'Forcing' the issue

Make Sunsets' raison d'etre, namely to shift the narrative surrounding solar radiation management.

Hi good people,

There are many climate newsletters that cover the day-to-day and the news well. In 2024, I plan to focus more on the stories others seem more reluctant to explore. Whether that’s owing to complexity, how fraught the discourse can be, or another reason, well, I’m here to find out.

EVs or renewable energy are more straightforward stories. I get it. Companies know how to sell cars and electricity, and the lifecycle analyses that corroborate emissions reductions and other benefits of these technologies are clear. Still, even taken together, the power sector and transportation are far less than half of the climate ‘story.’ It’s time to open the aperture.

Today I’ll synthesize some thoughts on solar radiation management and interview notes from a conversation with Make Sunsets, the only company I know of that’s trying to ‘force’ the issue of whether and why we should test stratospheric aerosol injection to cool the planet.

The newsletter in <40 words: There’s a growing chorus of people calling for ‘global cooling.’ To date, most climate practicioners have avoided even talking about it. It’s time to have the conversation, even if we never ‘do’ cooling at significant scale.


Whenever people – and especially climate operators, investors, and other climate practitioners – aren’t willing to discuss something, I get interested. 

A decade or so ago, climate practitioners didn’t want to talk about carbon removal. Presumably, part of the reason for this was that it felt like admitting defeat. It felt like admitting that emissions reductions weren’t on pace to meaningfully slow global warming.

A decade on carbon removal is one of the bright spots in a broader climate tech environment that’s seen a downturn in funding and faces numerous other headwinds, to say nothing of the fact that global greenhouse gas emissions also still rise every year (see above). Some of this change likely owes to the IPCC, a key ‘missionary’ in climate, adding carbon removal to its list of key solutions. In 2023, players like the U.S. government also got behind carbon removal in a big way, and private sector organizations like Frontier, an advanced market commitment for carbon removal, have added additional support.

I’m glad this has happened. I’m glad that folks were willing to have the carbon removal conversation and that countless private and public sector actors have since built a plucky, ambitious carbon removal industry from scratch. There’s no way of knowing whether carbon removal technology will prove scalable to volumes that would make a real difference. But it’s worth trying.

This seachange in sentiment also begs a central question, though. What other potential climate solutions are we still loath to talk about? Why is that? Will they follow a similar trajectory from hush-hush to mainstream soon?

Radiative forcing 101 

Solar radiation management (SRM) refers to efforts to reduce the amount of solar radiation that reaches Earth. There are plenty of ways to accomplish this. More on that soon. SRM reminds me a bit of where carbon removal was pre-2020. The discourse surrounding it is fraught. Many people don't want to entertain the idea of ‘doing’ it at any scale, in any form.  

Before we get into that, it might help to understand what 'radiative forcing' is. Radiative forcing is a measure used in climate science to quantify the influence of various factors on the Earth's energy balance, which in turn yield changes in temperatures. Specifically, radiative forcing is defined as the change in energy flux (watts / square meter) at the top of the atmosphere. 

As likely isn't news to you, greenhouse gas concentrations drive radiative forcing and changes in the Earth's energy flux. Greenhouse gasses trap outgoing infrared radiation, preventing it from escaping into space and leading to a warming effect. The higher the concentration of various greenhouse gasses in the atmosphere, the more 'energy' (as heat) the Earth retains. This is an example of positive radiative forcing, which tends to warm the Earth's surface. 

As we noted earlier, all the effort in climate tech and behind the energy transition has yet to slow the rise of annual greenhouse gas emissions globally. As a result, some people are now interested in ways to induce negative radiative forcing to cool the planet. As a back-up plan.

In the same way that different greenhouse gasses like carbon dioxide, methane, and nitrous oxide – as well as other agents like water vapor – drive positive radiative forcing, a variety of factors can yield negative radiative forcing.  Aerosols, which are tiny particles or droplets in the atmosphere, are an example.

Aerosols can have a cooling effect by reflecting sunlight back into space or by inducing cloud formation. This isn't fringe science – it's well understood. For example, maritime shipping has historically been a significant source of sulfur dioxide emissions, an aerosol with a negative radiative forcing impact. 

In 2020, the International Maritime Organization instituted new regulations to cut sulfur dioxide emissions from shipping. Sulfur dioxide is an air pollutant that’s bad for human and planetary health. Sulfur dioxide emissions and other pollutants from fossil fuel combustion contribute to millions of excess / premature air pollution deaths globally every year. It makes sense the IMO wanted to ‘clean up’ shipping a bit. 

The regulations have been effective. Both at cutting sulfur dioxide emissions and, inadvertently, at warming the planet. 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 a great deal of warming. Human activity has driven ~1.2° C of global warming (as of 2024, potentially up to 1.5° C) since the start of the Industrial Revolution. Estimates for future warming often range between 2° and 3° C, an additional ~0.8° C to 1.8° C above what we’re already living through. 0.05° C warning is, like, 3-6% of that. That’s a lot! 

The IMO and others studied and knew this could be a tradeoff from cutting sulfur dioxide emissions from shipping. A 2018 study predicted that “policymakers face tradeoffs whereby achieving human health benefits may be associated with climate change consequences.” The IMO went ahead and made the call anyways. Still, now some scientists, as well as environmental activist groups, are calling for restitution of this lost ‘geoengineering.’ They want to put sulfur back into the shipping fuel.

Forcing the issue: Why Make Sunsets exists

There’s at least one company working on SRM, or more specifically, stratospheric aerosol injection (SAI), that’s trying to ‘force’ the issue. To get us to at least discuss SRM and SAI openly. Make Sunsets got a bad wrap earlier this year when they launched balloons into the stratosphere in Mexico and released small amounts of sulfur dioxide from them.

People, including myself at the time, called out the ‘cooling cowboys’ and lambasted them for doing this without much oversight. But as the year went on, Make Sunsets kept at it. I started to wonder why few people (there have been some), especially on the climate side, engaged the team with an open mind. 

Make Sunsets actively offers you the opportunity to purchase a ‘Cooling Credit,*’ which they claim offsets one ton of CO2-driven warming for one year. If you visit their site and buy a credit, they’ll inject sulfur dioxide into the atmosphere via weather balloon. Simple as that. 

One of Make Sunsets’ weather balloons injecting sulfur dioxide into the atmosphere (courtesy of Make Sunsets)

I wanted to understand why they’re approaching SRM and SAI this way. Here’s a lightly edited transcription of a recent discussion between myself and Andrew Song of Make Sunsets:

Nick: Andrew, thank you for taking the time. I’d love to understand why Make Sunsets exists.

Andrew: At the most basic level, we think more people should know about solar radiation management. Based on how we've seen the market react, most people don't know that this thing is even a stop-gap solution. Most people think, “OK, we just stop burning fossil fuels. And everything will be OK.” Unfortunately, that's not true. 

Hence, you already see a lot more momentum for carbon removal. Meanwhile, SRM and stratospheric aerosol injection (‘SAI’) have typically been framed as bad. We inherited something with baggage on it. So we weren't surprised that we got negative reactions, especially since we’re two Silicon Valley guys. But we’ve leaned into it. That's who we are. We know how to get stuff done. Our goal is to get more people to understand what SAI is and why we might need it.

We're trying to force the issue a bit by offering Cooling Credits directly to consumers. As a form of protest. To say, “We are slightly cooling the Earth.” It's not a lot. In 2023, we've done the equivalent of removing 1,200 cars (5,596 ton-years) from the road for a year. But for two guys with some balloons, that’s not bad. It’s easier than actually stopping people from driving. We’re now on track to remove ~2,173 cars (10,000 ton-years) per year based on customers’ orders.

Nick: Understood. And to be sure, that’s not enduring, right? Like, it lasts for about a year?

Andrew: It's just a band-aid. It's a tourniquet. 

Nick: Let’s talk about the reception. 2023 was probably a strange year for you.

Andrew: The reception obviously has been mixed, often negative. But we need to start shifting the narrative towards asking the question of resource allocation. I think we should allocate less than 1% of climate tech funding to research some kind of solar radiation management. I.e., our dream is still a rounding error in terms of the whole landscape. Right now, the number is zero. 

Nick: What does the ideal narrative evolution for SRM & SAI look like for you?

Andrew: We want to flip the narrative from “We need to do more lab research” to “Hey, we can start deploying on a small scale and do research in the field, with field-level deployments.” We’re doing this slowly, right? We're not going to be crazy and say, we're going to inject a billion tons of this into the atmosphere tomorrow. We're not suicidal here. We live on the same planet as everyone else. 

The other problem is people see this as a doomsday scenario. The general association for the public is, “Oh, we're not going to do this until we're really out of hope. That, fundamentally, needs to be shifted to “OK, we may need this at a meaningful scale someday.” So we should test it now.

Nick: Yeah, otherwise, someday, maybe you do need to go from zero to one billion tons overnight. With zero idea of what might happen or how to do it. 

Andrew: Precisely.

Nick: So, in the short term, you want to do more deployments, raise awareness, shift our collective frames of reference with respect to SRM and SAI, etc… What’s the long-term goal?

Andrew: Yeah, absolutely. At the end of the day, I want this company to shut down as fast as possible, right? I don't want this to be a long-term thing where we're doing this for generations. That’s one of the reasons why we called it Make Sunsets. Because we want to sunset Make Sunsets some day. This shouldn't be a long-term thing. We have to decarbonize. We have to scale up carbon removal. But we're so far behind. I have two kids. And I am deeply, deeply afraid for their futures. We have got to do something, and nothing is happening fast enough.

Make Sunsets’ projections of the role SAI could play in bending the warming curve

Nick: How about sulfur dioxide in 'particular.' It’s obviously problematic outside of its cooling impact.

Andrew: We’re particle agnostic. It doesn't have to be sulfur dioxide, but it’s the most well-researched and is well-demonstrated as working as intended. 

It’s OK to be scared! 

In talking with Andrew, I found his propositions and Make Sunsets’ overall angle reasonable. Edgy, sure. But hardly beyond the pale. Absent much momentum elsewhere behind the idea of testing and researching SAI, they've taken it upon themselves to accelerate the field a bit. What they're doing doesn't have much more actual impact on the climate – whether positive or negative – than most small or medium-sized businesses.

So why are people in climate so reticent to entertain their ideas, let alone their small-scale SAI test? If anything, perhaps we should be looking to help them as much as possible, especially on the measurement and data-collection front. 

The view from the sulfur dioxide-distributing weather balloons (courtesy of Make Sunsets).

Honestly, I think it's because we're afraid. For one, we're in 'threat' all the time, already. Like Andrew, many of us likely spend time imagining – whether as part of our work or because we're inundated with the data – what different global warming scenarios portend for the future of the Earth, as well as for our own futures. And our neighbors'. And our families'. 

That said, I'd also posit that some of our fear stems in part from knowing, at some level, that if we start testing SRM, whether via SAI or any other approach, we might want to keep doing it. Maybe we'll love it. Like opening Pandora's box, once we test global cooling, maybe we'll never stop.

What I'm driving at here reminds me a bit of what's happened with the weight loss drug Ozempic recently. Like SAI, Ozempic only works if you keep taking it. And it puts a lot of people in a tizzy. "People should take responsibility for their own health!" "This is cheating!" "The obese should suffer!" (they don't say this last part out loud). Again, the discourse is fraught.

Is the best case scenario vis a vis human health that we improve the quality of food, expand access to it, re-envision all of our societal systems so fewer people are obese and / or diabetic and that folks exercise more, eat better, and in some cases, take more personal responsibility? Of course! 

But now that there's a nigh-miraculous weight loss drug that helps people lose weight very quickly when their health would otherwise actively suffer… can we deny them that? Can we ever close the proverbial Pandora's box? Probably not. Many people are taking (and raving about) Ozempic. Odds are you know someone who is, even if they haven't told you. 

Of course, there are many reasons to be wary of SRM and SAI:

  1. Complexity: As I often reiterate, the Earth’s climate is an incredibly complex system. No one knows what the second and third-order impacts of doing SRM at scale would be. Many of them could be harmful.

  2. Other harms: I understand why Make Sunsets is ‘particle agnostic’ for now, and why they’re working with sulfur dioxide given it’s track record. Still, as a known air pollutant that’s deleterious to human health, I’d personally like to see more energy put explicitly behind finding effective and otherwise inert particles for SAI. Perhaps it should be salt.

  3. Moral hazard: Dramatic emissions reductions are always the most preferred outcome. SRM or SAI isn’t a cure-all; it’s a palliative. Like Ozempic, it doesn’t solve any underlying issue. It treats the symptom.

Suffice it to say, I have no idea what would happen if someone launched a significantly sized SRM deployment tomorrow. I don’t think anyone does. Andrew and Make Sunsets don’t claim to, either. That’s the point. If your resistance to SRM is based on the argument that “We don’t know what the complex system-level impact will be,” you’re right. But shouldn’t that encourage us to test various approaches to SRM in discreet, confined, measurable ways?

The alternative is that some actor inevitably starts ‘doing’ global cooling at scale because they think it will benefit them. They’ll make that decision in a vacuum. That is unless we stop avoiding this conversation altogether and give global cooling some of the treatment, attention, and resource allocation that other adaptive climate technologies have enjoyed.

The net-net (tl;dr)

At the end of the day, most people I meet who work in climate are earnest, thoughtful, and well-intentioned. Andrew at Make Sunsets strikes me that way, too. Perhaps I’m overcredulous. Either way, most people working in climate – unlike some other industries – don’t want to play God.

The problem is humanity already does. Already has been. There is little land on Earth that isn’t impacted by human activities. There is little terrestrial land that isn’t under human management in some capacity. As Emma Marris writes in her book Wild Souls:

To make good environmental decisions, we must stop focusing on trying to remove or undo human influence, on turning back time or freezing the non-human world in amber. We must instead acknowledge the extent to which we have influenced our current world and take some responsibility for its future trajectory…

Emma Marris

It’s probably time to get over the idea that we can reverse course on the God-mode thing. Yes, the best case scenario, long-term, is that we learn to live in holistic harmony with the Earth again. In the interim, however, let’s admit we might need some conscientious global cooling someday.

Lemme know thoughts, especially if you vehemently disagree!

– Nick

*Just so it’s abundantly clear, I am not getting paid by Make Sunsets for anything

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