"Estimating global agricultural effects of geoengineering using volcanic eruptions"

This page contains resources for "Estimating global agricultural effects of geoengineering using volcanic eruptions" by Proctor, Hsiang, Burney, Burke, & Schlenker (Nature, 2018)

resources below:

1. Slide deck
2. Data visualizations
3. Paper in numbers
4. Frequently asked questions
5. Link to paper
6. Replication data

Presentation slides

Complete slide deck from an 90 minute academic research talk at the Harvard Solar Geoengineering research seminar. (35MB)

Data Visualizations

The Paper in Numbers

• The Mt Pinatubo eruption injected 20 million tons of sulfur dioxide into the atmosphere, increasing stratospheric aerosol optical depth by +0.15 on average globally
• This caused total sunlight to decline 2.5% globally (temporarily).
• We analyzed crop yields from 105 countries during this period.
• The dimming of sunlight caused maize yields (C4) to decline -9% on average and soy, rice & wheat yields (C3) to decline -5%.
• When we use these numbers to compute the overall effect of solar radiation management on global agriculture, we find that the effect of lost sunlight offsets the benefits of cooling, leading to no net benefits (or costs).

Frequently Asked questions

Q: What is "solar geoengineering"?

A: "Solar geoengineering" is the idea that we can use technology to cool the Earth (and reduce global warming) by reflecting sunlight back into space. It’s kind of like standing under a tree to cool off during a hot day. Though people have thought of a lot of different ways to do this, the most commonly proposed form of solar geoengineering is to inject particles of sulfate into the high atmosphere using airplanes. These particles turn into something like dust ("aerosols") in the high atmosphere (stratosphere) and reflect incoming sunlight back to outer space. One piece of evidence that this might work to mitigate climate change is that the Earth tends to cool following massive volcanic eruptions (e.g. Mt. Pinatubo), which similarly inject sulfur into the high atmosphere.

Q: What are the benefits and risks?

A: Solar geoengineering is appealing because it may be able to cool the earth quickly and is relatively inexpensive. Thus, the technology could potentially be a useful tool to reduce damages from climate change.

Many worry, however, that solar geoengineering could have unintended consequences. For example, potential side effects could result from damage to the Earth’s protective ozone layer, disagreement over setting the global thermostat, or reducing the available sunlight at the Earth’s surface.

Today, we still do not understand all of the benefits or all of the risks. To make informed decisions about its possible use, we need more research into both of these questions. 

Q: What did you find?

A: We studied the effect that solar geoengineering might have on global agricultural production and find that, as intended, the reduction in extreme heat benefits crop production. We also find, however, that the shading from solar geoengineering could make crops less productive, because crops use sunlight to grow. For agriculture, the unintended consequences of reducing sunlight offset the intended benefits from cooling. If we think of SRM as an experimental surgery, our findings suggest that the side effects are as bad as the cure.

Q: Does scattered light fertilize plants?

A: There is a theory in the field of "biometeorology" that posits that scattering light could increase crop growth by redistributing light from the sun-saturated leaves at the top of the plant to the shaded leaves below. A key scientific contribution of our paper was that, on net, scattering sunlight from large volcanic eruptions appears to decrease crop production because the damage from reducing total sunlight outweighs the benefits from increasing scattered sunlight. 

Q: How did you figure that out?

A: The problem in figuring out the consequences of solar geoengineering is that we can’t do a planetary-scale experiment without actually deploying the technology. The breakthrough here was realizing that we could learn something by studying the effects of giant volcanic eruptions that similarly inject sulfur into the atmosphere and cool the Earth.

We linked maize, soy, rice and wheat production from 105 countries from 1979-2009 to global satellite observations of these aerosols to study their effect on agriculture. Pairing these results with global climate models, we calculated that the loss of sunlight from a sulfate-based geoengineering program would cancel its intended benefits of protecting crops from damaging extreme heat. 

Q: Should we deploy solar geoengineering?

A: As a global community, we do not know nearly enough about the impacts of solar geoengineering to evaluate who would benefit, who would be harmed, and by how much – all of which are crucial to evaluate before deciding whether we ought to adopt a strategy with global effects.

For agriculture, our findings suggest that sulfate-based solar geoengineering might not work well to avoid the damaging effects of climate change. However, there are other sectors of the economy that could potentially benefit substantially (or be substantially damaged, we just don’t know).

In our analysis, we find some evidence that the type of particle used to reflect sunlight might have influenced how much crops were harmed. Thus, it is theoretically possible that one could design a particle that could cool the Earth with less damage to agricultural production.

Just because the first test of an experimental surgery had  side effects for a specific part of the human body does not mean that the procedure is always immediately abandoned. There are many illnesses that are so harmful that procedures known to cause side effects are sometimes still worth the risk. Similarly, research into geoengineering should not be entirely abandoned because our analysis demonstrated one adverse side effect, there may remain good reasons to eventually pursue such a strategy despite some known costs.

We believe solar geoengineering technologies may represent an important technology for global wellbeing and should be viewed with both caution and respect. Before deploying this technology, we need much more research into their benefits and risks.

Link to paper

You can download the paper here.

Replication data

You can find replication data and code here.

Or by searching "Estimating global agricultural effects of geoengineering using volcanic eruptions" in Zenodo.