Tech solutions (mega-projects) to our little climate problem

Let’s assume a few things. Whether you agree with them or not, for the purposes of this thread, let’s assume that in the aggregate we aren’t going to reduce CO2 emissions world wide by the targets the IPCC set out to keep us under 1.5 degrees C increase by 2050. The current trends are pretty much how it will play out. Let us further assume that we won’t be building a bunch of new nuclear power plants, nor will we be building 1000s of square miles of solar panels or wind farms, though the current trends on that score will continue as well. Let us further assume that battery powered cars will continue their current trends as well, but that we will still have an increasing number of fossil fuel burning ICE vehicles continuing to toss out CO2 for the foreseeable future.

IOW, assume for the sake of this thread that we aren’t going to stop global climate change by simply shutting down our technological world and the only silver bullets will be off the table for wide scale deployment because of real world reasons (i.e. we can’t build nuclear because we can’t, etc.). I know many won’t agree with the above, but if you can’t play along feel free to go to another thread.

So, the debate is…what technologies could we use to either cool the planet by blocking a percentage of the sun light or capture the carbon in large enough quantities to not only keep up with our production but to actually reduce it from 400 PPM to, oh, say 300 PPM or even more? And how feasible would they be to implement, not just cost but politically? Are there any technological solutions you can propose that might work and be feasible?

I’ll toss out a few I can think of off the top of my head. Albedo. We could basically make large parts of the earth white, somehow. This would reflect more sunlight off the planet (though I’m unsure if this would work with the green house effect becoming more prevalent). Sun shade. Basically, put a large shade or reflector at L1 to block or defuse, say, 1% of the sun light. This would be tough to do as you’d have to constantly be adjusting its orbit to ensure it stayed aligned. I also think this one would cost the most and be the most technologically challenging. Sulfur dioxide in the mesosphere. Essentially we’d be replicating what happens in a large volcanic eruption. Use large aircraft to move large amounts of sulfur dioxide into the mesosphere which would block sunlight before it gets down to where the green house effect is happening. I think this is the cheapest solution in terms of resources, but I don’t think it would be politically feasible (nor do I think the sun shade one would be either). Carbon capture. I guess this could break down into several possible scenarios including reforestation or genetic engineering of plants grown specifically to capture carbon or using artificial means to do so (though they would take massive amounts of energy which would be sort of a vicious cycle). I don’t even know if this one is possible with our current technology, though I know there have been some pilot programs for small scale tests of carbon capture equipment.

That’s about all I can think of. Maybe some combination of the above. If we could block 1% of the solar radiation hitting the earth I think it would lower the average temperature by something like .6-1.5 degrees C, which would be helpful. We’d still have the issue of too much CO2 in the atmosphere, but I think that we are on a path to eventually shift that…it’s just going to take longer than I think we have (JMHO and not part of this debate). So, what do you 'dopers think we could do?

Set off large numbers of nuclear bombs all over the place, to induce a nuclear winter. If correctly placed they could also reduce manufacturing emissions too.

Pretty sure that’s going to fail on the feasibility part, but good try. :stuck_out_tongue: And, with Trump in charge, we might get this unintentionally anyway…

The effect and duration of the nuclear winter hypothesis from the TTAPS report is almost certainly overstated because of the assumptions in the analysis, and at any rate setting off a bunch of nuclear weapons to produce the firestorms and updraft to create those conditions would do vastly more harm than good.

Blocking solar radiation is also going to have deleterious effects. The greenhouse gases (primarily carbon dioxide, but also methane and other gases) trap heat but do not produce it, so instead of having a problem with excessive temperature you’ll have the opposite effect, and the stored heat energy in the oceans will produce more dramatic thermal gradients. If you permanently block sunlight it will have significant but difficult to predict effects on the photosynthetic biome, and thus on the biosphere in general. Not a great plan.

The only practical way to mitigate climate change is to alter the atmosphere back to pre-Industrial composition of greenhouse gases by removal of carbon dioxide, and to prevent the injection of more carbon dioxide into the atmosphere. The o.p. posits a future in which carbon mitigation and migration away from carbon-producing energy sources is not an option (even though it is certainly possible to offset uses of hydrocarbon energy sources by point capture of carbon dioxide and transfer energy production from the most pollution sources to renewable energy sources like solar or wind without any major technology advances or the kind of capital investments that would be required for the fuel processing/enrichment/handling/disposal for light water nuclear fission) so this means needing to capture carbon dioxide from the atmosphere and separate the carbon, or otherwise contrive to precipitate it out carbon and release the oxygen.

The problem with this is that carbon dioxide is thin and diffuse, and is not a major component of the atmosphere (about 0.04% by volume, making 870 gigatons of carbon). This means that it is not only difficult to extract carbon dioxide from the atmosphere (like sorting through a Party Size bag of M&Ms to find the one purple one, over and over again) but to do so with industrial processes you also have to apply the energy to seperate oxygen or trap the carbon dioxide so that it does not sublimate and return to atmosphere, e.g. through cryogenic distillation and separation. There are a variety of methods for doing so but all are pretty energy intensive, and membrane/absorption processes are pretty low yield at ambient pressures and concentrations. The best way to do this is what is called an integrated gasification combined cycle, which actually produces hydrogen gas from fossil fuels injected into the process, which is a net energy producer, but the overall cycle efficiency is currently not very good.

Other methods use more natural biocapture (e.g. microalgae to biofuel) or mineral carbonization—essentially turning carbon dioxide into carbon-bearing rocks like the calcareous sediments produced by Coccolithophores. Unfortunately, the rates of carbon capture by these methods are very slow and only occur at the air-to-surface interface, so the potential rates at which this capture might occur just are not quick enough to mitigate global climate changes, and the challenges of scaling up microalgae biofuel production beyond minescule laboratory rates has many experts doubting that it will ever be a valid source of hydrocarbon fuel. (I am not so pessimistic but I think we’ll have to transition to a direct glucose-based energy system rather than more complex lipids that take a lot of energy and aromatic chains that require high pressure to form).

That leaves direct precipitation, and while there are some ‘visionaries’ who have suggested seeding the oceans with iron microfilaments to enhance absorption from the atmosphere. Setting aside that this might not really work (and there is no way to tell on a global scale without actually doing it), it will also lead to greater ocean acidification unless we can pull out the carbonic acid at the rate it is being produced, and if we fail to do so that may result in a massive dieoff of ocean life, from plankton to keystone species. This is really nothing more than a “Hail Mary!” pass that is just not a good idea for so many reasons it is beyond the scope of a single post to discuss them even in brief, but they can all be lumped together in the general category of “extinction catastrophe of all macroscopic life on Earth”.

So, really, there are no good, practical methods that don’t require essentially magical sources of non-polluting energy production to operate on an industrial scale that will act rapidly enough to mitigate the effects of climate change (e.g. within decades). This is not to say that we should not look to employ and research such methods because we may find improvements that make them more practical or at least partially offset the worst effects, but there is no reason for great optimism at this point. Although the o.p. had a prohibition against considering drawdowns of atmospheric carbon production, that is really the only practical way to limit the level of climate change and ecological damage, and even that is probably not enough to avert signifcant effects that will impact billions of people living in low laying coastal regions or who will be affected by extreme weather.

Jennifer Wilcox is one of the leading researchers on the topic of carbon capture, and her book, Carbon Capture is the closest thing to an authoritative text on the topic. She has a somewhat more optimistic view than what is discussed above even though this is really a survey of what is presented in the book, but she admits that mitigation of climate change effects is going to be most effectively addressed by point-of-release sequestration and conversion to low-carbon and renewable carbon neutral energy sources. Unfortuantely, the scale at which that needs to happen, and the period that it needs to occur in, is beyond what could reasonably be deployed without a massive coordinated global effort that there is no political will to support. Vaclav Smil has discussed this in numerous books. His Global Catastrophes and Trends: The Next Fifty Years addresses this in succinct fashion (albeit like drinking from a firehose for poeple not familiar with energy policy and markets) in chapters 3 and 4 and in the section of chapter 5 entitled “”Rational Attitudes”. For those not familiar with the details of energy history and usage, his Energy: A Beginner’s Guide offers a pretty gentle introduction into where energy comes from and the systems needed to extract, manage, and distirbute it in modern society.


I’ve worked on some very big engineering projects in my time. While in the movies the heroic project lead triumphs over small adversities, in real life the combination of not wanting to lose funding and not wanting to look like an idiot when the project doesn’t seem to be going well means that the managers keep going no matter what.
Since I agree that you won’t be able to test the solution adequately until you implement it, “engineering” solutions scare the shit out of me.
The project I worked on didn’t hurt the earth, and cost the company a billion bucks or so for not much, so no big deal. The company is well respected and the leaders were smart, by the way. And it was still a disaster.

I’m impressed! The failed projects I’ve worked on were only in the ten to hundred million dollar range, and the failures generally occurred in software (“It’s always software,” a structures engineer once said to me, despite the fact that I have seen hardware failures) or due to out-of-control requirements creep.

Testing a ‘prototype’ on a global scale is not really a confidence inspiring move, especially since I have experience with prototypes catching fire and burning to the ground. Well, it was actually just the one time, but it left an impressive burn hole in the asphalt regardless.


This was hardware design, but the difference between software and RTL design languages is pretty hard to determine these days.
I’m not bitter - I got out after a year and a quarter with some nice stock option money. But it didn’t do the careers of anyone who worked on it any good.

Just two things quickly.

One, the IPCC did not and does not set emissions targets. The targets from the Paris agreement were set by the governing body (called the COP – Conference of the Parties) of the UN Framework Convention on Climate Change (UNFCCC) which oversees international agreements. This is an important distinction because the IPCC is a scientific body that is policy neutral and their reports are intentionally non-prescriptive.

Two, for the reasons already stated and many others, any form of geoengineering is generally seen as extremely risky at best and a long shot that is likely to be very foolhardy. Sure, you can say that SO2 and such will effectively reduce insolation, and we even have evidence that it works. We also spent decades and billions of dollars to reduce SO2 emissions for very good reasons, not the least of which was that acid rain was killing our lakes and rivers and disintegrating urban structures. Any such substance is going to have known and likely many unknown side effects, too. And as an extra added bonus, if we tolerate increasing levels of atmospheric CO2 and use any such counteracting measure, if anything happened to the counteracting measure – or if it had to be discontinued because of unexpected side effects – the climate would be hit with such a massive and sudden increase in radiative forcing that the result would be utterly catastrophic. There’s also the matter of continuing ocean acidification, and gradually reduced capacity for continuing CO2 uptake.

There are similar arguments with CO2 sequestration – besides the main arguments with cost, difficulty, and uncertainty, there are critical questions of what to do with the result, and some of the proposals, like massive underground reservoirs, raise scary questions of possible release back to the atmosphere.

When all these things are considered in the aggregate, the challenge of just reducing emissions and moving to renewables seems like the lesser of the possible evils, with the most benefits and least side effects.

There are a variety of things we could do.

Boats in the pacific ocean that spray seawater high into the atmosphere to create clouds, reflecting light.

Put a giant mirror in space to block some sunlight.

Feed iron to algae in the oceans so they can absorb more CO2.

put coverings over some of the ice in the arctic to make it more melt resistant.

capture CO2 from the air and convert it into polymers.

use sulfur dioxide to negate some impacts of climate change.

The issue is that global warming is only part of the issue. All the excess CO2 is causing the oceans to acidify too, and keeping temperatures in check will not fix the ocean acidifcation issue.

None of these are practical; most could not be done on a scale that would have a measurable global effects, and the rest would have unknown impact and likely produce ancillary effects that would be worse than the problems of climate change.


Anything we do, no matter what it is, will have side-effects.

What sort of plants absorb the most CO2? Cover everything with that. It’s low-tech, obviously, but any planet-scale project needs to be that.

If we can’t do anything practical, we can’t do anything.


I was under the impression that with albedo yachts, once the boats were turned off then the effects would dissipate.

Its not a perfect solution, but neither is switching to natural gas. But natural gas produces 1/2 the CO2 per BTU produced, so its a stop gap solution until sustainable energy becomes large enough in scale to provide for all our energy needs.

I wouldn’t be surprised if some climate engineering is done to buy a few extra decades of time for humanity to switch to renewables.

Yeah, that’s like saying that if you stop eating poison, you will have the side effect of not getting sicker any more and maybe even getting better. If we stop polluting the atmosphere with greenhouse gases, the only physical “side effect” will be a gradual return to a more stable and more nominal climate. If we continue to pollute the atmosphere with unprecedented rates of CO2 increases and then pollute it even more with purported countermeasures, we’ll have side effects coming at us from ALL the destabilizing inputs.

Although I don’t endorse SO[sub]x[/sub]-type solutions, I have two questions about them. (I asked these questions earlier but can’t recall if I approved of the answers.)

(1) One suggestion is to use many large H-bombs to simulate a small volcano. Shouldn’t clever engineers be able to use drilling and explosives (possibly H-bombs) to stimulate a real volcano?

(2) The earth receives valuable low-entropy visible light. Both plant-life and solar panels rely on visible light. It is this “good” light that is blocked by sulfate. The earth returns high-entropy waste heat (infrared) to space. It is this waste expulsion that is blocked by greenhouse gases. A balance of CO[sub]2[/sub] and SO[sub]x[/sub] could keep the atmosphere at a constant temperature, but on balance, good photons would be traded for bad. I think such a change would have a significant effect on the daylight spectrum — would it be large enough for concern?

The ultimately ‘sustainable’ solution involves mitigating the worst carbon polluters in the near term (e.g. switching from coal to natural gas, and increasing PV and thermal solar) and conversion to next generation nuclear fission and biofuel, solar, and other renewables in the longer term, with the ultimate goal of controlled nuclear fusion. Notions of reclaiming atmospheric carbon in lieu of sustainable energy are essentially fantasy as the amount of energy required to capture atmospheric carbon exceed the carbon footprint without some non-carbon emitting energy source (which conventional nuclear fission is not when viewed from the end-to-end fuel cycle). So, without technology development there is no feasible solution that doesn’t make things worse except for advancing the state of the art of nuclear fission or fusion, or at least offsetting carbon emissions through PV and other solar applications.


Stranger, can you elaborate more on why you have dismissed the upper atmosphere injection method?

Freakanomics had this proposal. Essentially it was a permanent hose supported by aerostats to the upper atmosphere. A chemical plant at the base was supplying the reflective agent. Sulfur dioxide, as other posters allude to, is poisonous in itself, but we know it works and it’s possible to roughly estimate the cost for a project like this. (about 10 billion dollars is what I’ve seen published, even if that is incorrect by an order of magnitude that’s chump change compared to what it prevents)

What I read was that instead some kind of very small and reflective particle could be used, small enough that it would remain aloft for years.

Anyways, it sounded practical. Carbon capture requires almost as much energy as humanity has benefited from burning fossil fuels over the entire time we’ve been doing it, doesn’t it?

While the hose sounded cheap. And yes, it’s very easy to sternly talk about all the side effects, but as long as they aren’t worse than the disease, what choice do we have?

My guess is he’s concerned about unintended consequences.

I mean, ok, but dismissing a method that’s economically feasible in favor of one that isn’t isn’t smart. I’m sure there would be some side effects, but some of the worse warming scenarios involve self-amplifying ramp up of temperature and sections of the globe becoming uninhabitable to humans. Hard to imagine how the side effects could be worse than that.

There’s no “method that’s economically feasible”, or safe, even remotely on the horizon, and unlikely that there ever will be. Furthermore, we’ve had these discussions before, and I see little point in rehashing them yet again.

I’ll take the liberty of answering your question by cutting and pasting and slightly editing what I wrote before. Those interested can find my original comments at the above link and can navigate to the thread in question to see the larger discussion and other posts on the topic.

The experts who contributed to the IPCC Working Group III report on climate mitigation are a great deal more credible than the loons who wrote Freakonomics. In the WG3 report, the concept of artificial solar radiation management is mentioned only briefly in one chapter, only to state that both the efficacy of these methods and their risks are presently largely unknown, so they can’t be considered useful or feasible in any realistic timeframe, if ever. And that’s about all the attention it deserves.

Among the many problems with proposed substance injection into the atmosphere – of which sulphate aerosols are among the most reckless – is a whole slew of projected and unknown side effects, among which are ozone depletion and undesired changes to the hydrological cycle and regional weather, including the potential to create droughts in the most vulnerable regions on earth. It does nothing to mitigate other aspects of climate change like ocean acidification, may have little or no impact on polar albedo feedback and polar ice loss, and generally presents a vast array of unknowns with respect to climate response in general. And the fact that all such aerosols are short-lived means that if the material injections are not strictly maintained, the earth’s temperature would rebound with extraordinary rapidity and catastrophic consequences.

And then there is the matter of atmospheric pollution, the magnitude of which depends on how much material we need to inject. But the basic fact is that sulphate aerosols and nitrogen oxides are the predominant cause of acid rain. Acid rain was a major blight in the second half of the last century, responsible for poisoning our lakes and rivers and damaging buildings and urban infrastructure. Due to acid rain, more than 20,000 lakes in Ontario alone were acidified to the point of serious ecological damage including complete loss of life. I’ve personally seen some of these lakes in the years after acid rain was brought under control – lakes of incredible natural beauty, with still not a sign of life in them, not a single fish. The curtailment of these emissions stands today as arguably the most important success story in the history of the EPA, as well as a great example of successful cap and trade regimes. The acid rain story is one of the few great success stories in the history of pollution mitigation.

Real scientists consider climate change to be a serious problem with no easy fixes. The primary solution advocated by the most recent joint statement [PDF] of the national academies of the world’s 13 leading countries requires at least 50% reductions in global carbon emissions by 2050 and the creation of a low-carbon economy across the industrialized world, and secondary solutions involving region-specific adaptations and investigating new technologies like the feasibility of scalable carbon capture and sequestration. This generally echoes the most recent detailed findings of the latest IPCC AR5 assessments and the broad terms of the Paris climate accord (COP21) from December 2015. To the surprise of no one, magic solutions like one in Freakonomics are never mentioned.

That’s not a rational argument or a rational algorithm. Simply because a conservative group of scientists don’t discuss an idea is not evidence for it not being feasible. And in essence, you are saying that you know it won’t work because

a. A method that is used as an example to show it’s possible would cause mass acid rain.

b. There would be “unknown consequences”. As if that’s somehow scarier than the ones we know, which are going to make the planet increasingly uninhabitable.

What you keep skipping over is the numbers. If you need 100 billion dollars to build the injection mechanism and supply plant, that’s a fraction of the cost of the damage from losing arable land and flooding coastal cities. It’s also a fraction of the cost of reversing the CO2 emission.

Multiple countries could do it, and you would be able to accurately calculate the exact energy balance change with measuring satellites.

Basically, carbon capture is running the combustion reaction in reverse, except harder because the CO2 is at such a low concentration in the atmosphere. You can roughly estimate the cost as equal to the economic value of burning the fossil fuels originally.

That’s not going to work with any economy we have now, and the nuclear reactors to drive the reaction are impossibly expensive to build and run. You would likely need thousands of them.

The next problem you have is a tragedy of the commons problem. If the U.S. or EU takes it upon themselves to reverse the carbon emissions, but major polluters in China or Africa decide to burn even more fossil fuels, it actually ends up just being a huge economic drain on the countries that do it.

So maybe a stronger rebuttal is that the WG3 proposal is fantasy. It’s never going to happen with anything resembling present technology or reasonable extrapolations forward. (exponential increased manufacturing via more intelligent robots could do it, but this is a technology we don’t have now and there is not a guarantee we will have it in the next century)