A sunshade seems like a horrible idea. There are obvious implications from the increased motivation to use fossil fuels. Biodiversity will continue to plummet until there is an ecological collapse. The people with the keys to enable or disable the shade will be influenced by short term profit. Then once fossil fuels are gone there will be a giant energy crisis. Buying time is good only if that time is properly paid for. And there is the risk of unintended consequences.

https://en.wikipedia.org/wiki/Unintended_consequences

Are you really going to link to wikipedia's unintended consequences page? How about the unintended consequences of historical emissions - we have already put enough in the atmosphere to devastate Shanghai, Miami, Manhattan, and all of the coastal nations of the world. Are we going to throw up our hands and take a potentially life-saving, civilization-saving tool off the table? Species -- those are already dying off hugely, if anything the sunshade will slow this decimation by slowing warming.

Also, how do you imagine that Elon Musk is somehow going to elongate our usage of fossil fuels? Elon Musk has done more for EVs than any single person in human history, and you claim he's going to do something which will extend fossil fuel use?

Your post just doesn't add up, it sounds like you want further warming to occur?

As we all burn, we’ll be thankful, thinking: “we knew how to solve this, and could have, but decided not to because it wouldn’t have solved other problems as well.”

What we call "technologies" are really consequence-generating dynamics operating though a (possibly) small set of modalities, producing effects which can be classified on a pretty classic 2-D "consultant's matrix".

On one axis: beneficial vs. negative consequences.

On the other: immediate vs. eventual apparentness.

We tend to adopt technologies with immediately apparent and beneficial consequences.

This creates two sets of failures:

- Not adopting technologies with eventually-apparent beneficial consequences.

- Failing to reject technologies with eventually-apparent negative net consequences.

- Failing to adopt technlogies with non-apparent net benefits.

(We also do correctly reject technologies with immediately apparent harmful consequences.)

This is confounded by other factors. Technologies aren't single effects but sets (matrices) of effects, and can interact with other technologies.

There's a huge problem in that the non-apparent results, positive or negative, take time to become apparent. For various psychological, sociological, economic, and political reasons, there's also a frequent bias to promoting benefits over harms, at least by parties with an interest in the technology. (Those suspecting they may be disadvantaged will employ the opposite bias.)

When you're looking at planetary-scale actions and behaviours in which there's no ability to opt out (we're either all in or all out), then you've got a problem of assuming a major risk, and there being potential major negative unforseen consequences.

It's the unintended consequences of historical emissions which are the result of precisely that dynamic -- it was not widely seen when widespread use of coal, oil, and gas began, in the 18th, 19th, and 20th centuries, that these could have a relatively immediate (decades-to-centuries) impact on the state of the environment on Earth. Even when proposed mechanisms and cautions were sounded, resistance to those warnings grew -- Cassandra's Curse.

Fixing one problem by going whole-hog in on a new technology, without having the time or opportunity to consider what might happen as a result ... strikes many people as a trifle rash.

>How about the unintended consequences of historical emissions

We already know about them, for the most part. They're known-knowns or known-unknowns.

A sunshade is a giant cloud of unknown-unknowns, plus whatever we think we might anticipate.

A physical shade is at least something you can take down if it's working badly. Contrast this with the deeply horrifying "geoengineering" proposals to spray millions of tons of sulfate aerosols into the stratosphere:

https://en.wikipedia.org/wiki/Stratospheric_sulfur_aerosols

"Deeply horrifying"? Given the current situation, it sounds to me more like "cool, can we start doing it already?".

Given that we have a history of 'start doing it already' that has led to: - ozone destruction - plastic pollution in the seas - potential runaway global warming brought on by fossil fuel use - use of DDT and neocotinoids - introduction of pest species that destroy ecologies

do you really think we should be repeating the exact same approach? Because to me it sounds insane.

Our thoughtless embrace of technology has caused much of our current problems - thoughtless embrace of technology will not magically solve them.

It also led to vaccines, detergents, anesthetics, fridges, microwave ovens, books, computers, and everything else man-made that now makes our lives better. So let's not cherry-pick.

It's not our thoughtless embrace of technology that caused much of our problems - our problems were and are caused by people. In particular, by coordination problems. By our inability to do things together for long-term benefits. Our cherished democracy and free market only exacerbate this problem. So it's a good idea, IMO, to have a backup plan that doesn't require everyone to change their life styles - otherwise, in 50 years we may be wishing we had some prototyping done instead of it just being a theoretical idea.

But we didn't, for example, first test vaccines on the entire world population simultaneously. The scale of the potential initial risk is critical. Not "what could happen?" but "If there's an unintended consequence, how many people (or how large of an area) could it affect? I think in the case of the solar shields, the risk is beyond what most of us can comprehend.

I assume that you are assuming it will work exactly as expected.

Now that I've said that explicitly... how reasonable of an assumption does that sound?

Nah, it won't work exactly as expected. Nothing ever does. What matters is the distribution of possible consequences, viewed against the consequences we're trying to prevent.

I think we should prepare to have this tech ready for use in case things get significantly worse in the next few decades. In the meantime, there are less risky geoengineering approaches also worth investigating and pushing up the TRL ladder.

>can take down

How?

Collecting and disposing of 16 trillion objects is no small feat, before you consider fuel and energy to get there and back (or there and away).

I assume a sunshade in space would need to stay oriented as the Earth revolved around the Sun in order to deflect the sunlight. Therefore "take down" could simply mean disable the orientation equipment.

That's the magic of the L1 Lagrangian point[1]; it takes basically no effort to stay there and it is exactly between the earth and the sun.

Now L1 is an unstable point, so eventually the shades will drift out of position, but I imagine that will take a long time.

[1] https://en.wikipedia.org/wiki/Lagrangian_point

Staying in the correct place and staying oriented at the correct angle are two different things.

If you make it rotate at a speed of 1 rotation/year, it should stay still at the same angle relative to earth.

While halting warming is important, a Solar shade is an absolutely terrible way to do that. Shading out 2% of the light has obvious implications for global crop yields and for non crop plants that all rely on solar energy. It would also obviously reduce efficiency of solar electric power collectors, impeding their ability to replace fossil fuels. Global warming is a big problem, but a global food crisis is an even bigger one. A solar shade would buy time on the global warming problem while also creating a much bigger problem.

> A solar shade would buy time on the global warming problem while also creating a much bigger problem.

It had been pointed out that the main reason for warming, advanced level of CO2, leads to bigger agricultural growth, so here we have to opposite trends.

We'd prefer of course to have the shield controllable, and shadow only a small (like, 10%) fraction of solar energy. More, the shield likely won't be ready all at once, so we can have early indication for how it works being partially deployed.

Your post doesn’t add up. You start by pointing out the unintended consequences of burning fossil fuels, then continue to say that we should pursue solutions that allow us to continue burning fossil fuels sans serious short term repercussions. I think continuing to kick the can without proper longview regulation is only putting money in the disaster bank.

This mindset is a huge reason why so many people are skeptical of the climate change movement.

It’s not that climate change isn’t real, or even a question of whether human activity is the root cause. But faced with a solution which doesn’t require massive societal change of a particular sort, the solution is rejected out of hand.

Just because it doesn’t force a specific set of political changes which up until now have been punctuated by the threat of nothing less than Armageddon,... we cannot actually reject a cheap solution that takes Armageddon off the table, just because it may make the other goals harder to accomplish.

It is morally unacceptable to let the Earth burn rather than be left to solve issues of pollution and clean energy independent of the almost unfathomable toll of a 3°C future. That to me is frankly an untenable position when you contemplate the actual number of lives in the balance.

All solutions should be considered. But we have solutions (electrification, present renewables) that are less risky than sunshades in many ways. Also, sunshades don't help the ocean acidification. So it'd be diverting resources to a fragile solution of a sub-problem when we only have the resources to solve the problems in an integrated way.

I’m sorry but you and many other posters are missing two key and obvious things.

1. The single cheapest and quickest way to make a difference is to - en-masse - moderate our behaviours. But guess what? People are so wedded to their monster-truck-driving, plastic-consumable-disposing, distance-product-shipping, holiday-air-travelling lifestyles that they won’t (on the whole) bear even the slightest personal “burden”. The relatively moderate costs associated with behaviour-modifying policies (eg a carbon price), are vehemently and successfully opposed (or neutered) by governments all over the world. And the reason they are free to do so is because there’s no political cost to doing so. Given all that, why on earth would anyone think it’s going to be politically acceptable to fund even costlier and potentially fraught geo-engineering responses?

2. Shades will do nothing at all for the ongoing acidification of the oceans and the consequent marine species destruction.

> The single cheapest and quickest way to make a difference is to - en-masse - moderate our behaviours.

The cheapest and only long-term sustainable solution is to massively reduce the global population. Say we manage to massively transform society and half the average person’s ecological footprint. All that effort will be for nothing if we’re doubling our population in a couple of decades anyway. Any effort to modify our behavior will be pointless if we keep outbreeding the gains we make. By contrast, if we simply reduce the birthrate by a factor 10-100 we can drastically reduce our impact on our environment without any other changes.

Any other measure is just a stop-gap until we acknowledge the inconvenient truth: humanity is a plague. We’re breeding like cockroaches and if we don’t stop it we are doomed, regardless of any other measures taken.

I don't think it's simple, or easy, or inexpensive even, to achieve an en-masse change in global behavior. To me that seems like the most difficult, most expensive, and most costly way to try to solve the problem. Asking the world to "just consume less" is a very nice way of asking the world to enter a global depression. If the only answer is massively moderated consumption, the direct result is actually a lot of pain and suffering and destitution.

I am very much a technology optimist. I believe that technology is the route to providing sustainable solutions across the board in energy, transportation, agriculture, and materials. Even more, I believe that the only solution is for technology advances to make the sustainable solution to be the preferred solution. When going green is also cheaper, faster, better, then everyone goes green by default.

The role of government here is to align incentives and subsidize market-driven R&D efforts which result in technologically superior products that also happen to be sustainable which can win in a competitive marketplace on their own merits. The perfect example of this is EVs. EVs will totally supplant new ICE vehicle sales in the next couple decades because they will ultimately be a better vehicle in every possible metric.

I think we are seeing the same effects in terms of renewable energy that can now compete on cost even without subsidies, and we are in the beginning stages of where we need to go with agriculture (I'm sure actually much progress has been made, but I'm less familiar with that tech).

From a materials science perspective, we need better alternatives for clothing fibers, and better alternatives for plastics in our products and packaging. Cotton is biodegradable but takes far too much water to produce -- possibly something that further genetic modifications to cotton could reduce. Plastic blends in textiles are great for performance, but end up as microplastic in our waterways and oceans. The alternative isn't that everyone is going to switch to hemp. The alternative must be a better material developed that provides superior performance, longevity, texture, carbon footprint, and ultimately clean disposal or recyclability. Government's role is to align incentives for this R&D to occur by taxing externalities or subsidizing new products that present lower externalities.

As to the queston of controlling the effects of increased CO2, one of which is global warming, and another of which is ocean acidification, I think we will come to a point where we need ways to effectively reduce atmospheric CO2 independently of efforts to reduce CO2 emissions, and technology will ultimately afford us that.

I think it's an open question whether the timescale over which atmospheric CO2 may ever be brought back below, e.g. 300ppm, will require engineering a more direct solution to both ocean acidification, and global warming. Even if tomorrow anthropogenic CO2 emissions dropped to zero, how long would that even take? Solar shields and atmospheric CO2 extraction are technologies that warrant future research and discussion.

It is easy -- tax the pollutants and ban greenwashing marketing/lobbying. I am not the first to propose this: https://www.reddit.com/r/worldnews/comments/bxgd5p/single_mo...

The real obstacle is the confusion in the public opinion spurred by big oil marketing and lobbying. It's really hard to find quality information online, but it exists since many years and it's pushed down on purpose by interest groups. Here is an example:

Exxon, a big oil corporation, had accurate predictive models of climate change, agreeing with scientific consensus, already in 1982 and confirmed "it will cause dramatic environmental effects before the year 2050". https://twitter.com/i/status/1187719206562910209

Shortly after Exxon began to deny global warming and started "greenwashing" marketing campaigns, which today show up directly in the news articles on global warming, e.g., in The New York Times: https://twitter.com/status/1187435336185581570

A lot of people are skeptical of the climate change movement because they don’t want to change their behaviors or feel guilt about what they have personally done to contribute to it. That’s 100% it. Full stop.

We should be skeptical of any ways to address climate change that rely on technology and require very little behavior change.

Burning fossil fuels does more than just warm the planet, so trying to stop the planet from warming through some far out means wouldn’t address these other huge issues. Also, the easiest path to haunting climate change is to literally stop doing the damaging things.

I would add to it that a large part of this skepticism is fueled on purpose by respective interest groups. The real obstacle is the confusion in the public opinion spurred by big oil marketing and lobbying. It's really hard to find quality information online, but it exists since many years and it's pushed down on purpose by such interest groups. Here is an example:

Exxon, a big oil corporation, had accurate predictive models of climate change, agreeing with scientific consensus, already in 1982 and confirmed "it will cause dramatic environmental effects before the year 2050". https://twitter.com/i/status/1187719206562910209

Shortly after Exxon began to deny global warming and started "greenwashing" marketing campaigns, which today show up directly in the news articles on global warming, e.g., in The New York Times: https://twitter.com/status/1187435336185581570

The real reason this is a less than ideal solution is that, even assuming it works perfectly, and even with other forms of cooling, increased atmospheric carbon concentrations still contribute to ocean acidification and other chemical effects.

But you're right that The Climate Change Movement™ dismisses these things out of hand. This is because it is only incidentally about combating climate change. It is primarily about giving more power to approved politicians and bureaucracies. This is also why we have made no almost progress on the underlying issues. We were never meant to.

It's like Avengers: Infinity War, which is like Star Trek episode 13: The Conscience of the King. In reality it is a less hokey of a problem. It wouldn't be the people deciding to not put up the sunshade that would be the mass murderers, it would be the system in place that made such a conventionally attractive option off the table since it would cost more lives than it saved.

citing bad works of fiction does not help make the point

In both of those cases I am assuming the position of the bad guy/psychopath. Making allusions to pop culture isn't "citing" it. It's 1. a call to lighten up over a discussion of hypotheticals and 2. to appreciate that the philosophy of these greater good problems is nothing new.

While I see your concern about kicking the can down the road, the damage from the emissions we have already emitted could be devastating, so simply stopping emissions may not be good enough anyway. Even if we all got together tomorrow and stopped using fossil fuels in an instant, we're still going to need to invest in technologies to mitigate the damage done by our previous actions.

I think the proper way to read the GP's comment is "take every action we can".

Even if we stopped fossil far faster than the most optimistic estimates, sunshade is still a great idea. There is a ridiculous amount of upside to not burying 250 M people in water by 2100.

Further, have you thought about how we get off fossil for steel, concrete, plastics, hell even natural gas power plants? Climate change is the most important issue right now and even so, we are undeniably a fossil society. We need everything we can muster, and sunshade should be part of our tool kit to help the transition.

> have you thought about how we get off fossil for steel, concrete, plastics, hell even natural gas power plants?

Lots of people are thinking about these questions! Still early research phase, but the chemistry works out.

Steel -https://www.technologyreview.com/s/611961/this-mit-spinout-c...

Concrete - http://news.mit.edu/2019/carbon-dioxide-emissions-free-cemen...

Plastics - no carbon emitted as long as you don't burn your plastics. Could also capture emissions from a plastic incinerator if you really want to burn trash

Natural gas power plants - replace with solar/wind + batteries?

I've looked for info on why we don't use plastic for carbon sequestration, and haven't found anything significant. It seems like land-filling plastic, or minimal processing (compaction it melting into a more dense block form) might be better than attempting to recycle it all, once sequestration is taken into account.

Also, I suspect we'd be better off right now if we'd been land-filling plastic, instead of shipping it overseas to be burned, shredded, littered, dumped, or even discharged at sea. Even official estimates claim minimal percentages are actually being recycled, before accounting for fraud.

We might have significant reduced levels of micro-plastic in the ocean, and a greater amount of carbon sequestered, instead of the high cost and seemingly minimal benefit we've seen "recycling" plastic.

To sequester carbon, the plastic would have to come from biomass or direct air capture of CO2. Most of it just comes from fossil carbon.

We need more and better financial incentives (rebates, taxes, etc.)

Right now, I'd say it's the opposite. We need to stop giving financial incentives to recycle plastic. Going into the landfill ought to be the cheapest disposal methods, in most cases.

If we had an order of magnitude more electrical power and no greenhouse emissions from it we could do quite a lot. Desalination is a really big one. Chemical batteries won’t get us there, but pumped storage is an interesting avenue. I personally am a fan of fusion. The numbers check out with first gen power plants costing about 50% more per energy unit than fission/fossil.

It’s a neat idea and having the idea in itself is not bad. It’s how I expect that idea to be used based on who has decision making power and how they have been using that power.

I’m not saying stop drilling fossil fuels, because we need it for almost every part of our society. I’m saying we should be pushing harder down the path of not using fossil fuels as an energy source. If suddenly it becomes way more economical to burn fossil fuels then we’ll stop pursuing any alternatives. That’s just how it works. I wish it wasn’t.

Do you also oppose administering Gardasil to prevent HPV infections, on the grounds that youngsters will stop pursuing safe/marital sex?

Do you always make false equivalences between one on one social interactions and the driverless vehicle that is modern business practice?

This is evidence of Horseshoe Theory, really. Shouting about the failures of Capitalism during a crisis is essentially what the far-right does about Progressivism. "I told you so" mentality in dupes who bought the theory but never paid any attention to the practice.

Get down off your high horse and pay attention.

The car is not driverless. You are just backseat.

The greatest risk you run with your current attitude is that you contribute to the "it's a crisis but I have higher priorities" thinking. This is what bends the horseshoe, ideology. If we weren't in a crisis, I'd be more sympathetic.

I don’t like being accused of mental gymnastics by a gold medalist.

A sunshade is also a strategic weapon, from the POV of those nations whose insolation may be blocked (or even increased, using reflectors) at the whim of the foreign policy of the national power that controls the sunshade.

Not saying it's impossible or impractical, but the political consequences are non-trivial ... imagine being able to shave 10% off a nation's photovoltaic power capacity if they don't knuckle under to trade demands, or to mess with their storm frequency/weather patterns. It's a huge can of worms.

A thing which costs trillions of dollars will probably not be overpowered -- so I presume at no point will it be able to dim the light by 10%, wouldn't that be overkill?

Probably this will be governed by the UN.

There could be some interesting implications if you do have active control -- like "should we cool this area to move this huricane".

"Yeah, but we can't make it turn back over water, but instead of it hitting country A, it could hit country B".

If it's at the mercy of the UN, I doubt it makes it through the general assembly in any form, let alone past the security council. The nature of foreign policy would just make too many countries suspicious of ulterior motives.

not really because its so much hassle to even block the 2-4% of sunlight - there is no way to "focus" the shadow - reflectors are a whole different thing altogether

Is there a reason why you couldn't close some shades and open others to roughly guide the shade on a specific area on Earth? ( besides the fact that you need to have much higher shading capacity if you want to be able to significantly shade just one region)

That plan involves putting sunshades in L1, where most shades are visible from every sunlit point on earth. So you don't get to be picky, every shade shades everyone evenly.

There are other suggestions for placing sunshades in MEO. Each shade there is ~60% less effective than it would be in L1 (because of the time it would spend not shadowing any part of earth), but it is much closer, so putting them up there would be easier and cheaper. Those could in theory be regional.

However, it's been pointed out that sunshades would also necessarily be pretty damned good solar sails, so they might well make their own way to L1.

Why would they end up at l1? Wouldn't they get pushed away?

Yeah, I guess with very thin shades reflection is the only way, maybe if those were thicker and good heat conductors, you could shape them like very wide triangles and radiate the heat just a couple of degrees to the side, still protecting the Earth, but experiencing a lot less net force.

If station keeping is needed, I would think you would want to make the shades as big as possible.

>~60% less effective

Is that strictly due to time when it's casting a shadow, or does that take into account the geometry of the shadow cast and the flux density of the sunlight at each point (watts/m2)?

That'd be an interesting calculation to see.

the shades aren't even visible from earth. they are like dust or fog that don't let 2-4% of sunlight through. To have "sharp" shadow like you are proposing you need to have a lot more shades (say 10 times as many) in a completely different (lower) orbit. they would also need serious station-keeping and control since they need to stay between earth and the sun. I think they would need at least hundreds of meters of delta-V a day

This has been the basis of my Elon Musk-as-supervillian plot. First, Tesla Roadsters and the batteries needed to power them, then SolarCity solar panels, and finally rockets? What is his plan?

Tesla means a gigafactory’s worth of battery production, and the solar panels charge the batteries, but what are the rockets for? As discussed - a planet sized solar shade, casting the planet into darkness. Or at least into the shady side. Solar panels are mounted on the bright side of the solar shade, charging batteries on the shade. Those batteries get shuttled back to Earth on a rocket, and are replaced when the next rocket ship arrives. Musk becomes the primary provider of energy on Earth, selling energy where previously the Sun just gave the stuff away for free.

Selling energy to all the nations of Earth, just to run LEDs in order to grow plants, proves to be very lucrative, but at that point, Musk has no need for money. All that’s left is for him to use this power to open a rift to the next dimension over to get power over life and death itself, and the SOE’s agents can’t stop him. Or are they? (Last part stolen from parent poster and isn’t the book I’d write. Big fan though!)

> imagine being able to shave 10% off a nation's photovoltaic power

While shutting down 90% of the agriculture output and completely messing with local climate.

Countries can just retaliate with nukes.

There is no reason to believe that the existence of a sunshade would provide increased motivation to use more fossil fuels. Those feedback mechanisms are uncoupled. People use fossil fuels because they are cheap and available, the sunshade does nothing to affect their cheapness and availability.

I expect this kind of sunshade is inevitable now and that pressure is mounting to build it, and it is extremely fortunate that a capability has developed to build it very affordably (for a global project) and rapidly (at a push - 1 year!). Its likely just a matter of years or decades before warming events and modelling generate enough rational alarm to empower a global body to take control of global and continental solar insolation levels. Many thousands of individual sunshades can tilt using low power gyros, even in hourly timeframes to alter exactly when and where shading is applied to Earths regions and live weather systems, and also use a long term light-sail effect to keep themselves appropriately positioned while floating through the orbit-ally unstable Lagrange region.

Unfortunately even recognition of a capability to build such a thing will certainly reduce pressure to rapidly de-carbonize, even the acidification of the oceans is hailed as solvable now by putting vast but affordable quantities of mined olivine them.

Human depredation, mis-consumption and mis-appreciation of natural systems (as well as each other) remain gravely destructive and tragic modern persuasions until the narrative is healed.

Anything that could be achieved with a sunshade could be done thousands of times more cheaply by putting reflectors on roofs, on deserts, and on the sea surface. If you imagine putting that much reflector out would be too hard or too expensive, I guarantee lofting even a tiny fraction of it would be overwhelmingly more expensive and difficult.

The physics work out very differently because a lot of different wavelengths, some invisible are absorbed by the atmosphere (co2 and other absorbers) before and after reflecting off the ground. Sunshade designs have been considered viable by expert reviews. Main obstacle has been considered the cost of launching them to L1 estimated at a few trillion dollars. Spacex superheavy system is predicted to shrink that to a few billion dollars - a week or some of the global military budget. It would also need much thicker reflecting material on the ground / at sea to cope with weathering, tearing and pollution. Space is mainly very empty, the shades can be made from surprisingly light materials, and as I described before, the whole thing can be controllable to react to weather events. On ground installations take time an effort to alter.

It's still a net positive, and assuming shades are deployed, it would at least reduce the number required.

Reflectors in on the ground also have the benefit of being controllable.

When solar arrays are located over water they do alot of cooling because without them water reflects very little. Deserts already reflect a great deal of sunlight. Temperate land absorbs a great deal but it is in great demand for agriculture, aforestation and the remaining wildlife. Reflectors in space should be controllable, the power and gyroscopes required to rotate them at a snails pace can be tiny, a small percentage of the mass of the attached shade.

Mostly agree, but:

1) Solar isn't really cooling anything, it's just transferring the heat to the point of use through the grid.

2) There's a lot of square footage of pavement and rooftops before we need to seek out virgin land.

3)Adding any feature to a production of 16 trillion won't be trivial in cost or complexity. Anything besides passive steerage (akin to a solar-windsock) is going to sink the project, IMO. I suspect that once you start adding power, gyros, controls, communication, navigation, etc, it will be more economical/feasable to scale up the size of each deployable shade by 2+ orders of magnitude (4+ by area). Which isn't to say it would be feasible, just more feasible.

Good point about solar just transferring the energy. Im not sure how practical it is to brighten so many constructed surfaces like pavements and roads it makes a big impact and is tolerable to live with. An estimate that only 2.7% of the worlds land is urbanised, and 2/3rds being ocean... increasing its albedo significantly could be difficult. An advantage of space shading is it doesn't rotate out of play and can be concentrated a bit away from the edges of the globe where light is a bit more likely to reflect away.

Agreed it would be difficult and heavy to add minature gyroscopic and solar cell, comms and control unit to the 16 trillion disks proposal, since they are just 60cms wide. That plan seems basically like throwing confetti into L1, where it might get drifted away by solar ejections, out of stable orbit, in matter of years.

Since each of those disks is 1 gram and about 0.25 square meters, that scheme involves total of 4 trillion square meter shades orientated randomly. If shades are squares for simplicity and 8 meters in diameter, so 64 meters square and similar material would be 256 grams, add some stiffening and a control unit for say an extra 150 grams. Maybe a clever unfolding feature like an insects wing. Its a bit more material to launch but probably less than double at some control/shade ratio, and the tracking shades will block light about 30% more effectively than randomly orientated ones. Works out around 50 billion of the 400gram 8 meter wide shades with mini solar-comms-gyro units to produce. So I'm still overconfident in the practically of this kind of scheme, especially since cost to space has been minaturised since they previously had expert attention.

I have to admit its just one of those hunches Im hawking of late, cheers for following :)

I re-read the paper in detail. There's a lot more going on than the commentary on this page assumes, with some impressive calculations, but lots of unaccounted-for (and un-invented) elements, and even more unanswered questions.

For example, the author does assume 1gram (2ft diam) shields, but also specifies the necessity of precise angular orientation, and relatively modest location control / steering. This is to be accomplished by an unspecified number of "control satellites" using aimable mirrors and passive radiative pressure, which keeps the discs simple and the weight at 1 gram. Required disc area is ~7x the required total shading area, due to indecent angle and required transparency and spacing. A new gps-like network of "navigation beacons" will also be required to maintain spatial reference. He then says that to track individual disk locations/ orientation, that each disc needs a GPS-like nav receiver, 2 cameras, some processing/ communication ability, and a power supply, presumably solar. But he doesn't account for (or even reconsider) that there will be added weight and cost due to this.

He also doesn't consider the cost of inventing, manufacturing, and deploying the control satellites or the new type of nav beacon network, or even estimate how many of each will be needed. (GPS tech won't work, but if he knows that, he doesn't state it.)

There's other questionable assumptions, like a launch cadence of every 5 minutes for 10 years to leo, and that cost of launch will roughly equal cost of fuel due to the scale.

He also estimates the method of transfer from leo to L1 will require delta-v of 1km/s and assumes it will be solar powered / ion propelled, but leaves it at that, also without scope or cost.

It's interesting, but less convincing than I expected, given all the missing details, and also makes me more convinced that risk assessment, management and mitigation haven't thoughtfully been considered. That said, the shading, geometric layout, and required material properties calculations are quite impressive.

Slightly tangent, but in talking about the risks and unintended consequences if such a project, lots of potential issues have been mentioned (which is my bigger overall concern), but given the specs, a new one occurred to me: this design starts to look a lot like what might be required for true singularity type AI.

+/- 16 trillion self-powered, locally communicating "cellular" elements, each with some minimal sensory and processing capability. Add to that the mobility presumed by the author, and the fact that it is literally designed to block the sun, and you've got everything you need for a matrix rewrite...

Thanks for the info on the paper - I haven't read it, just seen a number of reports of different approaches to space shielding, that seem to establish its a physical/industrialy modest possibility (for a global project). It would be very early stages for the details of any project, I expect a well funded competition for competing designs and to be surprised and educated by actual designs. It just seems the prelimary designs already discussed establish its physically not unrealistic if launch capability can be sorted. 20 years ago ideas of huge wind turbines planted at sea and even floating were considered by most to be impractical or unproven, but the basic facts supported their possibility as major power sources - the density of air, the intensity of wind, the existence of resilient ocean hardware like oil rigs, the existence of very large aircraft wings. There was no end of unresolved details that could be counted to dissuade, but the broad limits were already visible and attractive. Rather than a Manhattan project to race to those limits, industry has grown slowly to approach them with not that much special funding to help.

The control coordination of trillions of L1 satelites doesnt strike me as a huge challenge to people already working in similar fields. I do some work on simulations and read about related technics. Control units just get individual and group call codes that they can respond to, in timed windows if helpful. A number of manager satellites beam signals to sectors and listen to responses. They could likely often pinpoint individual transmissions themselves with modern radar style tech, although trillion is a large number, sheilds will rarely eclipse one and other because they would be very dispersed and relatively small. They dont have to relay all messages individually through neighbours but perhaps could. The options for implementation are extensive but I believe familiar to network designers. They don't really have AI processing to do, its just a matter of maybe reporting their neighbors numbers so position can be determined and relayed so they know where to 'light-sail' and can receive schedules for when to let light past - if that becomes necessary or is deemed advantageous. Im just rambling but there are loads of possibilities for how to organize them. As a multi-node processor it would be rather slow because of the average latency between nodes being many kilometers, rather than millimeters to meters in a supercomputing cluster.

They are coupled. The consensus among scientists and economists for mitigating global warming is carbon pricing: https://www.reddit.com/r/worldnews/comments/bxgd5p/single_mo... If there is a sunshade, then the need for taxing emissions is reduced, what will directly impact the price of fossil fuels.

Personally, I'm terrified by how people here suddenly are so enthusiastic about the sunshade, without even knowing its side effects, when the problem can be solved at its source.

If you introduce a coupling, then yeah, they'll be coupled.

> Buying time is good only if that time is properly paid for.

Buying time is always good if it forestalls doom.

Climate change activists who let perfect be the enemy of good will get all of us killed.

Right now we aren't anywhere close to even trying to be on the agreed path towards "not too bad". Not "good" let alone "perfect".

Nothing short of catastrophic events will make people give up on their unsustainable lifestyle.

Sounds like the reasoning of a terrorist. Seriously.

If your primary goal is to force people to do something they don't want to do, on principle, call yourself an activist, a freedom-fighter, or a terrorist, I don't care. It's all the same to me.

If your primary goal is the survival of the human race, you shouldn't moralize.

You're the only one talking about morals here, I'm just stating facts. We have seen over 30 years of inaction since the inception of the IPCC, yet activists are the problem?

That's a clever way to inject your agenda, but I'm not having it. The immediate problem is ecological collapse, the proposed solution is a Sun-shade, and you're basically shouting that "we'll do nothing until we get to the bottom of the failures of Capitalism!"

Enough. This isn't a Parliament and you don't get a liberum veto.

>If your primary goal is the survival of the human race, you shouldn't moralize.

Could you expound on that a bit? The assertion alone doesn't parse.

Moralizing about the imperfect behavior of people during a crisis is essentially bikeshedding.

It makes me wonder about the people doing the moralizing: do they really care to contribute to the solution, or are they grinding their own personal axe about the behavior of others?

Yes, but we're rapidly approaching a point where the planet's own greenhouse gases take us several degrees further even if we stop emissions entirely. A sunshade could head that off, and give us time to pull CO2 back out of the atmosphere.

I think if there are not short term economic consequences to global warming then there will not be any solutions that get resources. This isn’t a wild speculation so much as it is the status quo.

Russia will benefit greatly by global warming, it also relies on oil exports, also benefit vy weakening Europe with an inflow of climatic reffugees, has incredible incentives to actively make it happen.

Why would Russia want to weaken the Europe? The better they are doing the more they need Russian oil and gas.

Is the gas demand that elastic though?

On the other hand a fractured/weak Europe means higher gas prices, no medling in russian affairs, less pressure by russian citizens drooling over the fence with their eyes fixed on european stability and wellfare, free hand to do as Russia pleases in ex Soviet states and so on.

By this logic weak Europe is equally beneficial to the US.

Russia (well, Putin) wants to be Europe, not just profit from or own it.

It will not

* that good black chernozem soul which makes up the Russian breadbasket would turn into desert in south of this region, while in the north the soil is too poor

* mass forest fires would choke the air

* melting permafrost would destroy existing badly maintained infrastructure and cities

If Russia is hoping for positives out of climate change they are in for a surprise

Maybe I was just regurgitating what the youtube channel Caspian Report was saying, but I think he suggested that Russia could just do agriculture up north and it would have the northern ocean open for sailing all year long and acces to hidrocarbons there.

Thinking deeply about it, would it actually lead to better outcomes for Russia?

Risks 1) Social destabilization driven by collapse of southern agricultural communities and their migration northward. Keep in mind that already the northern communities are being heavily impacted by the thaw of the permafrost that many cities and towns are built on - to establish more infrastructure means building on a growing swamp. To be able to get crops to market, it means building very long roads on a growing swamp as well - remember that Russia suffers from a lack of internal rivers to convey agricultural products throughout it's vast geography.

2) Consequences of disturbances to fish stocks for northern communities - who are dependent on either fish directly, or seals and other species indirectly

3) Limited societal benefit of new hydrocarbon resources given the existing klepto-oligarchy - it's unlikely that new resources will be used to stabilise the broader community or social fabric.

4) Possibility that they cannot exploit said hydrocarbons due to global moratoriums or increased uptake in alternative energy sources

5) Broader geopolitical implications of social collapse of soviet satellites; some of which are currently heavily dependent on current rainfall patterns for cotton, wheat and other grains - Kazakhstan, Turkmenistan, etc - if these countries go to the wall - what does that mean for the Russian state? It's likely that Russia would have to invest aggressively in shoring up the southern borders. 6) China; the eastern regions of Russia could be a tempting acquisition for China looking for new agricultural land or control of northern ports such as vladivostok as ice coverage decreases- further exacerbating pressures on the central Russian government.

There may be a point where such a project is appropriate, I'm just saying we're nowhere near that point. Such a risk is not something to be done preemptively, no matter how imminent.

Comments like this sound like "global warming isn't really a serious problem yet, so the only acceptable way to deal with it is to agree to my demands unconditionally - those alternatives are just too risky" to me.

I'm looking at it the other way- the risks of such a project are that big.

The problem is, I can look at the risks of something like this, or olivine beaches with Project Vesta [0], or sulfur dioxide in the upper atmosphere - and the worst cases there are still incomparable to the expected case for climate change. Like, the "I don't know how you would do this deliberately"-tier worst case for Project Vesta would be killing all sea life within 100km of the relevant islands, and that would suck! But with ocean acidification, that's going to happen anyways, and not just around those islands. And that sort of analysis makes me think that either

1. the alternate proposals won't work (at all, which seems unlikely)

2. the expected case for climate change isn't actually as bad as people are saying it is

or

3. people don't actually care about climate change as much as they care about using climate change to push their own agendas

Personally, I lean towards #3. But that still doesn't make me very happy with climate activists.

0: https://projectvesta.org/

Sadly I think #3 is true of many activists. Actual climate scientists are another matter; I've seen many of them advocate both geoengineering and nuclear power.

Not all that much risk, since the shade could be eliminated almost immediately by simply rotating each element ninety degrees.

The plan also requires a certain amount of stationkeeping, probably with solar sails, and if you can do that then you can also move the elements out of the way of the sun entirely, with a little time.

1) That assumes complexity not accounted for in cost, weight, or deployability. It's one thing to deploy a bunch of dumb disks. It's entirely another to deploy trillions of steerable drones. It's several orders of magnitude beyond what was suggested.

2) It sort of misses the point- that might address the known-unknowns of the primary effect (solar radiation hitting Earth). It does nothing to address unknown-unknowns or even secondary or tertiary effects.

The mere presence of the shields might block solar wind, distort Earth's magnetic field, reflect / refocus cosmic radiation, amplify affect of solar flares, interfere with radio or satellite communication...

We just don't know. And the stakes are too big, even compared to worst case global warming.

The bigger the potential impact a project has, the better prepared you should be to undo or mitigate it, before it causes problems worse than the ones it's meant to fix. I don't see that here.

If you look at the link in the original comment, you'll see the whole thing doesn't work at all unless the individual elements are steerable. So that is in fact what was suggested.

All the "mights" you mention can be easily evaluated by straightforward physics.

I did, but it's not realistic. Maybe passively "aimed", but not actively steered, and not commandable. And even passive aiming is unrealistic at that price, active steering increases costs by several orders of magnitude.

You can't possibly think that it's straightforward to model all those physical aspects for 16 trillion objects. We don't even have the 3-body solution solved; just predicting the gravitational behavior is unbelievably complex and chaotic. That many degrees of freedom is simply unsolvable (without quantum computing).

It's hubris to believe we can predict even basic behavior and interference of such a project, let alone intended or unintended side effects, whether known or unknown.

This is like saying treating lung cancer is a horrible idea because it will encourage more people to smoke.

Totally agreed, there is a degree of hubris in geo-engineering that is breathtaking. There is of course geo-engineering going on right now, climate change itself is the product of unintended consequences, but to submit that all we need to do is have intentional geo-engineering as a solution is the worst kind of myopathy.

I think the reverse is true. Rejecting geoengineering out of hand is essentially the "we shouldn't play god" argument, which is asinine and, in this case, suggests one's not taking the problem seriously.

I don't know of any scientist who thinks it's all we have to do. But a fair number of climate scientists think we need it to buy us some time while we decarbonize and draw CO2 down to a safe level.

Humans are running on hubris ever since we invented fire and other ways to manipulate environment. It is simply a question of scale.

Intentional projects would be an improvement over current state of unintentional changes.

I'm skeptical we can summon the political will to switch off of fossil fuels regardless if it's the only way to survive.

But the money is on the side of renewables - from [0]:

> Not a single coal-fired power plant along the Ohio River will be able to compete on price with new wind and solar power by 2025, according to a new report by energy analysts.

Solar prices are dropping so it'll eventually beat fossil fuels in the market. Sunshades or similar geoengineering projects may require less political will at the right price point and allow us to kick the can down the road long enough for our own greed to save us :)

[0] - https://insideclimatenews.org/news/25032019/coal-energy-cost...

What impact would a solar shade have on that? On agriculture and overall photosynthetic capacity?

I honestly don't know or know of any quality modeling of it.

Very good questions and I don't have the answer. I was mostly trying to respond to the concern that it's just kicking the can down the road.

But if we're speculating... with cheap launch capacity and cheap/efficient solar, we could start talking about building solar farms in space.

Also - again speculating - if the shade has limited coverage, there should be a temperature difference on the edge of the shadow. That may cause increased wind, which could benefit windmills.

I think wind would suffer because of less energy overall going into the system. I'm not an expert enough to know the answer.

I appreciate that there could be risks to this solution, but not ready to dismiss it as 'horrible'. I mean, fossil fuel usage is not something inherently evil-- minimizing its harmful effects is not something bad imo.

It’s a horrible idea. Is this the same “science is settled” crowd from the 1970’s who thought we should sprinkle black stuff at the poles melt the ice caps in prep for the coming ice age?

I agree that the idea sounds like the worst thing we could do. Let’s not forget, that EVERY LAST BIT of energy we’ve ever used or will use, has come from the sun. So hey, let’s cutoff our supply from it! That’ll help things out and secure energy availability for future generations!

At the end of the day, we’re a part of nature too, just doing our part to increase entropy via energy dispersion. Can’t stop the second law. Just gotta find ways to do it that kill us off slower.

Most fission nuclear power comes from primordial supernovae of blue giants during the early formation of our galaxy. Fusion would be novel energy from the creation of the universe if we could get it working.

Most of the energy we have used comes from the sun. Aside from nuclear.

What about geothermal and tidal? ;)

Good point! If our moon is slowly going to decay in it's orbit until it crashes into our planet we may as well get something out of it! Although part of it DOES come from the sun >_>

Such a sad thing to see the sunshade comment at the top.

That's got to be the cheapest solution to global warming I've heard of. I wonder what problems there are with it. The nice thing about it is if things start getting chilly (as we move into another glacial period one day) we can simply remove some of the shades again. The increased CO2 means more vegetation growth, which is nice. The only real problem at that point is ocean acidification, which I think won't be reversed by cooling things down again.

I wonder if we will one day regulate our climate on earth by shading hot areas and pointing mirrors at cold ones. There are all kinds of knock on effects of doing that, but it seems like a human thing to do. Modify the environment instead of adapting to it. That's kind of our thing.

Stratospheric Aerosol Injection [1] for emergency cooling sounds relatively cheap too, and has the advantage of a) mimicking a well-studied natural process and b) being inherently self-limiting. Your "if things start getting chilly" fallback may not be viable if e.g. a Kessler cascade locks us out of orbit.

[1] https://en.wikipedia.org/wiki/Stratospheric_aerosol_injectio...

> The only real problem at that point is ocean acidification, which I think won't be reversed by cooling things down again.

From what I understand, it will help... eventually.

If ambient temperatures come back to normal, then the ocean won't absorb as much CO2.

The bigger issue is the large amount of co2 that the ocean will quickly release back into the atmosphere as temperature and partial-pressure drop.

It would be better if we could come up with a way to neutralize / sequester the co2 already in the ocean.

That's Project Vesta: https://projectvesta.org/

Basically, artificial green-sand beaches which absorb CO2 as they weather.

Yes, I think so. I wonder by how much.

That's the cheapest you've heard of? Have you heard of carbon pricing? https://www.reddit.com/r/worldnews/comments/bxgd5p/single_mo...

Carbon pricing sounds like a cheaper and a more direct solution addressing the cause of the problem (more greenhouse gases in the atmosphere) instead of its effect (temperature rise). What could go wrong?

A solution to warming? Maybe. A solution to ocean acidification? No.

Removing the shades would be quite hard, dare I say impossible to do in large quantities. Fortunately you don't need to do so; they will eventually drift away under solar pressure. So if you don't need them anymore, stop refreshing the pack and it will eventually disperse, whereas if you need more, launch more.

Or just orient them sideways to block less light. That shouldn't cost much fuel, if any (using reaction wheels). I think it would be best to keep those at hand, just in case.

If feasible at all, make a part of those shades photovoltaic panels, and beam the energy back using microwaves, as that would provide an extra incentive to launch that (GEO might be more useful for that kind of setup, I have no idea what deltav it would take to transfer to/from both, but you could use ion thrusters since you have on-board power).

How do you orient them? The dumb ones weigh 1g. How much will they weigh if they're smart, powered, and have reaction wheels for orientation? That's orders of magnitude again.

Better to send up 10,000X dumb shades with random orientation and spin. Not only are the dumb ones much lighter, they're proportionally much cheaper too, since they're basically just structured aluminum foil rather than needing thrusters, reaction wheels, computers, etc.

Is there any way to "bleed" more heat (other than making the atmosphere thinner, which is obviously a double-edged sword, and not feasible anyway).

Would be interesting to keep inflow the same and reduce outflow, but I have no idea what I am talking about.

Reflective roofs/walls of buildings, basically make more IR and heat energy get reflected away from the surface.

You don't really make the atmosphere thinner by removing CO2 or methane...they are trace gasses relative to N2 and O2, CO2 is less than a .05% of the atmosphere, IIRC. So, you mostly want to prevent heat from hitting the Earth, or decrease the absorption (increase albedo), or you want to remove the heat-trapping gasses that will continue a warming cycle by trapping the heat we do get.

I think space sunshade's a decent idea, but we still need very aggressive decarbonization, as CO2 is very bad for the ocean, nevermind the heat trapping.

I have encountered reflectors that actually reflected visible light. I think they were called "mirrors". Maybe you have encoutered them too.

Infrared radiation only comes from things that have been heated (mostly) by that visible light. Any light reflected back into space without being converted to heat is energy that is somebody else's problem.

It would suck to have a world not too hot, but with no sea life left.

Allowing CO2 to increase without bound would eliminate the fisheries billions of people rely on for their protein.

So our solution to polluting our planet is to pollute the space around our planet as well?

What happens when those space shades get hit by micro meteorites causing them to alter or de orbit?

That's not comparable types of pollution. If it's something we put there on purpose and provides us a benefit, I'd say even use of the word pollution is incorrect.

I don't think there's a big micro meteorite problem at the Lagrange point, but if there were for arguments sake, then you need to plan for it and have a way to replace shades that get knocked out of position. It's not like the whole system would fail if you lose one shade. That's what engineering is about, planning for all the likely eventualities.

> What happens when those space shades get hit by micro meteorites causing them to alter or de orbit?

"0.6-meter diameter and a thickness of about 5 micrometers. The mass of each disk would be about a gram..."

Absolutely nothing.

I agree space pollution is a problem but I would imagine that these are thin enough that they would burn up in our atmosphere upon reentry if they de orbit onto earth.

The issue isn't whether or not they'll eventually deorbit and disintegrate on re-entry -- that's a given. The issue is that while they're slowly approaching the Earth, they're a hazard to spacecraft. Slamming into even a gram of mass at orbital velocities could damage a spacecraft.

L1 point is around 1,500,000 km from earth, they wouldn't be entering earth's atmosphere (unless we would want them to), interfering with any other satellites circling us or anything similar.

I'm not an expert but I would think gravitational forces could move them towards other bodies like Earth?

they would burn up in the atmosphere - they have not much mass individually

At $35/kg, that would cost about $750 billion. More than Musk could do on his own anytime soon, but definitely feasible as a global effort.

Each pound of methane would produce 2.75 pounds of CO2: https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085...

And each launch burns 240 tonnes of methane (launch mass minus rocket mass is 1200 but that's 4/5 oxygen): https://en.wikipedia.org/wiki/SpaceX_Starship

So that's 660 tonnes CO2 per launch times about 150,000 launches, or about a hundred megatons CO2. Given that we're emitting 36GT annually, that seems a good trade.

That's just launch to LEO, we need extra delta-v to L1, but potentially that could be from a fleet of solar-powered ion drive tugs. My quick google didn't turn up Starship payload capacity to L1.

If the shades can be manufactured on the moon from local materials, potentially this could be a lot cheaper, with almost zero emissions. It'd take longer to get started, but it'll take a long time before people agree on something like this anyway; if we're setting up lunar manufacturing anyway, this would be something to keep in mind.

If we could somehow capture the methane that's escaping from the clathrates under the sea and in the permafrost, it would be a net gain in terms of global warming to burn it up in a rocket engine and convert it to CO2. Methane has much more than 2.75 times the warming potential as the same mass of CO2.

A sunshade is not just a temporary band aid for global warming. It will likely be a necessary addition to our planet to manage the heat we will continue generating.

Our energy consumption and production continues increasing as society keeps advancing, and it will continue to do so as we unlock more diverse ways of harvesting and storing energy and using it. A mark of a technological civilization is the conversion of starlight into heat energy - the civilization converts the energy from the star into useful work which produces heat. The heat has to go somewhere.

Up until now, it's been fine just letting earth manage it (but we're obviously running into the limits of that with global warming), but as we start approaching planetary levels of energy consumption, we're going to start producing planetary levels of heat, and we're going to need to do something about it. The simplest and most straightforward way is by putting sunshades into orbit to limit the amount of sunlight that comes in to cool the planet. This works especially well if the sunshades are solar panes that can collect energy while they shield heat. It's attractive because it doesn't involve changing delicately balanced atmospheric composition, and they can be moved or rotated to adjust the amount of light coming in on demand.

But I think our energy consumption is miniscule on the scale of energy received from the Sun.

I did the math once, and a square of 300x300km of solar panels in the Sahara would cover all the world electricity demands.

The issue is with green house gases, cutting forests which alter the way Earth handles Sun's light, not out actual heat output which is minuscule compared to the heat of planet Earth.

I believe Elon came up with similar figures during his Powerwall presentation, along with how small of an area it would be to provide the batteries to complement the solar panels.

"300x300km of solar panels should be enough for everybody"

Joking aside, much like with memory, bandwidth and storage, we'll invent ways to use (all of the) energy if it is cheap enough.

Do you know the cost of putting only 1kg at the Sun-Earth L1 point? To give you an idea, the cost of putting a satellite in the geosynchronous orbit is about $30k/kg, and the geosynchronous orbit is only 36,000 km away.

But let's assume somehow miraculously we find a way to put objects at L1 as cheaply as the geosynchronous orbit. Your proposal would still cost $66 trillion. That's roughly the entire world's gdp. Do you really think this is going to be cheaper than reducing carbon emission?

For what it's worth, there is a BIG difference between 22 million tons to orbit (LEO), and the Sun-Earth L1 point, in terms of delta-v.

This delta-v map suggests roughly 2x vs. LEO: https://www.reddit.com/r/space/comments/1ktjfi/deltav_map_of...

Although it might be significantly easier with gravity assists.

The reflight turnaround time is off. SpaceX are aiming to turn around a vehicle from landing to launch readiness in 24 hours as a best case lower limit. It does not include payload integration. This also does not include the time it takes to wait for the launch window, launch, deploy a payload, de-orbit and land. Thats likely to be at least 24 hours, and often more. If operating beyond LEO a lot more. In practice I’d be surprised if the real cargo delivery rate was as much as a fifth of this. It’s still a staggering amount though.

Wouldn't solar radiation pressure blow them all over the place?

There would be a "unnatural" orbit where solar radiation pressure would cancel the mismatched orbit, I think.

So the shades would stay in equilibrium in a bit higher solar orbit than their velocity would permit without the light pressure.

I'm having trouble visualizing how this would be stable - from their reference frame (orbiting a Lagrange point), the pressure is coming unidirectionally. They'd be accelerated in one direction constantly, which seems like it couldn't possibly be stable.

Actually, you are right, I was talking as if the shades are just orbiting the Sun.

L1 orbits do require station keeping.

Perhaps you could cheat a bit by making the shades black or oscilating/slanting them a bit forward/rearwards as to do the station keeping with very little fuel? Or shaping them like a lense to direct most light away from Earth, but not to experience too much net force?

Or they are just designed to be expendable?

For what it's worth, Wikipedia suggests making them shaped like a lens.

Yes. They need serious stationkeeping.

Do they? It seems to me that it'd be a lot simpler to send up dumb sunshades, and then simply keep launching more as previous ones drift. The linked sunshades would only weigh a gram each. How much would a sunshade weigh if it had to be an entire spacecraft capable of stationkeeping? Many orders of magnitude more.

You can't station-keep indefinitely anyway (your fuel will run out), so just launching lots more dumb sunshades seem like the more effective and cheaper solution.

While I think x,y,z will be an issue, I think the bigger problem is orientation.

Any sort of station keeping is going to add significant mass, complexity, and cost.

Why does orientation matter? Just throw up enough dumb sunshades. It costs a lot more in station-keeping to get the orientation correct than to just let it be random.

And keep in mind that, absent active station-keeping, you need a mix of many different orientations to block out the Sun throughout the year. And you're not going to perfectly remove any spin anyway.

I agree that would be the smart way to do it, but that would at least double the scope, probably more, since orthogonal area is a cosine function. There's also oblique reflection to consider.

Why do you assume that the linked paper hasn't already taken this into consideration? They know that they're basically just structured aluminum foil, weighing in at 1 gram each, and completely dumb; why would they be assuming orientation at all? The reasonable thing to do would be to assume random orientation (especially over time, i.e. rotation, and over the orbit).

I actually agree(d) with that reasoning, I also initially assumed random placement. Others on this page suggested them being steerable.

But we're both very wrong- I read the whole paper. Some aspects are well thought out and highly technical, while others are glossed over as requirements tbd.

Briefly: He does intend to steer/ orient the discs using radiative pressure from a network of control satellites and gps-like navigation "beacons", but overlap is also required to take into account the required oblique angles and transparency of the discs.

I'm left being very impressed with the provided technical details of the disk constellation, but even more skeptical overall, mostly due to lack of detail on some major supporting elements. He offers no detail of the required deployment method, or even the scope of the required navigation and control network. He also states each disk will require a gps-like receiver, 2 cameras, some power and processing capability, and a method of communicating with said networks, all while still assuming 1g per disc and no added cost...

It's not conceptual level, so much as it's conceptual for maybe one out of dozens of required massively scaled elements.

Also, it addresses no risk management / mitigation concerns.

The carbon cost of manufacture and transport seems like it would absolutely dwarf any benefit to such a scheme.

20 million tons of plastic to manufacture is small comparing to world production - and we're talking about world effects here. Launch pollution is calculated...

Not as much as you'd think, because they're actually lenses. They just redirect the light away to miss Earth, rather than blocking it entirely.

And if that works, and we restore a more normal cycle, how do we avert the next ice-age with all that space junk?

L1 is unstable, and the disks will be pushed away by the solar wind, so I suppose theses disks will disperse eventually.

I think some amount of clumping might be expected before dispersal, depending on material properties.

Lots of objects in space are designed using origami, so if we have a motor or little piezo-electric strip to apply tension, we could reverse the folding process and have them go from max size to minimum size on signal.

If it isn't automatic the case, the material for the discs could be designed such that it dissolves in the normal solar radiation after a decade or so.

Can't dissolve without a solvent.

Sorry, that is nonsense. You are over-interpreting a term. Put a plastic bag into the sun for some months and it will break into tiny pieces on the slightest touch. The radiation outside the earth atmosphere is way more dissolving than the sun shine on the ground. So a material could be chosen so that it desintegrates, if you don't like the term "dissolve", in a certain timespan in space. Actually, it will be a challenge to make sure that those disks hold up long enough.

Sorry, I thought we were having a science based discussion where words have meanings...

We're talking about retrieval difficulty in a worst case scenario. Even if it disintegrates, you've left a cloud of particulate matter that's going to create even more unintended consequences and is more difficult to collect / move / mitigate.

I think it was plenty clear what I was trying to say. I am not a native English speaker, but in German, the term "auflösen" literally means to dissolve in a solution, yet, no one would have misunderstood it in the context of space. For most people it is quite obvious, there is no solvant in space.

So if you feel the need to correct my use language, please do it in a constructive manner.

Do you know what happened to USA flags which astronauts installed on the Moon?

I don't- but if it "disappeared" it would likely be disintegration and dispersal, or possibly sublimation.

But it certainly didn't dissolve.

We remove it?

How would one prevent the cloud of sunshades from clumping together due to gravitation? The effect on a single disk on the outskirt of the cloud should be equivalent to the attraction of a 16 million ton mass at the center of mass of the cloud.

Would we need to spin the cloud? (perhaps forming a galaxy-like shape)

They'll need station keeping anyways [0], but is 16 million tons actually enough to create substantial gravitational force?

Looks like the circle would be approximately 1100 kilometers in radius (per wikipedia), according to this random calculator [1] 20 million tons at 1100 km creates a force of 0.000000000001103 N/kg.

I don't think gravity is likely to be the biggest problem.

[0] Solar wind will push them, the lagrange point they would sit as is actually a "point" and anywhere nearby you slowly drift out of it

[1] https://www.omnicalculator.com/physics/gravitational-force

The wiki page says they would need some stationkeeping, probably using small solar sails.

Great! Reduce plant growth and carbon sequestration by 2%! Reduce solar yield by 2%

Then put up another shield.

Drop yields more.

Put up another shield.

Wasteland.

I don't know much about sunshades, but it looks like the wikipedia article assumes the sunshade would block/filter light across the entire planet. Couldn't we have a significant effect by blocking a small percentage of light during the summer months toward the poles?

If we can keep the poles cooler, we could increase the ice cap, reduce melt, and affect only a small number of living creatures.

My initial searches have turned up nothing related to this, and I'm a total novice, so just asking the question.

> If we can keep the poles cooler, we could increase the ice cap, reduce melt, and affect only a small number of living creatures.

And more ice means a higher albedo, so more sunlight is reflected back into space. But I see the challenges of partial blocking as a lot higher than in the general case - you need to keep two hemispheres in place and synchronise them with the tilt of the planet as it orbits the sun.

The idea of exploring and possibly colonizing other worlds has nothing to do with our ecology and everything to do with the fact that a comet could hit earth and destroy our entire species at any moment and we wouldn't really have enough time to react properly. Add planets to your species and you reduce the chances that your entire civilization could be gone in an instance.

They both require certain degrees of geo-engineering, even if the scopes are entirely different.

I find it amusing that people who think 2-4 degrees over decades is an insurmountable problem, but creating an entire hospitable atmosphere on another planet is doable.

This reminded me of Kim Stanley Robinson’s Mars trilogy - an awful lot of it is about the technical processes and political issues presented by terraforming, and one of the techniques explored is the use of giant space-borne mirrors, both for shading and increased insolation, depending on the target body.

16 trillion small, unsteerable, solar sails all sitting at the boundary between the Sun and Earth's gravitational influence. As light pressure pushes these things out of the L1 point they will all make their way to the Earth where they will enter the atmosphere and give up their gravitational potential as heat. Does their shading effect counter the fact that they will all give back some heat?

The potential energy is close to the energy used during launch. And every time we launch a rocket/sat (and then it comes back eventually) we heat up the atmosphere a bit.

The potential energy due to gravity is separate from the potential energy due to embedded chemical energy, which I suspect would be bigger for such a shape, given drag. (Since energy is proportional to velocity-squared.)

Wouldn't increasing cloud cover be the same solution and just like way easier?

Sunshades are more persistent. The cloud I make will disappear after not very long, so I'd need to make more.

But it will consume several percents of world's total energy supply, in fuel. That is, burn more fuel than airlines do. Clearly not possible. Even 1/10 as much (which is still the scale of Berlin airlift) is problematic.

Wouldn't this be basically the "scarring the sky" thing that the matrix used as a symbol of a desperate, foolish attempt to avoid the consequences for our mistakes? lol

Unintended consequences are a bitch. How can people smart enough to "design" these types of projects be so arrogant?

Even removing the co2 that we've added to the atmosphere and sequestering it may not be free of negative consequences. That is the magnitude of uncertainty we need to be discussing and debating. At this point, blocking the sun is just crazy, and not because of feasibility, constructibility, or cost.

Edit: Look at the disaster of updating the Washington DC water system for a supposed "fully understood" lead mitigation project that went unbelievably wrong, because of bad assumptions and factors not initially considered to relevant (unknown unknowns). And there was no controversy over such a conservative "fix" (other than maybe cost given necessity).

https://en.m.wikipedia.org/wiki/Lead_contamination_in_Washin...