Paul's Internet Landfill/ 2024/ Sulphate Geoengineering is Stupid

Sulphate Geoengineering is Probably Stupid

Now that we are experiencing the effects of climate change firsthand, pressure is mounting for silver-bullet solutions. Geoengineering is raising its ugly head. We are being told that we are now out of time and only geoengineering can buy us the space to fix the climate. Maybe this is true and maybe this is not, but I feel geoengineering solutions that block out the sun are the wrong solution.

Most of the geoengineering discourse I have seen involves pumping sulphates into the stratosphere. This will block the sun by making the stratosphere less reflective. Then less sunlight will get to the Earth and it will cool down. The idea is that then we will have fewer droughts and fires. We believe this will work because volcanos erupt and then the climate cools down.

An alternative to pumping sulphates into the stratosphere is to put satellites into orbit that have giant umbrella panels that will block the sun for us. This is also a dumb idea.

There are a bunch of debates around geoengineering. People are worried about geopolitics, because some countries will benefit and others will not. There are debates about who will carry this out, and how much geoengineering is the right amount. There is not a lot of discussion about the fact that this form of geoengineering would very likely be a disaster that leads to war and famine.

My thinking around this synthesized from listening to two podcasts. One is an interview with pundit Gwynne Dyer, whose superpower is sounding confident about everything. Dyer has written a book which strongly suggests we should experiment with sulphate geoengineering, with the main drawback being that the cooling will not be uniform across the Earth, causing geopolitical conflict. He is of the opinion that people who oppose experimentation with geoengineering are foolish.

The second podcast is from the Long Now, where Neil Stephenson promoted his book Termination Shock, in which some billionaire unilaterally implements geoengineering. (I have not read this book, although it sounds interesting.) Stephenson starts his seminar by reading a series of historical accounts of climate cooling following volcanic eruptions, as evidence that geoengineering works. But these accounts also document "years without summers" and massive crop failures. It turns out that plants don't just need temperatures to thrive; they also need sunlight, and these geoengineering approaches work by BLOCKING OUT THE SUN.

If you block out the sun then less sun hits the earth. Presumably, plants don't grow as well and crops fail. If crops fail there are food shortages. If there are food shortages prices spike, and there is civil unrest (see: Donald Trump and probably PP). If there is civil unrest there can be war, and war destabilizes society even more than climate change does.

In addition, farmers are already having a difficult time due to weather fluctuations from climate change. This episode is one snapshot of how tough farmers are finding things, but there are many other examples.

From what I can tell the fundamental error we are making in considering sulphate geoengineering is that we are confusing heat and light. We want to reduce the heat on Earth. We do not necessarily want to reduce the light. This approach to geoengineering conflates the two. Furthermore, if we take Dyer's advice and geoengineer to the point where the temperature is stable and not increasing, that means we will block out more and more of the sun each year (since we will continue to pump out carbon dioxide each year indefinitely). So less and less light would hit the earth, and the crop failures could get worse each season.

Maybe there is a way to make this form of geoengineering work. But the first question people should ask is "what will this geoengineering do to crop yields?" There does not seem to be much mainstream conversation about this.

My gut feeling is that reducing the amount of light that hits the earth will harm plant growth, but the research indicates the story is more complicated. Uncle Wikipedia's page on geoengineering points to the 2021 International Panel on Climate Change (IPCC) backgrounder report . On page 66 of the associated PDF (page 2476 of the report) there is a paragraph indicating low certainty:

There is low confidence and large uncertainty in projected impacts of SRM on crop yields due in part to a limited number of studies. Because SRM would result in only a slight reduction in CO 2 concentrations relative to the emission scenario without SRM (Chapter 5, WGI), the CO 2 fertilisation effect on plant productivity is nearly the same in emissions scenarios with and without SRM. Nevertheless, changes in climate due to SRM are likely to have some impacts on crop yields. A single study indicates MCB may reduce crop failure rates compared with climate change from a doubling of CO2 pre-industrial concentrations (Parkes et al., 2015). Models suggest SAI cooling would reduce crop productivity at higher latitudes compared with a scenario without SRM by reducing the growing season length, but benefit crop productivity in lower latitudes by reducing heat stress (Pongratz et al., 2012; Xia et al., 2014; Zhan et al., 2019). Crop productivity is also projected to be reduced where SAI reduces rainfall relative to the scenario without SRM, including a case where reduced Asian summer monsoon rainfall causes a reduction in groundnut yields (Xia et al., 2014; Yang et al., 2016). SAI will increase the fraction of diffuse sunlight, which is projected to increase photosynthesis in forested canopy, but will reduce the direct and total available sunlight, which tends to reduce photosynthesis. As total sunlight is reduced, there is a net reduction in crop photosynthesis with the result that any benefits to crops from avoided heat stress may be offset by reduced photosynthesis, as indicated by a single statistical modelling study (Proctor et al., 2018). SAI would reduce average surface ozone concentration (Xia et al., 2017) mainly as a result of aerosol-induced reduction in stratospheric ozone in polar regions, resulting in reduced downward transport of ozone to the troposphere (Pitari et al., 2014; Tilmes et al., 2018). The reduction in stratospheric ozone also allows more UV radiation to reach the surface. The reduction in surface ozone, together with an increase in surface UV radiation, would have important implications for crop yields but there is low confidence in our understanding of the net impact.

SRM is "solar radiation modification", aka "blocking out the sun. MCB is "marine cloud brightening". SAI is "stratospheric aerosol interventions", which is pumping sulphates int the stratosphere. There are a number of other possible interventions listed in the report.

I did not thoroughly follow all the citations in this report, but I did look a little at "diffuse sunlight". The idea here is that directing sunlight straight at plants is LESS effective for photosynthesis than by scattering the light around using clouds (or sulphates) because more photons hit lower-lying leaves on plants that would otherwise be shaded. There is one extraordinary claim that diffusing light using sunshades can increase productivity of photosynthesis even when total radiation is decreased but most other studies I found played the trick of comparing the effect of diffuse vs direct radiation when the total light levels are the same. Here are some papers I partially comprehended:

I do not understand this research field well, but it still sounds to me as if we cannot depend upon increased light diffusion to offset the loss of total sunlight that hits the earth. We doubly cannot depend upon this effect with solar parasols, since the diffusion of light happens in outer space. With stratospheric aerosols, it is not clear to me how much of the light will be diffuse and not direct (if it is diffuse I expect that we will have many more cloudy/hazy days even in summertime).

The other reasonable argument in favor of sulphate geoengineering is the argument that we have already run the experiment. Uncle Wikipedia's article on Global Cooling argues that the world went through some cooling because coal burning was pumping so much aerosol in the air. Since crop yields did not fail catastrophically in this time, we should not be as afraid as I am. In fact, one prominent paper from Mercado et al 2009 argued that between 1960 and 1999 photosynthesis efficiency improved because of all the coal-generated sulphates in the air. The paper is behind a paywall so I did not read it, but one question I have with respect to this is whether we are talking about the same effect. Did sulphates from coal burning end up in the stratosphere, where we are planning to pump sulphates via geoengineering? Or were they at lower atmospheric levels? Does that make a different? My understanding is that we do not want sulphates at low atmospheric levels because then we get smog.

After glancing at the research, my uncertainty remains high. I still feel that the primary question we ask when considering sulphate geoengineering is what happens to crop yields. We do not have a lot of wiggle room here. Sulphates supposedly do not last long in the atmosphere (1-3 years?) but that is long enough for multiple seasons of crops to fail. So even a short experiment run on a global scale could have dire consequences.

Similarly, I worry about actual volcanos. Say we start an experiment and then a real live volcano blows up and spews thousands of tonnes of more sulphates (and ash!) into the atmosphere. Then we could be in for a double dose of cooling, which sounds catastrophic. Can we predict volcanic action precisely enough to schedule our geoengineering correctly?

The other thing about this debate that seems stupid is that the same evidence that inspires us to consider pumping sulphates into the stratosphere is the evidence that suggests it could be a terrible idea. Any model that pretends to understand the effects of sulphates should also be able to account for the effects of disasters like The Year Without a Summer from 1816. If those models say that sulphates during 1816 would have been okay actually, then we cannot trust those models. I do not think we have a lot of evidence that sulphate geoengineering will fix things, but we do have concrete evidence that something about volcanos (maybe the sulphates, maybe the ash, maybe something else) can do a lot of damage.