We should not let the Earth overheat!

I’ve been putting this one off but no longer. Let’s talk about geoengineering.

At Terraform Industries, we’re developing a carbon neutral supply chain for cheap, unlimited hydrocarbons derived only from sunlight and air. With this and similar technologies, I’m confident that humanity will move beyond fossil fuels as soon as 2040, and not a moment too soon.

In other words, congratulations everyone, we did it! Between synthetic fuels and electrification, we’ve solved the climate challenge. There’s some implementation to be done but salvation no longer requires mass starvation or global totalitarianism or fusion-powered cell phones. 

If only it were this simple. Yes, relatively soon we’ll slow down on putting new CO2 into the air, and plants eat up to 5 GT per year. But, we are still living beneath a sky with 2 teratons of excess CO2 emitted over the last 200 years, which will continue to warm the Earth for centuries to come. As the Earth warms, damage to the environment, ice caps, arctic greenhouse gas stores, and human lives will only intensify. 

With synthetic fuel and electrification, the Earth may end up like a patient who made it to the OR only to bleed out because no-one applied a tourniquet when they had a chance.

Fortunately, we have a chance. Synthetic fuel takes care of new CO2 emission, and two specific kinds of geoengineering can take care of legacy warming in a way that safeguards our planet’s wellbeing for future generations and staunches the bleeding for the next couple of crucial decades while we get the job done.

The first task is to sop up excess legacy CO2. The solution here is cheap and straightforward. Accelerated weathering of mafic rocks increases the surface area available to absorb CO2. There are a bunch of ways of doing this, but the easiest and cheapest seems to be to grind up a couple of tropical volcanic mountains and sluice the resulting rock flour into the warm, shallow oceans. The rock dust floats around for a few weeks absorbing CO2 before sinking, permanently sequestering the CO2. In fact, oceanic carbonate rock (limestone, dolomite, etc) currently stores far more CO2, laid down over hundreds of millions of years by coral and other reef-building organisms, than exists in the atmosphere and oceans.

Campbell Nilsen wrote a great piece about this recently so I won’t go into vast detail. [And another as a follow up to this, on stratospheric particles.] Overall costs could drop below $20/T-CO2, which means we can soak up one of the two excess teratons of CO2, returning atmospheric CO2 to about 350 ppm, for about $400b/year over the next 40 years. Not cheap, but better than the alternative, and that’s while letting plants do 20% of the work. They could do all of it if we could wait 200 years, but we can’t. By then the Earth would have warmed beyond the point where we can sustain agriculture and trade, which means mass starvation. I’m going to go out on a limb here and say that avoidable mass starvation is a moral catastrophe and we should not do it.

So much for CO2. We’ll no longer extract it and we can sequester it for trivial cost and environmental impact compared to the inevitable outcome of doing nothing.

How do we keep the world cool for the next few decades while we upgrade our industry to a post-carbon world and scale up CO2 removal? It does us no good to be stable at 350 ppm by 2060 if we’ve already lost Greenland, the West Antarctic ice sheet, and 7 m + 4 m of coastline respectively. Of course neither ice sheet could float completely in just 40 years but our (in)actions in the next few decades could easily lock in 11 m of irreversible global sea level rise, to crush our descendants behind ever higher tides over the next century or so. Even if we successfully decarbonize and sequester excess CO2. And that doesn’t include other impacts of warmer weather, including famine, flood, fire, wet bulb mass fatalities, displacement, conflict…

What we need is a short term tourniquet to take the edge off global heating while we give the long term fixes time to work. 

Fortunately, we have one and it’s safe, cheap, and effective. I’m talking about Solar Radiation Management. The problem with the CO2 we emit every day is that it sits in the atmosphere for hundreds of years and reduces the amount of heat the Earth is able to radiate. Not by much, but enough to warm the planet dangerously. In effect, it has made the planet slightly darker. 

To compensate, we need some way to make the planet slightly lighter, to keep it in balance. In aggregate, the most reflective feature of the Earth is clouds, which reflect some of the sun’s light back into space. Relatively minuscule quantities of sulfur dioxide (SO2) in the stratosphere are extremely reflective, scattering some of the sun’s light before it hits the Earth, and in the process contributing to the atmospheric haze that gives sunsets their characteristic red color. 

Stepping beyond the scolds, the gatekeepers, the fatalists and the “nyet” men, we’re going to have to do something like this if we don’t want to ruin the prospects of humanity for 100 generations, so now is the time to think about it. 

You may have heard of stratospheric SO2 injection if you read “Ministry for the Future” by Kim Stanley Robinson or “Termination Shock” by Neal Stephenson, or followed what happened after the eruption of Mt Pinatubo in 1991, which lowered global temperatures by 0.5C for a year. While I’m looking forward to writing a side-by-side review of them both soon, in the real world, SO2 injection is a lot less dramatic than in either novel!

Stratospheric SO2 rains out of the atmosphere after a year or so, so unlike CO2 emissions it is relatively easy to control the dosing and the magnitude of the desired effect. SO2 injection can be ramped up or down as required on short timescales. As a rough rule of thumb, 1 g of stratospheric SO2 offsets the warming of 1 T of CO2 for 1 year. 

In fact, since the desulfurization of marine fuel over the last decade we’re seeing a substantial reduction in ground-level emission of SO2 and an increase in ocean heating in the North Atlantic and Pacific, potentially accounting for increased variability in rainfall on the eastern margins of both oceans. Ground level SO2 emission is regulated pollution, and for a good reason. It quickly falls out as sulfurous acid rain, harming the environment and not doing very much for cooling. SO2 stays in the stratosphere for much longer, so the relatively small quantities needed for cooling don’t cause concentrated acidic fallout as they would near, eg, a factory or refinery.

In “Termination Shock”, SO2 is delivered to the stratosphere using a giant gun in Texas (of course) while in “Ministry for the Future”, India unilaterally delivers it using a fleet of custom-built aircraft after 50 million people die in a wet bulb heat wave event. In fact, it’s much easier than this. 

The start up Make Sunsets is delivering trivial quantities of SO2 to the atmosphere using weather balloons. Trivial, in the sense that for a trivial quantity of money, any of their customers (including me) can effectively offset the warming caused by their unavoidable CO2 emissions for a lifetime. Make Sunsets is showing that it is both legal and effective to tweak the emission profile of a single person to avoid global heating.

But if we’re doing this at global scale, we’re going to have to think bigger. Filling the largest practical single-use balloon with a lifting mixture of 2/3 hydrogen and 1/3 SO2, plus a tiny pressure-activated bursting mechanism, could get costs as low as 35c/kg. 

1 kg of SO2 offsets 1000 T of CO2 for 1 year. With enhanced weathering, 1000 T of CO2 would cost at least $20k to deal with, and existing DAC+sequestration methods currently cost more like $1m. 35c! Now we’re talking. 

A balloon composed of 20 micron LLDPE with a diameter of 10 m could be inflated as it is unrolled in a continuous process similar to the Sealed Air packaging system https://www.youtube.com/watch?v=tG92ac2YC0k. A balloon 1000 m long would weigh 500 kg and be filled to a depth of 50 m, containing ~5 T of gasses, of which 95% (by weight) is SO2 and the remainder is H2 to keep it buoyant. 

As the balloon flies to 20 km or so, reducing atmospheric pressure causes steady inflation of the balloon until it is completely full. If the hydrogen mixture is burned to release the SO2, the LLDPE membrane will not return to the surface of the Earth.

Total cost is about $500 for the balloon, $300 for the H2, and $350 for the sulfur, which can be converted into SO2 by combustion. Adding 50% for overhead, we get $1700 per balloon or 35c/kg-SO2. One balloon offsets the warming of 350,000 Americans for one year. In other words, if just 1000 people in the US (and 10,000 worldwide) care enough to spend <$2000/year on launching the most giant, most awesome balloons to the stratosphere, we can offset CO2 heating effects until CO2 emissions and sequestration are under control. If they have a modest sailboat, they could even release the balloons without anyone even knowing about it. 

Indeed, if we want to offset the heat of 1 teraton of CO2, we need to launch 1 million tonnes of SO2 per year, costing just $350m/year. This is about 5% of the US’ annual production of sulfur. This costs less than 0.1% on an annual basis of the 40 year program to sequester a trillion tonnes of CO2. Just 200,000 of the 5 T balloons would be required annually, though in principle they could be made almost any size and released almost anywhere.