Humanity is already doing one thing that is provably and materially reducing global warming. We have successfully cooled the planet by ~0.5℃ over the past 20 years by emitting sulfur dioxide into the atmosphere. If it weren't for this, we would have already surpassed 1.5℃ of warming.
What is sulfur dioxide? Soot. Put another way, the soot emitted by coal-fired power plants and diesel engines has already bought us 20-30 years of extra time.
Coal plants also emit tons of carbon dioxide, of course. And sulfur dioxide is really nasty in other ways: it causes respiratory problems and acid rain. Obviously burning more coal is not the solution to climate change.
But, ironically, an unintended consequence of taking lots of coal power plants offline is that we'll actually reduce the amount of sulfur dioxide we're putting into the atmosphere, causing the planet to warm even faster.
When I saw the chart above, I was shocked. I previously thought that atmospheric aerosols - one type of "geoengineering" - were both unproven and highly risky. That's not the case — we have concrete evidence that aerosols successfully cool the earth without causing calamitous side effects. Past volcanic eruptions provide further real-world evidence.
What would it require to scale this up and reverse warming by 1℃ or more, taking us back to 1900-era levels? And why aren't we already doing more to use aerosols to mitigate global warming, at least as a short-term measure?
The science is clear: stratospheric aerosol injection (SAI) is effective, feasible, and not too costly. But there are no advocacy groups working to implement SAI. We propose a new group that makes reversing global warming a reality.
What it takes
"To counter the man-made warming projected for the next 50 years, the authors calculate it would be necessary to release about 4 million tonnes of sulphuric acid into the atmosphere each year. And the most efficient way to do this would be by tapping into large-scale air circulations.
Air rises at the tropics, and from there circulates around the world in great currents. This makes it the ideal spot for releasing particulate matter. But how high up the materials are released is also important – higher usually means better dispersal, but the cost of technology goes up with altitude too. Based on modelling, the authors suggest that between 18-25 kilometres up is probably the best compromise between cost and efficiency."
From CarbonBrief
Who: A private company or nonprofit organization; a national government; or an international body.
Technical: Appears easily solved. We know how to fly planes and drop things out of them. A custom-built plane would be significantly more efficient.
Capital: The total cost, above, is estimated at $3B/year. I think this is worth more investigation - but by any comparison, single-digit billions is a bargain. Financing could come from donations, private capital, and/or governments.
Regulatory Blocks: Unregulated today. No explicit international block / enforcement. National governments might try to block or interfere.
Governance: TBD; propose international advisory/governance body with all stakeholders that has little/no actual enforcement ability
Liability: Difficult to assign; could be a major sticking point; ideally would buy insurance policies or convince reinsurers to contribute coverage
Public Opinion: This is the hardest one, I think. Most comments on Reddit reference "Snowpiercer" or "The Matrix" (in which SAI led to apocalypse). You need to win the battle for public opinion early for this to have a chance.
Guardrails: All data about the project should be published publicly, so that the global scientific community can monitor the effects.
Goals
- Positively influence public opinion
- Convene a community (virtually and in-person) to promote the cause
- Lobby for federal research funding
- Recruit a team to execute on SAI deployment.
Big-picture, I imagine a stepwise series of goals:
(1) Safely add enough stratospheric aerosols to replace the soot that would have been emitted by coal-fired power plants going offline and big diesel engines converting to electric.
(2) Safely add enough stratospheric aerosols to reduce warming by 0.5℃, roughly the same effect as 2000-2019 sulfur dioxide emissions.
(3) Safely add enough stratospheric aerosols to reduce warming by an additional 1℃, roughly 3x more aerosol impact than has already occurred in the past 20 years.
Risks and Perceived Risks
- This "magic bullet" makes people stop decarbonizing (moral hazard risk)
- Stratospheric ozone loss
- Regional changes in precipitation
- Decreased sunlight —> decreased crop yields
- Heating of the lower tropical stratosphere
- Sulfates falling out of the air
- Unknown risks
- Liability
Why isn't anyone talking about this?
Fear of side effects. I was very sympathetic to this argument until I learned that we are already pumping a ton of aerosols into the atmosphere from coal power plants with no apparent side effects from the stuff that makes it into the upper atmosphere. It seems like global warming is the problem here, not sulfur dioxide in the stratosphere.
Experts manipulating public opinion to make sure we achieve the "right" solutions even at the expense of intellectual honesty in public statements. For the conspiracy-minded among us, this explanation finds a fair amount of anecdotal evidence. The Economist says: "a lot of climate scientists and others believe that talk of solar geoengineering is a siren call that could lure policymakers away from the course of greenhouse-gas cuts" — i.e., it's an unproven shortcut that could offer an easy way out for the fossil fuel industry and politicians. I think the fear is something like: ExxonMobil seized on geoengineering, puts all their weight behind it, and then claims that CO2 emissions are no longer really a problem, so we can keep burning fossil fuels.
If this line of thinking actually influenced the IPCC's report, I would lose a lot of faith in the ability of scientists to dictate public policy.
A Swiss-led proposal that suggested an expert assessment on geoengineering and its governance, made to the Fourth Session of the UN Environment Assembly (UNEA) in March 2019, failed, unsurprisingly. Until now, most governments, civil society organizations, and climate researchers have avoided an in-depth conversation on SRM. The reasons for reluctance differ substantially. Most climate policy advocates and scientists fear that debating governance and normalizing SRM as part of the policy mix could obstruct mitigation efforts by creating the misleading perception that injecting aerosols could be a substitute for reducing emissions. Governments fundamentally opposed to massive emissions reductions either do not want to debate SRM because it would mean acknowledging that climate change is a serious threat, or they avoid a governance conversation because they do not want to bind their hands prematurely.
What Scientists Are Saying
Though the study of stratospheric aerosol injection (SAI) has evolved from its status as a “former pariah” (Kintisch, 2010) to the periphery of scholarly respectability, views on the proper governance of SAI research remain tainted by early misunderstandings of this prospective climate intervention. Prior to Crutzen’s 2006 clarion call (Crutzen, 2006), the geoengineering field was generally considered taboo due to concerns that pursuing it would hamper emissions reductions efforts. While the annual output of scholarly papers has since multiplied from a trickle to a steady stream, views on SAI research governance have often run ahead of a detailed understanding of the technology and have failed to incorporate new research in the field. As a result, restrictive SAI research governance regimes are out-of-date, limiting funding for the field in general and diverting attention away from research into reservations which are well supported.
And past volcanic eruptions also provide concrete evidence:
When Mount Pinatubo erupted in the Philippines in 1991, it injected an estimated 20 million tonnes of sulfur dioxide into the stratosphere — the atmospheric layer that stretches from about 10 to 50 kilometres above Earth's surface. The eruption created a haze of sulfate particles that cooled the planet by around 0.5 °C. For about 18 months, Earth’s average temperature returned to what it was before the arrival of the steam engine. (Nature)
Conclusion
To be clear, stratospheric aerosol injection is not a panacea and it doesn't solve climate change. Too much CO2 in the atmosphere causes lots of other problems, like ocean acidification. But cooling the planet back to where it was 20 or 100 years ago would buy us time to decarbonize the economy.
I circulated this document to a few friends, and the overwhelming feedback was that this concept will be quickly politicized. The decision to pump aerosols into the stratosphere is no longer a question of science; it's a question of politics. Determining how to build both an elite coalition and a popular movement behind this work; when to ask permission, and when to ask forgiveness; and how to engage with state actors are the complex considerations ahead.
Now is the time to act.
Trenbirth diagram
