We Have the Technology. Airplanes Could Spray Particles into the Atmosphere to Battle Climate Change. But Should We?

If climate change models are correct, humanity is working itself—and dragging the rest of life on Earth with it—into a corner. Scientific pleas to control emissions and battle climate change are starting to have some effect, but not enough. So now we have some tough decisions looming.

If you haven’t heard the terms “solar geoengineering” and “stratospheric aerosol injection”, you should probably get used to them. They represent a scientifically and technologically realistic plan for controlling climate change when all other governance and economic models can’t get it done. The idea has been around for a while, but deemed too expensive in the past.

Now a new research paper in the Environmental Research Letters analyzes what’s needed to use aircraft to spray sulfates into the stratosphere to cool the climate. The two authors are Wake Smith from Yale, and Gernot Wagner from Harvard. And once you get past your shock at the idea, if you feel any that is, the paper presents some well-thought out parameters for the whole enterprise.

“…a hypothetical deployment program starting 15 years from now, … would be technically possible strictly from an engineering perspective.” – Dr. Gernot Wagner, co-Director of Harvard’s Solar Geoengineering Research Program.

First of all, let’s dispel a couple myths. This has nothing to do with dimming the Sun, chemtrails, or mind control. Nothing humanity can do could dim the Sun. Chemtrails are ignorant fever dreams, and mind control is just…whatever. Both Smith and Wagner are serious people, and they deserve to be paid attention to.

Wagner is a research associate and lecturer at Harvard, co-Director of Harvard’s Solar Geoengineering Research Program, and author of the book “Climate Shock.” Smith has an MBA and a career in commercial aviation and finance behind him, and writes on the logistics and costs of solar radiation management and geo engineering. These two are well-equipped to conduct this research.

To Battle Climate Change

What are we really talking about here?

Let’s imagine a world where scientists have discovered that our emissions are heating up the globe and that people are too reluctant to make changes to their emissions. Our governance methods and economic methods aren’t getting the job done. You don’t really have to imagine it because that’s basically where we are.

In that situation, scientists are bound to try and come up with technological solutions while still hoping that politics and economics eventually get it right. And that leads us to these two ideas: solar geoengineering, and stratospheric aerosol injection (SAI).

When Mt. Pinatubo erupted in the Philippines in 1991, it lofted 20 million tonnes of SO2 into the atmosphere. Global temperatures dropped 0.5 Celsius in the next couple years. Image Credit: By U.S. Geological Survey Photograph taken by Richard P. Hoblitt. – Archived source link, Public Domain,

Solar Geoengineering and Stratospheric Aerosol Injection

Solar geoengineering is also called “solar radiation management” (SRM). The idea is to make the atmosphere reflect some more of the Sun’s radiation back into space. SRM seeks to increase Earth’s albedo, or reflectivity.

Some SRM methods propose protecting and restoring Earth’s naturally reflective surfaces, like sea ice, snow, and glaciers. These would involve massive engineering projects, and would be expensive. There’s also no guarantee they’ll work.

The new study released by Smith and Wagner focuses on another much talked-about SRM: stratospheric aerosol injection (SAI).

Stratospheric Aerosol Injection is centered around the idea of injecting sulphates into the atmosphere, about 20 kilometers high, in the stratosphere. It’s reasoned that SAI could counter most climatic changes, be relatively inexpensive, could take effect quickly, and it would be reversible in its direct climatic effects. Sounds pretty good, but there’ve been some drawbacks.

Early ideas in SAI proposed using artillery, existing aircraft, or balloons to inject sulphates, or their precursors, into the stratosphere. But each one of these has its own problems. The new research focuses on developing new aircraft to deliver the sulphates into the stratosphere.

Using Aircraft to Battle Climate Change

Flying 20 kilometers high into the stratosphere is not an easy thing to do. It’s not something that we’d need to do only a few times, so that we could just use expensive rockets and eat the cost. A successful SAI project would be a multi-year project involving a fleet of specialized aircraft stationed at multiple bases around the world.

In their study, Smith and Wagner analyze the costs and development timelines for a fleet of aircraft that could halve the increase in anthropogenic radiative forcing. The fleet would start small and grow over time, and would begin operations in 15 years. They looked at existing aircraft and concluded that none of them are practical. The 15 years allows ample time to develop the required aircraft and get it tested and licensed.

The study looked at existing aircraft like NASA’s Global Hawk. It can carry large payloads to high altitudes for 24 hours. But the Global Hawk, like all other existing aircraft, is not capable of meeting SAIL’s requirements. Image Credit: NASA Photo / Tom MIller

“No existing aircraft has the combination of altitude and payload capabilities required.” – Wake Smith, study co-author.

Sustained flight at 20 kms altitude requires specialized aircraft. The fuselage and wings need to be different than anything we have now, and the engines would have to be specialized. To conduct their study, they consulted several aircraft manufacturers, engine manufacturers, and other companies including Airbus, Atlas Air, Boeing, Bombardier, GE Engines, Gulfstream, Lockheed Martin, NASA, Near Space Corporation, Northrup Grumman, Rolls Royce Engines, and others.

They call their proposed aircraft SAIL: Stratospheric Aerosol Injection Lofter.

The two researchers are clear about their motives. They’re not making any judgement about using SAIL to battle climate change. They just wanted to flesh out the idea and see what a realistic SAI program might look like, and what the timeline and effectiveness might be.

One of the study’s authors, Dr Gernot Wagner, said, “While we don’t make any judgement about the desirability of SAI, we do show that a hypothetical deployment program starting 15 years from now, while both highly uncertain and ambitious, would be technically possible strictly from an engineering perspective. It would also be remarkably inexpensive, at an average of around $2 to 2.5 billion per year over the first 15 years.”

Other studies have concluded that existing aircraft could be modified to battle climate change, but the pair of scientists found that that isn’t the case. In a press release, Wake Smith said, “I became intrigued by the engineering questions around SAI and the many studies that purport to show that modified existing planes could do the job. Turns out that is not so. It would indeed take an entirely new plane design to do SAI under reasonable albeit entirely hypothetical parameters. No existing aircraft has the combination of altitude and payload capabilities required.”

NASA’s WB-57 is another high-altitude research airplane that the study authors deemed unsuitable for SAIL. Image: NASA/Johnson Space Center.

This new SAIL aircraft would need to carry a 25 ton payload to 20 km altitude and sustain flight there. So what would this new aircraft look like?

The aircraft itself would need larger wings, double the size of current aircraft, and double the thrust too. “We developed the specifications for SAIL with direct input from several aerospace and engine companies. It’s equivalent in weight to a large narrow body passenger aircraft. But to sustain level flight at 20 kms, it needs roughly double the wing area of an equivalently sized airliner, and double the thrust, with four engines instead of two,” said Smith.

According to the study, SAIL’s fuselage would seem stubby and narrow, sized to accommodate a “heavy but dense mass of molten sulfur, rather than the large volume of space and air required for passenger comfort. SAIL would therefore have considerably wider wingspan than length.”

The engines would be modified versions of existing engines called “low-bypass.” Though these engines exist, they aren’t used much because they’re not fuel efficient. They out-perform other engines at these extreme altitudes though.

The two researchers propose starting with 8 aircraft flying about 4000 flights per year, and increasing by 4000 each year as more aircraft are brought online. 15 years after starting operations, the fleet would number almost 1000. They would fly from an array of bases around the globe, at latitudes of 15 and 30 degrees north and south of the equator. The goal would be to inject ~0.1 Mt of S in year one, increasing at a rate of ~0.1 Mt yr linearly thereafter.

Detailed table of SAIL’s flight activity. Image: Smith and Wagner, 2018.

The Cost of Using SAIL to Battle Climate Change

Smith and Wagner conclude that their SAIL program would not be that expensive. Their analysis shows that the program would cost about $2.25 billion per year over the first 15 years of deployment. This includes the design, testing, and manufacture of a new aircraft type, the modification of existing engines, and operational costs. That’s not much compared to the $240 billion the US economy has lost in the last decade because of climate change.

In a press release, Dr Wagner said, “Given the potential benefits of halving average projected increases in radiative forcing from a particular date onward, these numbers invoke the ‘incredible economics’ of solar geoengineering. Dozens of countries could fund such a program, and the required technology is not particularly exotic.”

The ultimate goal of a SAIL program would be to buy us time. It would not solve our emission problem. SAIL is only a temporary mitigation method. It won’t lower CO2 in the atmosphere, and it won’t stop the other effects of climate change like ocean acidification. It merely reflects some sunlight back into space.

Should We Use SAIL to Battle Climate Change?

Here’s where it gets tricky. Assuming that Wagner and Smith are correct, should we use SAIL to battle climate change?

There are some fears around the idea of technological climate modification. Some organizations fear that developing this kind of technology would allow a rogue regime to do it in secret. The authors dispel this fear, saying it would be impossible to hide this level of flight activity involving partner countries around the globe.

Smith said, “No global SAI program of the scale and nature discussed here could reasonably expect to maintain secrecy. Even our hypothesized Year one deployment program entails 4000 flights at unusually high altitudes by airliner-sized aircraft in multiple flight corridors in both hemispheres. This is far too much aviation activity to remain undetected, and once detected, such a program could be deterred.”

Some climate change activists are wary of SAI because they think it will create apathy towards reducing emission. They say we would become reliant on it, and would create and excuse to not lowering our GHG emissions. Over at Geoengineering Monitor you can find these concerns explained and expanded on. They’re concerned that large companies involved in fossil fuel extraction would fund geoengineering projects which would allow them to continue business as usual.

The Geoengineering Monitor’s “HOME Manifesto.” It’s a little over-dramatic, but it gets their point across. Image: Geoengineering Monitor.

In any case, using high-altitude aircraft to battle climate change is all for discussion purposes at this point. There’s a body called the Convention on Biological Diversity (CBD). Under the CBD, 193 countries signed a moratorium on geoengineering and agreed that there needs to be a global mechanism in place to govern it.

But the SAIL program is a framework that wouldn’t start operations until 15 years from now. Is 15 years long enough to develop a global mechanism for a geoengineering plan to battle climate change? One would hope so.

We’re backing ourselves into a corner. The longer we wait to take meaningful action on emissions, the more draconian our measures will need to be. Our fears, both founded and unfounded, will need to be overcome if we want to use SAIL to fight the effects of climate change.

We got ourselves into this situation and we’ll have to get ourselves out of it.


Evan Gough

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