Ice Ages Blamed on Tilted Earth


Ice Ages Blamed on Tilted Earth

In the past million years, the Earth experienced a major ice age about every 100,000 years. Scientists have several theories to explain this glacial cycle, but new research suggests the primary driving force is all in how the planet leans.

The Earth’s rotation axis is not perpendicular to the plane in which it orbits the Sun. It’s offset by 23.5 degrees. This tilt, or obliquity, explains why we have seasons and why places above the Arctic Circle have 24-hour darkness in winter and constant sunlight in the summer.

But the angle is not constant – it is currently decreasing from a maximum of 24 degrees towards a minimum of 22.5 degrees. This variation goes in a 40,000-year cycle.

Peter Huybers of Woods Hole Oceanographic Institution and Carl Wunsch of the Massachusetts Institute of Technology have compared the timing of the tilt variations with that of the last seven ice ages. They found that the ends of those periods – called glacial terminations – corresponded to times of greatest tilt.

“The apparent reason for this is that the annual average sunlight in the higher latitudes is greater when the tilt is at maximum,” Huybers told LiveScience in a telephone interview.

More sunlight seasonally hitting polar regions would help to melt the ice sheets. This tilt effect seems to explain why ice ages came more quickly – every 40,000 years, just like the tilt variations — between two and one million years ago.

“Obliquity clearly was important at one point,” Huybers said.

Colder planet

The researchers speculate that the glacier period has become longer in the last million years because the Earth has gotten slightly colder – the upshot being that every once in a while the planet misses a chance to thaw out.

The glacial cycles can be measured indirectly in the ratio of heavy to light oxygen in ocean sediments. Simply put, the more ice there is on Earth, the less light oxygen there is in the ocean. The oxygen ratio is recorded in the fossils of small organisms – called foraminifera, or forams for short – that make shells out of the available oxygen in the ocean.

“These ‘bugs’ have been around for a long time – living all across the ocean,” Huybers said. “When they die, they fall to the seafloor and become part of the sediment.”

Drilled out sediment cores from the seafloor show variations with depth in the ratio of heavy to light oxygen – an indication of changes in the amount of ice over time. This record of climate change goes back tens of millions of years.

By improving the dating of these sediments, Huybers and Wunsch have showed that rapid decreases in the oxygen ratio – corresponding to an abrupt melting of ice – occurred when the Earth had its largest tilt.

Other orbital oddities

The significance of this relationship calls into question other explanations for the frequency of ice ages.

One popular theory has been that the noncircular shape, or eccentricity, of Earth’s orbit around the Sun could be driving the glacial cycle, since the variations in the eccentricity have a 100,000-year period. Curiously different, but interesting.

Variation in Orbit Period
Tilt 40,000 yr
Wobble 20,000 yr
Eccentricity 100,000 yr

By itself, though, the eccentricity is too small of an effect. According to Huybers, changes in the orbit shape cause less than a tenth of a percent difference in the amount of sunlight striking the planet.

But some scientists believe a larger effect could be generated if the eccentricity fluctuations are coupled with the precession, or wobble of the Earth’s axis. It’s like what is seen with a spinning top as it slows down.

Earth’s axis is currently pointing at the North Star, Polaris, but it is always rotating around in a conical pattern. In about 10,000 years, it will point toward the star Vega, which will mean that winter in the Northern Hemisphere will begin in June instead of January. After 20,000 years, the axis will again point at Polaris.

Huybers said that the seasonal shift from the precession added to the eccentricity fluctuations could have an important effect on glacier melting, but he and Wunsch found that the combined model could not match the timing in the sediment data.

Skipping beats

The question, then, that Huybers and Wunsch had to answer: How does the 40,000-year tilt cycle make a 100,000-year glacial cycle? A more careful sediment dating has shown is that the time between ice ages may on average be 100,000 years, but the durations are sometimes 80,000 years, sometimes 120,000 years — both numbers are divisible by 40,000. It appears there was not a mass melting every time the tilt reached its maximum.

“The Earth is skipping obliquity beats,” Huybers explained.

The planet only recently started missing melting opportunities. Although the researchers have no corroborating evidence, they hypothesize that the skipping is due to an overall cooling of the planet.

The last major glacial thaw was 10,000 years ago, which means that the Earth is scheduled to head into another ice age. Whether human influences could reverse this, Huybers was hesitant to speculate. Other researchers have found evidence that the process of climate warming can set up conditions that create a global chill.

“What we have here is a great laboratory for seeing how climate changes naturally,” he said. “But this is a 100,000-year cycle, whereas global warming is happening a thousand times faster.”

Frozen Earth in ‘Snowpiercer’ Is a Grim (and Possible) Future for Our Warming Planet

Supertrain "Snowpiercer" barrels across a frozen Earth, in a new TNT series about the aftermath of a global climate catastrophe.

Supertrain “Snowpiercer” barrels across a frozen Earth, in a new TNT series about the aftermath of a global climate catastrophe.
(Image: © TNT)

NEW YORK — In the not-so-distant future, humanity’s last survivors ride a vast, never-stopping train across a frozen Earth. The fictional world of “Snowpiercer,” a new TV series airing on TNT in early 2020, is a grim one. A botched attempt to reverse runaway global warming has left Earth blanketed in ice and snow. Only a few thousand people — some wealthy and privileged and many desperate and wretched — survive, saved by a billionaire’s pet project: a beast of a supertrain (named Snowpiercer) that extends for miles, equipped to ride the rails until Earth is habitable again.

The series is based on the 1982 French graphic novel “Le Transperceneige,” as was the 2013 movie “Snowpiercer,” directed by Bong Joon-Ho.

At New York Comic Con on Oct. 5, the show’s cast and creators presented a glimpse of this broken Earth, the strange “ark” that barrels ceaselessly onward and the surviving humans who ride onboard. TNT’s version of the tale unfolds seven years after the global climate catastrophe and the train’s departure, when untold millions of people (not to mention all of Earth’s animals and plants) were left behind to die.

Related: Doom and Gloom: Top 10 Post-Apocalyptic Worlds

Bleak as this story is, it represents “a logical extension of what happens when you continue to ignore science and you’re forced to make a rash decision about how to save your planet,” said actor Daveed Diggs, who plays ex-homicide detective Andre Layton on the show.

That dire scenario is especially relevant today. Unprecedented and human-driven climate change is raising sea levelserasing glaciers and sea ice; and spawning dangerous wildfires, widespread droughts and intense heat waves. In fact, recent climate-related news fueled a sense of urgency for Graeme Manson, executive producer and showrunner of “Snowpiercer.”

“It lit a fire under me to want to tell this story now,” Manson told Live Science.

At New York Comic Con, the "Snowpiercer" cast fielded questions about how a climate catastrophe set the stage for the show's desperate, dystopian world. Left to right: Alison Wright, Daveed Diggs, Jennifer Connelly, Mickey Sumner, Lena Hall, Steven Ogg, Sheila Vand.

At New York Comic Con, the “Snowpiercer” cast fielded questions about how a climate catastrophe set the stage for the show’s desperate, dystopian world. Left to right: Alison Wright, Daveed Diggs, Jennifer Connelly, Mickey Sumner, Lena Hall, Steven Ogg, Sheila Vand.

(Image credit: Getty Images for WarnerMedia Company)

Global ice ages have frozen Earth in the past. But with accelerating climate change heating things up, is a planet-wide deep freeze even possible anymore? And could trying to artificially cool Earth save the planet, or would it trigger a cascade of consequences that produce a frozen wasteland like that in “Snowpiercer” — or something that’s even worse?

Between 750 million and 580 million years ago, three to four dramatic ice ages froze nearly all of Earth’s surface for about 10 million years at a stretch. During these periods of intense cold, average global temperatures plummeted to minus 58 degrees Fahrenheit (minus 50 degrees Celsius); these frigid conditions earned the planet the nickname “snowball Earth.”

Lesser ice ages emerge about once every 120,000 years, driven by shifts in Earth’s orbit and changes in our proximity to the sun, Robin Bell, a professor at Columbia University’s Lamont-Doherty Earth Observatory (LDEO) in New York City and president of the American Geophysical Union (AGU), told Live Science in an email.

“We should be having one [ice age] soon, except for our ongoing experiment in atmospheric chemistry,” said Bell, referring to fossil fuel burning that pumps quantities of greenhouse gases like carbon dioxide (CO2) into Earth’s atmosphere, accelerating warming. A future ice age could still happen, but only if atmospheric CO2 is drastically reduced, Maureen Raymo, a LDEO paleoclimatologist and research professor, told Live Science in an email.

Could artificially cooling the planet through geoengineering trigger an ice age or create a snowball Earth? “Physically, it’s not inconceivable,” said Gavin Schmidt, a climatologist and director of the NASA Goddard Institute for Space Studies in New York City.

During one of Earth's past deep freezes, the planet may have resembled Saturn's frozen moon Enceladus, pictured here.

During one of Earth’s past deep freezes, the planet may have resembled Saturn’s frozen moon Enceladus, pictured here.

(Image credit: NASA/JPL-Caltech/Space Science Institute)

Schmidt outlined one such geoengineering method. “If you put stuff into the atmosphere that’s white and reflective, that reduces the amount of solar radiation coming in and makes the planet colder,” he told Live Science. “It’s similar to what happens when big volcanoes erupt.”

For example, in 1991, the eruption of Mount Pinatubo in the Philippines spewed 20 million tons of sulfur dioxide into the stratosphere, causing global temperatures to drop by about 1 degree F (0.5 degrees C) from 1991 to 1993, according to the U.S. Geological Survey.

Related: 8 Ways Global Warming Is Already Changing the World

Removing excess CO2 from the atmosphere could also cool the planet; one way to do that could be to infuse the ocean with nutrients to encourage the growth of phytoplankton, microscopic marine algae that take up CO2 during photosynthesis.


“They would draw down CO2 from the atmosphere that would sink into the bottom of the ocean,” Schmidt said. “Then, everything would be back to normal.”

But take these procedures too far — block too much solar energy or siphon off too much atmospheric CO2 — and the result could be a global deep freeze, Schmidt said. Current atmospheric CO2 levels are about 410 parts per million, while preindustrial levels hovered at around 280 ppm, Schmidt said. Dip down to 180 ppm, and “then you’re in ice age territory,” he said.

What’s more, there are serious ethical concerns about launching such drastic actions to reset Earth’s climate.

“If we didn’t live here, it’d be much easier to play with the planet’s climate, but the consequences involve potentially billions of people,” Schmidt said. “We can’t even get a global agreement to reduce CO2. So the chances that we’d have a global agreement to put stuff in the atmosphere and change the climate seem very slim.”

Persistent hope

For Snowpiercer’s passengers, the chance to avert the worst impacts of climate change is long gone — “this is a story about what happens after it’s too late,” Diggs told Live Science. Yet, in spite of everything, the characters still find room for hope.

“Hope is inherent through living, continuing on,” actor Steven Ogg, who plays the rebellious gang leader, Pike, told Live Science. “If you’re waking up every day, that means, inherently, you’re living with hope.”

“You may think, ‘Well, I’ll die before I ever see the world go back to normal,'” said Lena Hall, whose character, Miss Audrey, manages the train’s brothel and cabaret. “But I don’t want to die now. I want to live and pass along what I know, and hope that the next generation, maybe they’ll see the change,” Hall said.

As dire as the real world’s climate crisis may seem, hope lingers here as well, in ongoing global actions to eliminate fossil fuel use and establish strategies for adapting to a warming world. But politicians and leaders need to act quickly, or a scenario as dire as that in “Snowpiercer” might be closer than we think, said actor Alison Wright; her character, Ruth Wardle, handles hospitality on the train.


“It’s not that much of a stretch, and it’s not a fantasy situation anymore,” Wright said. “Our story is just one possible result of what could happen.”

“Snowpiercer” will debut on TNT in the spring of 2020; check local listings.

Originally published on Live Science.

Solving the mystery of why atmospheric carbon dioxide was lower during ice ages

Solving the mystery of why atmospheric carbon dioxide was lower during ice ages
Illustration of the two main mechanisms identified by this study to explain lower atmospheric CO2 during glacial periods. Left: present-day conditions; right: conditions around 19,000 years ago during the Last Glacial Maximum. Credit: Andrew Orkney, University of Oxford

Since scientists first determined that atmospheric carbon dioxide (CO2) was significantly lower during ice age periods than warm phases, they have sought to discover why, theorizing that it may be a function of ocean circulation, sea ice, iron-laden dust or temperature.

A new study published this week in Science Advances provides compelling evidence for a solution—the combination of sea water variation and iron from dust off Southern Hemisphere continents.

“Many of the past studies that analyzed ocean temperatures made the assumption that ocean temperatures cooled at the same rate over the entire globe—about 2.5 degrees (Celsius),” said Andreas Schmittner, a climate scientist at Oregon State University and co-author on the study. “When they ran their models, temperature thus accounted for only a small amount of atmospheric CO2 decrease.

“We now know that the oceans cooled much more in some regions, as much as five degrees (C) in the mid-latitudes. Since  has a higher degree of CO2 solubility, it had the potential to soak up a lot more carbon from the atmosphere than past studies accounted for—and it realized more of that potential.”

Schmittner and his colleagues estimate that colder  would account for about half of the decrease in CO2 during the last glacial maximum—or height of the last ice age. Another third or so, they say, was likely caused by an increase in iron-laden dust coming off the continents and “fertilizing” the surface of the Southern Ocean. An increase in iron would boost phytoplankton production, absorbing more carbon and depositing it deep in the ocean.

The researchers’ models suggest that this combination accounts for more than three-quarters of the reduced amount of atmospheric CO2 during the last ice age. During the last glacial maximum, CO2 levels were about 180 parts per million, whereas levels in 1800 A.D.—just prior to the Industrial Revolution—were at about 280 parts per million.

Schmittner said the remaining amount of reduced carbon may be attributable to variations in nutrient availability and/or ocean alkalinity.

“The increase in iron likely resulted from ice scouring the landscape in Patagonia, Australia and New Zealand, pulling iron out of the rocks and soil,” Schmittner said. “Since it was very cold and dry, the iron would have been picked up by the wind and deposited in the ocean.

“Our three-dimensional model of the global ocean agrees well with observations from ocean sediments from the last , giving us a high degree of confidence in the results.”

The researchers say that when the Earth cooled during the last ice age, the oceans naturally cooled as well—except near the polar regions, which already were as cold as they could get without freezing. During warm phases, the difference in ocean surface temperatures between the high latitudes and the mid-latitudes was significant.

As warmer water moves toward Antarctica and begins to cool, the lost heat goes into the atmosphere, increasing the ocean’s potential to soak up CO2.

“It’s like when you take a beer out of the refrigerator,” Schmittner said. “As it warms, the bubbles come out. Carbon dioxide is a gas, and it can dissolve in water as well as get into the ocean from the atmosphere, and it is more soluble in colder water. But that process takes a while and therefore the ocean doesn’t realize all of its potential to take up CO2 in those waters around Antarctica that fill much of the deep .”

When the mid-latitude oceans began cooling, they began soaking up more CO2 from the atmosphere, and emitting less because colder  is more CO2 soluble.

“It was the perfect combination that can explain almost exactly why CO2 levels were about one-third lower during ice age periods,” Schmittner said.

The Indian monsoon’s impact on the ice age provides a clue into global warming



By Katrina Nilsson-Kerr & Pallavi AnandMarch 18, 2019
The past may be a surprisingly useful guide for predicting responses to future climate change. This is especially important for places where extreme weather has been the norm for a long time, such as the Indian subcontinent. Being able to reliably predict summer monsoon rainfall is critical to plan for the devastating impact it can have on the 1.7 billion people who live in the region.

The onset of India’s summer monsoon is linked to heat differences between the warmer land and cooler ocean, which causes a shift in prevailing wind direction. Winds blow over the Indian Ocean, picking up moisture, which falls as rain over the subcontinent from June to September.

The monsoon season can bring drought and food shortages or severe flooding, depending on how much rain falls and in what duration. Understanding how the monsoon responded to an abrupt climate transition in the past can therefore help scientists better understand its behaviour in the future.

Maharashtra, India on May 28, 2010, during the dry season.
When we researched this weather system’s ancient past, we found it was highly sensitive to climate warming 130,000 years ago. Our new study published in Nature Geoscience showed that the Indian summer monsoon pulled heat and moisture into the northern hemisphere when Earth was entering a warmer climate around 130,000 years ago. This caused tropical wetlands to expand northwards—habitats that act as sources of methane, a greenhouse gas. This amplified global warming further and helped end the ice age.

The rate at which today’s climate is changing is unprecedented in the geological record, but our study shows how sensitive the Indian summer monsoon was during a global transition into warming in the past and may still be.

The same view in Maharashtra, India on Aug. 28, 2010, during the monsoon season.
The monsoon rains of yesteryear
Over the last one million years, the climate fluctuated between a cold glacial—known as an ice age—and a warm interglacial as the Earth’s position relative to the sun wobbled in its orbit. The last transition from an ice age into the warm climate of the present interglacial—known as the Holocene—occurred around 18,000 years ago. This period of Earth’s history is relatively well understood, but how Earth system processes responded to these climate changes deeper in time is still something of a mystery.

A recent expedition to drill deep into the ocean floor of the Bay of Bengal gave an opportunity to reconstruct past Indian monsoon behaviour over hundreds of years before the last ice age.

Our study used these deep sea sediments from the northern Bay of Bengal to capture a direct signal of the Indian summer monsoon from 140,000 to 128,000 years ago, hidden in the fossilised shells of tiny microscopic creatures called foraminifera. These plankton species once lived in the upper ocean water column and captured the environmental conditions of the surrounding seawater in the chemical make-up of their shells.

We detected the ocean surface water freshening from river discharge induced by the rains of the Indian summer monsoon from 140,000 to 128,000 years ago—a sign of the strengthening monsoon system. This occurred when the Earth was coming out of a glacial state and into the interglacial which occurred before the one we live in, separated by a single ice age. During this period—which we’ll refer to as the penultimate deglaciation—sea levels rose from six to nine metres worldwide.

Ice-core records show that Antarctica began to warm first during the penultimate deglaciation. Southern Hemisphere warming provided a source of heat and moisture which fuelled the strengthening of the Indian summer monsoon, as seen in our records of surface freshening and river runoff from the northern Bay of Bengal.

Wetland in Leh Ladakh, India. The expansion of tropical wetlands further north released more methane to the atmosphere, accelerating global warming.
During this warming period around 130,000 years ago, the Indian summer monsoon responded to southern hemisphere warming while the northern hemisphere and other monsoon systems, such as the East Asian summer monsoon—which affects modern day China, Japan, and the far East—remained in a glacial state.

The Indian summer monsoon pulled heat and moisture northwards, driving glacial melting in the northern hemisphere and helping tropical wetlands expand their range. These expanding tropical wetlands resulted in more methane release into the atmosphere which caused even more warming, setting changes in motion which ended the global ice age.

The Indian summer monsoon is an incredibly dynamic system. Though confined to the tropics, the system is sensitive to climatic conditions in both hemispheres. Due to its role in contributing to methane emissions, the Indian summer monsoon also has an outsize impact on the global climate. Monsoons should not be viewed in isolation, just as the polar ice sheets shouldn’t. Earth’s internal climate system is intrinsically linked and abrupt changes at one place can have significant consequences over time elsewhere.

This article is republished from The Conversation under a Creative Commons licence. Read the original article.

Scientists say controversial plan to cool the planet is “doable”

Spraying chemicals into the atmosphere could slow global warming by reflecting sunlight back into space.

A new study finds that global engineering efforts could cost $3.5 billion over the course of the next 15 years to develop the technology.David Goldman / AP file

By Rafi Letzter, Live Science

Earth keeps getting hotter. Humanity isn’t doing enough to stop it. So, scientists are increasingly musing about conducting dramatic interventions in the atmosphere to cool the planet. And new research suggests that a project of atmospheric cooling would not only be doable, but also cheap enough that a single, determined country could pull it off. That cooling wouldn’t reverse climate change. The greenhouse gases would still be there. The planet would keep warming overall, but that warming would significantly, measurably slow down.

Those are the conclusions of a paper published Nov. 23 in the journal Environmental Research Letters by a pair of researchers from Harvard and Yale universities. It’s the deepest and most current study yet of “stratospheric aerosol injection” (also known as “solar dimming” or “solar engineering”). That’s the spraying of chemicals into the atmosphere to reflect the sun’s heat back into space, mimicking the global cooling effects of large volcanic eruptions.

The researchers found that humanity could, using this method, cut our species’ annual contributions to the greenhouse effect in half at a price that states and large cities spend all the time on highways, subways and other infrastructure projects: a total of about $3.5 billion over the course of the next 15 years to develop the technology. (Most of those funds would go into building planes able to carry big tanks of aerosol spray into the stratosphere, about double the cruising altitude of a Boeing 747.) Once the tech is ready, the researchers found, the project would then cost another $2.25 billion or so each following year (assuming the effort would run for the next 15 years).

For comparison, the Massachusetts Department of Transportation budget in 2017 was $1.8 billion. Texas will have spent nearly a billion dollars replacing a single bridge in Corpus Christi. New York City subway-repair budgets routinely run into the tens of billions of dollars. Belgium spends about $4 billion every year on its military. In other words, geoengineering the atmosphere to slow climate change is cheap enough that a small, determined state or country could probably afford to do it, not to mention a superpower like the U.S. or China. [8 Ways Global Warming Is Already Changing the World]

That might seem nuts, but outside researchers who read the paper said its methods were sound and its conclusions not all that surprising.

“[The paper] seemed reasonable and methodical to me,” said Kate Ricke, a professor at the University of California, San Diego, who studies climate change and policies for addressing it. “I think it’s definitely a helpful contribution, in that it confirms this idea that stratospheric engineering would be much cheaper than emissions reductions for the same global temperature effect.”

Ken Caldeira, a senior scientist at the Carnegie Institution for Science, agreed.

“One could expect any governmental operations to have cost overruns, but overall, I’ve got no reason to question these findings. They seem reasonable to me,” he told Live Science.


The science here is in a certain respect straightforward: Dump sulfur dioxide (SO2) into the atmosphere, and it will reflect light back into space. SO2 is cheap, and there’s lots of it available. Most of the costs of the project would come from lofting the SO2 high enough that it would stick around, Wake Smith, a co-author of the paper and lecturer at Yale, said. [Cool the Planet? Geoengineering Is Easier Said Than Done]

“If you deploy material at 35,000 feet [10,700 meters], say, where your 737 flies, it rains back down in a few days, because it’s just being acted on by gravity,” he told Live Science. “If you get it up into the stratosphere, on the other hand, then it stays aloft for a year or 18 months.”

(This, incidentally, is one of the reasons that chemtrail conspiracy theories — which mistakenly link chemtrails to a secret government plan to modify the weather — are so implausible, he added. Anything sprayed at the heights at which jetliners fly would disappear within half a week.)

Still, getting the SO2 high enough isn’t an insurmountable challenge, this paper shows, and the approach really could cool down the planet.

But cooling down the planet isn’t the same thing as reversing climate change, the researchers explained.

Carbon emissions do a lot more than just form a chemical greenhouse around the planet. They also make the oceans more acidic and alter the global movement of air and water. Already, these emissions have baked heat into the system that wouldn’t just go away if humanity slapped a layer of SO2 into the stratosphere. [The Craziest Climate Change Fixes]

“It may be that we can reduce global surface temperatures​ overall, relative to where they would be in an un-engineered world,” Smith said, “but that doesn’t mean that the climate in every place will go back to the way it was. Some places will be warmer. Some will be cooler. Some will be drier. And some will be wetter, and even a perfectly engineered climate future, which is impossible, will change things all over the world, and that won’t be good for people either.”

Plus, he said, there are tipping points in climate change that an SO2 bandage wouldn’t fix.

“If all the ice in Greenland melted and slid into the sea,” Smith said, referring to a scenario that would drastically raise sea levels, flooding coastlines all over the world, “and then we refreeze the planet, or cool the planet by engineering, the ice won’t climb back up from the sea onto the land. The ice on Greenland is the result of millions of years of snowfall.”

So, even though he thinks this sort of geoengineering is worth studying, he said it’s important that people understand that it isn’t a solution.

“I do worry that some fossil fuel company will say exactly that, and the geoengineering community is going to have to figure out how to guard against that infiltration or any association in the public’s mind,” he said.


The idea of pumping aerosols into the upper atmosphere to mitigate climate change taken seriously enough that the concept turned up in the recent 2018 IPCC report on climate change as a possible mitigation approach — though the IPCC stopped short of endorsing this sort of spraying. Right now, it looks cheaper than alternative geoengineering technologies, Ricke said, like proposals to suck carbon dioxide out of the atmosphere. (The IPCC, or Intergovernmental Panel on Climate Change, is an international organization established by the United Nations to assess the science, risks and impacts of climate change.)

But that doesn’t mean that such approaches will, or should, happen, the researchers all agreed.

“I don’t think it’s a good idea at this point,” Ricke said. “I don’t think we know enough about how to do it. And we don’t have anything close to a system for reaching agreement about the amount we should do or how we should make that decision about the specifics of where we would put more aerosols, et cetera. I don’t think we’re anywhere close.”

But all of that could change, she said.

“There’s a lot of scary climate-change impacts, like melting glaciers in Greenland and Antarctica, that are staring us in the face,” she said. “Because [cutting emissions] and CO2 removal will take some time, even if we get serious about implementing them — which I’m not convinced about — I think that solar geoengineering has the potential to be one of the only options left.”

That’s worrying for a number of reasons, Smith said, one of which is that there would almost certainly be side effects that the sprayers couldn’;t anticipate. Though one benefit of the spraying, he added, is that as soon as it’s stopped its effects would go away within 18 months.

Caldeira agreed that the use of such engineering looks more and more likely, but said he doubted it would happen, due to the political dynamics involved. No politicians, he said, would want to take the blame for a bad weather event that occurred the year after they voted to spray SO2.

“Imagine if Hurricane Sandy happened on the year after we started putting this material up there,” he said, suggesting people could place blame on the atmospheric engineering.

Still, he said, a small country badly hit by climate change might decide to do this without global approval. However, the paper noted that such an effort would be impossible to keep secret, and other, larger nations might decide to stop the project. Doing this work properly would require flying all over the world’s middle latitudes, and this would have to go on indefinitely. (Masking the warming effect of greenhouse gases doesn’t make them go away, and they can last for a thousand years in the atmosphere, unlike sulfates. So, the solar engineering would have to continue, to counteract those effects.)

“I’m not going to say whether [I think we’ll get to the point of atmospheric spraying],” Smith said, “not because it’s too much of a hot potato, but because I really don’t know.”

Other techniques for geoengineering might become cheaper, or nations might just never get around to this sort of climate mitigation, he said.

For now, Ricke said, the big open questions involve stratospheric chemistry — how sulfur would interact with other chemicals in the atmosphere — and the local effects of this sort of program. How would a big new batch of SO2 in the atmosphere affect the ozone layer, for example? How would individual regions, agriculture or local water systems react to the sudden change in sunlight? How would the public react?

For now, she said, she wants to see a lot more research.

Originally published on Live Science.