Stabilize at 350 ppm or risk ice-free planet, warn NASA, Yale, Sheffield, Versailles, Boston et al

The good news: We can avoid multimeter sea level rise, the loss of the inland glaciers that provide water to a billion people, rapid expansion of the subtropical deserts, and mass extinctions — each of which is all-but inevitable on our current path of unrestrained greenhouse gas emissions.

The not-so-good news: We will probably need an ultimate target of 350 ppm (or lower) for atmospheric carbon dioxide — if you accept the analysis of ten leading climate scientists from around the world.

And yes, the authors of “Target Atmospheric CO2: Where Should Humanity Aim?” in The Open Atmospheric Science Journal are painfully aware we’re already at 385 ppm and rising 2 ppm a year. That is why they propose the self-described “Herculean” task of phasing out coal use that does not capture CO2 over the next 20-25.” And that requires a global CO2 emissions profile that looks something like this:


[Note to Hansen et al: Big pet peeve — I think you confuse the general reader by labeling your y-axis “CO2 Emissions” while expressing the units in billion metric tons of carbon. This helps foster errors in the media and elsewhere (see “The biggest source of mistakes: C vs. CO2“).]

Actually, even the ultra-sharp emissions cuts depicted in the figure won’t do the trick. We would still need “reforestation of degraded land and improved agricultural practices that retain soil carbon” (aka biochar to the rescue) to “lower atmospheric CO2 by as much as 50 ppm.”

More not-so-good news: That kind of emission reduction isn’t going to happen, not even under President Obama, not even close. Heck, I doubt it would happen under a President Hansen. We just are not going to see 350 ppm this century. Unfortunately, the authors “infer from the Cenozoic data that CO2 was the dominant Cenozoic forcing, that CO2 was only ~450 ppm when Antarctica glaciated, and that glaciation is reversible.”

That is, if we stabilize at 450 ppm (or higher) we risk returning the planet to conditions when it was largely ice free, when sea levels were higher by 70 meters — more than 200 feet! Yet, “Equilibrium sea level rise for today’s 385 ppm CO2 is at least several meters, judging from paleoclimate history.” Equally worrisome,

Theory and models indicate that subtropical regions expand poleward with global warming. Data reveal a 4-degree latitudinal shift already, larger than model predictions, yielding increased aridity in southern United States, the Mediterranean region, Australia and parts of Africa. Impacts of this climate shift support the conclusion that 385 ppm CO2 is already deleterious.

In short, widespread desertification and coastal flooding, Hell and High Water, is nigh (see also “Is 450 ppm politically possible? Part 0: The alternative is humanity’s self-destruction“).

Some slightly good news: The paper does suffer from one inherent analytical weakness that makes it (a tad) less dire than it appears.

Even if you accept their analysis (which many will not), the authors do not know how long we can overshoot 350, which is a function of not just the duration of the overshoot, but the magnitude (i.e. how high concentrations go). They write:

This target [350 ppm] must be pursued on a timescale of decades, as paleoclimate and ongoing changes, and the ocean response time, suggest that it would be foolhardy to allow CO2 to stay in the dangerous zone for centuries.

Well of course it would be foolhardy, but “centuries is a long time. The ill-defined difference between decades and centuries is key here.

What if we could keep the peak at or below 450 ppm, and start concentrations declining by 2100, which would almost certainly require near-zero if not net-negative global emissions, and then get back to near 350 ppm by, say 2150 and then even lower by 2200? Would that be good enough? With a World War II scale effort for the next few decades, we could stay below 450 (see “Is 450 ppm (or less) politically possible? Part 2: The Solution“). My take away from this paper is that we would need to keep up that level of effort well into the next century — to get back below current levels.

But in some sense whether the ultimate target is 350, 400, or 450 doesn’t matter as much as some people seem to think. You can’t hit any of those targets without strong and relentless action starting January 20, 2009. Further delay risks catastrophe:

Humanity’s task of moderating human-caused global climate change is urgent. Ocean and ice sheet inertias provide a buffer delaying full response by centuries, but there is a danger that human-made forcings could drive the climate system beyond tipping points such that change proceeds out of our control.

That, of course, is a central point of this blog.

The authors note that “it appears still feasible to avert catastrophic climate change,” but their final warning deserves notice:

Present policies, with continued construction of coal-fired power plants without CO2 capture, suggest that decision-makers do not appreciate the gravity of the situation. [Note to Hansen et al: That is the understatement of the year.] We must begin to move now toward the era beyond fossil fuels. Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects.

The most difficult task, phase-out over the next 20-25 years of coal use that does not capture CO2, is herculean, yet feasible when compared with the efforts that went into World War II. The stakes, for all life on the planet, surpass those of any previous crisis. The greatest danger is continued ignorance and denial, which could make tragic consequences unavoidable.

Okay, so we should have listened to Hansen two decades ago (see “Right for 27 years: 1981 Hansen study finds warming trend that could raise sea levels“). The time to act is yesterday.

One final point. Much of the analysis in this paper is a refinement of Hansen’s earlier analysis arguing that the real-world or long-term climate sensitivity of the planet to doubled CO2 [550 ppm] is 6°C — twice the short-term or fast-feedback-only climate sensitivity used by the IPCC. [This post is a bit clearer on the difference between the two sensitivities.] Some people think Hansen is wrong about this issue (start here). If I am reading that criticism correctly, then I think Hansen responds to it in his new paper.

Also, if I am reading Hansen’s paper correctly, then I think he may be mostly right for a different reason than he thinks, which is to say, I think the carbon-cycle feedbacks (including the tundra melting, the peatlands drying out, and sink saturation) act as the equivalent of the amplifiers that he models: “Additional warming, due to slow climate feedbacks including loss of ice and spread of flora over the vast high-latitude land area in the Northern Hemisphere, approximately doubles equilibrium climate sensitivity.”

In short, if you get near 450 ppm and stay there for any length of time, you will shoot up to 700 to 1000 ppm, which certainly gets you an ice-free planet and other unimaginably catastrophic impacts.

Another way to put this is that the IPCC was right when it wrote last year:

Climate-carbon cycle coupling is expected to add carbon dioxide to the atmosphere as the climate system warms, but the magnitude of this feedback is uncertain. This increases the uncertainty in the trajectory of carbon dioxide emissions required to achieve a particular stabilisation level of atmospheric carbon dioxide concentration. Based on current understanding of climate carbon cycle feedback, model studies suggest that to stabilise at 450 ppm carbon dioxide, could require that cumulative emissions over the 21st century be reduced from an average of approximately 670 [630 to 710] GtC to approximately 490 [375 to 600] GtC. Similarly, to stabilise at 1000 ppm this feedback could require that cumulative emissions be reduced from a model average of approximately 1415 [1340 to 1490] GtC to approximately 1100 [980 to 1250] GtC.

We’re at more than 8 GtC/yr (billion metric tons of carbon per year) and rising 3% annually. We need to average below 5 GtC/yr — and maybe considerably less — for the whole century to avert catastrophe. We need to be near zero or below by 2100.

My Bottom Line: Let’s start working now toward stabilizing below 450 ppm, while climate scientists figure out if in fact we need to ultimately get below 350.

You can read the Yale University press release on the Hansen et al paper here.


24 Responses to Stabilize at 350 ppm or risk ice-free planet, warn NASA, Yale, Sheffield, Versailles, Boston et al

  1. paulm says:

    “…That kind of emission reduction isn’t going to happen, not even under President Obama, not even close. Heck, I doubt it would happen under a President Hansen. We just are not going to see 350 ppm this century.”

    Keep your chin up. Lets all whistle together – “Always look on the bright side of life…”

    There may be a negative (or should that be positive) tipping point in there somewhere ahead.

  2. Hmmm. Is your “WWII-style effort for the rest of the century” is probably an exaggeration of the scale of the effort required.

    As some point, we will develop technology to take CO2 out of the atmosphere and sequester it. Without such technology, we are screwed.

    The next question is how much such technology will cost to take a tonne of carbon out of the . A reasonable guess at this point is $250 per tonne of CO2 – to make it easy, $1000/ tonne of carbon.

    Let’s assume we take 5 billion tonnes of carbon out of the atmosphere every year at that price. That’s 5 trillion dollars a year.

    World GDP as of 2006 was around $65 trillion a year. The cost of such action would therefore represent 7% of world GDP. By 2050, such action would be, at a reasonable guess, about 2.5% of world GDP.

    For comparison, during WWII, military expenditure accounted for a third of US GDP, I believe.

    [JR: I’m not sure that percent of GDP is the right way to scale this. By WWII-scale effort, I was not talking about a “third of US GDP” scale effort as the need to direct resources and manufacturing and human capital on the same scale — and, perhaps as important, with the same speed.]

  3. John Mashey says:


    Can you say why you assume world GDP nearly triples by 2050?

    [I’ve looked at lots of models that would say so. However, Ayres&Warr seem more compelling, i.e., that a big component of GDP growth is energy, most of energy comes from fossil fuels, and (oil&gas at least) will be peaking.

    See last page especially of Ayres, 2005 @ ASPO.

    [Note: his analysis implies that we have to go all-out on energy efficiency & sustainable supplies, or see GDP decrease, not increase.]

    I do not assert that Ayres is necessarily right, but I’d be delighted to have someone explain to me why he’s wrong.

  4. Steve Bloom says:

    Joe, the difficulty with focusing on that “analytical weakness” is that it increases risk since it will tend to lead to more time spent above 350 ppm. The message politicians will hear is that delay now can be traded for stronger action later (a line of argument which ought to sound unpleasantly familiar). That Hansen identifies centuries of 350+ CO2 as a clear hazard doesn’t mean that he thinks staying at such levels for decades is without risk. IOW, I think you’re reading too much into that passage. Will you ask Hansen to clarify?

    Also, I suspect it may be the case that within relevant time-scales improved modeling won’t be able to narrow the uncertainties enough to help with figuring out how much CO2 is too much.

  5. rpauli says:

    Oh… you mean it is supposed to be “for ourselves AND our posterity” ??

    I thought it was “for ourselves OR our posterity”

  6. jorleh says:

    Do you really believe we are cutting our emissions at all? Have a look of 2% more emissions during the last decade per year.

    I don´t see any possibility cutting world wide emissions before the day the catastrophe is at hand, there to be seen and understood by the billions of us.

    We are, however, only smart apes, nothing more.

    [JR: Who ever said I believe we are cutting our emissions? We aren’t — but we could. That’s the whole point of this blog.]

  7. The “technofix” solution does not even exist, and never, ever will. There are several problems with this:

    a) the energy to do this doesn’t exist;
    b) the political leadership doesn’t exit;
    c) the technology doesn’t exist;
    d) the infrastructure required to support this doesn’t exist;

    BUT — assuming that all of the above can be simply ignored, the real cost of carbon sequestering via technology is the positive feedbacks it creates by the technology itself. That is to say, the development and deployment of any such technology itself makes more carbon. Therefore, such a technology would have be highly efficient, similar to the EROEI issues surrounding any energy source.

    There is also the issue of “reductions don’t work” as Hansen pointed out in his paper. Even a 80% reduction won’t work according to Hansen, because of the long lifetimes of C02 and other gases in the atmosphere. We would have had to have the “technofix” solution over two decades ago for this approach to work. The temperature rises are already there, we are dealing with a problem that has already set in motion positive feedback loops that will take at least a century to fully realize their own potential. This isn’t something we can “stop” with a technofix of any magnitude.

    Reality is smacking us in the face (lives) on all of these issues. We are also out of time, already. The bottom line is we are not going to fix this, it’s not only impossible now (similar to trying to move the Earth out of it’s orbit), it is actually inconceivable to scientists.

  8. alex says:

    At least this is getting to the crux of the debate. I get frustrated by endless discussions of what battery technology we need for our EV’s, as if that is going to fix anything!

    The bottom line is that mankind (all of us) need to agree an intense carbon consumption diet, with sharp year on year falls. The market can be left to figure out what it wants to use the carbon for.

    The missing factor is political will, and this only comes ultimately from popular pressure – which is acutely missing. The world’s population needs to understand that they can continue BAU for only last a few more decades before it falls apart. Until people are frightened enough they will ignore the problem.

  9. vakibs says:


    Aiming for 450 ppm is not an option. Just by phasing out coal (by 2030) CO2 levels can be brought down to 420 ppm. This is eminently doable, even assuming we will be burning all our known petrol and natural gas reserves.

    We should aim for something higher. We should aim to leave a portion of our known natural gas reserves in the ground.

    The big problem with your thinking is that you continuously speak of yearly CO2 emissions. They have no direct import on the climate situation. The number that matters is the amount of fossil fuels that we leave buried underneath.

    We should have a prescribed quota of fossil fuels that we will dig up, how we use up this quota is immaterial. By all means, we can burn a lot of fossil fuels in the immediate future if that is meant to the construction of new energy plants. On the other hand, reducing fossil fuel usage with no long term energy plan is meaningless.

    By 2050 (or even earlier), we will have an active plan for sucking CO2 in the atmosphere. It could be a Lackner process of direct CO2 capture, or extensive forestry and sequestering carbon through biochar, or digging up mineral stones which absorb CO2, or dissolving CO2 in alkaline earth silicates, or in ocean water or foamed materials through a catalyst.. The underlying denominator for each of these processes is that they need a lot of energy, which makes it imperative that we have a massive construction program for new energy plants. Energy will also be needed for desalination of water – a very pressing need in the future for growing populations.

    Nuclear power is critical in meeting this energy demand.

    [JR: Never said it wasn’t — though I wouldn’t use the word “critical.” I’d say “probably helpful.”]

  10. Joe, one point of confusion for many will be the use of CO2 only stabilization targets, whereas the IPCC and many policy-makers are talking in carbon dioxide equivalents (CO2e).

    I raised this issue with Hansen when he distributed the draft of his paper earlier this year and he replied the use of CO2e has “caused great confusion, to no benefit — we can and should talk about CO2 — the other GHGs affect this by only plus or minus 25 ppm, as I try to make clear — the other GHGs are important, as it is a lot better if they reduce the CO2 requirement by 10 or 20 ppm, rather than exacerbate it by that much — but whoever started this should NOT have introduced CO2-equivalent, which just confuses everybody — so I have got rid of it — when I talk about CO2 amount, I mean CO2 amount — that is the best way to go.”

    I believe the final paper includes a note about CO2e as a result of this discussion.

    While a world-leading climate scientist such as Hansen has the credentials to choose not to use CO2e, most policy-makers are stuck with the approach adopted by the IPCC, which uses CO2e (as non-climate scientists, who are we to judge that Hansen et al are right if the IPCC does not adopt it).

    The differences between the usages of CO2 and CO2e are very significant and care must be taken not to confuse them. The terms are very different quantitatively as is evident from the following points draw from the IPCC (2007) Working Group III report, at page 102:

    • Atmospheric carbon dioxide reached 379 ppm in 2005 and was increasing by around 2 ppm per year.

    • Including the effect of all long-lived greenhouse gases such as methane, the total concentration of atmospheric greenhouse gases was around 455 ppm carbon dioxide equivalents in 2005 (range 433-477 ppm).

    • However, the cooling effects of aerosols and landuse changes reduce radiative forcing so that the net forcing of human activities was about 375 ppm carbon dioxide equivalents for 2005 (range 311-435 ppm).

    While net forcing of all greenhouse gases, aerosols and landuse changes is roughly equal to the effect of carbon dioxide alone at the present time, this may not remain the case in the future particularly if atmospheric pollution levels decrease (thereby reducing the cooling effects of aerosols).

    Stabilizing at 450 ppm CO2 alone could mean significantly higher levels of stabilization when measured in CO2e, leading to much higher levels of temperature rise than 2°C. For instance, if the cooling effect from aerosols was to approach zero in the future due to improved pollution controls, stabilization of atmospheric CO2 at 450 ppm might lead to a net warming effect around 520 ppm CO2e.

    There is a real potential for governments and policy-makers to misunderstand and mis-apply information based on using either CO2 only figures or CO2e. In such circumstances, perhaps the best solution is to clearly flag the differences in the usage of these terms.

    There is some further discussion of these issues in the context of stabilizing temperature rises and ocean acidification at

  11. charlie says:

    Is global warming too important to leave to the scientists? I think this would be an excellent case study. Assuming Hansen’s numbers to be true, it is a very unhelpful argument when making the political argument.

  12. Sam says:

    “We can avoid multimeter sea level rise, the loss of the inland glaciers that provide water to a billion people,”

    I don’t know where you get a “billion people.” The loss of the Himilayan glaciers alone means more like 2.5 billion people, including India, Pakistan, China, and other parts of southeast Asia. The loss of the Rocky Mtn glaciers are a few tens of millions of millions more. Granted, rainfall will help a little. Of course, that assumes that the monsoons still come, and the southwest US doesn’t have one of its multidecade (century?) long droughts.

    I wish I didn’t find pessimism so damned realistic.

    [JR: No. The inland glaciers are not the sole source of water for those 2.5 billion people. Also, remember, part of their function is to act as a reservoir, to store Precipitation in the form of snow. If you lose the inland glaciers, it is an unmitigated catastrophe, but it doesn’t mean that 2.5 billion people are without water. So that’s why I use the 1 billion figure. Hope that cheers you up!]

  13. paulm says:

    A nagging concern I have is that fossil fuels are effectively permanent CO2 draw down. I can’t see how any sizable part of these reserves would have naturally been reintroduced back in to the atmosphere.

    Is this the case?

    Does that mean that the only way that AGW carbon will be drwan back out is if we extract the carbon specifically with our technology?

  14. paulm says:

    Whats worse than rising sea-level and monster storms?…
    may be were not addressing this enough here.

    “The Darkening Sea”,613595.shtml

    “…the effects of climate change are not limited to global warming: they extend to the sea, where the chemistry of the water is being changed and creating a profound threat to the food chain, starting at the bottom.”

  15. Sam says:

    >>JR: No. The inland glaciers are not the sole source of water for those 2.5 billion people.
    True enough, but the glaciers feed the main rivers in the region, which are an important part of the other source of water. And they are using up their aquifers at an alarming rate, although there have been some beginning efforts to harness the monsoons with rainwater harvesting in some provinces (see When the Rivers Run Dry by Fred Pearce for one recent source on all of this). And they are also polluting existing sources of water at an alarming rate.
    >>Also, remember, part of their function is to act as a reservoir, to store Precipitation in the form of snow.
    Yes, that is one reason why they are so useful. but what happens when there is no–or too little–snow? If the glaciers disappear, it will be because it will rain rather than snow (to the extent that there is precipitation at all–and who knows how precipitation will be affected?). I don’t know what is happening in the Himilayas w/r/t snow (I can guess), but snowmelt has been diminishing in the Rockies, as well as coming earlier. And of course, dams to store the water won’t be much help if it continues to warm–evaporation will see to that (cf. the predictions about Lake Mead effectively going dry by 2020).

    I know, I need to get in touch with my inherited Jewish belief in miracles rather than–or at least in addition to–our deep-seated sense of imminent doom.

  16. David B. Benson says:

    Robert Merkel — Your estimate of the cost of removing carbon dioxide is about a factor of ten too high. Enhanced weathering of (certain) minerals permanently removes the carbon dioxide, is completely natural and safe.

    Olivine weathering:

    “Rocks Could Be Harnessed To Sponge Vast Amounts Of Carbon Dioxide From Air”:

  17. David B. Benson says:

    Because if we don’t, the bogs will do us in:

    “Global Warming Predicted To Hasten Carbon Release From Peat Bogs”:

  18. The Rest of the Biochar Story:

    Charles Mann (“1491”)in the Sept. National Geographic has a wonderful soils article which places Terra Preta / Biochar soils center stage.
    I think Biochar has climbed the pinnacle, the Combined English and other language circulation of NGM is nearly nine million monthly with more than fifty million readers monthly!
    We need to encourage more coverage now, to ride Mann’s coattails to public critical mass.

    Please put this (soil) bug in your colleague’s ears. These issues need to gain traction among all the various disciplines who have an iron in this fire.

    I love the “MEGO” factor theme Mann built the story around. Lord… how I KNOW that reaction.

    I like his characterization concerning the pot shards found in Terra Preta soils;

    so filled with pottery – “It was as if the river’s first inhabitants had
    thrown a huge, rowdy frat party, smashing every plate in sight, then
    buried the evidence.”

    A couple of researchers I was not aware of were quoted, and I’ll be sending them posts about our Biochar group:…guid=122501696

    and data base;

    I also have been trying to convince Michael Pollan ( NYT Food Columnist, Author ) to do a follow up story, with pleading emails to him

    Since the NGM cover reads “WHERE FOOD BEGINS” , I thought this would be right down his alley and focus more attention on Mann’s work.

    I’ve admiried his ability since “Botany of Desire” to over come the “MEGO” factor (My Eyes Glaze Over) and make food & agriculture into page turners.

    It’s what Mann hasn’t covered that I thought should interest any writer as a follow up article.

    The Biochar provisions by Sen.Ken Salazar in the 07 farm bill,

    Dr, James Hansen’s Global warming solutions paper and letter to the G-8 conference last month, and coming article in Science,

    The many new university programs & field studies, in temperate soils

    Glomalin’s role in soil tilth & Terra Preta,

    The International Biochar Initiative Conference Sept 8 in New Castle;

    Given the current “Crisis” atmosphere concerning energy, soil sustainability, food vs. Biofuels, and Climate Change what other subject addresses them all?
    Biochar, the modern version of an ancient Amazonian agricultural practice called Terra Preta (black earth), is gaining widespread credibility as a way to address world hunger, climate change, rural poverty, deforestation, and energy shortages… SIMULTANEOUSLY!

    This technology represents the most comprehensive, low cost, and productive approach to long term stewardship and sustainability.
    Terra Preta Soils a process for Carbon Negative Bio fuels, massive Carbon sequestration,10X Lower Methane & N2O soil emissions, and 3X Fertility Too. Every 1 ton of Biomass yields 1/3 ton Charcoal for soil Sequestration.

    Carbon to the Soil, the only ubiquitous and economic place to put it.

    540 289 9750

  19. John: I have a little bet on just this topic. I’m aware of the view that without fossil fuels our economy will just dry up, but I just don’t buy it, myself.

    Joe: fair enough, but fraction of GDP isn’t a terrible proxy for the amount of intellectual and physical effort we put into.

    David: I certainly hope I’ve overestimated. But I was trying to take a very conservative approach to how much the kind of change Joe thinks (and I agree) is necessary, might possibly cost, and show that the effort won’t necessitate anything like the privations endured during WWII.

  20. EcoSapiens says:

    Amidst the scale of the challenges and inadequate political and social response, there are a few encouraging signs of change in Wales, UK that indicate what might just be possible with a fair wind.

    We now have the first few public sector organisations looking at the implications of a 9% annual reduction in CO2 levels, and Jane Davidson, Wales’ minister for Envt Sustainability & Housing has asked all National Parks (which represent 20% of our land area) to work through 3, 6 & 9% reduction sceanrios. Discussions have also started around the potential for a country-wide shift to Cradle to Cradle production and to ways of embedding national food security within ten to fifteen years. This small country was the crucible of the first industrial revolution – let’s hope it can provide a low carbon, zero landfill template for the next one.

  21. Jonas says:

    The reason why Romm (and others at Gristmill) are afraid of the 350 number, is because it means a massive investment in carbon-negative bioenergy, that is: biomass electricity coupled to CCS, biohydrogen coupled to CCS, and biochar. All bio that is, and not so much wind or solar or geothermal.

    This is so because these bioenergy technologies can yield carbon-negative energy, whereas the weak renewables only yield carbon-neutral energy and thus won’t do (they won’t do because we need to remove CO2 from the atmosphere, and wind, solar and geothermal don’t do that; negative emissions bioenergy does.)

    Read Hansen’s text, page 227 (the key passage of the text, called “Policy Relevance” of this article – not mentioned by Romm, because it’s all “bio”).

    Desire to reduce airborne CO2 raises the question of whether CO2 could be drawn from the air artificially. There are no large-scale technologies for CO2 air capture now, but with strong research and development support and industrial scale pilot projects sustained over decades it may be possible to achieve costs ~$200/tC or perhaps less. At $200/tC, the cost of removing 50 ppm of CO2 is ~$20 trillion.

    Improved agricultural and forestry practices offer a more natural way to draw down CO2. Deforestation contributed a net emission of 60±30 ppm over the past few hundred years, of which ~20 ppm CO2 remains in the air today.

    Reforestation could absorb a substantial fraction of the 60±30 ppm net deforestation emission.

    Carbon sequestration in soil also has significant potential. Biochar, produced in pyrolysis of residues from crops, forestry, and animal wastes, can be used to restore soil fertility while storing carbon for centuries to millennia. Biochar helps soil retain nutrients and fertilizers, reducing emissions of GHGs such as N2O. Replacing slash-and-burn agriculture with slash-and-char and use of agricultural and forestry wastes for biochar production could provide a CO2 drawdown of ~8 ppm or more in half a century.

    [In the Supplementary Material Section] we define a forest/ soil drawdown scenario that reaches 50 ppm by 2150. This scenario returns CO2 below 350 ppm late this century, after about 100 years above that level.

    More rapid drawdown could be provided by CO2 capture at power plants fueled by gas and biofuels [that is: carbon-negative bioenergy – biomass power plants coupled to CCS]. Low-input high-diversity biofuels grown on degraded or marginal lands, with associated biochar production, could accelerate CO2 drawdown, but the nature of a biofuel approach must be carefully designed.

    A rising price on carbon emissions and payment for carbon sequestration is surely needed to make drawdown of airborne CO2 a reality. A 50 ppm drawdown via agricultural and forestry practices seems plausible. But if most of the CO2 in coal is put into the air, no such “natural” drawdown of CO2 to 350 ppm is feasible. Indeed, if the world continues on a business-as-usual path for even another decade without initiating phase-out of unconstrained coal use, prospects for avoiding a dangerously large, extended overshoot of the 350 ppm level will be dim.

    Romm is uncomfortable with Hansen’s message, because it implies a massive investment in bioenergy – the type of renewable that Romm, for some bizarre reason, can’t stand.

    Anything less than a 350 aim means you’re a fake green.

    Check the guys who take Hansen’s message serious: November 10, 2008:
    Scientists suggest carbon dioxide levels already in danger zone – urge investments in carbon-negative energy, biochar

  22. David B. Benson says:

    Jonas — I’m all in favor of biochar sequestration, but suggest assisting by enhanced mineral weathering. I posted some links in this thread earlier. My cost estimates start at $140 per tonne of carbon removed and then drop (for several reasons) to about half that. Others think that it can be done for only $35 per tonne of carbon removed. I hope so, but am dubious.

    In any case, this appears much less expensive, eventually, than even the most optimistic estimates for coal-based CCS.

  23. Mark in MN says:

    What a load of BS!

  24. David Lewis says:

    A professor Keith at the University of Calgary has a pilot plant that removes CO2 from ordinary university air that costs 100 kwhr of electricity to remove one tonne of CO2. 100 kwhr of electricity where I live, retail, costs $7.

    But I think we should all run around like chickens with our heads cut off proclaiming James Hansen is a jerk because he can’t flesh out to Romm’s satisfaction how it is that civilization could possibly stabilize the CO2 concentration in the atmosphere at 325- 350 ppm. No new technology will ever be developed, no new political will will ever develop, no one cares, and nothing will be done, other than exactly what Romm thinks is possible in today’s political environment. So make sure you don’t read about the prof in Calgary.