Difference between revisions of "Geoengineering"

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[https://e360.yale.edu/features/geoengineer-the-planet-more-scientists-now-say-it-must-be-an-option Geoengineer the Planet? More Scientists Now Say It Must Be an Option] Fred Pearce; Yale E360; 29 May 2019
[https://e360.yale.edu/features/geoengineer-the-planet-more-scientists-now-say-it-must-be-an-option Geoengineer the Planet? More Scientists Now Say It Must Be an Option] Fred Pearce; Yale E360; 29 May 2019
: Human intervention with the climate system has long been viewed as an ill-advised and risky step to slow global warming. But with carbon emissions soaring, initiatives to study and develop geoengineering technologies are gaining traction as a potential last resort.
: Human intervention with the climate system has long been viewed as an ill-advised and risky step to slow global warming. But with carbon emissions soaring, initiatives to study and develop geoengineering technologies are gaining traction as a potential last resort.
''See also [[carbon sequestration]]''
== Solar ==
== Solar ==
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:Which is what makes a new paper released on Monday in Nature Climate Change so alluring. It shows that undertaking half measures to block the sun could end up providing the benefit of a cooler planet without many of the adverse impacts on other parts of the climate system. The results suggest there could be a role for geoengineering to play in saving us from a climate catastrophe, though it’s hardly the last word on what that role could be, or even if it’s worth the risk. And there are a few important caveats showing that there’s still a lot of research needed on the topic.
:Which is what makes a new paper released on Monday in Nature Climate Change so alluring. It shows that undertaking half measures to block the sun could end up providing the benefit of a cooler planet without many of the adverse impacts on other parts of the climate system. The results suggest there could be a role for geoengineering to play in saving us from a climate catastrophe, though it’s hardly the last word on what that role could be, or even if it’s worth the risk. And there are a few important caveats showing that there’s still a lot of research needed on the topic.
== [[Carbon sequestration]]* ==
== Aerosols ==
== Aerosols ==

Latest revision as of 15:45, 29 June 2020

What is geoengineering—and why should you care? by James Temple in MIT Technology Review, 9 Aug 2019

As the threats of climate change grow, we’re all likely to hear more and more about the possibilities, and dangers, of geoengineering. Here’s what it means.

It’s becoming clear that we won’t cut carbon emissions soon enough to prevent catastrophic climate change. But there may be ways to cool the planet more quickly and buy us a little more time to shift away from fossil fuels.

They’re known collectively as geoengineering, and though it was once a scientific taboo, a growing number of researchers are running computer simulations and proposing small-scale outdoor experiments. Even some legislators have begun discussing what role these technologies could play (see “The growing case for geoengineering”).

But what is geoengineering exactly?

Traditionally, geoengineering has encompassed two very different things: sucking carbon dioxide out of the sky so the atmosphere will trap less heat, and reflecting more sunlight away from the planet so less heat is absorbed in the first place.

The first of these, known as “carbon removal” or “negative emissions technologies,” is something that scholars now largely agree we’ll need to do in order to avoid dangerous levels of warming (see “One man’s two-decade quest to suck greenhouse gas out of the sky”). Most no longer call it “geoengineering”—to avoid associating it with the second, more contentious branch, known as solar geoengineering.

This is a blanket term that includes ideas like setting up sun shields in space or dispersing microscopic particles in the air in various ways to make coastal clouds more reflective, dissipate heat-trapping cirrus clouds, or scatter sunlight in the stratosphere.

The word geoengineering suggests a planetary-scale technology. But some researchers have looked at the possibility of conducting it in localized ways as well, exploring various methods that might protect coral reefs, coastal redwoods, and ice sheets.

Where did the idea come from?

It’s not a particularly new idea. In 1965, President Lyndon Johnson’s Science Advisory Committee warned it might be necessary to increase the reflectivity of the Earth to offset rising greenhouse-gas emissions. The committee went so far as to suggest sprinkling reflective particles across the oceans. (It’s revealing that in this, the first ever presidential report on the threat of climate change, the idea of cutting emissions didn’t seem worth mentioning, as author Jeff Goodell notes in How to Cool the Planet.)

But the best-known form of solar geoengineering involves spraying particles into the stratosphere, sometimes known as “stratospheric injection” or “stratospheric aerosol scattering.” (Sorry, we don’t come up with the names.) That’s in part because nature has already demonstrated it’s possible.

Most famously, the massive eruption of Mt. Pinatubo in the summer of 1991 spewed some 20 million tons of sulfur dioxide into the sky. By reflecting sunlight back into space, the particles in the stratosphere helped push global temperatures down about 0.5 °C over the next two years.

And while we don’t have precise data, huge volcanic eruptions in the distant past had similar effects. The explosion of Mount Tambora in Indonesia in 1815 was famously followed by the “Year Without a Summer” in 1816, a gloomy period that may have helped inspire the creation of two of literature’s most enduring horror creatures, vampires and Frankenstein’s monster.

Soviet climatologist Mikhail Budyko is generally credited as the first to suggest we could counteract climate change by mimicking this volcanic phenomenon. He raised the possibility of burning sulfur in the stratosphere in a 1974 book.

In the following decades, the concept occasionally popped up in research papers and at scientific conferences, but it didn’t gain much attention until the late summer of 2006, when Paul Crutzen, a Nobel Prize–winning atmospheric chemist, called for geoengineering research in an article in Climatic Change. That was particularly significant because Crutzen had won his Nobel for research on the dangers of the growing ozone hole, and one of the known effects of sulfur dioxide is ozone depletion.

In other words, he thought climate change was such a threat that it was worth exploring a remedy he knew could pose other serious dangers.

So could geoengineering be the solution to climate change, relieving us of the hassle of cutting back on fossil fuels?

No—although the idea that it does is surely why some energy executives and Republican legislators have taken an interest. But even if it works (on which more below), it’s at best a temporary stay of execution.

It does little to address other climate dangers, notably including ocean acidification, or the considerable environmental damage from extracting and burning finite fossil fuels. And greater levels of geoengineering may increase other disruptions in the climate system, so we can’t just keep doing more and more of it to offset ever rising emissions.

How is geoengineering being researched?

In the years since Crutzen’s paper, more researchers have studied geoengineering, mainly using computer simulations or small lab experiments to explore whether it would really work, how it might be done, what sorts of particles could be used, and what environmental side effects it might produce.

The computer modeling consistently shows it would reduce global temperatures, sea-level rise, and certain other climate impacts. But some studies have found that high doses of certain particles might also damage the protective ozone layer, alter global precipitation patterns, and reduce crop growth in certain areas.

Others researchers have found that these risks can be reduced, if not eliminated, by using particles other than sulfur dioxide and by limiting the extent of geoengineering.

But no one would suggest we’ve arrived at the final answer on most of these questions. Researchers in the field believe we need to do a lot more modeling work to explore these issues in greater detail. And it’s also clear that simulations can only tell us so much, which is why some are proposing small outdoor experiments.

Has anybody conducted real-world geoengineering experiments?

In 2009, Russian scientists conducted what is believed the be the first outdoor geoengineering experiment. They mounted aerosol generators on a helicopter and car and sprayed particles as high as 200 meters (660 feet). The scientists claimed, in a paper published in Russian Meteorology and Hydrology, that the experiment had reduced the amount of sunlight that reached the surface. (It’s worth noting that Yuri Izrael, a climate skeptic and scientific advisor to Vladimir Putin, was the lead author of the study as well as the editor of the journal.)

One of the first attempts to conduct an experiment that was openly advertised in advance as geoengineering-related, known as the SPICE project, was ultimately scrapped. The idea was to pump particles up a pipe to a high-altitude balloon that would scatter them in the stratosphere. But the proposal prompted a public backlash, particularly after it emerged that some of the researchers had already applied for patents on the technology.

Scientists at Harvard have proposed what could be the next and most formal geoengineering experiment to date. They hope to launch a balloon equipped with propellers and sensors that would spray a tiny amount of calcium carbonate in the stratosphere. The aircraft would then fly through the plume and attempt to measure things like how broadly the particles disperse, how they interact with other gases, and how reflective they are. The team has already raised the funds, put an advisory committee in place, contracted with a balloon company, and begun development work on the necessary hardware. (See “Geoengineering is very controversial. How can you do experiments? Harvard has some ideas.”)

Meanwhile, researchers at the University of Washington—in partnership with Xerox’s Palo Alto Research Center and other groups—have proposed small-scale experiments as part of a larger research program to learn more about the potential of “marine cloud brightening.” The idea, first floated by the British physicist John Latham in 1990, is that spraying tiny salt particles from seawater toward low-lying clouds above the sea could form additional droplets, increasing the surface area—and thus reflectivity—of the clouds. The team is currently raising funds to develop a “cloud-physics research instrument” and test it by spraying a small amount of sea-salt mist somewhere off the US Pacific Coast.

There have also been some early efforts in other areas of geoengineering, including more than a dozen so-called iron-fertilization experiments in the open ocean, according to Nature. The concept there is that dumping iron into the water would stimulate the growth of phytoplankton, which would pull carbon dioxide out of the air. But scientists have questioned how well it really works, and what sorts of side effects it could have on ocean ecosystems. Environmental groups and others also criticized early efforts in this area, arguing that they went ahead without proper permission or scientific oversight.

Is anybody actually doing geoengineering?

Researchers stress that these experiments aren’t actual geoengineering: the amounts of material involved are far too small to alter global temperatures. Indeed, despite a vast and varied array of online conspiracy theories to the contrary, feverishly spread by chemtrails truthers, nobody is conducting planetary-scale geoengineering today.

At least, nobody is on purpose. You could argue that burning massive amounts of fossil fuels is a form of geoengineering, just an inadvertent and very dumb one. And we also know that sulfur pollution from coal plants and ships has likely reduced global temperatures. Indeed, new UN rules requiring ships to emit less sulfur might actually raise temperatures slightly (see “We’re about to kill a massive, accidental experiment in reducing global warming”).

There’s also a long and rich history of efforts in the US and China, among other places, to seed clouds with particles to increase snow or rainfall (see “Weather engineering in China”). But the results are mixed, and local weather modification is a far cry from attempting to twist the knob on the entire climate system.

Isn’t geoengineering controversial?


There are real concerns about conducting, researching, or even discussing geoengineering.

Critics argue that openly talking about the possibility of a technological “solution” to climate change (it’s not a solution, as explained above) will ease pressure to address the root cause of the problem: rising greenhouse-gas emissions. And some believe that moving forward with outdoor experiments is a slippery slope. It could create incentives to conduct ever bigger experiments, until we’re effectively doing geoengineering without having collectively determined to.

A technology that knows no national bounds also poses complex, if not insurmountable, geopolitical questions. Who should decide, and who should have a say in, whether we proceed with such an effort? How do you settle on a single global average temperature to aim for, since it will affect different nations in very different ways? And if we can’t settle on one, or come to a consensus on whether to deploy the technology at all, will some nation or individual do it anyway as climate catastrophes multiply? If so, could that spark conflicts, even wars?

Some argue it’s playing God to tinker with a system as complex as the climate. Or that it’s simply foolish to counteract one pollutant with another, or to try to fix a technocratic failure with a technocratic solution.

A final concern, and an indisputable one, is that modeling and experiments will only tell us so much. We can’t really know how well geoengineering will work and what the consequences will be until we actually try it—and at that point, we’re all stuck with the results.

Then why on earth is anyone considering it?

Few serious people would describe themselves as geoengineering advocates.

Scientists who study it profess ambivalence and openly acknowledge it’s not the best solution to climate change. But they worry that society is locking in dangerous levels of warming and extreme weather by continuing to build power plants, vehicles, and cities that will pump out greenhouse gases for decades to come. So a growing number of academics say it would be irresponsible not to explore something that could potentially save many, many lives, as well as species and ecosystems—as long as it’s used alongside serious efforts to slash emissions.

Yes, it’s dangerous, they say—but compared to what? More dangerous than the climate-change-driven famine, flooding, fires, extinctions, and migration that we’re already beginning to see? As those effects worsen, the public and politicians may come to think that tinkering with the entire planet’s atmosphere is a risk worth taking.

Oxford Geoengineering Programme? Oxford Martin School

Will Developing Nations Hack the Climate? Kristan Uhlenbrock; UnDark; 18 Jul 2016

What if the poor and developing nations most vulnerable to climate change took matters into their own hands with geoengineering?

Geoengineer the Planet? More Scientists Now Say It Must Be an Option Fred Pearce; Yale E360; 29 May 2019

Human intervention with the climate system has long been viewed as an ill-advised and risky step to slow global warming. But with carbon emissions soaring, initiatives to study and develop geoengineering technologies are gaining traction as a potential last resort.

See also carbon sequestration


Solar geoengineering: Science fiction – or saviour? DAVID KEITH, EDWARD PARSON; GLOBE AND MAIL; 8 Dec 2017

People's initial reactions when they learn about the prospect of solar geoengineering typically involve some mix of horror and relief: horror at the prospect of a dangerous and uncontrolled technical fix, and relief that new technologies may offer the prospect of additional reductions in this century's severe climate risks.
But wherever your views fall on this spectrum, the case for serious research on solar geoengineering, and serious examination of its governance challenges, is compelling. Indeed, it is becoming increasingly likely that some form of climate engineering will be necessary to achieve the Paris target of limiting planetary heating to well below 2 C.
Solar geoengineering – one type of climate engineering – would involve reflecting a small amount of incoming sunlight back to space. The most plausible method is to use aircraft to make a fine mist of reflective material in the stratosphere, where it would act like a thin cloud reflecting a little sunlight back to space. Neither science fiction nor saviour, the goal of such intentional climate intervention would be to offset some of the climate changes caused by elevated greenhouse gases.
Most climate models agree that carefully managed solar geoengineering can reduce projected changes in both temperature and precipitation over nearly all the Earth's land surface. It can slow and likely reverse sea level rise, and provide some reduction to rapidly mounting threats to coral reefs, by slowing both rising temperatures and ocean acidification. It appears particularly effective at slowing current and projected increases in the strength of tropical hurricanes.
How should the world consider climate engineering? As a taboo, pushed aside from the centre of climate policy? Or, as a risky solution embraced all too quickly by opponents of emissions cuts? Between these polar extremes lies a wide range of opportunities for responsible exploration – and a great opportunity for Canada to exercise effective international leadership.

How artificially brightened clouds could stop climate change Tim Smedley; BBC; 26 Feb 2019

Marine stratocumulus clouds are particularly important, covering around 20% of the Earth’s surface while reflecting 30% of total solar radiation. Stratocumulus clouds also cool the ocean surface directly below. Proposals to make these clouds whiter – or “marine cloud brightening” – are amongst the more serious projects now being considered by various bodies, including the US National Academies of Sciences, Engineering, and Medicine’s new “solar geoengineering” committee.
Stephen Salter, Emeritus professor at the University of Edinburgh, has been one of the leading voices of this movement. In the 1970s, when Salter was working on waves and tidal power, he came across studies examining the pollution trails left by shipping. Much like the aeroplane trails we see criss-crossing the sky, satellite imagery had revealed that shipping left similar tracks in the air above the ocean – and the research revealed that these trails were also brightening existing clouds.
“Spraying about 10 cubic metres per second could undo all the [global warming] damage we’ve done to the world up until now,” Salter claims. And, he says, the annual cost would be less than the cost to host the annual UN Climate Conference – between $100-$200 million each year.
Salter calculates that a fleet of 300 of his autonomous ships could reduce global temperatures by 1.5C. He also believes that smaller fleets could be deployed to counter-act regional extreme weather events. Hurricane seasons and El Niño, exacerbated by high sea temperatures, could be tamed by targeted cooling via marine cloud brightening. A PhD thesis from the University of Leeds in 2012 stated that cloud brightening could, “decrease sea surface temperatures during peak tropical cyclone season… [reducing] the energy available for convection and may reduce intensity of storms”.
A rival US academic team – The MCB Project – is less gung-ho than Salter. Kelly Wanser, the principal director of The MCB Project, is based in Silicon Valley.
Her team’s design is similar to commercial snow-making machines for ski resorts, yet capable of spraying “particles ten thousand times smaller [than snow]… at three trillion particles per second”. The MCB Project hopes to test this near Monterey Bay, California, where marine stratocumulus clouds waft overland. They would start with a single cloud to track its impact.
“One of the strengths of marine cloud brightening is it can be very gradually scaled,” says Wanser. “You [can] get a pretty good grasp of whether and how you are brightening clouds, without doing things that impact climate or weather.”
There is another approach to solar radiation management that shares the benefits – and the risks – evenly across the globe. Stratospheric aerosol scattering (SAS) is more analogous to Mount Pinatubo: instead of spraying aerosols into the lower atmosphere, you scatter them 10km above the clouds. This suspended, almost static veil of particles – too thin to be visible from the ground – would reflect a proportion of sunlight back into space. Computer modelling by the US National Center for Atmospheric Research in 2017 suggested that for every teragram of particles (one trillion grams – roughly the mass of the Golden Gate Bridge) injected in the atmosphere, a global average temperature reduction of 0.2C could be achieved.
Harvard's Solar Geoengineering Research Program are leading the work on SAS. Elizabeth Burns, its program director, is at pains to tell me, “solar geoengineering could only be a potential complement to emissions reduction. It could not replace those efforts”. This is no “quick fix”, she says. “We really do need to reduce emissions to zero if we want to address climate change.”

Irvine et al

Halving warming with idealized solar geoengineering moderates key climate hazards Peter Irvine, Kerry Emanuel, Jie He, Larry W. Horowitz, Gabriel Vecchi, David Keith; Nature Climate Change; 11 Mar 2019

Solar geoengineering (SG) has the potential to restore average surface temperatures by increasing planetary albedo, but this could reduce precipitation. Thus, although SG might reduce globally aggregated risks, it may increase climate risks for some regions. Here, using the high-resolution forecast-oriented low ocean resolution (HiFLOR) model—which resolves tropical cyclones and has an improved representation of present-day precipitation extremes—alongside 12 models from the Geoengineering Model Intercomparison Project (GeoMIP), we analyse the fraction of locations that see their local climate change exacerbated or moderated by SG. Rather than restoring temperatures, we assume that SG is applied to halve the warming produced by doubling CO2 (half-SG). In HiFLOR, half-SG offsets most of the CO2-induced increase of simulated tropical cyclone intensity. Moreover, neither temperature, water availability, extreme temperature nor extreme precipitation are exacerbated under half-SG when averaged over any Intergovernmental Panel on Climate Change (IPCC) Special Report on Extremes (SREX) region. Indeed, for both extreme precipitation and water availability, less than 0.4% of the ice-free land surface sees exacerbation. Thus, while concerns about the inequality of solar geoengineering impacts are appropriate, the quantitative extent of inequality may be overstated.

Scientists: Maybe If We Only Dim the Sun a Little It Won’t Backfire Horribly Brian Kahn; Earther; 11 Mar 2019?

When it comes to geoengineering the planet to cool the climate, there’s rightfully a lot of hesitation. Blocking incoming sunlight might seem like a quick fix to rising temperatures, but doing so could quickly tie up humanity in a decades-long project with alarming side effects like shifting precipitation patterns and changes in hurricane season.
Which is what makes a new paper released on Monday in Nature Climate Change so alluring. It shows that undertaking half measures to block the sun could end up providing the benefit of a cooler planet without many of the adverse impacts on other parts of the climate system. The results suggest there could be a role for geoengineering to play in saving us from a climate catastrophe, though it’s hardly the last word on what that role could be, or even if it’s worth the risk. And there are a few important caveats showing that there’s still a lot of research needed on the topic.


Devil’s Bargain Eric Holthaus; Grist; 8 Feb 2018

Air pollution from burning coal, driving cars, and using fire to clear land, among other activities, is the fourth-leading cause of death worldwide, killing about 5.5 million people each year. Nearly everybody is at risk, with roughly 92 percent of us living in places with dangerously polluted air. That alone makes reducing air pollution a necessary goal.
And yet we can’t live without aerosols, at least some of them. Natural aerosols — bits of dust, salt, smoke, and organic compounds emitted from plants — are an integral part of our planet’s atmosphere. Clouds probably wouldn’t be able to make rain without them. But as with greenhouse gases, human activity has resulted in too many aerosols (the excess is air pollution), with the bulk of the human-emitted aerosols lingering in the lower atmosphere, worsening their impact on our health. The result is a devil’s bargain: Aerosols are necessary for normal weather and help moderate rising temperatures, but they’re also killing us.
According to a new study, we might be locked in this deadly embrace. Research by an international team of scientists recently published in the journal Geophysical Research Letters says that the cooling effect of aerosols is so large that it has masked as much as half of the warming effect from greenhouse gases. So aerosols can’t be wiped out. Take them away and temperatures would soar overnight.
Turns out we have been unwittingly geoengineering for decades, and just like in the movies, it’s gone off the rails.

Climate Impacts From a Removal of Anthropogenic Aerosol Emissions B. H. Samset, M. Sand, C. J. Smith, S. E. Bauer, P. M. Forster, J. S. Fuglestvedt, S. Osprey, C.-F. Schleussner; Geophysical Research Letters; 24 Jan 2018

Limiting global warming to 1.5 or 2.0°C requires strong mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline, due to coemission with GHG, and measures to improve air quality. However, the combined climate effect of GHG and aerosol emissions over the industrial era is poorly constrained. Here we show the climate impacts from removing present-day anthropogenic aerosol emissions and compare them to the impacts from moderate GHG-dominated global warming. Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase. We find a higher sensitivity of extreme events to aerosol reductions, per degree of surface warming, in particular over the major aerosol emission regions. Under near-term warming, we find that regional climate change will depend strongly on the balance between aerosol and GHG forcing.
Plain Language Summary
To keep within 1.5 or 2° of global warming, we need massive reductions of greenhouse gas emissions. At the same time, aerosol emissions will be strongly reduced. We show how cleaning up aerosols, predominantly sulfate, may add an additional half a degree of global warming, with impacts that strengthen those from greenhouse gas warming. The northern hemisphere is found to be more sensitive to aerosol removal than greenhouse gas warming, because of where the aerosols are emitted today. This means that it does not only matter whether or not we reach international climate targets. It also matters how we get there.

Polar ice

Can we refreeze the Arctic? Scientists are beginning to ask Chelsea Harvey; E&E News; 6 Mar 2018

Part one of a three-part series.
... researchers are turning their attention to the ever-more-vulnerable Arctic and Antarctic regions with increasingly ambitious ideas to protect them.
Recent proposals include the use of giant pumps to refreeze vanishing Arctic sea ice — an idea scientists say would not only preserve the landscape but also slow the region's rapid warming — and building huge mounds on the seafloor aimed at preventing warm water from melting glaciers. A number of these ideas were presented at the American Geophysical Union's conference in December, as reported by Oceans Deeply.
So far, they're just ideas. But the concept of polar geoengineering — physically manipulating conditions in the Arctic and Antarctic to try to protect the ice, if only temporarily — has been flickering within the scientific community for years.
In 2009, glaciologist Jason Box of the Geological Survey of Denmark and Greenland suggested covering sections of the Greenland ice sheet with reflective material, similar to the efforts in Europe's mountain glaciers. He went so far as to demonstrate the process on a small swath of the ice sheet in a project documented on the Discovery Channel's "Ways to Save the Planet" program.
It's uncertain whether this relatively simple idea — let alone more complex technological fixes — could ever be applied at a scale that would make a difference across the Arctic or Antarctic. Still, it's a field that some scientists believe is worth exploring, because what happens at the poles has such great potential to affect the rest of the world.

Albedo / radiation modification

Shipping in the Arctic to Cool Off the Planet ajdavis2004; Climate CoLab

With help from the multi-billion dollar trans-ocean shipping industry we can open Arctic-night ice-pack, and use these openings to grow and thicken ice to increase summer albedo. This intervention will keep the planet from accumulating excess energy, halting global warming, while providing habitat for Arctic sea life and year-round trade for Arctic human communities.

Will Dimming the Sun Cool the Planet and Help Crops? Annie Sneed; Scientific American; 8 Aug 2018

As Earth’s temperature steadily climbs and international action to curtail heat-trapping greenhouse gases falters, climate change poses such a dire threat that scientists are now seriously investigating geoengineering as a last-ditch attempt to cool the planet.
But deliberately manipulating Earth’s climate could obviously have unintended consequences, so “it’s very important that we study it before anyone tries to use it,” says Solomon Hsiang, a professor of public policy at the University of California, Berkeley. “We should know what we’re getting ourselves into.” Hsiang and a team of researchers aimed to find out with a new study that looks at how one type of proposed geoengineering—injecting tons of tiny particles into the atmosphere to deflect sunlight and shade the planet—would affect a very important system: agricultural crops.
A growing body of research suggests heat stress from global warming could crimp harvests—a major concern for global food security. For example, a study published in June found corn yields would drop overall and see more year-to-year variability as temperatures rise. Solar geoengineering, then, would seem like a potential way to ease the agrarian climate burden. It even offers the additional benefit of scattering the sun’s rays, creating the kind of diffuse light that many plants tend to prefer. But there is a potential snag: Plants would receive less light overall for photosynthesis. What remains unclear is which effect wins out, and so whether such geoengineering would ultimately hurt or help agriculture. Hsiang’s new study, published Wednesday in Nature, attempts to determine the overall effect.