Geoengineering: Blocking sunlight to cool Earth won't reduce crop damage from global warming

August 8, 2018, University of California - Berkeley
One proposal for solar geoengineering is to inject sulfate aerosols into the atmosphere, similar to what happens after large volcanic eruptions. The blanket of smog acts as an umbrella, reducing sunlight and temperatures a few percent to counter global warming. Credit: Stephen McNally and Hulda Nelson, UC Berkeley

Injecting particles into the atmosphere to cool the planet and counter the warming effects of climate change would do nothing to offset the crop damage from rising global temperatures, according to a new analysis by University of California, Berkeley, researchers.

By analyzing the past effects of Earth-cooling , and the response of crops to changes in , the team concluded that any improvements in yield from cooler temperatures would be negated by lower productivity due to reduced sunlight. The findings have important implications for our understanding of , one proposed method for helping humanity manage the impacts of global warming.

"Shading the planet keeps things cooler, which helps crops grow better. But plants also need sunlight to grow, so blocking sunlight can affect growth. For agriculture, the unintended impacts of solar are equal in magnitude to the benefits," said lead author Jonathan Proctor, a UC Berkeley doctoral candidate in the Department of Agricultural and Resource Economics. "It's a bit like performing an experimental surgery; the side-effects of treatment appear to be as bad as the illness."

"Unknown unknowns make everybody nervous when it comes to global policies, as they should," said Solomon Hsiang, co-lead author of the study and Chancellor's Associate Professor of Public Policy at UC Berkeley. "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 geoengineering tries to copy."

Hsiang is director of UC Berkeley's Global Policy Laboratory, where Proctor is a doctoral fellow.

Proctor and Hsiang will publish their findings online in the journal Nature on August 8.

Some people have pointed to past episodes of global cooling caused by gases emitted during , such as Mt. Pinatubo in the Philippines in 1991, and argued that humans could purposely inject sulfate aerosols into the upper atmosphere to artificially cool Earth and alleviate the greenhouse warming caused by increased levels of . Aerosols—in this case, minute droplets of sulfuric acid—reflect a small percentage of sunlight back into space, reducing the temperature a few degrees.

"It's like putting an umbrella over your head when you're hot," Proctor said. "If you put a global sunshade up, it would slow warming."

Pinatubo, for example, injected about 20 million tons of sulfur dioxide into the atmosphere, reducing sunlight by about 2.5 percent and lowering the average global temperature by about half a degree Celsius (nearly 1 degree Fahrenheit).

The team 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, the team calculated that the loss of sunlight from a sulfate-based geoengineering program would cancel its intended benefits of protecting crops from damaging extreme heat.

A veil of stratospheric sulfate aerosols circles the Earth in the months following the massive 1991 eruption of Mount Pinatubo. These aerosols cooled and shaded the earth's croplands, shown in green. Each frame of the animation shows one month of data, from June 1991 to September 1993. The appearance of "holes" near the poles occurs because of missing data due to the lack of satellite observations in those regions Credit: Jonathan Proctor and Solomon Hsiang

"It's similar to using one credit card to pay off another credit card: at the end of the day, you end up where you started without having solved the problem," Hsiang said.

Some earlier studies suggested that aerosols might improve crop yields also by scattering sunlight and allowing more of the sun's energy to reach interior leaves typically shaded by upper canopy leaves. This benefit of scattering appears to be weaker than previously thought.

"We are the first to use actual experimental and observational evidence to get at the total impacts that sulfate-based geoengineering might have on yields," Proctor said. "Before I started the study, I thought the net impact of changes in sunlight would be positive, so I was quite surprised by the finding that scattering light decreases yields."

Despite the study's conclusions, Proctor said, "I don't think we should necessarily write off solar geoengineering. For agriculture, it might not work that well, but there are other sectors of the economy that could potentially benefit substantially."

Proctor and Hsiang noted that their methods could be used to investigate the impact of geoengineering on other segments of the economy, human health and the functioning of natural ecosystems.

They did not address other types of geoengineering, such as capture and storage of carbon dioxide, or issues surrounding geoengineering, such as its impact on Earth's protective ozone layer and who gets to set Earth's thermostat.

"Society needs to be objective about geoengineering technologies and develop a clear understanding of the potential benefits, costs and risks," Proctor said. "At present, uncertainty about these factors dwarfs what we understand."

The authors emphasize the need for more research into the human and ecological consequences of geoengineering, both good and bad.

"The most certain way to reduce damages to crops and, in turn, people's livelihood and well-being, is reducing carbon emissions," Proctor said.

"Perhaps what is most important is that we have respect for the potential scale, power and risks of geoengineering technologies," Hsiang said. "Sunlight powers everything on the planet, so we must understand the possible outcomes if we are going to try to manage it."

Explore further: Climate engineering, once started, would have severe impacts if stopped

More information: Estimating global agricultural impacts of geoengineering using volcanic eruptions, Nature (2018). DOI: 10.1038/s41586-018-0417-3 , https://www.nature.com/articles/s41586-018-0417-3

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17 comments

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barakn
4.2 / 5 (5) Aug 08, 2018
Doesn't address a few other questions, like whether the sulfates will provide a fertilizing effect or will cause acid rain issues, but a good effort nonetheless. Geoengineering is nothing to be taken lightly.
aksdad
2.5 / 5 (8) Aug 08, 2018
We are the first to use actual experimental and observational evidence to get at the total impacts that sulfate-based geoengineering might have on yields

Too bad no one has validated the claim that so-called "climate change" (global warming) will cause widespread crop damage. The predictions are based on computer models, not "actual experimental and observational evidence".

In fact, every dire prediction about global warming is based on computer models, not observations. The alarm about climate change is the biggest hoax in modern history.

The current "change" in climate is so slow as to be easily adapted to and, so far, falls within the natural variation in climate over the past several thousand years.
barakn
3.8 / 5 (9) Aug 08, 2018
In fact, every dire prediction about global warming is based on computer models, not observations.
Some are made based on observations on previous periods of high CO2, so right there you've been caught lying, aksdad. How many of your other statements are lies?
guptm
2.3 / 5 (3) Aug 08, 2018
Is Sun the cause? I thought humans were the cause of warming. Some people are determined to destroy my planet, but they won't succeed.
Old_C_Code
1.6 / 5 (5) Aug 08, 2018
Climate science should be categorized as a humanity now, as these rich university administrators give out degrees with no useful knowledge attached, and the suckers who got huge student loans to pay can't remove them via bankruptcy. But then I know several people with Comp Sci degrees that can't program... heh
unrealone1
2.6 / 5 (5) Aug 08, 2018
The Earth has been cooling for 8,000 years
https://en.wikipe...ture.svg

48,000 Brits dead after worst winter in 42 years: 7th April 2018
https://www.daily...talities

Winter death toll 'to exceed 40,000'
Campaigners say the figures are a "tragedy" and that more should be done to help vulnerable elderly people 01 Feb 2015
https://www.teleg...000.html
unrealone1
2.6 / 5 (5) Aug 08, 2018
http://www.climatecooling.org/
Learn how the leaked emails of ClimateGate explain how scientists hid the Medieval Warm Period (when Vikings settled Greenland) and present cooling - the only way for the present warmth to be "unprecedented".
unrealone1
2 / 5 (4) Aug 08, 2018
Russia's Wheat Crop Under Threat From Miserable Start to Spring.
Cold weather in central areas and the Volga valley delayed the resumption of winter wheat growth by about two to three weeks compared with last year,
https://www.bloom...o-spring

Russian 2018 grain crop estimate slashed by two leading forecasters
MOSCOW (Reuters) - Leading Russian agricultural consulting firms SovEcon and IKAR have cut their estimates for the country's 2018 grain harvest due to cold wet conditions in the key spring wheat regions of Siberia and the Urals.
https://www.reute...CN1J50HH
howhot3
4.2 / 5 (5) Aug 08, 2018
The predictions are based on computer models, not "actual experimental and observational evidence".


Computer models are based on "actual experimental and observation evidence" and compared with real past climate data and validated. To blame the computer models is simply burying your head in the sand to ignore reality, It is more accurate than the computer models used to design your diesel pickup truck!

The current "change" in climate is so slow as to be easily adapted to and, so far, falls within the natural variation in climate over the past several thousand years.
It's not slow at all. Global average temps have increased 1.5C over pre-industrial temps to current time (2018). Prior to that it was flatlined for a few million years or so. If you've not seen extreme weather yet, you must live a very sheltered life.
unrealone1
2 / 5 (4) Aug 08, 2018
U.S. farmers have sharply reduced wheat plantings in recent years because of a global supply glut and falling wheat consumption due to dietary trends. Last year, domestic consumption of wheat flour fell to its lowest level since 1989.
http://fingfx.tho...dex.html
https://www.reute...BN1E518Y
Cooling will help this?
howhot3
3 / 5 (4) Aug 08, 2018
Denier goons love to hear themselves. It's how they get their jollies. So cooling is your ignorance showing. Instead here is a headline from today, HSBC; one of the largest global banks released this warning that was quickly in the news
One of the largest banks issued an alarming warning that Earth is running out of the resources to sustain life

https://www.busin...e-2018-8

So while that is going on; extreme heat is absolutely crippling countries over the globe. I don't see how you get a record high temp in Tokyo and it's cooling. Your charts don't make sense.
michael_frishberg
5 / 5 (2) Aug 08, 2018
How many fewer feet of photosynthesis will occur in the sea, when sulphur blocks sunlight? We've been doing "geoengineering" since language developed, and, we are now painted into a biologically non-viable ecological niche, we didn't evolve under the Earth's current and soon to be more radical, climate regime.
zz5555
5 / 5 (4) Aug 08, 2018
But then I know several people with Comp Sci degrees that can't program... heh

What always seemed strange to me was that so many people with scant knowledge in science (and little interest in learning) feel that their anti-science comments have any relevancy on a science website. But there you are. ;)
unrealone1
1 / 5 (1) Aug 09, 2018
@zz5555 Al Gore can use a Forklift and run PowerPoint = $800 million!
Thorium Boy
1 / 5 (1) Aug 09, 2018
Anyone who has any notion of injecting sulfur or carbon particles into the atmosphere should be shot.
eachus
not rated yet Aug 09, 2018
Anyone who has any notion of injecting sulfur or carbon particles into the atmosphere should be shot.


Don't worry, the will get those dirty, nasty volcanoes and calderas to do the dirty deed, and shooting volcanoes is not very satisfying.

The way the climate works, is it gets warmer every year, then a VEI 5, 6, or 7 eruptions comes along to put all that sulfur and carbon into the upper atmosphere and temperatures plunge quick;y. The most recent VEI 7 was Mt. Tambora in 1815. As a result, 1816 was remembered as the year without a summer. Snow fell in New England in July and August.

There were two major eruptions in 1991, Mt Pinatubo in the Philippines, and Mount Hudson in Chile. Mt Hudson was a strong VEI 5, and Mt Pinatubo was a stronger than average VEI 6. These probably account for the "pause" in global warming. A repeat of (VEI 7) Mt. Tambora would kill millions due to starvation, and a VEI 8 would probably kill a majority of the human population.
Whart1984
not rated yet Aug 13, 2018
Actually most of geoengineering methods proposed recently could have quite opposite effect: for example the release of aerosols may extend droughts rather than bring cooling and cloudy skies. Not only the aerosols are transparent for infrared radiation, but they also serve as a condensation nuclei of fog, which precipitates in too small droplets for to condense in rain. Such an aerosol merely evaporates above coast without bringing rain.
Best of all, it can even reflect the heat radiated by land back

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