Cooling the Planet with Weather Balloons?
If we want to stop climate change, some say we should consider geo-engineering
Ok, so I saw this tweet and was immediately intrigued:
Casey even conveniently included a direction for research, so I decided to run the numbers on this idea:
So what is the unit cost of delivering SO2 to the stratosphere?
Fact Check
First, let’s get the unit cost of all the materials we will need for launch:
Cost of 1 Weather Balloon
1500g Weather Balloon $135 (link)
Weight: 1500g
Manufacturer & P/N: Totex TA1500
Material: Natural Latex
Burst Diameter: 31.0ft
Neck Diameter: 3.0cm
Neck Length: 12.0cm
Cost of SO2
SO2 is waste. You’d need to figure out logistics, but you can probably get it for free if you can take it off the hands of oil plants. You might even be able to get paid to take it off the hands of oil plants. Let’s say it’s “free”, for now.
Cost of H2
$1-5/kg
How high do we need to go?
Well, our tallest rainclouds reach up to about 20,000m (20km), and we’ll want to be above those, well into the stratosphere, to avoid contamination of the clouds with the SO2 released from the balloons, so let’s set a target of 25km, which also happens to be about the height that many current weather balloons burst.
The atmospheric pressure at 25km seems to be ~2000 Pa.
How much gas can our balloon hold?
Well, the burst diameter is 9.44m, so the burst volume would be 440m^3.
As the balloon rises high into the atmosphere, air pressure goes down dramatically, and the gases inside expand. If the burst volume is 440m^3 of gas at 25km / 2000Pa, how much gas is that at STP (101kPa)?
It’s sadly only 10m^3. This is because the pressure drops so rapidly as the balloon rises. If we were able to burst the balloon at even 20km, atmospheric pressure would almost triple, giving us closer to 27m^3 of fill gas. But we’ll move forward with 10.
To double-check my math, I used this balloon calculator, which gave a figure of about ~450 cubic feet = 12.7 cubic meters of helium able to reach 25,000m, so it seems we’re pretty close.
A Lifty Mixture
So we have 10m^3 of gas, and we need to create 1500g = 1.5kg of lift, plus a little bit so it doesn’t just float there. Call it 1.6kg of lift.
In order to get that amount of lift, about 60% of our gas will need to be hydrogen. Formula here.
So that leaves us with 40% SO2 or about 4 cubic meters of SO2 per balloon.
The Final Unit Cost
Our total cost for launching each balloon will be:
1 weather balloon ($135)
6 cubic meters H2 ($3)
4 cubic meters SO2 (free?)
So $67 to get 2 cubic meters of SO2 in the stratosphere, or ~$33.5 per cubic meter. Remember that depending on where we launch in the Stratosphere, our price changes dramatically. If we could launch it to 10000m, we can launch 10x the volume of gas, so our unit cost would go down to $3.5 per cubic meter. I’m sure this is possible somewhere, as the stratosphere goes as low as 6km above sea level (at which point, costs could go as low as $2 per cubic meter, or so).
Please check out my final math here.
IS THAT ALL??
Well, no. Actually, if you look at our costs, you can see that they’re almost entirely the weather balloon itself, which is suspicious. Why does 1500g of LDPE (low-density polyethylene) cost $135?
Well, it makes sense, weather balloons are sensitive and we don’t normally need to send very many up. But let’s say we wanted to send millions of balloons and produce them at scale?
The price of LDPE is about $1/lb, or $2.2/kg. That means we should be able to produce our 1500g balloon for $3.3 if we were perfectly efficient, which is an almost 95% savings on our unit costs. Being more realistic, and giving ourselves a $25 cost for at-scale LDPE balloons still brings our 10,000m price all the way down to a whopping $1.2 per cubic meter of SO2 yeeted1 into the stratosphere.
So What? How many cubic meters do we need to launch to limit global warming? Is this even safe?
On both counts, I’m not sure, and this is about the limit of the time I have to do napkin math, so I’ll save answering those questions for next time, but it would be fun homework for the reader. Casey, if you know, I’d be curious. There seems to be some discussion here that might provide interesting trailheads, though I haven’t looked into it.
Keep in mind that Sulfur Dioxide (SO2) is the same stuff that cools the climate when volcanoes erupt, so one neat aspect of this plan is that it’s basically simulating volcanic cooling, for the price of $7 per cubic meter. Perhaps we should just be triggering volcanos in the ocean? Who knows.
y e e t !