Must-see: Bill McKibben on David Letterman

But Dave, though well-informed, gets one of his facts wrong

The founder of and the author most recently of the must-read book Eaarth “” has a great interview with David Letterman.  Dave is more knowledgeable on climate and energy issues than the vast majority of ‘real’ journalists, though he makes one mistake:

Always amazing to see a person as well known as Letterman who sees the situation in more dire terms than a guy like McKibben (see Letterman rages on global warming: “We are so screwed!”)

Letterman does make an inaccurate statement toward the end (around 10:30) to effect that if we stopped all carbon emissions tomorrow, “the planet would continue to heat precipitously for another 60 years.”   McKibben should not have said “that’s right.”  He should have explained that this isn’t true.  RealClimate explained this in March based on a Nature Geoscience letter by Mathews and Weaver (sub. reqd.):

The upper line is often what is referred to as the ‘climate change commitment’ (for instance Wigley, 2005). This is the warming you get if we keep CO2 (and other GHG and pollutant levels) constant at today’s values. (Technically, the figure shows the case staying at year 2000 values). In such a scenario, the planet still has a radiative imbalance, and the warming will continue until the oceans have warmed sufficiently to equalise the situation – giving an additional 0.3 to 0.8ºC warming over the 21st Century. Thus the conclusion has been that because of climate inertia, further warming is inevitable.

However, constant concentrations of CO2 imply a change in emissions – specifically an immediate cut of around 60 to 70% globally and continued further cuts over time. Matthews and Weaver make the point that this is a little arbitrary and that the true impact of climate inertia would be seen only with emissions cut to zero. That is, if we define the commitment as the consequence only of past emissions, then you should set future emissions to zero before you calculate it. This is a valid point, and the consequence of that is seen in the lower lines in the figure.

CO2 concentrations would start to fall immediately since the ocean and terrestrial biosphere would continue to absorb more carbon than they release as long as the CO2 level in the atmosphere is higher than pre-industrial levels (approximately). And subsequent temperatures (depending slightly on the model you are using) would either be flat or slightly decreasing. With this definition then, there is no climate change commitment because of climate inertia. Instead, the reason for the likely continuation of the warming is that we can’t get to zero emissions any time soon because of societal, economic or technological inertia.

That is an interesting reframing of an issue that comes up all the time in discussions of adaptation and mitigation. This is because it demonstrates that adaptation (over and above what is necessary to reduce vulnerabilities to current climate conditions) is unnecessary if mitigation is dramatic enough.

However, the practical implication of this reframing is small. We are clearly not going to get to zero emissions any time soon, and even the 60-70% cuts required to stabilise concentrations initially seem a long way off. Thus as a practical matter, it doesn’t really matter whether the inertia is climatic or societal or technological or economic because the globe will continue to warm under all realistic scenarios (what we do have a possible control over is the magnitude of that warming).

We don’t want to make an angels dancing on the head of a pin argument.  We are, under any politically plausible scenario, committed to more warming.  That said, humanity still controls its destiny at this point, and we almost certainly can avoid “precipitous” warming, but it would require us to take action that is much stronger and faster than the status quo media understands or the anti-science conservatives in this country will abide.

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43 Responses to Must-see: Bill McKibben on David Letterman

  1. Joe – I think you’re being too harsh on the pair of them about this zero emissions scenario, because there are a number of subtleties here that need to be teased out.

    First, the “zero emissions” scenario considered in M&W is not necessarily what most people would understand by zero emissions. They mean no further net contribution of CO2 to the atmosphere from any source, including, for example, land use change (which represents something like 1/3 of total net CO2 growth). So, they don’t just mean no more fossil fuels, they mean no more expansion of agricultural land use, no more chopping down rainforests, and no more desertification. I think most people would interpret “zero emissions” to mean zero fossil fuel use.

    Second, M&W didn’t do the appropriate thing with sulphate aerosols. They left these constant in their simulations, while reducing carbon emissions to zero. In the admittedly counter-factual world in which net CO2 emissions drop to zero instantly, sulphate aerosols would also drop to zero (after all, they come from fossil fuels too). As these have a large net cooling effect, the cooling trend in their graphs is more likely to be an artifact of the sulphate emissions, rather than a response to the slow decline in CO2 concentrations.

    The bottom line is that CO2 stays in the atmosphere on timescales from decades to centuries, and all the time that the concentrations are elevated over pre-industrial levels, we can expect a warming to occur until the earth reaches a new radiative balance. This makes CO2 unlike any other form of pollution we have encountered (with the exception of radioactive waste). It means stopping production doesn’t fix the problem. It also probably means that no matter how fast we get mitigation policies in place, we’ll still need some form of capture and sequestration of CO2 (e.g. air capture) to stay within the 2 degrees threshold. In other words, zero net emissions won’t be enough – we’ll need negative net emissions.

    [JR: Not certain where I was “harsh.” Frankly, I thought I was letting them go pretty easy, since Dave was trying to spin this as the whole situation being hopeless based on his misunderstanding. I think you are entering into the “angels dancing on the head of a pin” scenario. The wrong word, which I highlighted, was “precipitously.” But more importantly was the wrong conclusion — it’s hopeless on purely scientific grounds. It isn’t. It may be hopeless on political grounds, but that is an entirely different matter. The bottom line is that most viewers came away with a misimpression, I think. Not a big deal, but a medium deal.]

  2. Erik Schimek says:

    I appreciate seeing an articulate spokesman in a public forum like this.

    One point worth noting: Bill related the temperature in Celsius (1 degree) to an American audience. To the vast majority of Americans, the threat of a 3-4 degree temperature increase comes across as laughably insignificant.

  3. Wit'sEnd says:

    “CO2 concentrations would start to fall immediately since the ocean and terrestrial biosphere would continue to absorb more carbon than they release as long as the CO2 level in the atmosphere is higher than pre-industrial levels (approximately)”

    The biosphere isn’t going to continue to absorb more carbon than it releases if we continue to put ozone into the air. We are killing forests all over the earth already.

  4. fj2 says:

    It is really good seeing Bill McKibben on David Letterman. A lot more of this media exposure with him and his type would be a big help.

    There has to be some visioning on what civilization will be like committed to survival.

  5. fj2 says:

    More and more it seems that the best place to do the sequestering will be the world’s oceans.

  6. Joe – I think the result of a “zero emissions now” scenario isn’t entirely an angels-on-a-pinhead discussion, because it has important implications for whether the zero net emissions will ever be enough to stop the warming. So, say we reach zero net emissions by mid-century, through some miracle of aggressive action. Will the warming stop at that point, or will it continue for decades or centuries to come? M&W’s result seems to suggest it would stop immediately, and start to cool. My interpretation of their experiment means temperatures would continue to rise. So, it comes down to the issue of how likely we are to need large scale sequestration to work as well as aggressive emissions cuts. In other words, we should aim for negative net emissions rather than zero net emissions. I don’t think either is entirely hopeless, but it sure would be nice if people comprehended the magnitude of the task.

    Why does this matter, given that even zero net emissions seems politically unlikely? I think it matters because it underpins a a key point in the public (lack of) understanding of the challenge – that we can’t just wait until we can no longer stand the heat and then turn off the hot tap. We have to turn it off decades in advance of that point, because even then we’re committed to a lot more warming to come…

  7. If the planet was in a CO2 equilibrium before we started burning fossil fuels, what mechanism would pull out all the extra tons we have already put in the atmosphere?
    And I heard somewhere that there is a 4 decade lag time between CO2 and temperature… that the warming we are experiencing now is the result of the CO2 we put in the atmosphere in the ’70s. Is that wrong?

  8. Leland Palmer says:

    With massive worldwide implementation of BECCS – if every coal fired power plant in the world were converted to biomass or charcoal fuel and the CO2 captured and sequestered- we could be down to net zero emissions probably within a decade, I think.

    Oh, it would be a massive job, but with the cooperation and commitment of our core financial elite, it could be done. Cars would have to be electric or plug in hybrid, and a WWII scale effort would be required.

    From Wikipedia, BECCS:

    Bio-energy with carbon capture and storage (BECCS) is a greenhouse gas mitigation technology which produces negative carbon emissions by combining biomass use with carbon capture and storage.[1] It was pointed out in the IPCC Fourth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) as a key technology for reaching low carbon dioxide atmospheric concentration targets.[2] The negative emissions that can be produced by BECCS has been estimated by the Royal Society to be equivalent to a 50 to 150 ppm decrease in global atmospheric carbon dioxide concentrations.[3]

    The concept of BECCS is drawn from the integration of biomass processing industries or biomass fuelled power plants with carbon capture and storage.

    It would be a massive job, but I am convinced it could be done. The carbon negative impact of BECCS would make net zero emissions possible, I think.

    If a high temperature gas turbine topping cycle were added to the power plants, enhancing their efficiency, the change could even be done at a reasonable cost- perhaps even at a long term profit, I think.

    We’re still at the stage though, IMO, in which our financial elites foolishly or malignantly think that they can profit from melting the Arctic sea ice and drilling for oil in the Arctic Ocean.

    I favor a massive civil suit brought by the U.S. Justice Department and as many States as possible against the fossil fuel industries, bankrupting them and securing payment from super rich stockholders for punitive damages. Another option would be for the President to declare a state of emergency and seize the power plants, at least, and possibly the oil corporations too, while simultaneously pursuing the climate change civil suit.

    The coal fired power plants could then be converted to BECCS by force. The oil corporations could be converted to biofuels production from algae, using some of the CO2 from the BECCS power plants or from other biomass sources. The auto industry could either be seized or coerced into producing hybrid or electric vehicles. For batteries, we could use either lithium ion or nickel metal hydride.

    It is possible to get our act together. But to do so would require breaking the power of Koch and ExxonMobil, and going after our super rich families for climate damages.

    We are fortunate in our President, to have Obama, who at least acknowledges the problem. But we need a leader capable of managing a massive radical transformation, not a leader with an apparently irrepressible desire to compromise. And the President would have to be protected from real or political assassination.

    We are so screwed…but not because a technological transformation is impossible.

  9. paulm says:

    Have to agree with Letterman on this one.

  10. Leif says:

    More carbon comes from the loss of gigantic areas of dead forests from pine beetles, and the loss of 40% of the ocean phytoplankten and counting. Of course we should not disregard the out gassing of the melting tundra. On top of that we have the difficulty of adding carbon to the oceans without adding to the acidification of same, further disrupting the food web. Continued logging of the biggest trees the world over is equivalent to removing the Elephants of the carbon eaters and replacing them with shrews.

    Gosh, Looks like we got our work cut out for us. We have a world full of idle hungry people that could help with proper incentives and starvation for motivation, but the corporate world wants us to continue to buy, consume, waste, and most important to quit thinking.

  11. Jeff Huggins says:

    Not It!

    Let me be clear: I applaud Bill for his heroic efforts and for trying and doing a very good job on most parts of the conversation.

    And, I applaud David for featuring the issue and for his positive support.

    But that conversation — net net — is “not it”. It left FAR too much lack of clarity — and indeed invited misunderstanding — when it comes to understanding that’s central to human motivation.

    The problem is not one of arguing over how many angels fit onto the head of a pin. I admire getting things right, and the matter of scientific correctness is an important one, of course, though that particular matter might seem to some TO be arguing over small stuff and seem to others TO be big stuff. But either way, that’s not the real and larger problem here, with the interview.

    The much larger problem is that, because of the use of highly ambiguous language, because of the incorrect response at the end, because of the comedic style of Letterman and Bill’s too-scientific/academic style, combined, and because an important part of human motivation necessarily involves the need to understand that “my action (of some sort) can at least contribute to making a difference”, and also because of a few other aspects of the interview — WITH ALL OF THESE THINGS COMBINED — the interview left the net impression that disaster is coming, that nothing can be done, and that it (global warming) all makes for a fine topic by which Nero may choose to fiddle as Rome burns.

    IF we want to validly motivate people, we have to do interviews VERY differently. Here, I’m talking about the emphasis, the ready answers, and the attitude and style of both interviewer and interviewed. I’m not talking about changing interviewer and interviewed: Letterman and McKibben are key folks, of course, and many others should also be having these discussions too. But, I AM talking about preparedness, emphasis, the attitude and posture taken while talking about this — hint, it’s not the same as talking about the next fad, the location of a new Mosque, compensation on Wall Street, or etc. — and so forth.

    The NET TAKE-AWAY from the interview, on whether we can (and should) do much of anything to face and address the problem — other than “get ready to adapt” — is (to be honest) deeply disappointing. That’s not, of course, because either McKibben or Letterman think that actions won’t help, or that we shouldn’t bother. Instead, it’s because they used highly ambiguous language on that key matter, were less-than-prepared for that sort of question, got an answer incorrect (as it sounds), and treated the whole discussion as just another late-night discussion with an author, scientist, and “environmental activist”.

    A nice conversation. Nothing we can do. Nero, you can keep on fiddling.

    Again, I applaud the efforts, but not the net result. If we all want people — including all of us, including me, including etc. — to get out for actions and activities, and to take these matters seriously, as they should be taken, then (in my view) we should make sure that vital interviews and messaging go well. After all, “what good will it do?” if I dedicate days to get active on this front, and continue to attend the events, and if many of us get active, and yet if the impression is left that “we’re all doomed!” every time one of the movement’s leaders has an ambiguous interview on late-night TV, with millions watching?

    I listened to a conference call a few weeks ago, and perhaps the central message was “the Senate failed”, with another being “we need to redouble”. In this recent interview, one of the main take-away messages (not intended) was “disaster is coming, and nothing we can do will change things for as long as we live”.

    So, it sounds like this is the case . . .

    * The Senate failed
    * We need to redouble
    * Disaster is coming, and nothing we can do will change that for as long as we live

    Although I applaud physical science — and I love the physical sciences — I think it’s time that we do a better job checking with life-scientists, psychologists, poets, and so forth regarding what is motivating and what isn’t. The message reflected by the three points just mentioned is partly correct, partly incorrect, and almost entirely un-motivating.

    If we don’t improve our messaging soon, I’m going to take up the fiddle.

    Sorry for the rant. But really!



  12. mike roddy says:

    McKibben was excellent on TV, and thanks for the discourse on the zero emissions scenarios.

    Steve Easterbrook, I’m glad you’re bringing up the subject of land sequestration, which is rarely covered on any of the climate blogs, and support your belief that land use emissions may be 1/3 of the total, or 33%. Many believe that the IPCC estimate of 18% is far too low.

    Here’s a Forest Voice article with background research that I wrote on deforestation and sequestration potential in the US:,

    The US has a far higher percentage of deforestation than almost any tropical country, and our Western forests sequestered more carbon per acre than tropical forests, by far. Americans not only led the world in CO2 emissions until recently, we have also led the world in excessive industrial logging, including replacement with climate change vulnerable tree plantations.

    Leland, I’m interested in biochar as a mitigation strategy. Please provide a link, or send me info at

  13. mike roddy says:

    Franklin and Harmon wrote a paper in 1990 calculating the emissions of our having liquidated the coastal forests of Oregon and Washington alone at 6 billion tons CO2 equivalent. This was an environmental atrocity, enabled by Congress (with subsidies), “green” groups, and the media.

    Canadian forests are burning because of excessive logging in addition to climate change: intact forests are cooler and damper, and far more resistant to conflagrations, as Easterbrook pointed out for the Amazon.

  14. Robert Brulle says:

    I have a question on this scenario as outlined by Joe. Haven’t we already set off some self-accelerating mechanisms, such as: 1) the soon to come disappearance of the arctic ice cap, and the subsequent melting of the permafrost, 2) Decreases in the ocean phytoplankton and the ability to absorb CO2, or 3) increases in soil respiration, thus leading to more GHG emissions regardless of human actions?

    So if we take these factors into account, that even if we humans stopped all of our activities that emit GHG (including land use), wouldn’t temperatures and CO2 levels continue to increase for a while till it reaches a new equilibrium due to these feedback effects?


    [JR: I did mean to mention the feedback effects, which could certainly alter the calculation. If we went to zero total emissions tomorrow, though, I’m inclined to think that we could handle those. This is where we get into angels dancing on the head of a pin. In a world in which we went to zero tomorrow, we could then spend the rest of the century going negative and … that of course is the problem with alternative universes. Once you leave the plane of reality, pretty much anything goes.

    Again, it was not so much the technical underpinning of Dave’s statement that bothered me, as it was the use of the word “precipitously” and the message that it’s all over.]

  15. Nancy says:

    Leland Palmer, what a fascinating post. It seems impossible, but so did flying to the moon a few decades ago. I hope I live long enough to see the changes you write about.

  16. Barry says:

    Hansen’s data says our planet’s landmasses — mainly vegetation and soils — are still a significant net sink of CO2.

    On page 120 of his excellent book, “Storms of my Grandchildren”, he says:

    “The fact that the Earth’s land masses continue to produce a net sink of carbon dioxide provides a glimmer of hope for the task of stabilizing climate. This carbon sink occurs despite large-scale deforestation in many parts of the world, as well as agricultural practices that tend to release soil carbon to the atmosphere. Improved agricultural and forestry practices could significantly increase the uptake of carbon dioxide…”

    The data shows that the percentage of our fossil CO2 that stays in the air has been nearly constant for fifty years at 56%. The amount going into sinks of ocean and land has also been constant at 44%.

    This continuing net sink is what would allow CO2 ppm to fall under zero-emissions scenario. If we also reform land-use, as Hansen says we must to avoid dangerous tipping points, then we can increase this sink. We can draw down CO2 ppm and return to a safe 350 ppm level.

    But the earth has become a net SOURCE of CO2 many times in the past. If we push the warming to tipping points reached in the past, we will lose this valuable sink and lose control of climate warming.

    The two key data points to watch, Hansen says, are rate of fossil fuel CO2 emissions and the annual growth of CO2 in the atmosphere. Those will tell us the size of the planet’s CO2 sink or CO2 source. He updates these values on his website.

    Much more detail on this in his chapter “Is There Still Time?”.

  17. Leif says:

    Good Rant Jeff, @ 11. I feel you are absolutely right yet again. Humanity needs to sing in a resounding chorus to beat this “boogie man,” not walk around with a long face moaning all is lost. That only becomes a self fulfilling prophesy.

  18. Barry says:

    RE: Beam Me Up Scotty (#7)

    One reason the earth absorbing more tonnes of CO2 into oceans and land masses now than it did in pre-industrial times is that many “sinks” are driven by the concentration of CO2 in the air.

    For example, the higher the concentration of CO2 in the air the more will be dissolved into oceans at a given temperature.

    Of course the majority of our fossil CO2 stays in the air even so.

    On your second point about warming lag time, it is true that when we add a new fossil CO2 molecule to the atmosphere it stays for decades. All that time it is warming the planet. So, yes our 1970 emissions are still up there warming away.

    However the total warming at any point depends on the CO2 ppm in the air. If we draw this down we can reduce the warming. In other words, at zero-emissions, the earth’s sinks would start pulling some of those past emissions from the air and thus reducing their warming impact.

    Hope that is clear. If not I highly recommend Hansen’s book for anyone wanting to understand the climate science and key data points.

  19. Will Koroluk says:

    Mike @ #12: Your tinyurl link is broken.

  20. Jeff Huggins says:

    To Be Clear

    To add to (or clarify) my earlier comment, I also think a key part of the problem has to do with the word “precipitous” and the whole net implicit take-away that nothing we do will matter for a long, long, long, long time . . . and longer.

    It won’t matter much to our children and grandchildren, and to other species, and to other peoples, if we don’t take effective action to address climate change because we didn’t believe the science, or because we didn’t care, or because we chose to see matters as hopeless, or because we couldn’t get our messaging together, or because the media mucked things up. It hardly matters. The climate won’t care either. The impression left that “nothing we do will matter much” is incorrect, to an important degree, and it is just as problematic as not understanding the science in the first place, from the standpoint of outcomes.

    Back to the drawing board.



  21. Christopher S. Johnson says:

    Hi, I wanted to add a point that is obvious on it’s surface, and is the second-half of this whole conversation. And not only the chart above, but Susan Solomon’s NOAA 2009 paper is also clear about it. It is not said plainly enough, whether on Letterman OR Climate Progress:

    Whether some continued warming happens or not after reaching “zero” emissions, it will be more than a thousand years for that concentration and it’s negative effects to “heal”. We are stuck on a flat line for hundreds and hundreds of years! It doesn’t get “better” (pre-industrial levels) in an amount of time frame that matters. It just “sucks less” than if we continued businesses as usual. This is the “clogged bathtub” effect because CO2 takes that long to precess down.

  22. Robert Brulle says:

    One of the best aspects of this blog site is that we can have actually informative conversations. Since I am a social scientists struggling with the climate science, this is a real help.

    On the question – is it too late? My question has a couple of components:

    1. Is it too late (back in the real world) to avoid more than 2 degrees of temperature increase? I hear a lot of talk about this, but none of it squares with the paper by Ramanathan and Feng who argue that:
    “The observed increase in the concentration of greenhouse gases (GHGs) since the preindustrial era has most likely committed the world to a warming of 2.4°C (1.4°C to 4.3°C) above the preindustrial surface temperatures. ”

    Are these guys wrong? I can’t judge this paper, as it is outside of my field. If they are right, then talk about keeping the temperature changes below 2 degrees is just wishful thinking.

    2. Necessary reductions – can we mitigate to avoid dangerous climate change? Here I am looking at the paper by Anderson and Bows, who state that the most optimistic level of mitigation we could hope for is 650 ppm, which puts us up at around 4 degrees at best. They conclude:
    “ultimately, the latest scientific understanding of climate change allied with current emissions trens and a commitment to limiting average global temperature inceases to below 4 degrees C avove pre-industrial levels demands a radical reframing of boht the climate chang e agenda, and the economic characterization of contemporary society.”

    So what I see here is that the very BEST we can hope for is to stay below 650 PPM and 4 degrees.

    Isn’t the question now which circle of hell we want to be in?

    I claim no specialized expertise in this area, so I would appreciate any clarifications and explanations. I would love to be convinced that I am wrong.


    Ramanathan, V., and Feng, Y. 2008 On avoiding dangerous anthropogenic interfenrence with the climate system; formidable challenges ahead. PMAS 105(38) 14245-14250

    Anderson, K, and Bows, A. 2008. Reframing the climate change challenge in light of post-2000 emissions trends. Phil Trans. R. Soc. A

    [JR: 2C is not a sharp demarcation between sustainability and unmitigated catastrophe. Also, nobody knows how long we could go afford to go above 450 before we have to get back to 350. But from my perspective, 650 is not a plausible scenario. Either you keep as close to 450 as possible and get back below 350 asap, certainly no later than 2150, ideally sooner, or you are probably going to 800 to 1000 ppm. Muddling through at 550 or 650 while the feedbacks are kicking in strikes me as highly implausible now.]

  23. Rabid Doomsayer says:

    The Milankovitch cycles provide a really gentle nudge to the climate and it swings in and out of ice ages. We have given the climate the biggest kick it has had in tens of millions of years if not more. Surely the response we can expect will be great.

    Already the sinks are not absorbing as much and we know CO2 increases with temperature naturally, the northern icecap is disappearing fast and we face a number of methane bombs. The ignored slow feedbacks are not so far away now.

    Civilization is fragile, I have doubts it can survive what is already inevitable. BAU for another fifty years and humans might be one of the species that goes extinct.

    Our doom is not yet certain, but certainty is not far away.

  24. paulm says:

    I think you have to consider what kind of message and rhetoric is needed. I think Letterman is closer to what is needed than what scientists, policy makers and leaders have been doing so far.

    The majority still have absolutely no clue of the magnitude of the impact of the current warming trend. And by the time they do we will have committed to a 6-10C???? world. They are just realizing what GW can mean with the recent extreme events.

    It is time people heard it like it is.

  25. Robert Brulle says:

    While I agree with you on the science, the most optimistic scenario outlined by Anderson and Bows is 650 ppm. So where is the hole in their argument that leads you to say we can stay around 450 – 500 ppm?

    I would really like to think that it is not too late to keep climate change under control. But is it a fair reading of the literature to say that is a matter of debate now in the scientific community?

    If we delay massive action for several years (which seems likely given the rise of the no-nothing Republicans to power), aren’t we sooner or later going to pass a point where climate change processes spin out of human control?


  26. OregonStream says:

    Scotty, inertia in the climate system/the fact that it takes a few decades for atmospheric and cryospheric conditions to largely respond to a given change in CO2, is a good reason for acting before effects are widely apparent to a majority of temperate-region dwellers. Already there are preliminary signs that carbon-sequestering phytoplankton are affected by climate change, and there are other potential effects on sink efficiency. The oceans are especially important, along with any extra efforts humans might make to enhance or preserve terrestrial carbon sinks/reservoirs. And also monitor methane in both the Arctic and Antarctica. It would take quite a burst to overwhelm the methane cycle, but emissions above background could be a contributing factor.

  27. Paul K2 says:

    I am not as pessimistic as some comments here; a substantial reduction in carbon emissions will have a substantial impact on the excess inventory of carbon in the atmosphere.

    Imagine if man stops emitting carbon into the atmosphere… How would the Earth respond? One of the preaching skeptics (Tom Fuller) asked this question, and below is my paraphrased and revised attempt to answer this question. Of course to do this properly requires a full global climate model, but at least this semi-quantatively shows the major factors controlling the rate that we might be able to reduce carbon levels in the atmosphere.

    Before we address the impact of an immediate cut-off in carbon emissions, we need to address the equilibrium of the Earth before the ramp of CO2 from man’s activities. My take is that the Earth must have been pretty close to a steady state dynamic system in terms of both CO2 distribution and thermal energy distribution. The CO2 levels hadn’t changed that much in several thousand years, so the Earth had reached a steady state where the CO2 in the oceans, soils, and vegetation exchanged with CO2 in the atmosphere with no significant inventory changes. (Over longer periods of time, this steady state condition has been disrupted many times.) The CO2 exchange with the oceans varied from net absorption to net outflow depending on the region of the planet and seasonal influences, but for the planet as whole system over the entire year, the inflows to the atmosphere were in balance with the outflows. Now some could argue, that a perfect steady state system is unlikely, but whatever imbalances existed, the net imbalance was small enough that the atmospheric CO2 level was relatively stable. The net changes n CO2 levels were quite small compared to the experiment mankind was about to run on the planetary system.

    In short order (150 years) man’s activities have increased the CO2 level and added about 224 GtC (gigatons of carbon) net to the atmosphere, bringing the total carbon in the atmosphere to about 750 GtC. Another 180 GtC has been net absorbed by carbon sinks, primarily the soils and ocean. Of the total carbon released by man, about 80% is from fossil fuels, and the remainder primarily from deforestation impacts where the store of carbon in plant matter around the planet has been depleted. We have measured the buildup of CO2 in the atmosphere, verified that it was manmade and recent by using several different kinds of analyses including carbon isotope data, information from atmospheric nuclear tests, etc. There are multiple lines of evidence that support the result that the buildup in CO2 was caused by man’s activities.

    Clearly the Earth is not in a steady state since the CO2 emissions ramp started. The oceans and soils have absorbed a large fraction of the CO2 added to the atmosphere, and the ocean has the ability to absorb a great deal of carbon before an equilibrium is reached. The uptake of CO2 by the oceans is clearly transfer rate limited, and not equilibrium limited. Current carbon emissions release over 8.7 GtC to the atmosphere each year. The oceans can only take up about 2.4 GtC per year (net accumulation), and this rate has increased as the carbon inventory in the atmosphere has increased (due to the rising partial pressure of CO2). When the carbon inventory in the atmosphere starts dropping (hopefully this happens), the uptake rate will begin declining again. If the ocean and soil sinks are combined, about 3.9 GtC per year can be absorbed by these sinks. Right now, with man releasing 8.7 GtC per year into the atmosphere, the carbon sinks can’t keep up with the emissions, resulting in a net build in the excess atmospheric carbon inventory of 4.8 GtC per year. To express these numbers differently, only about 55% of total carbon emissions end up in the airborne fraction; the rest of the carbon (45%) is absorbed by carbon sinks.

    So if we stop emitting CO2 from burning fossil fuels immediately (and any CO2 positive feedbacks like permafrost melt releases suddenly stopped as well), the excess carbon inventory in the atmosphere will begin to drop by about 2.2 GtC per year for the first several years, instead of the current increase of 4.8 GtC per year. This would be a huge achievement!

    Let me take some liberties, and try and estimate the rate that the excess CO2 inventory in the atmosphere would fall. A decent estimate of the average uptake by the carbon sinks for the first 20 years or so would be about 2.1 GtC per year, so at the end of this time the excess carbon inventory will have dropped from about 224 GtC to about 180 GtC. But now the uptake rate by the carbon sinks will slow, since the partial pressure of CO2 in the atmosphere has declined. The sinks will now be absorbing only about 2.0 GtC per year, so the next 20 years would only take out 40 GtC, and the excess inventory will drop to about 140 GtC. But now the sinks will only be absorbing about 1.9 GtC per year, and the rate will continue to decline. We might estimate the next 20 years take out another 38 GtC, with the excess inventory dropping to about 102 GtC. So in sixty years after a complete shutdown of carbon additions to the atmosphere, the excess carbon inventory in the atmosphere has been reduced more than half. The CO2 level in atmosphere will have fallen back to 328 ppm (this rough questimate is based on a complete elimination of fossil fuel carbon emissions). But then things start to get messy, because the ocean has been heating all this time.

    The ocean is currently heating up annually with a very large accumulation of heat (about 20 times the thermal energy released by fossil fuels) This estimate is derived from sea level rise and the thermal expansion of sea water. There is a good deal of uncertainty in this estimate, since we can’t be sure how much of the sea level rise is due to land based ice melt versus thermal expansion. (Some skeptics claim that land based ice isn’t melting or is increasing, in which case the ocean heating rate is much higher! I wonder if these skeptics know they are making a case for increased global heating, when they argue that land based ice melt is much less than currently estimated?) Reasonable estimates of land based ice melt result in more reasonable ocean heating rates calculated from the thermal expansion of sea water (after the SLR due to ice melt has been subtracted). The ocean heating rate, and distribution of this heat in the ocean is very important for estimating the planetary response to a sharp cutback in CO2 emissions.

    The amount of thermal energy that is is required to heat the atmosphere (to account for the observed rise of 0.16 to 0.2 deg C per decade) is much smaller than the thermal energy heating the ocean; the ocean heating rate is roughly 80 times the atmospheric heating rate. Even if man is successful in curtailing CO2 emissions, the ocean will continue to heat at approximately the same rate until the oceans approach equilibrium CO2 saturation. The upper levels of the ocean should become saturated with CO2 for the higher temperature water due to ocean heating. So even with a curtailment of CO2 emissions, the upper level ocean zone temperatures could rise to a point where CO2 uptake stalls, and in many parts of the ocean, outgassing begins. This is a complicated analysis, and without a model, the declining uptake by the oceans is difficult to estimate.

    To illustrate this, let me present my hope (wishing on a star). I hope that most of the net CO2 uptake is caused by up welling cold deep ocean waters that haven’t been exposed to the CO2 in the atmosphere for hundreds of years. If this is the case, then the warming level of the oceans won’t be as large a problem. But if the net absorption rate in the oceans is being set all over the globe in the mixed ocean layer, instead of in specific upwelling zones, then the rising ocean heat content could make it very difficult to reduce CO2 levels below some limit, even with drastic cutbacks. The rising temperature of the seawater in the mixed layer will reduce absorption rate of the ocean carbon sink.

    If we delay cutting carbon emissions too long, the oceans could possibly heat up enough to substantially reduce the rate that the ocean carbon sink is removing carbon from the atmosphere, and this means it will take even more drastic carbon emission reductions to get lower atmospheric carbon concentrations. Adopting a wait and see attitude, in order to prevent unnecessary expenditures, could backfire in a big way and result in much larger expenditures to reach the more stringent carbon emission reductions needed in the future. I hate to use the phrase “tipping point”, but that is what it could be.

    Clearly we do not have enough information on the ocean carbon sink mechanisms, and we need a much better ocean model. In addition, we need more information on ocean heating and much better metrics on the ocean heating rate and distribution of heat absorbed into the ocean.

    So back to the original question: the time to halve the excess CO2 inventory that has been added to the atmosphere (by human activity) if we start immediately (and eliminated carbon emissions) is about 50-60 years, and this would get CO2 levels significantly below 350 ppm. But to remove all of the excess carbon inventory will take thousands of years (even with the total elimination of fossil fuels), and likely over 30,000 years. The time to start is now.

  28. Leif says:

    An impressive effort Paul K2 @27. My concerns that make me more pessimistic are the facts that:
    1. The ocean is becoming more acidic, which in itself presents major disruption to the food web and a large portion of humanities protean source. More CO2 is not recommended.
    2. This also presents a complication to the ability of the oceans to absorb carbon at rates commensurate with the past. Shell formation is a very good carbon sink that acidification is compromising as we speak.
    3. The earth’s forests the world over are a mere shadow of their former grander and as such, surely cannot absorb carbon at equivalent pre-industrial amounts.
    4. The same can be said for the expansive prairies of the world tilled and turned to farm crops.
    5. Even the slight temperature rise of ~3/4 C has started to melt the permafrost and thus changing that source from a sink to an emitter of CO2 and methane.
    The list goes on…
    Even the death of billions of people cremated will add to the CO2. It would be nice to turn this inevitable source into a carbon sink if possible. Freeze dried and chipped and composted has been suggested and might be practical with renewable energy power input.

    I would love to share your optimism, but still feel a hefty dose of pessimism is warranted.

  29. Lewis C says:

    Jeff at 11 –

    I share your concern at the impression given by Letterman and not refuted by Bill McKibben that “there’s nothing we can do” (that will make a difference). This is precisely the demoralization of activism that the delayers would pay gold for, and, further, given peoples’ tendency to decline to acknowledge problems for which there is no visible solution, it further serves the corruption by delaying full public recognition of the issue.

    This is not to suggest that self-censorship should be applied but rather that, in such interviews, time has to be spent on discussing solutions commensurate with the problem, if the recognition and the morale for action it to be raised.

    Letterman’s use of ‘precipitously’ would thus have been quite legitimate to describe the warming post anthro-emissions had it been qualified as resulting from the failure to apply feasible additional measures, such as an early and large-scale carbon recovery program.

    That there would be such warming post anthro-emissions has now been partly acknowledged by Gavin at Real Climate, with a post titled Climate Change Commitment II. In this he acknowledges some of the limitations of the earlier post regarding the Matthew & Weaver paper, and describes a more rounded appraisal to include some of the effects of the full spread of GHGs as well as the coolant aerosols.

    Given the lack of open access to the M&W paper, as well as its very limited focus, it is hard to follow just why Gavin felt it offset the longstanding consensus that the oceans’ surface temperature, which governs global surface air temperature, lags several decades behind the potential warming due to rising GHG concentrations. Certainly, under the M&W Cold Turkey Scenario of ending GHG outputs, [CTS] the sinks would continue to remove airborne CO2, but the sea surface temperature would also continue to rise until it reached the point of fully reflecting the forcing of the hypothetically reduced CO2e concentration.

    And from that rising sea temperature we should see surface air temperature rising for the period of convergence. Given undiminished sinks, that are currently removing ~1.8ppmv /yr of CO2, alongside the fact that we’ve raised CO2 by around 60ppmv in the last 35 years, the period of continuing global warming even under CTS would be of many years duration.

    This is not to say that the limitations of the M&W paper are at all improper, so long as the conclusions are qualified by remarking the impacts of the various relevant phenomena not discussed. Otherwise it is simply providing a falsely optimistic impression of our prospects. Given that the paper is paywalled, and Gavin’s lack of description of any such qualifications, it’s not clear if they were provided. (Which is another example of why it is absurd for Nature to withhold full publication rights within a fortnight from the best and most serious of sites like CP & RC).

    The critical phenomena relevant to the CTS conclusions include a whole spread of observed and projected changes, under three headings:

    influences projected as causing the decline of the carbon sinks’ capacity include:
    – the rising incidence of extreme drought and of wildfire and of directly toxic emissions diminishing net carbon intake by terrestrial biomass;
    – the rising ocean temperature diminishing its carbon intake;
    – the rising ocean acidification diminishing its carbon intake;
    – the rising ocean temperature stratification reducing deep water mixing and thus its surface intake of CO2;
    – the falling population of oceanic plankton diminishing its carbon intake and sequestration on the seabed.

    influences projected as raising CO2e ppmv during continued warming as the sinks decline include:
    – the combined carbon outputs of the full range of currently accelerating interactive carbon feedbacks, including Peat > DOC, pest infestation of forest, permafrost melt, clathrates melt, etc;
    – the increase of water vapour in the atmosphere acting both as a potent GHG and as a destabilizer of climate exacerbating the impacts of drought and of floods on the terrestrial carbon sinks;

    influences projected as directly raising observed global warming include:
    – the oceans’ increasing temperature stratification and decline of deep water mixing reducing their heat-sink capacity;
    – the cryosphere’s declining area reducing planetary albido and, as less surface area of ice becomes available for melting, reducing its function as a heat sink;
    – the removal, along with our GHG emissions, of the annual output of coolant aerosols.

    While some of the above are not easily quantified and some are still controversial, they seem worth listing together to make clear the utter improbability of an end to anthro GHG emissions providing an end to additional warming. Thus my main critique of the M&W paper would be its cold-turkey basis; had they started with a “best case post-anthro-emissions” scenario in say 2040, and addressed the full range of influences projected by that date, they’d have come to a very different and far more informative and useful conclusion.

    From this wider perspective, Letterman’s use of ‘precipitously’ to describe the warming post anthro-GHG outputs seems both justified and to be warmly welcomed – it is all too rare that any TV-media employee has acknowledged the scope of the jeopardy – His failure to qualify that remark with discussion of the measures necessary to reduce, peak and diminish that ongoing warming is a real pity, but I guess it’s a part of the learning curve.



  30. Mark4884 says:

    Paul K2

    Thank you for that lucidly laid-out, plausible and hopeful scenario. The numbers you use fit my reading of the literature. That said, could you possibly list the specific key source/s you used?



  31. Richard Brenne says:

    Both McKibben and Letterman did an outstanding job. Compare their conversation to any you’ve heard or read outside of Climate Progress. It was absolutely world-class in every way.

    Yes, Dave’s a little doomerish – it was like I was back at dinner with Romm’s All-Stars (who I love and agree with) – but there isn’t one perfect psychological approach to this message. There need to be millions of voices raised as loudly as possible like this. While the Right can create a unified message between the largest corporations and almost all fundamentalists (even if to me it’s a marriage made in hell), on the Left we bicker about people who are for the most part saying exactly what we want them to say. If our egos prevent us from unity in such a situation, then there might truly be no hope.

    We’ve all been waiting for someone with a large audience to say “absolutely” to the question about global warming influencing the weather. Bill made that connection as clearly, succinctly and emphatically as possible.

    So why aren’t we lauding them? They got it about 98 per cent right, when I don’t know that 100 per cent right is even possible in an exchange like that.

    Letterman is paid to be funny. The fact that he was funny while getting to the heart of the matter better than essentially all mainstream journalists put together means we need to thank, applaud and support his efforts, and of course McKibben’s and everyone like them.

    The key players here and myself don’t have enough hairs to split. Yes we should each be working on our talking points and trying to grow our audiences and as always I appreciate the many informed commenters here, but what we most need is a million messages like this one in all media, all the time. Really a superlative job, Bill. Bill and Joe and the rest of us need to hit it out of the park like this every chance we get.

  32. Whatshisname says:

    Outdoor sports fans, players and coaches in Texas may not be willing to utter the words “Global Warming” or “Climate Change,” but they are certainly reacting to rising temperatures. Noticed the other night that high school refs are now calling timeouts for mandatory water breaks. You may also recall the recent auctioning of the Texas Rangers baseball team. Earlier this year, a largely unnoticed report compiled by Fox Sports (of all people) cited the obvious: potential buyers were scared away because rising temperatures were driving down attendance.

  33. adelady says:

    I’m rather in favour of Letterman and his ilk making these kinds of statements. It then means that the scientists can then be seen as messengers of hope. We can do lots of things to stop this from being as bad as Mr Letterman (or whoever) said. It is a serious problem, but we’ve solved serious problems before. Here’s half a dozen ways to get started.

    Yes the world will be different. But people have moved into apparently hostile worlds and mad a good go of it before. This time it’s the world moving towards more hostile conditions. But we can deal with it. Here’s another half a dozen things we can do.

  34. Jeff Huggins says:

    Dear Richard (Comment 31)

    Richard, I agree with part of what you are saying: We need many more people talking, many more interviews, many more people raising the issue of global warming, and so forth, and many approaches will be necessary, and we should cooperate more, and give each other moral support, and conversations as they happen will be different and can’t all be scripted, and so forth. This (i.e., global warming) is not a problem that can or will be solved by being hesitant to talk about it because of over-worry about saying precisely the right thing, so to speak. I agree with most of the “raw data” in your comment.

    But I disagree (if I understand your comment correctly) on the one point, raised in my earlier comment. We aren’t just a little off message (or off the actionable truth) if a main theme and “take away” of a conversation is that disaster is inevitable and there’s nothing we can do to make any difference that will arrive during our lifetimes or even the likely lifetimes of our children. Such a message is WAY off track, and too many of them will do more harm than good. In my view, people like Bill McKibben (and also Letterman, if he considers the subject important) are top-quality enough that they should realize that such a message is debilitating. It’s a matter of what motivates people (to some sort of responsible understanding and commensurate action) and what doesn’t.

    If we think that the way to raise awareness and understanding is via ten million conversations, worded any which way, in which most of them convey the reality of climate change well but also leave the impression that disaster is coming and there’s nothing that can be done, we’ll end up with large chunks of the population that understand the reality of climate change (progress there) but that continue business as usual based on the belief that nothing will matter anyway.

    My earlier point is not to suggest that narrow scripted conversations are necessary, nor is it (I think) picky perfectionism. I agree with most of the points in your Comment 31. But, the “no hope” take-away left by the present interview is not just a small problem: It’s a debilitating one from the standpoint of human motivation and change management. Our leaders should get better — much better — at understanding that and at knowing how to respond to that sort of question. Indeed, the question is of such importance that “response” is not even the best approach. Any serious conversation about climate change, in front of a large audience, should proactively include at least a comment or two on what we can and should do and on what DIFFERENCE we can still make, and why we should. This issue shouldn’t require a sort of automated scripting, without understanding, as if it’s just an important “talking point” to be included, for reasons we know not what. Instead, the leaders of the movement should have a deep understanding of what motivates and what doesn’t, and they should (in their own words, from their own hearts, without the need for precise scripting) understand NOT to leave the impression that nothing we do will matter. Leaving such an impression is just as bad (in the overall scheme of things) as leaving the impression that CO2 doesn’t cause problems after all.

    Sorry for the “critique” of the present interview. I (of course) applaud Bill’s efforts — he’s a hero — and also David’s attention to the matter. We need many more folks like them. But, that does not mean that we will do well having growing numbers of discussions that all leave the impression that nothing we do will matter. That’s a debilitating impression. That’s a flaw (in “messaging” I suppose, but more importantly in understanding what’s important to convey naturally!) that we should rid ourselves of, I think.

    Cheers for now,

    Be Well,


  35. Leif says:

    Spot on to both of you, Jeff and Richard. Solutions are available and perhaps the direction need is emphasis on solutions that lead to the big picture. Such as the link by fj2,2 # 6 in an earlier post on CP.
    This kind of coordinated attack by functional government and moral people made major positive inroads into the problem of hunger in a Brazilian city and has achieved most of the goals we aspire to without mentioning AGW once. Most importantly it proved that it is possible for people and government to function and solve a major problem, (hunger in a city of ~1.2 million @ ~ one penny/day/ person), at low cost and improvement to all.
    Food is a right, water is a right, air is a right, Sustainability is a right.

  36. Lewis C says:

    Jeff and Richard –

    I have to agree with both the perspectives you advance – that we urgently need plain spoken descriptions of the degree of jeopardy society faces, and we also need the raising of morale for and commitment to action.

    This conundrum has played into the hands of the delayers both to the extent of activists, scientists and politicians accepting degrees of self-censorship
    – e.g. where’s the public discussion of the feedbacks ?
    and by its generating demoralisation and fatalism among a significant fraction of GW-aware people, most particularly the young.

    Indeed, if I were running an astro-turf shill operation, pushing the doomer line across the internet would certainly be one priority, given the importance of young people as the core of effective activism.

    As things stand, it is doubtful that even 1/4th of 1% of the ~40 million Americans between 16 and 25 could be called committed activists – and empowering that 100,000 young people is surely the critical start to raising the necessary grass roots demand for change. We (who seem here on CP to be mostly over 50) have to ensure that the messaging is both explicit regarding the existential threat yet also encourages participation rather than depressing the hell out of it.

    The pivotal issue for resolving this is not simply in describing the speed with which GHG outputs can be ended – which looks impracticable before say 2040 – but in facing up to what is to be done about the feedbacks. These are quite a stunner to the morale of anyone looking openly at our prospects, once it is realized that they are numerous, diverse in function, already accelerating, interactive, and predictably vast in effect.

    The fact that ending GHG outputs by 2040 is increasingly unlikely to control the feedbacks thereafter means that additional measures for their control must start to be openly discussed if a coherent message of a soluble problem is to be presented to young people. The degree of self-censorship that has hushed discussion of the feedbacks, and particularly of the commensurate carbon recovery and interim albido restoration programs for their control, has to be deeply depressing – if we did manage to end emissions, but we’ve no acceptable means of controlling the feedbacks, what’s the point in striving for change ?
    “So party on, dude!”

    Therefore it seems to me that it is the open discussion of the means of the feedbacks’ control that is most lacking in the environment movement. The fallacy that because something could be done really badly it should be dismissed from serious discussion has held sway too long. We need urgently to start thinking outside of the dysfunctional box of “Shut down the emissions – end the problem.” It offers neither a viable path out of climate destabilization, nor the recruits needed to cut that path open.



  37. fj2 says:

    #35 Leif, Absolutely!

    It is really important to start showing the simple practical solutions that increase quality of life at the same time greatly mitigating climate change; perhaps something like “Global Warming Futures” would be a good addition to Climate Progress in addition to the daily “Global Warming News”.

    In the developing world certain things are relatively easy like the 430 million cyclists and 120 million who use electric bikes in China who would likely jump at the chance to use derivative technology at the same low-cost and low environmental footprints but with speed, range, comfort, and safety capabilities beyond transportation systems based on automobiles.

    As a startup along similar lines MIT and others have assisted Guatemalans in using basic human power and bicycle technology to improve the quality of life: the “bottom of the pyramid” approach. With successes more advancements will hopefully follow that will mitigate climate change on much larger scales when local economics is sufficient to make solar and other low-carbon energy sources practical and good economic sense.

    And, for the developed world lifestyles that are practical, comfortable, and more secure from Revkin’s “Labor (Less) Day” featuring economist Julie Schor and her video describing a personal economic model:

    These kinds of things could help increase the comfort level for many people in this period of tremendous change and insecurity with common sense practical approaches to achieve a comfortable future at the same time mitigating climate change.

  38. fj2 says:

    #37 fj2 continued,

    Actually, Climate Progress has a lot of this positive stuff, as do many others, but it seems the focus should be perhaps much more optimistic, extensive, and truly scale-appropriate to start providing critical paths to preventing the apocalyptic trajectory we are currently on.

    . . . It’s probably important to provide a “vision thing” much more accessible than the “wedge” approach.

  39. fj2 says:

    #38 fj2 continued,

    It seems that extremely effective human-capital focus leveraging the resources of this nation’s information and communications technology powerhouses such as Google, IBM, Microsoft, Verizon, social networks, etc. could provide the types of communal and peer-based initiatives that would get us on the critical paths to serious mitigation efforts, at the same time improving federal and local governance and quality of life.

  40. fj2 says:

    #39 fj2 continued,

    Bloomberg’s New York City DoITT and other agencies working with other cities may be good ways to achieve the rapid implementation of such an ambitious framework of initiatives.

  41. Leif says:

    Small victories make big victories imaginable and thus obtainable.
    Just reading about solving hunger in a SA city of 1.2 million people for a penny a day/person makes most anything seem possible.

  42. Michael W says:

    “anti-science conservative”
    Joe, do you realize you will need the conservatives on board if there is to be any significant climate action? Packaging/labeling them this way might be a bad move.

    -Michael W

  43. Fred Heutte says:

    The best answer I’ve heard came from sociologist Immanuel Wallerstein at the US Social Forum in Detroit this June when he was asked why, well past retirement age, he keeps going and stays positive in the face of all the bad news (including climate). He paused for a moment and said, “What else can we possibly do!”