missing from this analysis is how we are going to feed the population once all of the world's arable lands have been returned to forest.


    As pointed out by William, permaculture is labour intensive.  So much so that feeding a population by permaculture is not feasible unless every familly has its own permaculture garden.  With the labour hours of all famillies dedicated to just feeding themselves, there is no excess labour for such luxuries as geting an education, publishing books or newpapers, manufacturing any electronic equipment (including radios) having a civic life, and a democratic governance, long distant transport, long distance communications except by courier, or a population of the Earth greater than about 1 billion.

    The great danger of global warming is primarilly that it will create conditions that will result in the collapse of world trade.  Failing that, it may cause deaths in the millions but our civilization will struggle on.  With the collapse of world trade, however, we will face deaths in the billions from war, starvation and disease.

    Killian's solution to that threat is to embrace the threat as the solution.

    My opinion is different.  I think if we are going to be forced back into another dark age; we should at least put up a fight.

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  25. William @ 20, the Guy McPherson essay in turn links to a disgusting article by that doyen of the radical Right, James FishingDelingpole, which concludes;

    "Our culture deserves better than to have the terms of debate dictated by malign, politically motivated, professional offence-takers.

    Let's stop surrendering and start fighting back."

    I couldn't have put it better myself.

    After reading what Delingpole wrote (and subsequently disinfecting my monitor), I am amazed that he is given oxygen. Surely he is smart enough to know he is batting for the wrong side? Still, his rhetoric is so inflammatory, I'm glad he doesn't bat for us: stuff like that from this side would do untold damage to getting the message, about stopping AGW, out in a sane and rational way.

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  26. I find the preceding comments extremely interesting and important. I looked at this post and the first few comments yesterday, printed the Matthews and Solomon op-ed, and resolved to read that short piece this morning, review any additional comments, collect a few resources, and formulate a comment of my own. I woke at 5:30, it is now 7:49, I have run out of time. I have scanned quickly the last half of the comments. I would like to be in e-mail contact with many of the commenters. Click on the author at and send me an e-mail if you agree.

    I am not a scientist of any sort. I am not a mathematician. But I think I can understand some science and some mathematics and some other things. It is critical to remove the "violence" (i.e., arguing to get others to adopt your view) from the "violent agreement" (Wyoming@19). That is, we need to convert argument to discussion. The reason is nicely put in two sentences in J.B. Calhoun's 1970 Ekistics paper: "Thus, in the presence of this increased exposure to value conflict, there will be required an augmented awareness of the necessity for others to maintain value sets differing from one's own. Furthermore, realizing one's own functional role requires expenditure of considerable effort in assisting others to fulfill the objectives of their value sets. [pp. 431-432]" This was in the context of describing his predicted conceptual revolution 7 in ~2018 AD (for context, revolution 2 was the Living-Agricultural Revolution of about 8157 BC; revolution 5 was the Scientific-Exploitive Revolution of about 1868 AD).  His simplistic model was originally presented in December 1968  at the AAAS annual meeting in Dallas (Frontiers of Science Lecture III). I can send a pdf format scan of that paper to those who contact me.

    I have some understand of systems dynamics. For example, in the spring of 1971, the local Sierra Club chapter asked me to give a talk on the "Limits to Growth" model. I prepared and gave a two-hour presentation. The first third was a basic introduction to systems dynamics, the second third was a description of Forrester's "World Dynamics" model and results of my study of multiple scenarios, sensitivities of various couplings in that model, etc., and the last third was on the current status of the work in progress in Dennis Meadows group at MIT and what might be expected from it.

    Much of the discussion here is great, but somewhat in the wrong place, in my opinion. This site is a "debunk denialism, explain the consensus science, and maintain an acquaintance with the real ongoing 'debate' about the fine points" forum in the broad sense of "forum." But we do need a serious discussions along the lines of the preceding comments so that we can (metaphorically) find our places in the choir and sing out in harmony sufficiently well and increasing loudly to cause the needed paradigm shifts (William@20; also see Makem & Clancy: A Place In The Choir).

    With regard to the temperature-CO2 equilbrium and temperature change from the pre-industrial temperature, one suggestion is Teq =0.98(C - 280), where Teq is the equilibrium temperature change from the pre-industrial temperature in degrees C and C is the atmospheric CO2 concentration in ppm, from Byalko, Phys. Usp. 55(1) 103-108 (2012). There, the estimated time of relaxation to equilibrium is 650-750 years. I quote the concluding two paragraphs from that paper:

        The practical consequences of the forecasts of the energy sector and the corresponding solutions of the relaxation equations are quite substantial. The main conclusion is as follows: all actions to 'correct' the atmosphere begin to affect the average temperature of the planet with a noticeable delay. Thus, in the radical scenario, the maximum CO2 emission occurs in 2030, but its maximum concentration is attained only in 2042, and the temperature reaches some limit (possibly, a maximum) only by the end of the 21st century.
        The warming leads to one more unpleasant consequence, which is that climate perturbations increase proportionally to the time derivative of temperature [19]. A qualitative conclusion hence follows: weather anomalies will become maximal by the middle of the 21st century, when the CO2 concentration passes its maximum. This statement relates to the radical scenario, while the inertial scenario is completely catastrophic both for temperature and for weather anomalies. The humanitarian consequences of global warming cannot be evaluated in the framework of a physical approach to climate problems.

    I apologize for my comment being somewhat disjointed (had less than three hours of sleep last night and am falling further behind schedule).

    -- Bill

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  27. Shouldn't the "about 340 ppm by 2300, approximately the same level as it was in 1980. In the next 200 years" be the next 287 years ? I'm getting so old I'm losing track of decades so it might be me.

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    Moderator Response:

    [AS] Oops. You are not the only one getting old! I changed it to "300 years". Thank you.

  28. @ Doug #22, as an introduction to how biomass is torrefacted. Indeed is used in roating coffee beans but has more links with making charcoal

    BTW used coffee ground is an excellent fuel for gassification.

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  29. @Killian #11 James Hansen et al (many persons) do say in your reference "scenarios all assume a massive 100 GtC reforestation program, essentially restoring biospheric carbon content to its natural level". That 100 GtC (47 ppmv CO2) is 91% of a Brazilian rain forest (only +8% of the current land biomass so it's possible). 50 ppmv CO2 = 106,631,500,000 t carbon. Brazilian rain forest (10% of the Earth's carbon store) has 110,000,000,000 tC (52 ppmv CO2) on 3,375,413 sq. km. Hansen et al have the 100 GtC being bio-sequestered over 2031-2080. Since the data I've seen shows ~+1 ppmv CO2/yr from land use clearing, just stopping that would be really handy over 67 years. It would be great, and interesting, if we were some other species that might do those things that Hansen et al recommend but I think James Hansen might be confusing us with some superior species (a whole bunch of you maybe). A 2nd Brazilian rain forest or equivalent complex mix on our planet does not seem to mesh well with our actual interests that I see in the daily news.

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  30. Bill Everett @26, 0.98*(CO2 concentration - 280) represents a climate sensitivity of 274.4 C per doubling of CO2, a figure which is definitely wrong.  Are you sure you have not misquoted the equation?  If not, I would not be quoting Byalko as a guru on climate change. 

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  31. @Bill Evert #26. The equotation is subtracting ppm (a ratio) from degrees celcius (a measurement of energy) multiplying by an unknown 0.98. That formula can not be correct.  

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  32. Andy:

    The analogy I use with people is that of the 'climate flywheel', which we have gradually accelerated up over the last 200 years or so -- but particlualrly over the last 50 years at an ever increasing rate. So if we stopped emissions today the flywheeel would keep turning and would only very slowly lose speed over the forthcoming millenia. Only by actively removing greenhouse gasses from the atmosphere could we create a brake and actually begin to slow down that flywheel.

    Of course the real problem is that, as of the moment, we don't show any inclination to even consider reducing the rate of acceleration. 

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  33. Bill Everett @26 equilibrium temperature "Teq =0.98(C - 280)" must have some elements missed, in life haste possibly. I just readily found "" with a bunch of familiar looking numbers and formulae I recall from Drs. Randall, Trenberth, Hansen & others video lectures the last few weeks like the Watts m**-2 forcing (no feedback) = 5.35*LN(CO2/CO2<base>). I'd suggest searching each of those to find the agreement from expert sources before using, but that site doesn't seem to be pushing an agenda, no diatribes just some related quoting after the numbers.

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  34. 1)Byalko (2012) get the formula from a regression of T and CO2 for last 780Kyr

    2)The reference [19] to Byalko (2010)

    "...climate perturbations increase proportionally to the time derivative of temperature [19] ..." is a very general discussion of basins of stability, and does not convince me yet.

    That said, i do like Byalko (2012) teasing the 40Kyr periodicity out of a simple model.


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  35. Small typo: I think there was supposed to be a "(C)" after temperature change in the Figure 1 description.

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    Moderator Response:

    [AS] Thanks, fixed.

  36. According to Aradhna Tripati, a UCLA assistant professor in the department of Earth and space sciences and the department of atmospheric and oceanic sciences:


    “The last time carbon dioxide levels were apparently as high as they are today — and were sustained at those levels — global temperatures were 5 to 10 degrees Fahrenheit higher than they are today, the sea level was approximately 75 to 120 feet higher than today, there was no permanent sea ice cap in the Arctic and very little ice on Antarctica and Greenland,”


    This does not seem to jive with the Science article which asserts that if CO2 emissions were to stop today, the global temperature would not go up. Every CO2 vs global temp graph I can remember seeing indicates that that there is a significant time lag between CO2 concentration and global temp.


    We now know that 90% of the heat imbalance caused by AGW is in the deep oceans.  This heat, along some time scale, will eventually become unsequestered and actually increase temperatures, yes?


    Every report I remember reading has implied that the 0.8C global temperature increase we have seen is by no means all that we can expect 400 ppm CO2 to deliver.


    Now, one article in Science comes out, and we are supposed to believe its assertions?  This is not making sense to me.

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  37. Gingerbaker: Every report I remember reading has implied that the 0.8C global temperature increase we have seen is by no means all that we can expect 400 ppm CO2 to deliver.

    Indeed, that's what the blue line in Figure 1C shows; albeit for 380ppm, a level that we have already passed and may not see again for centuries or even millennia.

    As I understand it, it is not that the heat in the deep ocean will come back, it is more like the deep sequestration of surface warming, as we have observed it over recent decades may not continue. In other words, the air conditioning currently provided to us by the oceans may falter.

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  38. @Gingerbaker #36. Yes. Dr. Trenberth states the estimate of 0.9+/-0.4 wm**-2 at present time. In my layperson opinion oceans S.B. stated even more profoundly, if only to clarify for the unbiased but unknowledgeable members of public. "Global Warming" IS the increasing trend of heat in the ocean. Surface temperatures are a proxy measurement, subject to periodic vagaries. I think it's misleading to consider that "Global Warming" ends when the TOA radiation becomes balanced. I think it ends when the oceans regain whatever is their natural temperature gradient from surface to sea bed, and then when TOA radiation becomes balanced. This because oceans have ~40 times heat capacity of all freshwater and ~550 times heat capacity of all air + land (as deep as relevant). If, as example, +2.8 degrees C was needed to balance TOA radiation then I would think by simple logic that "Global Warming" ends when the oceans are +2.8 degrees C warmer, in the absence of that warming changing the forcing of course.

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  39. Gingerbaker @36, if all anthropogenic emissions ceased, CO2 levels in the atmosphere would approximately halve over the course of 200 years as CO2 is absorbed into the ocean.  This reduction in CO2 concentration (shown in red above) approximately balances the increase in global temperatures due to the "commitment", ie, the increase as the Earth achieves equilbrium.  Therefore the two approximately cancell out, resulting in no change in temperature.  

    Over the following 10 thousand years, the CO2 will be removed from the ocean, drawing down CO2 levels to preindustrial levels.  The draw down is sufficiently slow that in one to two thousand years, when slow feedbacks have had time to reach equilibrium, the temperature will still remain at current elevated levels, ie, the draw down in CO2 will be approximately balanced by the increase in temperature resulting from such slow feedbacks as reduced albedo due to the melt back of icesheets.

    "Aproximately" in both cases is leaves a fairly wide margin and there may be a slight increase or decrease in the long term, and disparities of rate may result in significant temperature fluctuations.

    These scenarios are only relevant if we in fact cease net anthropogenic emissions.  As some emissions (eg, methane from rice paddies) are simpy unavoidable, that means an ongoing deliberate sequestration process.  Further, it is economically unfeasible to cease emissions in less than 20 years, and probably in less than 40 years.  Finally, such scenarios are only relevant if there are no large increases in natural emissions as a feedback to increased global temperatures, something some people argue has already started happening.

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  40. A logical question that should have been asked before publication is: "What do the authors expect the world GDP will be 200, 400, 600, or 1000 years in the future?" 

    Of course, such a question would likely demolish the premise of the paper, so it's not surprising it wasn't asked.

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  41. Andy, thanks for this great piece. One quible: In the second full paragraph, you say:

    "many mistakenly believe that the climate system is going to send more warming our way no matter what we choose to do. Taken to an extreme, that viewpoint can lead to a fatalistic approach, in which efforts to mitigate climate change by cutting emissions are seen as futile"


    My concern for now is not how valid various run-away gw scenarios may or may not be (I may get to that in a seperate post). But how you stated this sounds (though it may not be your intention) as if you think we should not consider valid any science that might make us feel sad or dispondent, since it may prevent people from taking effective action.


    It seems to me that this is essentially what Inhofe and others do when they admit that they accepted climate science until they started considering what tax or other policy consequences of accepting the science might be.


    The science is the science. We need to evaluate it on its own merits, not on what we think people's reactions to it might be or what politicies might be implemented because of it.


    Would you agree that we should look at the science, even if it does take us into places we may be emotionally and politically uncomfortable with?


    (Again, I think I am reacting to how some may interpret what you said as you stated it, more than what I would like to assume you actually think. Just looking for some clarity.)

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  42. wili@41


    Yes, I do believe that we should follow the science, wherever it leads and however gloomy the prospect is. Frankly, I find the whole prospect of climate change and our response to it a rather uncomfortable and gloomy one. However, I have spoken to individuals who are very depressed because they believe that we are already on an unstoppable path to disaster; that climate feedbacks are out of control and will continue to worsen, no matter what we do. That is not (yet) correct and, as a misconception, could be taken to mean that resistance is useless, a somewhat self-fulfilling prophecy.

    The science says that we need not feel fatalisitic, but neither can we afford to wait. Of course, this prescription will change the longer we procrastinate.

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  43. Mark Bahner@40

    I don't want to have to guess what you mean, could you be more specific? I am not sure what premise Matthews and Solomon could have made that would be demolished by asking, or even answering, such a question about the economics of the far future.

    I don't think that anyone has the slightest clue what world GDP will be in several centuries' time. It depends on so many variables, among them population, technology, resources, plagues and, yes, even climate change.

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  44. I disagree with point (2). Even if the graph C red line with flat temp next 300 yrs was correct I would disagree because "Global Warming" isn't changes in surface temperature, it's increase in the ocean heat content. Dr. Trenberth says in lecture 2 yrs ago there's 0.9+/-0.4 wm**-2 radiation imbalance and I believe him to be likely close enough because he seems knowledgeable. If temperature goes flat it's just because ocean mixing happens to match radiation imbalance. It would even be possible for radiation imbalance and temperature change both to be ~0 as much as is noticeable with "Global Warming" continuing, the heat just passes through unobtrusively (depending on the superbness of instrumentation & theory). As example only, if +1.5 degrees C happens to be the final average surface temperature then I see no reason why "Global Warming" would stop until the deep oceans entirely are +1.5 degrees C than they were a hundred years ago, or whatever is the base line for this. Furthermore, I think it's important not to mix'n'match phrases like "heat up" and "Global Warming" and also the trite ones bandied about (not in this post or comments) because that's going to confuse the heck out of non-scientists - when you say "heat up the planet" they'll think temperature of the bits they see. And "the planet" has a middley bit you know, apparently there's some molten rock. Shouldn't be calling "the ecosphere" "the planet". It really needs mention of the ecosphere, perhaps even some reference as to how deep in the earth and oceans is being considered.

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  45. My prior post would have better said example +0.9 degrees C since that is the red line value. Example value makes no difference to the comment text though. 

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  46. grindupBaker:

    I agree that we should be more careful in how we use "global warming" in a casual way to refer to warming of the surface temperatures and/or warming of the oceans, particularly the deep oceans. This is especially true now, as more research indicates that the recent slowdown in the rate of surface temperature increase is more than fully compensated for by warming in the oceans.

    On the other hand, I think that "heat up the planet" is fine in non-technical discourse, since everyone can safely assume that, since we are talking about climate change, the 'planet" means the bits we and other life forms inhabit and that we are not particularly concerned with the warming effect on the solid, rocky Earth. Neither should we object to casual use of  "heat up the planet" on the grounds that parts of the atmosphere, like the stratosphere, are experiencing anthropogenic cooling.

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  47. I don't want to have to guess what you mean, could you be more specific? I am not sure what premise Matthews and Solomon could have made that would be demolished by asking, or even answering, such a question about the economics of the far future.

    It's basically pretty simple. Matthews and Solomon are completely wrong in claiming that global warming is "irreversible". If adding CO2 to the atmosphere warms the planet, then taking CO2 from the atmosphere will cool the planet.

    Human beings know how to remove ambient CO2 from the atmosphere. It's simply a question of what the cost is, and whether human beings are willing to pay that cost. Whether human beings are willing to pay the cost of removing CO2 from the atmosphere in turn depends on how much money humans have.

    In a recent edition of The Atlantic, Daniel Sarewitz and Roger Pielke Jr note, "While the cost of air capture is largely speculative—current estimates range from $20 to $2,000 per ton of carbon dioxide removed—..."

    Removing CO2 from ambient air

    Let's take a number in the middle of that range...about $1000 per metric ton of CO2 removed from ambient air. Since there are about 7.8 billion metric tons of CO2 per ppm in the atmosphere, that means it would take $7.8 trillion to remove 1 ppm of CO2 from the atmosphere.

    That may seem significant now (about 10 percent of world GDP for 1 ppm removed). But by 2100 or 2200, the world GDP could easily be 10, 100, or even 1000 time larger than it is today.

    If the world GDP is 100 times larger than today, it follows that 10 percent of the world GDP could remove 100 ppm of CO2 from the atmosphere per year. The U.S. spent about 10 percent of its GDP on the military during the Cold War period of the 1950s to 1980s, so obviously 10 percent of GDP isn't crippling. If the world GDP is 100 times larger, then spending 10 percent of GDP for 10 years would remove 1000 ppm of CO2 from the atmosphere.

    Therefore, global warming is only "irreversible" if world economic growth stops in the near future. Economic science indicates that is unlikely. So it's not surprising that Matthews and Solomon ignored likely future economic growth.

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  48. Mark Bahner...  Aren't you ignoring the fact that the relative cost of removing the CO2 would also rise with the growth of the world economy?  And at the same time, you have CO2 emissions continuing to rise, so can you actually remove CO2 as fast as you're adding it?  And why not just skip that entire process and just not put it into the atmosphere in the first place?

    If the cost of removing it is $1000 per ton, why not just tack on, say, 10% of that same cost ($100/ton) as a tax on carbon emissions, as a tax and dividend plan, then the economic impact would be negligable at worst, and potentially would fuel very rapid, and economically beneficial, technological development.

    And hey, let's not wait.  If the issue is that we're going to have to pull those CO2 concentrations down, add that $100/ton tax today.  That would clearly be the most economically advantageous course of action, bar none.

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  49. Rob Honeycutt:

    "Mark Bahner... Aren't you ignoring the fact that the relative cost of removing the CO2 would also rise with the growth of the world economy?"

    No, I'm ignoring the fact that the cost of removing a metric ton of CO2 would likely fall with the growth of the world economy. That is, what might cost $1000 per metric ton to remove in 2013, will likely fall to a small fraction of that, as humans learn how to do it more efficiently.

    Oops. Lunchtime is over. :-( I'll try to address your other comments later tonight or tomorrow.

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  50. Mark...  I find it fascinating how the article you link states that "...a shift to carbon-free energy remains the Platonic ideal" whereas there are, very clearly, existing and fully developed technologies to do this.  The rate of growth in solar and wind are much greater than that of other FF energy sources.  And, there are currently no – exactly zero – CCS power plants currently operating (AFAIK).

    It seems to me the "Platonic ideal" is completely opposite to what the article reports, which is not unusual, given that it comes from Roger Pielke Jr.

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