• Geoengineering is a term that refers to technology that can alter Earth's natural cycles to cool down the planet. It's being increasingly discussed as a potential way to address climate change.
• Putting mirrors in space, capturing carbon dioxide, and seeding clouds with particles are all ways of manipulating weather or the atmosphere.
• But some scientists and politicians think geoengineering could damage the planet or lead to war. 
• Here are 11 strategies researchers have put forth to hack the planet and combat climate change.

Oceans are hotter than they've ever been in recorded history. Ice Sheets are melting at unprecedented rates. Sea-level rise threatens countless species, coastal cities, and local economies.

As researchers' warnings about the consequences of climate change get more dire, some scientists and politicians are suggesting we do more than just curb our greenhouse-gas emissions — they want to hack our climate.

The technical term for this is geoengineering.

The concept evokes fantastical images of weather-controlling satellites, giant space mirrors, and carbon-sucking tubes. But some techniques for modifying Earth's atmosphere aren't in the realm of fantasy.

In fact, discussions about manipulating the atmosphere to cool the planet are growing increasingly mainstream. Climeworks, a company that captures carbon dioxide from the air, opened its first commercial plant in Switzerland in 2017. Y Combinator, Silicon Valley's largest incubator, has requested proposals from geoengineering-focused start-ups. And some political candidates, including presidential hopeful Andrew Yang, think the US needs to beat other countries to these technologies.

Read more: Longshot presidential candidate Andrew Yang thinks rogue geoengineering could cause a war

But other experts are less than convinced that these planet hacks are a good idea.

"The side effects may be almost as bad as the disease you're trying to cure," author and environmental activist Bill McKibben told Business Insider. What's more, McKibben said, geoengineering does little to address other problems that arise from greenhouse-gas emissions, such as ocean acidification. 

Here are 11 potential geoengineering methods that have been proposed so far.

There are two main types of geoengineering. The first is carbon capture, which entails removing carbon dioxide from the atmosphere.

Carbon capture and storage (CCS) is becoming widely accepted as a safe and potentially effective climate-change-fighting tool. Many people see it as a way to simply undo the changes that human activity is already causing.

Power plants in the US and Canada have already started utilizing CCS to lower their emissions. In the fall of 2014, the Boundary Dam Power Station near Estevan, Saskatchewan became one of the first power stations in the world to successfully use the technology.

According to the Center for Climate and Energy Solutions, 21 commercial-scale carbon capture projects are operating around the world, and 22 more were in developmentas of 2017.

In some cases, CCS technology can also prevent carbon emissions from entering the atmosphere at all. Instead, carbon dioxide that's created when coal burns or electricity is generated can be captured in a plant, then transported and stored somewhere else.

Some companies are already developing promising carbon-capture technologies.

Norway's state-owned carbon-capture technology coordinator, GassNova is facilitating financial support for the development, demonstration, and pilot studies of CCS technologies in the country.

A New York-based start-up, Global Thermostat, uses carbon sponges to absorb carbon dioxide directly from the atmosphere, smokestacks, or both.

The company is building its first commercial-scale direct-air carbon-capture plant in Huntsville, Alabama. Global Thermostat cofounder Graciela Chichilnisky told Grist that once the plant is up and running, it will suck "up to a million tons of CO2 per year or more — all removed from air," 

Carbon Engineering, a British Columbia-based company owned in part by Bill Gates, is also striving to open commercial plants to pull carbon dioxide directly out of the the air.

One of the biggest issues with these carbon-capture technologies, however, is figuring out where to put the carbon dioxide after it's captured.

According to the Carbon Capture and Storage Association, storage sinks for captured carbon are typically deep underground in depleted oil and gas fields.

A Saskatchewan-based carbon storage effort, the Weyburn-Midale CO2 Monitoring and Storage project, has successfully moved and injected stored carbon into two depleted oil fields.

In 2008, a facility on an island in the Barents Sea stored nearly 4 tons of carbon in an offshore subsurface reservoir.

Captured carbon could also get stored in containers filled with carbon-dioxide-eating or converting algae and bacteria.

These storage units are sometimes called bioreactors. A company in Quebec City, Canada called CO2 Solution has genetically engineered E. coli bacteria to produce enzymes that convert the carbon dioxide into an alternative form called bicarbonate.

According to a 2010 study, algae ponds are also effective at naturally capturing carbon through photosynthesis. 

Some companies are trying to turn the carbon they capture into useful materials.

In May 2017, the Zurich-based company Climeworks opened its first commercial carbon-capture plant, which compresses captured carbon dioxide and turns it into fertilizer.

A company called Blue Planet converts carbon dioxide into bicarbonate then uses that to make building materials.

Blue Planet takes carbon dioxide that has been captured from factories — like California's largest power plant in Moss Landing — and turns it into into a limestone coating that covers the company's proprietary concrete building material.

Blue Planet's products aren't yet available in big enough quantities for large-scale projects, according to Caltrans, but the company is currently developing a larger production facility in the San Francisco Bay Area.

Despite the fact that Blue Planet's products aren't on the commercial market yet, its bicarbonate rocks were included in the construction of part of San Francisco International Airport.

Another major planet-hacking strategy is solar geoengineering, which involves injecting particles or clouds into the sky that reflect sunlight back into space.

This is also called solar radiation management or albedo modification. (Albedo is the term for how much light or radiation is reflected back from Earth's surface.)

Ultimately, solar geoengineering aims increase the amount of solar radiation that gets reflected out into space from Earth in order to cool down the planet.

But none of these technologies have gotten off the ground yet, so to speak. In fact, most are so controversial that they haven't even been tested.

The idea for solar geoengineering is inspired by the effects of volcanic eruptions.

When volcanoes fill the skies with sulfur and ash, that causes more sunlight to be reflected away from the planet, and the Earth cools.

Nearly 200 years ago, Mount Tambora in Indonesia underwent the most deadly volcanic eruption in recorded history, according to NASA. Some scientists believe the eruption was responsible for a severe summertime cold snap the following year that triggered killer frosts in New England and Europe.

This volcanic effect could be mimicked via a technique called stratospheric aerosol scattering. This involves injecting the upper atmosphere with tiny reflective particles like sulfuric acid or aerosols.

The idea is that these particles would reflect some sunlight away from Earth and back into space.

Harvard University's solar geoengineering research program is currently trying to model how clouds of such particles in the atmosphere would behave using small, steerable balloons.

The research program also suggests that we could brighten marine clouds so they reflect more sunlight. (The closer an object's color is to white — or the brighter it is — the more light it reflects.)

Mirrors, of course, also reflect sunlight. So some scientists have floated the idea of putting giant mirrors in space.

In the 2000s, a scientist named Lowell Wood from Lawrence Livermore National Laboratory suggested that a giant space mirror made of aluminum mesh could combat climate change. But he warned that the device would need to be 600,000 square miles in area — about the size of Greenland — to do any good. That would probable be prohibitively expensive.

"It would be like a window screen made of exceedingly fine metal wire," Wood explained to Popular Science in 2005.

More than a decade later, the idea of a space mirror is still hypothetical. 

Eliminating or thinning some cirrus clouds —a type of cloud that sits high in the atmosphere and absorbs radiation — could be another way to send heat back into space.

This effort would involve reducing high-altitude cirrus clouds by seeding them with water-depleting aerosols. 

These wispy clouds don't do much to reflect sunlight, but they do a lion's share of radiation trapping. So thinning them could theoretically help cool the Earth because that would provide more pathways for planet-warming solar radiation to escape into space.

One technology that manipulates the clouds is already in use today. It doesn't really address climate change, but it does allow us to make it rain when and where we want.

Cloud seeding is a way to make it rain or snow by dropping silver ions into the atmosphere.  Rainstorms happen when enough moisture collects around particles in the air, so these ions provide additional particles for moisture to glom onto.

The technology has already been tested by the governments of China, Russia, and the United Arab Emirates.

According to Pacific Standard Magazine, the technique has been in use for 75 years, and even helps with drought relief in the western US. In 2015, Texas experienced a 34% uptick in the length of rainfall thanks to cloud seeding.

Instead of focusing on clouds, some researchers are looking into ways to save melting Arctic ice. Ice sheets are responsible for reflecting lots of sunlight into space, so less ice means less heat leaving the planet.

A 2018 study showed that the 75% loss of Arctic ice volume that we've seen since 1979 — and the related loss of sunlight-reflecting surfaces — has significantly contributed to our warming planet. 

A nonprofit called Ice911 wants to spread tiny glass beads around the Arctic that mimic ice's reflective abilities.

Ice911's glass microsphere beads are tiny, hollow, and made from sand. They look like snow.

Leslie Field, the founder of Ice911, wants to spread the beads all over the Arctic in the hopes of making the polar ice more reflective and less prone to melting.

"Multi-year ice, the reflective ice in the Arctic, was historically the Earth's heat shield," Field recently told Fast Company. "It's not there to do that anymore."

The group is still testing its technology near Barrow, Alaska. In 2017, Ice911 covered more than three football fields of ice in glass beads, and in 2018, the organization deployed an additional 161,000 square feet of beads. Early results were promising: Treated areas showed higher reflectivity and less ice melt than untreated areas.

Alternatively, some researchers are pushing to shore up melting ice from the bottom up.

A recent article in the journal Nature suggested using geoengineering to preserve continental ice sheets by targeting the places where the ice meets warming ocean water.

One proposed technique is to raise artificial ridges to protect the weakening margins of glaciers. But scientists warn that such a project could cost billions of dollars.

Beyond all of these options, researchers and investors are also thinking about geoengineering strategies that sound like something out of science fiction.

Y Combinator, a prestigious incubator that boasts alums like Dropbox and Airbnb, issued a request last year for start-ups focusing on what they call "frontier technology ideas" for geoengineering.

"It's time to invest and avidly pursue a new wave of technological solutions to this problem — including those that are risky, unproven, even unlikely to work. It's time to take big swings at this," the company wrote in an announcement on their website.

Examples of these frontier solutions include developing genetically engineered phytoplankton that take in carbon dioxide via photosynthesis, and flooding deserts to create micro-oases that serve as carbon sinks. 

Such concepts "straddle the border between very difficult to science fiction," the company wrote.

Wilder still is a proposal to create a cloud of asteroid dust in space that would shield the Earth from sunlight.

A group of Scottish scientists suggested this idea in 2012.

Their plan called for pushing an asteroid to a specific point in space where it would feel equal gravitational pulls from the Earth and sun, so would remain anchored in place. Then a spacecraft would land on the asteroid and hurl asteroid dust into space.

The researchers said their plan would reduce the amount of sunlight hitting Earth by almost 2%, which would be enough to offset some 5 degrees Fahrenheit of warming.

Needless to say, the plan has many downsides, including the risk that the asteroid could accidentally get directed towards Earth.

In general, any geoengineering project or proposal that involves tweaking the delicate chemistry of Earth's atmosphere and its cycles faces enormous opposition.

Many scientists are particularly concerned about solar geoengineering experiments because most models predict that the effects will be felt differently around the globe, even in spots far from the initial location. For example, if solar geoengineering technology gets deployed in the southern hemisphere, that could impacts ocean temperature and wind speeds, leading to more hurricanes in the northern hemisphere.

Plus, a failed geoengineering technology could leave Earth's atmospheric chemistry irreversibly altered. We could end up damaging the ozone layer, for example, which protects us from harmful ultraviolet radiation.

However, a recent study asserted that it is possible to tweak the atmosphere in a way that would prevent other parts of the planet from experiencing weather backlash.

The study, published in the journal Nature Climate Change, modeled a scenario in which small amounts of geoengineering would decrease temperatures all over the world. Although such an initiative would perturb the climate in new ways, the authors wrote, those disturbances would be negligible compared to the havoc that climate change is already wreaking via droughts and rising sea-levels.

They suggested forming an international research program to investigate this option further.

Yet some scientists and politicians are already warning that geoengineering could lead to war.

"I've got a list of 27 reasons we shouldn't do it," Alan Robock, an environmental science professor at Rutgers and an expert on geoengineering, previously told Business Insider.

He worries a rogue country could pull the trigger on an atmospheric-transformation project that affects the entire world. The resulting conflicts with other nations could ultimately could escalate to nuclear war, Robock said.

Andrew Yang echoed similar concerns. If China start playing with atmospheric modifications on its own, rather than as part of a global initiative, Yang said, he expects the worst.

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