002 | The Offset Problem: Why Scientists Say Cooling Credits Don't Add Up
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The Offset Problem: Why Scientists Say Cooling Credits Don't Add Up
📘 Summary of: "'Cooling Credits' Are Not a Viable Climate Solution" from Climatic Change Volume 176 - 2023 by Michael Diamond, Kelly Wanser and Olivier Boucher.
A new kind of carbon credit emerges
Private companies have started selling small amounts of "cooling credits,” or claims to have offset carbon emissions, not by removing CO2 from the atmosphere, but by reflecting extra sunlight back to space by adding tiny particles called aerosols to slightly brighten the atmosphere and clouds. Instead of funding carbon offsets like tree planting, buyers pay to offset a quantity of greenhouse gas warming by funding emission of aerosols, for example sulfur dioxide released from balloons, to reflect a small amount of sunlight.
A 2023 paper analyzed the science of cooling credits, finding that several fundamental differences make aerosol cooling a poor substitute for reducing greenhouse gas warming:
The climate effects of greenhouse gases, which are long-lived and diffuse, and aerosols, which are short-lived and localized, are not equivalent, creating a fundamental mismatch for carbon markets.
Aerosol emissions also produce side effects that must be accounted for, and require central coordination to minimize, making a market of independent actors emitting aerosols for profit a dangerous approach.
Because aerosol effects vary strongly with location and conditions, unlike the effects of well-mixed gases like carbon dioxide, cooling effects associated with specific emissions into the atmosphere vary, and are very hard, and perhaps impossible, to anticipate and quantify with current technology.
Since 2023, public and private investment in and policy consideration of approaches to reflecting sunlight to cool climate have grown, increasing the importance of understanding their evidence basis.
The science isn't ready
Michael Diamond from Florida State University, along with Olivier Boucher and Kelly Wanser, examined the science of cooling credits and found the evidence base severely lacking. Scientists don't fully understand how aerosols interact with clouds, how long cooling effects last, or how they vary across regions and seasons. The observing systems needed to verify that interventions work as intended don't exist yet and would require massive investments in balloon measurements, aircraft observations and satellite technology.
Even the most basic question –how much cooling would result from a given amount of aerosol injection– remains largely unanswered. Without this fundamental knowledge, claims about offsetting specific amounts of greenhouse gas warming lack a basis.
Unlike CO2, aerosol effects vary in time and space
The researchers identified an even more fundamental problem: greenhouse gases and aerosols affect the atmospheric system in different ways, making direct comparisons nearly impossible regardless of scientific uncertainty.
Greenhouse gases like CO2 stay in the atmosphere for decades to centuries, causing warming that builds up over time. The effects are persistent, cumulative and relatively uniform across the globe.
Aerosols provide only temporary cooling that lasts days to a year or two, depending on where they're dispersed.
The temporal mismatch creates obvious problems. A company could purchase cooling credits to offset emissions from a coal plant that will warm the planet for centuries, but the corresponding aerosol cooling might dissipate within months. The effects simply don't match up in duration or persistence.
Aerosol effects are also localized, particularly for proposals to modify clouds in the lower atmosphere, where both sunlight reflection and side effects like changing precipitation patterns vary depending on the location of the aerosols, weather and other factors.
Side effects are serious, uncertain and hard to quantify
Greenhouse gases and aerosols create entirely different environmental risks. Rising CO2 levels acidify oceans, alter precipitation patterns and shift growing seasons. Aerosol interventions might temporarily reduce global temperatures, but they don't address ocean acidification and could create their own regional weather disruptions and seasonal changes. In the stratosphere aerosols may affect the world’s protective ozone layer and wavelengths of light reaching the ground.
The researchers argue that treating these different environmental impacts as equivalent oversimplifies complex trade-offs. It's not just about temperature effects; it's about impacts on all parts of the Earth system, and the need to maximize safety and minimize harm.
The monitoring challenge
Even if scientific uncertainties were resolved, verifying that aerosol interventions produce claimed cooling effects would require unprecedented global monitoring capabilities. Current atmospheric observation systems weren't designed to detect intentional interventions. Distinguishing between natural weather variations and intervention-induced changes would require sophisticated analysis over multiple years.
A fundamental category error
The authors don't dismiss the possibility that commercial mechanisms might be needed if aerosol cooling strategies were ever used. But they draw a clear distinction between potential future funding mechanisms versus the current practice of selling credits akin to carbon offsets in a marketplace of independent actors. Although aerosol cooling is a poor substitute for reducing greenhouse gases, and thus a poor candidate for any kind of “credit”-based system, it could plausibly complement efforts to reduce climate risks from greenhouse gas warming by providing fast-acting but temporary relief from the worst of global warming.
They conclude that cooling credits are unlikely to be viable environmentally, and therefore economically, either now or in the foreseeable future. They represent a flawed framework, with a structure that runs counter to the central requirement to ‘maximize safety and minimize harm.
To the extent that solar climate interventions might be a part of a future portfolio of climate responses, cooling credits are not a safe approach and unworkable as a business opportunity.
The Final Cut: “Cooling credits” sell particle releases into the atmosphere, but there’s no reliable way to measure or verify their effects– and strong reasons to doubt they could meaningfully offset greenhouse gas impacts. The science needed to quantify these outcomes doesn’t yet exist. The atmosphere is too complex and the risks too high for profit motives to drive large-scale interventions without the evidence needed to ensure safety and avoid harm.
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