19 October 2023 |

Is it time to dim the sun?


At the beginning of this year, there weren’t many people sticking their necks out for geoengineering. At least not the tech that most folks now think of when the word ‘geoengineering’ comes up, namely solar radiation management (‘SRM’). 

What is SRM? It’s a large category, though at this point, most SRM proponents propose putting particles into the air to block sunlight; giant tethered sun shields haven’t yet come back into vogue. As to what particles do the best job at blocking sunlight without causing too much downstream damage elsewhere, well, that’s a topic of debate too. 

Before that debate can happen though, a first debate – on whether we should even talk about SRM at all – needed to shift in tenor. In 2021, SRM as a category was conspicuously dropped from an IPCC report. Other scientists loudly decried it and the ‘cascading impacts’ it could have. Almost no one was discussing it, especially not from a venture-backed startup perspective.

Fast forward to the current moment in 2023, and geoengineering is back on the table, perhaps not yet among the IPCC, but certainly with many prominent voices in climate.  

  • Investors: At Climate Tech Week in New York, Chris Sacca, founder of Lowercarbon Capital, stated that he’s definitely interested in spraying salt into the Earth’s atmosphere to reflect sunlight and that SRM may become entirely necessary (paywall). 
  • Policymakers: The White House Office of Science and Technology Policy is working on a five-year research study that will analyze different techniques to modify the amount of sunlight that reaches the Earth to ameliorate global warming.
  • Scientists: Prominent scientists, such as Ken Caldeira, are ‘warming’ up to the idea, too, as covered in this piece in Scientific American.

This is narrative formation in real-time. Two years ago, the common knowledge was that SRM was out. Now, it’s back in.

There are two questions I’ll address next. 

  1. How does this narrative shift happen? 
  2. Is it good?
Is it time to dim the sun? Some say so… (Shutterstock)

How narrative shift happens

Narrative shifts don’t always require a massive tug of war. Sometimes, they’re occasioned by a series of subtle nudges.

Many things need to happen once a narrative shift is underway to reinforce it. My writing this newsletter is part of that process. But planting the seeds of narrative shift is often done – and highly intentionally, I might add – with just a few trial balloons.

Here, I’m speaking both literally and figuratively of trial balloons.

Earlier this year, Make Sunsets, an SRM company, launched literal trial balloons into the atmosphere to release small amounts of sulfur dioxide to achieve a solar radiation-forcing effect. The experiment was much maligned as it flew against regulation, but arguably more importantly, it flew against the common knowledge around SRM at the time, which was that we shouldn’t even think about it. 

Figurative trial balloons refer to the process by which what I’ll refer to as ‘missionaries’ – i.e., people who hold sway – test ideas, often via the media. Mind you, these are not always well-intentioned or ‘good’ people, but let’s put that aside for now.

People who analyze Federal Reserve policy talk about figurative trial balloons a lot. Federal Reserve officials are constantly making speeches, and they use language, both in the ideas and potential policies they describe and the way they describe them, as a very real lever in their toolkit. If Jerome Powell wants to influence interest rates, all he has to do is suggest that the Federal Reserve is in the early stages of considering shifting the U.S.’s long-term inflation target from 2% to 2.5%. 

That’s how I see the three bullets listed in the first section of this email that enumerated various influential voices coming out in favor of, or even just considering, SRM. Those are all trial balloons that plant seeds, test reactions, and see whether the shift might have legs if pushed harder.

In this case, I think the narrative shift is pretty sticky. Of course, the litany of negative impacts we’re already seeing worldwide from global warming have helped bring SRM back into the spotlight, or sunlight, as it were. But the combination of SRM trial balloons (again, both literally and figuratively) and missionaries coming out in support (even if tepid) of SRM has made a big difference.

Now, publications like mine will write about this narrative shift and SRM. And that does the heavy lifting of concretizing the change in common knowledge

Importantly, you don’t have to accept this as a reader. You should make up your own mind on where you stand. But, for better or for worse, you can’t really stem the tide of the shift once it’s underway.

Is it good?

The allure of SRM is that it’s one way to shift the climate rapidly, too, not just the narrative. And it wouldn’t require as massive a tug of war as, say, building many more nuclear power plants.

Climate change is moving fast. The solutions and adaptive measures we’re comfortable with will continue to shift similarly quickly, as will the conversations surrounding them.

It’s silly that we get in a twist when it comes to SRM—we geoengineer every day, both as a society and as individuals. When you get on a plane, as I will tomorrow, you’re stepping into a geoengineering machine. When you turn on the lights in your house, that process is made possible by geoengineering machines. 

All our devices and all our collective efforts have helped emit 1.5 trillion tons of CO2 into the atmosphere and continue to raise the bar every day. Excellent work; that’s an unfathomable amount.

At the bare minimum, I think it’s good if there are studies on what the potential of SRM is. Of course, these studies should try their best to evaluate all other implications SRM would have. Admittedly, the list of those implications is long, ranging from air pollution’s impact on human health to the impact of less solar radiation on agriculture and beyond. That’s part of why SRM gets everyone so riled up – understanding all the downstream effects would be incredibly hard, nigh impossible. 

But the truth is we never really know how tinkering with incredibly complex systems, like the Earth’s climate, will play out. And we’ve already done SRM in the past with great success. As shown below, sulfur dioxide emissions, which ships used to spew, can significantly decelerate global warming. 

On this beat, a recent analysis by Carbon Brief estimated: 

…the likely side-effect of the 2020 regulations to cut air pollution from shipping is to increase global temperatures by around 0.05C by 2050.

That might not sound like very much, but it’s actually a great deal of warming. The regulations in question are European Union regulations to cut SO2 emissions from shipping, not global ones. Those regulations were inadvertently, yet effectively, anti-SRM. Which should to hit home that: 

  • Even our well-intentioned efforts don’t always work out the way we planned them 
  • One group’s SRM policy decisions can yield a lot of global warming or global cooling impact. SRM is a high-leverage solution, whether you like it or not.

My main point is this: It would be imprudent not to evaluate SRM as a part of our arsenal to adapt to climate change. Especially as our modeling capabilities improve alongside breakthroughs in compute and AI. 

There aren’t all that many other options. There’s carbon removal, which, at scale, could help reverse the meteoric rise in atmospheric CO2 concentrations. That’s not the same as reversing climate change, but it could help.

But even carbon removal, while ostensibly much safer, is incredibly divisive. And it’s much, much more expensive. As I wrote back in February (lightly edited with some new additions):

By some estimates, SRM could drive 1°C of global cooling for as little as $10B

In contrast, it costs $500+ to remove one tonne of CO2 from the atmosphere with currently available direct air capture methods. To remove 1 billion tonnes – still only one week’s worth of global greenhouse gas emissions – you’re looking at a tab totaling $500B. And removing even 1 billion tonnes of carbon from the atmosphere wouldn’t drive anywhere close to 1°C of global cooling.

That’s an oversimplification, sure, but the order of magnitude is important.

P.S. I’d be remiss if I didn’t mention that using sulfur dioxide specifically may well not be the right solution. It is an air pollutant that already impacts human health significantly

But maybe other particles, whether sea salt or other substances or chemical entrepreneurs and researchers will devise, may be more innocuous and just as effective. Shouldn’t we find out?

The net-net

To close with a thought experiment, imagine if Tuvalu, an island nation in the Pacific that’s facing an existential threat in the form of sea level rise, launched a large-scale SRM deployment tomorrow. Would you blame them? To weave in a favorite Pete Seeger song, “Whose side [would you] be on?”
I like this thought experiment because everyone in climate would freak out. But at the same time, with the experiment underway, they would all also be very keenly interested in tracking its results.