Cloud brightening hits a salty snag

The proposal known as solar radiation management is complicated. It just got moreso. Released Wednesday:

Fossum, K.N., Ovadnevaite, J., Ceburnis, D. et al. “Sea-spray regulates sulfate cloud droplet activation over oceans“, Climate and Atmospheric Science, 3(14): (2020).
https://doi.org/10.1038/s41612-020-0116-2

[open access]

The above is an experimental essay regarding the effects of salt spray upon an artificial proposed technique to enhance the Twomey Effect.

Solar geoengineering attempts to mitigate some of the effects of climate disruption by fossil fuel emissions using various technologies to increase Earth’s albedo. While there are water droplet-based techniques, many involve injecting Sulphur-derived droplets into atmosphere at differing heights, because these droplets are bright. Were these to succeed, increasing albedo means that less solar radiation would reach Earth’s surface, thus cooling it. (See also.)

Assuming this remedy worked, meaning it controls increases in surface and oceanic temperatures, this will not solve ocean acidification, because carbonic acid and related concentrations in oceans will continue to increase, as long as emissions from fossil fuels and agriculture continue. Moreover, there are attendant risks: These particles fall out of atmosphere so they need to be continually replenished. There are concerns, as noted in a talk cited here by the late Professor Wally Broecker, that there may not be sufficient sulfur supply, or this may pinch the market for sulfur impacting prices of other products which demand it. If the replenishment were interrupted, say, by a war or a pandemic, there are concerns regarding the impulse response of a climate system where the blocking of radiation is suddenly released (“termination shock”).

Professor David Keith of Harvard University is a proponent of these measures. There are many, including Professor Ray Pierrehumbert, who are highly skeptical and suspicious (“albedo hacking”, originally due to Kintisch from 2010).

And there are also concerns this might not work, at least not well. And, the reasoning goes, if large scale impacts to humanity on the planet are to be safeguarded by betting on such a technique, especially if there’s a moral hazard that the true solution, stopping emissions from fossil fuel burning, will be hindered by the technology’s possibilities, it better be known to work, and work well.

One measure, cloud brightening, was dealt a blow by the paper cited at the top. It should be noted that

Horowitz, H. M., Holmes, C., Wright, A., Sherwen, T., Wang, X., Evans, M., et al. ( 2020). “Effects of sea salt aerosol emissions for marine cloud brightening on atmospheric chemistry: Implications for radiative forcing“, Geophysical Research Letters, 47,
e2019GL085838. https://doi.org/10.1029/2019GL085838

(Also open access)

also reported on interactions of sea salt with aerosols in the marine cloud brightening case.

The net, from the Abstract by Fossum, et al:

We present new experimental results from the remote Southern Ocean illustrating that, for a given updraft, the peak supersaturation reached in cloud, and consequently the number of droplets activated on sulfate nuclei, is strongly but inversely proportional to the concentration of sea-salt activated despite a 10-fold lower abundance. Greater sea-spray nuclei availability mostly suppresses sulfate aerosol activation leading to an overall decrease in cloud droplet concentrations; however, for high vertical updrafts and low sulfate aerosol availability, increased sea-spray can augment cloud droplet concentrations. This newly identified effect where sea-salt nuclei indirectly controls sulfate nuclei activation into cloud droplets could potentially lead to changes in the albedo of marine boundary layer clouds by as much as 30%.

The atmosphere is a complicated beastie.

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This entry was posted in adaptation, American Association for the Advancement of Science, American Meteorological Association, atmosphere, being carbon dioxide, carbon dioxide, chemistry, climate disruption, climate mitigation, climate nightmares, climate policy, cloud brightening, ecomodernism, emissions, geoengineering, global warming, Ken Caldeira, leaving fossil fuels in the ground, meteorological models, meteorology, mitigating climate disruption, NASA, National Center for Atmospheric Research, oceanography, Principles of Planetary Climate, Ray Pierrehumbert, risk, solar radiation management, sustainability, Wally Broecker, water vapor, wishful environmentalism, zero carbon. Bookmark the permalink.

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