How We Scale

We need to deploy ~1.1 million tons of Cooling Credits every year to cool earth by 0.5C. This is not a small number:) Given that our current payloads are less than 2 kg of Cooling Credits, "how can you possibly scale to do this" is a reasonable question. Reasonable-ish: we don't know exactly how we'll scale to via our actions move global temperatures back into a sustainable zone and keep them there, and at this point we shouldn't even pretend like we have to. Our (and everyone's) job is to do things that help, scale them up over time, and become more extreme as the emergency that is climate change escalates. We don't know exactly how we'll deploy ~30 million times more than we have so far, but we do have broad plans for how we can get it done.

Balloons 

There are only 2 ways we switch from our current weather balloons: ROI or customer demand. Excluding labor, it costs us less than $0.20 to deploy a Cooling Credit. Generating our own hydrogen via electrolysis will drop this below $0.10. And labor isn't an issue at 100x current scale: 2 people can deploy at least 10,000 Cooling Credits in a day. We'll want to switch when we are deploying 10+ tons per month or sooner. Then, polyethylene balloons will make sense. NASA does regular flights with 4-ton payload capacities. The hard part of these NASA flights is controlling where the balloons go and keeping them up for a long time... neither of which we care about. We haven't built it yet, but we'll get to where we're using commercially-available polyethylene sheeting to make our own balloons. Our friend Casey sketches out the broad-stroke idea here. So! If balloons are how we deploy at the megaton scale, we'll need to get really cheap hydrogen and gigantic balloons. We're happy to buy these if we find someone willing to sell at a reasonable price, but we will be able to make both of these in-house if we need to. With polyethylene costs in the neighborhood of $1200/ton, machinery to make sheets something you can literally order online, and Project Loon proving a small team of crazy people can make much more complicated balloons, we don't write off our friendly inflatable friends as a potential tool for deployment at scale.

Planes

Depending on what value you place on future suffering from climate change, one can argue we should build nothing and simply deploy with existing planes. A MIG-29 can fly into the stratosphere; you used to be able to book a flight on one. You can sometimes buy a batch of them (theoretically, at least; I'm guessing if I show up in Tajikistan with a check political complications will ensue) . They carry 4 tons per flight of payload.  I'm not smart enough to understand the fuel requirements, but let's assume it's 10x less fuel-efficient than normal flight (no idea if this is reasonable). Fuel capacity 3500 kg and range of 1430 km = 1430/3500 ~.41 km/kg. So let's say we go 22 km up * 10 because an arc and going up * 2 because back down = 440km traveled / 0.41kg/km = 1073 kg fuel used. Jet fuel's somewhere around $0.82 per kg, so we get up and back for $0.82*1073 ~ $900. This seems too cheap. Let's say we burn the whole tank to go up and back: $0.82*3500 = $2870. 2 tons sulfur to make 4 tons sulfur dioxide at ~$200/ton = $400 sulfur cost. Assuming we get the planes for free and the pilots don't charge us and the planes never break, jet fuel and sulfur gets us to 2870 + 400 = $3270 to deploy 4 tons of SO2. We're at less than one-tenth of a cent per Cooling Credit; planes are starting to look good.
Next-generation planes will look even better. NASA and several startups are making real progress on supersonic jets (supersonic tends to get us the flight ceiling we need); we're very unlikely to build a custom, high-altitude, human-operated plane. If I had to bet on how we deploy at scale to cool Earth by .5 Celsius within the next 2 decades, my money is on via supersonic jets carrying sulfur tanks or as a fuel additive.

Skytubes

A tethered tube to the stratosphere is almost definitely the lowest-cost per g delivered. And it's elegant: deliver just what we want up when we want it! This pushes the boundaries of material science, but we can probably build it (we as in 'humanity'; way over Make Sunsets' heads). But, where? Some country needs to decide to 1. allow this to be built and 2. keep it going when others complain. The first is hard, and the second borders on impossible. So! I'd rank this as most efficient and least likely to be built within the next 20 years.

Overall Improvements

We can do a lot that'll make almost any future deployments better, regardless of how we provide lift. Some of the highest-impact next steps:

1. Make SO2 in-stratosphere: Move only sulfur up and use the sparse oxygen to make SO2 will get us ~twice as much cooling per gram transported (S molecular weight = 32.065 u, while O = 15.999 u). You have to lift a sulfur burning mechanism and prove that it works, but this becomes less a pain as your balloon gets bigger or you are flying a plane to create the plume.
2. Measure via satellite: stop flying any sensors and instead deploy such large quantities per flight that impact can be measured by existing satellites.
3. Prove people want this: sounds corny and salesy, but convincing companies and governments that people are already starting to demand (and even buy) deployments matters, a lot.

Nopes

To dispense with things that aren't likely to work:

1. Rockets: too much money for all the fuel, lots of emissions, and not usually reusable. In comparison, high-altitude jets are likely Pareto efficient.
2. Blowing up volcanoes: other molecules go up that create warming, too much Bond villain association even for me, and collateral damage
3. Diamonds / other dusts: yes, eventually many different things! We have our hands full for now with SO2, and nature has proven for thousands of years that it works safely. So, we'll stick with biomimicry until/unless customer demand insists on something fancier;

And then...

So! that's at least our framework for how we get this much bigger to materially Cool Earth. We'll get it done just in time for space shades to put us out of business;)

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