Geoengineering – The Tipping Point

Back in 2013 I wrote about how we are approaching a tipping point, where public opinion on geoengineering suddenly starts to shift:

Many express the fear that merely researching geoengineering schemes will automatically legitimate them, however hare-brained they are. There’s some merit to that fear. But I suspect that public opinion on geoengineering will suddenly tip from “unthinkable!” to “let’s do it now!” as soon as global warming becomes perceived as a real and present threat. This is especially true because oil, coal and gas companies have a big interest in finding solutions to global warming that don’t make them stop digging.

I argued that because of this, we need to start thinking hard about the issues now.

I think we should start serious research on geoengineering schemes, including actual experiments, not just calculations and simulations. I think we should do this with an open mind about whether we’ll decide that these schemes are good ideas or bad. Either way, we need to learn more about them. Simultaneously, we need an intelligent, well-informed debate about the many ethical, legal and political aspects.

I think this tipping point is getting very close now: close enough to be discussed in popular media. Like this:

• Ezra Klein, Should we dim the Sun? Will we even have a choice?, New York Times, 9 February 2021.

This is Ezra Klein interviewing Elizabeth Kolbert, author of The Sixth Extinction. She just wrote a book Under a White Sky: The Nature of the Future.. It’s about how we’ve altered nature so much, and are so trapped in relying on this, that there’s no way to go back to the good old days. At this point, any attempt to ‘go back’ amounts to going forward in another direction.

I’ll quote a bit:

Ezra Klein: Your book reads as an argument that we are past the point when we have the luxury of saying that things like geoengineering are off limits because we shouldn’t change the world that much. We’ve already changed it so much that the unthinkable now has to be thought.

Elizabeth Kolbert: I think that’s a reasonable interpretation. I think you could read it as, we are past the point of having that luxury. You could also read it as a species that has managed to muck up the atmosphere one way thinking about mucking up the atmosphere another way — what could possibly go wrong? I think those are both very valid readings.

Ezra Klein: You have a wonderful quote in the geoengineering chapter of your book from Andy Parker, who is a project director for the Solar Radiation Management Governance Initiative. He says, “We live in a world where deliberately dimming the [expletive] sun might be less risky than not doing it.” That feels like quite an indictment of the human race and where we’ve gotten ourselves to with all our knowledge and all our power.

Elizabeth Kolbert: I think that does sort of sum things up. We are in this very deep — there are only wrong answers, only hard choices at this point. Nothing easy from here on in.

Ezra Klein: What do you think of geoengineering?

Elizabeth Kolbert: I very consciously avoided coming down very clearly on that. But some very, very smart people are thinking about it and are very worried that it may be our best option at a certain point. And I think they may, unfortunately, be right — but wow, it’s dimming the [expletive] sun, you know?

Ezra Klein: I think how people feel about geoengineering depends on how they feel about the traditional political pathway. Do you think there is a significant chance that traditional politics are going to do enough to keep us under 2 degrees of warming?

Elizabeth Kolbert: Many, many scientists and many nations — especially the low-lying island nations that could disappear between here and 2 degrees — would say that’s really too high. So there’s a stretch goal, if you want, in the Paris accord of 1.5 degrees.

If you’re going to be honest about it, I think you have to say we’re basically at 1.5 degrees now. So that is not just a hard goal to reach; it’s getting to be almost geophysically impossible. Now, 2 degrees — presumably, it is still physically possible to do it.

Then that gets to the point you’re making: Is the world set up to do this? And the problem is not just that in the U.S. we are legislatively gridlocked — that, so far at least, we have been really incapable of taking significant action. And I do want to add, the U.S. is still the biggest single source of greenhouse gases that are up there in the atmosphere right now.

But then you have to look all around the world at all of the major players in this drama — China, which is now the single biggest emitter on an annual basis; the E.U., which is a very big emitter; India, which is increasingly a large emitter. So you have to ask, are we all going to get our act together?

Ezra Klein: One of the questions that I struggle with most in my own work right now is, what do you do if you believe that it is no longer politically plausible that normal politics will get to a reasonable outcome here? Sometimes I think about technological solutions — huge amounts of money being spent on not just renewables, but potentially studying things like geoengineering. Sometimes I wonder about things that are somewhere between political activism and extra-political. Where are you on this?

Elizabeth Kolbert: When we get into the “what could happen now owing to our failures,” that’s certainly where geoengineering comes in. A lot of very smart people are saying, look at the political system. It’s just not capable of moving fast enough. And the last 30 years are a pretty depressing proof of that.

And, as you say, you’re led either to a technofix or you’re led to a carbon dictatorship. I don’t know what you’re led to if you say, we just are incapable of moving fast enough under politics as they are. And the point, I think, that’s really important is on some level, it’s unknowable. How people will react all around the world, this is going to affect everyone. It’s going to affect some people much more brutally than others.

18 Responses to Geoengineering – The Tipping Point

  1. Allen Knutson says:

    There’s an interesting discussion of this at Kevin Drum’s new (old) blog:

    For fifteen years I waited for evidence that the world would make even the mildest efforts to enter this fight. But this is a global problem that demands a global response, and on that score we’ve gotten almost nothing.

    Roughly speaking, all it takes is a fleet of about a hundred aircraft spraying loads of sulfate aerosols 24/7. The cost would be in the range of $5-10 billion a year, which is peanuts, and it would lower the temperature of the earth by about a twentieth of a degree per year. We would slowly get back to a manageable level, and then continue spraying to keep temps steady.

    It’s a terrible idea. But is it a worse idea than warming of 3ºC? Nope. And it’s not even close.

    • John Baez says:

      That’s very interesting—thanks! It reminds me of my interview with Greg Benford back in 2011. He calls the 2010’s the Decade of Dithering:

      GB: The US has inflight refueling aircraft such as the KC-10 Extender that with minor changes spread aerosols at relevant altitudes, and pilots who know how to fly big sausages filled with fluids.

      Rather than diatomaceous earth, I now think ordinary SO2 or H2S will work, if there’s enough water at the relevant altitudes. Turns out the pollutant issue is minor, since it would be only a percent or so of the SO2 already in the Arctic troposphere. The point is to spread aerosols to diminish sunlight and look for signals of less sunlight on the ground, changes in sea ice loss rates in summer, etc. It’s hard to do a weak experiment and be sure you see a signal. Doing regional experiments helps, so you can see a signal before the aerosols spread much. It’s a first step, an in-principle experiment.

      Simulations show it can stop the sea ice retreat. Many fear if we lose the sea ice in summer ocean currents may alter; nobody really knows. We do know that the tundra is softening as it thaws, making roads impassible and shifting many wildlife patterns, with unforeseen long term effects. Cooling the Arctic back to, say, the 1950 summer temperature range would cost maybe $300 million/year, i.e., nothing. Simulations show to do this globally, offsetting say CO2 at 500 ppm, might cost a few billion dollars per year. That doesn’t help ocean acidification, but it’s a start on the temperature problem.

      JB: There’s an interesting blog on Arctic political, military and business developments:

      • Anatoly Karlin, Arctic Progress.

      Here’s the overview:

      Today, global warming is kick-starting Arctic history. The accelerating melting of Arctic sea ice promises to open up circumpolar shipping routes, halving the time needed for container ships and tankers to travel between Europe and East Asia. As the ice and permafrost retreat, the physical infrastructure of industrial civilization will overspread the region […]. The four major populated regions encircling the Arctic Ocean—Alaska, Russia, Canada, Scandinavia (ARCS)—are all set for massive economic expansion in the decades ahead. But the flowering of industrial civilization’s fruit in the thawing Far North carries within it the seeds of its perils. The opening of the Arctic is making border disputes more serious and spurring Russian and Canadian military buildups in the region. The warming of the Arctic could also accelerate global warming—and not just through the increased economic activity and hydrocarbons production. One disturbing possibility is that the melting of the Siberian permafrost will release vast amounts of methane, a greenhouse gas that is far more potent than CO2, into the atmosphere, and tip the world into runaway climate change.

      But anyway, unlike many people, I’m not mentioning risks associated with geoengineering in order to instantly foreclose discussion of it, because I know there are also risks associated with not doing it. If we rule out doing anything really new because it’s too expensive or too risky, we might wind up locking ourselves in a “business as usual” scenario. And that could be even more risky—and perhaps ultimately more expensive as well.

      GB: Yes, no end of problems. Most impressive is how they look like a descending spiral, self-reinforcing.

      Certainly countries now scramble for Arctic resources, trade routes opened by thawing—all likely to become hotly contested strategic assets. So too melting Himalayan glaciers can perhaps trigger “water wars” in Asia—especially India and China, two vast lands of very different cultures. Then, coming on later, come rising sea levels. Florida starts to go away. The list is endless and therefore uninteresting. We all saturate.

      So droughts, floods, desertification, hammering weather events—they draw ever less attention as they grow more common. Maybe Darfur is the first “climate war.” It’s plausible.

      The Arctic is the canary in the climate coalmine. Cutting CO2 emissions will take far too long to significantly affect the sea ice. Permafrost melts there, giving additional positive feedback. Methane release from the not-so-perma-frost is the most dangerous amplifying feedback in the entire carbon cycle. As John Nissen has repeatedly called attention to, the permafrost permamelt holds a staggering 1.5 trillion tons of frozen carbon, about twice as much carbon as is in the atmosphere. Much would emerge as methane. Methane is 25 times as potent a heat-trapping gas as CO2 over a century, and 72 times as potent over the first 20 years! The carbon is locked in a freezer. Yet that’s the part of the planet warming up the fastest. Really bad news:

      • Kevin Schaefer, Tingjun Zhang, Lori Bruhwiler and Andrew P. Barrett, Amount and timing of permafrost carbon release in response to climate warming, Tellus, 15 February 2011.

      Abstract: The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO2 concentrations and amplify surface warming to initiate a positive permafrost carbon feedback (PCF) on climate. We use surface weather from three global climate models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29-59% decrease in permafrost area and a 53-97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190±64 gigatonnes of carbon. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the arctic from a carbon sink to a source after the mid-2020s and is strong enough to cancel 42-88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.

      Particularly interesting is the slowing of thermohaline circulation.  In John Nissen’s “two scenarios” work there’s an uncomfortably cool future—if the Gulf Stream were to be diverted by meltwater flowing into NW Atlantic. There’s also an unbearably hot future, if the methane from not-so-permafrost and causes global warming to spiral out of control. So we have a terrifying menu.

      JB: I recently interviewed Nathan Urban here. He explained a paper where he estimated the chance that the Atlantic current you’re talking about could collapse. (Technically, it’s the Atlantic meridional overturning circulation, not quite the same as the Gulf Stream.) They got a 10% chance of it happening in two centuries, assuming a business as usual scenario. But there are a lot of uncertainties in the modeling here.

      Back to geoengineering. I want to talk about some ways it could go wrong, how soon we’d find out if it did, and what we could do then.

      For example, you say we’ll put sulfur dioxide in the atmosphere below 15 kilometers, and most of the ozone is above 20 kilometers. That’s good, but then I wonder how much sulfur dioxide will diffuse upwards. As the name suggests, the stratosphere is “stratified” —there’s not much turbulence. That’s reassuring. But I guess one reason to do experiments is to see exactly what really happens.

      GB: It’s really the only way to go forward. I fear we are now in the Decade of Dithering that will end with the deadly 2020s. Only then will experiments get done and issues engaged. All else, as tempting as ideas and simulations are, spell delay if they do not couple with real field experiments—from nozzle sizes on up to albedo measures —which finally decide.

      JB: Okay. But what are some other things that could go wrong with this sulfur dioxide scheme? I know you’re not eager to focus on the dangers, but you must be able to imagine some plausible ones: you’re an SF writer, after all. If you say you can’t think of any, I won’t believe you! And part of good design is looking for possible failure modes.

      GB: Plenty can go wrong with so vast an idea. But we can learn from volcanoes, that give us useful experiments, though sloppy and noisy ones, about putting aerosols into the air. Monitoring those can teach us a lot with little expense.

      We can fail to get the aerosols to avoid clumping, so they fall out too fast. Or we can somehow trigger a big shift in rainfall patterns—a special danger in a system already loaded with surplus energy, as is already displaying anomalies like the bitter winters in Europe, floods in Pakistan, drought in Darfur. Indeed, some of Alan Robock’s simulations of Arctic aerosol use show a several percent decline in monsoon rain—though that may be a plus, since flooding is the #1 cause of death and destruction during the Indian monsoon.

      Mostly, it might just plain fail to work. Guessing outcomes is useless, though.  Here’s where experiment rules, not simulations. This is engineering, which learns from mistakes. Consider the early days of aviation. Having more time to develop and test a system gives more time to learn how to avoid unwanted impacts. Of course, having a system ready also increases the probability of premature deployment; life is about choices and dangers.

      More important right now than developing capability, is understanding the consequences of deployment of that capability by doing field experiments. One thing we know: both science and engineering advance most quickly by using the dance of theory with experiment. Neglecting this, preferring only experiment, is a fundamental mistake.

      JB: Switching gears slightly: in March last year you went to the Asilomar Conference on climate intervention technologies. I’ve read the report:

      • Asilomar Scientific Organizing Committee, The Asilomar Conference Recommendations on Principles for Research into Climate Engineering Techniques, Climate Institute, Washington DC, 2010.

      It seems unobjectionable and a bit bland, no doubt deliberately so, with recommendations like this:

      “Public participation and consultation in research planning and oversight, assessments, and development of decision-making mechanisms and processes must be provided.”

      What were some interesting things that you learned there? And what’ll happen next?

      GB: It was the Woodstock of the policy wonks. I found it depressing. Not much actual science got discussed, and most just fearlessly called for more research, forming of panels and committees, etc. This is how bureaucracy digests a problem, turning it quite often into fertilizer.

      I’m a physicist who does both theory and experiment. I want to see work that combines those to give us real information and paths to follow. I don’t see that anywhere now. Congress might hand out money for it but after the GAO report on geoengineering last September there seems little movement.

      I did see some people pushing their carbon capture companies, to widespread disbelief. The simple things we could do right now like our CROPS carbon capture proposal are neglected, while entrepreneur companies hope for a government scheme to pay for sucking CO2 from the air. That’ll be the day!—far into the crisis, I think, maybe several decades from now. I also saw fine ideas pushed aside in favor of policy wonk initiatives. It was a classic triumph of process over results. As is many areas dominated by social scientists, people seemed to be saying, “Nobody can blame us if we go through the motions.”

      That Decade of Dithering is upon us now. The great danger is that tipping points may not be obvious, even as we cross them. They may present as small events that nonetheless take us over an horizon from which we can never return.

      For example, the loss of Greenland ice. Once the ice sheet melts down to an altitude below that needed to maintain it, we’ve lost it. The melt lubricates the glacier base and starts a slide we cannot stop. There are proposals of how to block that—essentially, draw the water out from the base as fast as it appears—but nobody’s funding such studies.

      A reasonable, ongoing climate control program might cost $100 million annually. That includes small field experiments, trials with spraying aerosols, etc. We now spend about $5 billion per year globally studying the problem, so climate control studies would be 1/50 of that.

      Even now, we may already be too late for a tipping point—we still barely glimpse the horrors we could be visiting on our children and their grandchildren’s grandchildren.

  2. If carbon dioxide dispersed at high altitudes is a major part of the problem, and if that carbon dioxide persists at altitude for a long time – I’ve heard for up to three years – then the solution proposed just creates a bigger problem. Jet engines burn iso-octane, to get carbon dioxide and water, 8 moles of carbon dioxide for every mole of iso-octane burned. Figure a fuel load of 10,000 gallons for 3000 miles of flight. That’s 80,000 lbs. The molecular weight of iso-octane, C8H18, is about 114g/mole, and there are 454g/lb. 114g * 4 = 456g, so there are about 4 moles per pound, or roughly 320,000 moles of iso-octane in a fuel load. And you wind up with 2,560,000 moles of carbon dioxide gas formed, at 22.4 liters/mole. And that’s just one aircraft flying for roughly 8 hours. So the solution may be making the problem a lot worse, especially if the sulfates rain out quicker than the carbon dioxide. And sulfate groundwater pollution is already a big problem for aquifers. I’d suggest a different approach, one involving, say, nuclear power to generate electricity – and putting an end to most jet travel.

    • John Baez says:

      In the short or medium term the SO2 deliberately released by the aircraft would cool the Earth vastly more than the CO2 put out as exhaust would warm it—that’s why this form of geoengineering is taken seriously. According to Wikipedia,

      one kilogram of well placed sulfur in the stratosphere would roughly offset the warming effect of several hundred thousand kilograms of carbon dioxide.

      But if you don’t like planes you can use balloons:

      More here:

      • Wikipedia, Stratospheric aerosol injection.

      I think any risks due to the SO2 or CO2 emitted in the process of stratospheric aerosol injection are dwarfed by the risk of changing the climate in a way you don’t like.

      • It’s not sulfur per se, it’s sulfur dioxide or sulfuric acid which is under consideration. They’re talking about placing it at altitudes of roughly 58,000 feet – the top of the troposphere a/k/a the tropopause. If you see a thunderhead with a flat top like an anvil, you’re essentially looking at the tropopause – “Well-developed cumulonimbus clouds are characterized by a flat, anvil-like top (anvil dome), caused by wind shear or inversion near the tropopause. The shelf of the anvil may precede the main cloud’s vertical component for many kilometres, and be accompanied by lightning. Occasionally, rising air parcels surpass the equilibrium level (due to momentum) and form an overshooting top culminating at the maximum parcel level. When vertically developed, this largest of all clouds usually extends through all three cloud regions. Even the smallest cumulonimbus cloud dwarfs its neighbors in comparison.”

        So you end up with rainout – and the rainout is acid rain, which has bad effects on the environment –

      • John Baez says:

        I believe the amounts of sulfuric acid produced by this form of geoengineering are small compared to those involved in acid rain. In any event, this is something people have studied, so it doesn’t make much sense to argue about it before we read the literature. Here’s one paper:

        • Kravitz, B., Robock, A., Oman, L., Stenchikov, G., & Marquardt, A. B, Sulfuric acid deposition from stratospheric geoengineering with sulfate aerosols, Journal of Geophysical Research: Atmospheres 114 (2009).

        Abstract. We used a general circulation model of Earth’s climate to conduct geoengineering experiments involving stratospheric injection of sulfur dioxide and analyzed the resulting deposition of sulfate. When sulfur dioxide is injected into the tropical or Arctic stratosphere, the main additional surface deposition of sulfate occurs in midlatitude bands, because of strong cross‐tropopause flux in the jet stream regions. We used critical load studies to determine the effects of this increase in sulfate deposition on terrestrial ecosystems by assuming the upper limit of hydration of all sulfate aerosols into sulfuric acid. For annual injection of 5 Tg of SO2 into the tropical stratosphere or 3 Tg of SO2 into the Arctic stratosphere, neither the maximum point value of sulfate deposition of approximately 1.5 mEq m−2 a−1 nor the largest additional deposition that would result from geoengineering of approximately 0.05 mEq m−2 a−1 is enough to negatively impact most ecosystems.

  3. Bruce Smith says:

    This blog post

    is about Biden’s science advisor, and seems to me to hint, without directly saying, that its authors are involved somehow in advising that advisor, and lists science-related blogs (including Azimuth) which they think are relevant to that project.

    Maybe this is worth looking into, if you want to try getting new support for these ideas…

    • John Baez says:

      Neat! I can’t really tell if R.J. Lipton and K.W. Regan are advising Biden’s new science advisor, Eric Lander… or why they are choosing to recommend Azimuth in the same blog post that they’re announcing Eric Lander’s new job. I suppose I could ask.

      At one point Eric Lander lived in the same building as my wife Lisa on Bishop Allen Drive in Cambridge—you’ve been there. It was an old Victorian house subdivided into three units. Back then he was leading the human genome project.

      I hadn’t known he was so mathematical! I should have tried to talk to him.

      Peter Cameron wrote:

      Eric, with a good background in algebraic number theory, took to it immediately. The coding theorists had taken an integer matrix and considered its row space over the finite field with p elements. Eric observed that, if instead you took the row space over the p-adic numbers, then you could reduce it modulo arbitrary powers of p, and get a chain of codes, with the property that duality reversed the order in the chain (so if the power of p involved was odd then the code in the middle was self-dual).

      Eric’s thesis took off from there, and at the end he turned it into a book with the title Symmetric Designs: An Algebraic Approach.

  4. Sir Light says:

    I wonder why the idea of putting a fleet of thin aluminium foil spacecraft into orbit to directly block sunlight is not discussed as a possible solution to climate change. This is by far much more futuristic approach than ordinary emission cutting techniques, and since the foil has to be thin it have big mass and therefore the launch costs should be comparable to other climate mitigation techniques.

    • John Baez says:

      How much aluminum foil do you need to put into orbit to create, say, a 0.1% decrease in incoming solar radiation? How much would this cost?

      How do you reduce the reflectivity when it gets too cool? How much would this cost? (With sulfur dioxide you just wait; it gradually goes away.)

  5. Len says:

    There are approaches to geo-engineering besides stratospheric aerosols. These include things like removing CO2 from the atmosphere, planting shade tress, seeding clouds, or painting mountain-tops to reflect sunlight. I would especially encourage research into seeding clouds– ships and other things are already seeding clouds, so we need to understand what we are already doing.

    I’m very skeptical of stratospheric aerosols for a lot of reasons, but we aren’t dealing with a bank account, where it’s as simple as balancing heat-in and heat-out.

    1) Heat tends to enter the atmosphere near the tropics and leave near the poles. CO2 prevents heat from escaping, so we are seeing more heating near the poles.

    2) The difference in temperature between the mid-latitudes and the poles maintains the jet stream, and the weakening of the jet stream is one of the main drivers of extreme weather events today.

    3) Blocking incoming sunlight would tend to cool the tropics more than the poles and this would further weaken the temperature gradient. It might therefore make for more extreme weather events.

    Whatever your thoughts on stratospheric aerosols, it is only one potential geoengineering strategy. I would focus my energy on understanding what we are already doing, looking for ways to reduce emissions and/or remove greenhouse gases from the atmosphere, and adapting to the changes already underway.

    • Can you elaborate on strategies for painting mountain tops? How much benefit could be expected from this, given that this could only be done at certain specific locales?

    • John Baez says:

      Len wrote:

      Whatever your thoughts on stratospheric aerosols, it is only one potential geoengineering strategy. I would focus my energy on understanding what we are already doing, looking for ways to reduce emissions and/or remove greenhouse gases from the atmosphere, and adapting to the changes already underway.

      I agree with these two sentences.

      Reducing emissions is great: there are even many ways to do it and save money, and we haven’t adopted those nearly as fast as we should.

      Removing greenhouses gases from the atmosphere is harder, but there’s a lot we can do, and I’ve written about that:

      Can we fix the air?, Azimuth, 12 January 2020.

      Adaptation is also hugely important.

      My point in this article, as in the last, is not to advocate geoengineering but to warn people that sometime—and I think sometime soon, probably before 2040 but maybe much sooner—public opinion will flip to embracing geoengineering, and it will be almost unstoppable. So, we have to think about it and study it.

      The main defects I see of geoengineering with stratospheric aerosols are the one you pointed out—it will change weather patterns in ways that may not be easy to predict—and that it won’t do anything to stop ocean acidification.

  6. Ocean fertilization seems like it ought to be discussed in any consideration of large-scale geo-engineering.

    • John Baez says:

      I wrote about about ocean fertilization here here a while ago. At the time, the results seemed disappointing. But maybe things have changed?

      • The Wikipedia article seems to indicate that subsequent studies have yielded more promising results. But I have not looked at the original papers.

        The things I like about ocean fertilization (if it works at scale) are:

        It actually sequesters carbon and mitigates ocean acidification.
        Increased fishery yields are an almost baked-in consequence of any successful ocean fertilization program. And, while that does not technically sequester any carbon, it does feed a hungry planet. Which is an important subsidiary goal in any program to mitigate the deleterious effects of climate change.

        • One word: Malthus. Any programme which increases the amount of food merely shoves the over-population problem into the future. The population of Earth needs to be low enough to be sustainable.

          One could even argue that it is morally better to let N people starve now if that somehow forces a move to a more sustainable world, rather than M people starving later, as well inevitably be the case, with M>N.

  7. One word: Malthus.

    Malthus was wrong. And so is this. Hint: birthrates in industrialized countries have all fallen below (in many cases far below) replacement.

    But I don’t think a comment thread on Geoengineering is the right place to debate 1970s-style “Population Bomb” ideas.

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