Protecting Our Climate by Turning CO2 Into Stone

The biggest task of this century is to reduce the emissions of CO2 into the atmosphere, to slow down climate change. One key technology is to capture the CO2 from power plants and factories to prevent it from affecting the climate. But how can we store this captured CO2 in a safe and permanent manner? In this article, we report on a method that has been demonstrated in Iceland, in which CO2 is injected deep into the ground and turned into stone—a natural way of dealing with CO2 emissions!

of fossil fuels for power plants, cars, and airplanes. Burning fossil fuels FOSSIL FUELS Fossil fuels are formed over millions of years from organic matter, such as buried plants and animals. Fossil fuels include coal, natural gas, and oil, but burning of these fuels releases a lot of CO . Fossil fuels are the largest contributor to Climate change.
releases greenhouse gases, mostly carbon dioxide (CO ), which in turn increase the greenhouse e ect and lead to rising temperatures.

GREENHOUSE EFFECT
The e ect the greenhouse gases have on the atmosphere by trapping heat and warming the Earth's surface. This rise in temperature, known as global warming, increases the

GLOBAL WARMING
The warming we are experiencing due to the increased greenhouse e ect. number of wildfires, speeds up the melting of glaciers, and causes rising sea levels. In addition, global warming leads to more extreme weather events, such as droughts, storms, and heavy rainfall. The continued emission of greenhouse gases will cause further warming of the atmosphere and oceans, which will cause permanent changes in the earth's climate, increasing the likelihood of severe impacts for people and ecosystems.
The biggest task of this century is to reduce the emission of CO into the atmosphere, to help slow down global warming. This means changing from fossil fuels to renewable energy sources. In addition, we need to conserve our resources on Earth, plant trees, and restore land that has been damaged through human activities. But some CO emissions are hard to get rid of, including the CO released from cement and steel factories, for example. There are also places where renewable energy is not an option and fossil fuels still need to be burned. How is it possible to minimize such CO emissions?

NATURE'S WAY OF REDUCING EMISSIONS
One key technology for reducing emissions is to capture the CO that is produced by power plants and factories. This prevents the CO from being released into the atmosphere and limits the e ects of climate change. But where can we store this captured CO ? How can it be

CLIMATE CHANGE
The change of the Earth's climate due to the increased greenhouse e ect causing warming of the Earth's surface. put away in a safe and permanent way?
In Iceland, a method has been developed that takes this captured CO and turns it into stone, deep underground. This might sound like magic, but it is actually the Earth's way of getting rid of excess CO from the atmosphere: nature turns the CO into stone using metals that are present in certain rocks [ ]. The best rocks for this process are volcanic rocks, such as basalt and peridotite, which contain a

VOLCANIC ROCKS
Rocks formed from lava erupted from a volcano or from magma that escapes from the roots of volcanos but does not make it to the surface and solidifies within the subsurface. lot of the metals needed for this reaction. In nature, this is a slow progress-too slow to prevent the global warming that is currently a ecting the Earth.
An Icelandic project called Carbfix speeds up this natural progress. The CO is dissolved in water, the same way a soda machine makes sparkling water (Figure ). The water with the dissolved CO is then pumped deep into the ground. If this sparkling water is pumped into the right kinds of rocks, the rocks release metals that mix with the CO in the water and turn the CO into stone. This process safely and permanently removes the CO from the atmosphere, since rocks cannot leak out of the ground.

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April | Volume | Article | Figure   Figure The Carbfix process. CO is captured from an emission source, such as power plant or a factory. The CO is then dissolved in water, just as in a soda machine. This sparkling water is then injected deep underground, where it is turned to stone through natural processes that involve the metals contained within certain types of rock.
This technology is being used at a geothermal power plant in Hellisheidi, in Iceland. Geothermal plants use steam from geothermal fields which contains a fraction of CO , and in the process of producing electricity this CO is released. The CO emitted from the power plant is dissolved in water in a structure called a scrubbing tower. The CO -charged water is then injected into the ground using a device called an injection well, which reaches over , m down into the earth. The basalt at this depth is perfect for this method, since it contains the metals needed for turning CO into stone. Currently, about , tons of CO are turned into stone every year at the Hellisheidi geothermal plant, instead of being released to the atmosphere. This is equivalent to the annual emissions from about , cars [ ].
Currently the Hellisheidi power plant is the only facility where this technology is being demonstrated. About , tons of CO have been injected and turned into stone since the process started in . However, there are plans for more widespread use of the technology and, in , the Carbfix process will be applied to a second geothermal plant in Iceland. There are also other and even more innovative plans for turning CO to stone soon.

REMOVING CO FROM THE ATMOSPHERE
Climate scientists have predicted that stopping new emissions of CO will not be enough to tackle climate change. In the future, we will need to start removing the CO that we have already emitted into the atmosphere [ ]. There are several ways to remove CO from the atmosphere, including planting trees and restoring the health of soils that have been contaminated or overused through farming. Since we need to remove a lot of CO as quickly as possible, we will also need to rely on technology that captures CO directly from the atmosphere.

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April | Volume | Article | Figure   Figure In the future, the Carbfix process may be widely used for capturing CO from power plants and factories, or directly from the atmosphere, and injecting it into the ground -both onshore and o shore.

Figure
Locations where rocks suitable for turning CO into stone can be found. Light brown indicates the youngest parts of the oceanic ridges and areas with volcanic rocks that are suitable for turning CO into stone (from carbfix.com/atlas).
This technology is called direct air capture (DAC) and it is being

DIRECT AIR CAPTURE
Capturing of CO that has already been emitted to the atmosphere. developed in several places around the globe.
The first example of DAC technology, combined with the Carbfix technology, has been ongoing in Iceland since . The company Climeworks has developed a facility that has been removing CO directly from the atmosphere. The facility draws in air and filters out the CO , which is then dissolved in water, injected into the earth, and turned into stone [ ]. The facility can remove about tons of CO every year, an amount roughly equivalent to that removed by about , trees.
This experiment must be done on a much larger scale in the future. A scale-up of the DAC facility is planned in Iceland in the upcoming years, which will help to increase the amount of CO captured within stone underground. There is, however, a big task ahead.

THE FUTURE OF REMOVING CO FROM THE ATMOSPHERE
Now you know that the ingredients for turning CO to stone include a source of CO , volcanic rocks, and water. In some cases, we will need to transport the CO via pipelines or ships to a location where we can inject it into the right kind of rocks ( Figure ). Volcanic rocks, such as basalt and peridotite, are very abundant. In fact, basalt is the most common rock type on the surface of the Earth, covering most of the ocean floor and about % of the continents (Figure ). The global storage potential of all the basalt on Earth is larger than the CO emissions that would be produced from burning all fossil fuels on Earth [ ]. This means we have plenty of the right kinds of rock to successfully store CO in minerals that would otherwise a ect our atmosphere. Water can be scarce in some areas, so scientists are now exploring ways of supplying the necessary water directly from natural underground reservoirs or using seawater.
There is a big task ahead in terms of capturing and storing CO . In the coming years, to protect the Earth and human lives, we need to capture and store CO on a much greater scale. CO must be captured from factory emissions, power plants, and directly from the atmosphere. The question that remains is how much CO will we be able to turn into stone, and whether this amount will be enough to contribute to protecting the Earth and its inhabitants from the dangerous e ects of worsening climate change.  . doi: . /frym. .

CONFLICT OF INTEREST:
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
COPYRIGHT © Snaebjörnsdóttir, Steinþórsdóttir, Snorradóttir and Helgason. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

YOUNG REVIEWERS
FDR-HB_PERU IGEM TEAM, AGES: -We are a synthetic biology team with the international Genetically Engineered Machine (iGEM) in Lima, Peru. We are the only high school team in Latin America and are proud of our work with creating a detector for cadmium using bacteria. Most of us are second language learners and the age range of our group isyears old. We love GMOs! AUTHORS SANDRA Ó. SNAEBJÖRNSDÓTTIR I have been fascinated by rocks in all their forms since I was a kid traveling around Iceland with my grandparents. I was intrigued by mountains in all their shapes and later on the deep buried rocks we can bring to the surface by drilling wells into the ground. For the past couple of years, I have studied the nature's way of storing CO -how CO interacts with rocks to be turned to stone. I hope this process is a key to some of the solutions we need to solve the climate crisis. *sandraos@carbfix.com

KATRÍN STEINÞÓRSDÓTTIR
My interest in rocks started when I was a kid as my neighborhood's playground had these smooth black rocks called basalt. Later on, I studied volcanoes that form these rocks. Now, I am working on another similar rock type that forms under the earth's kids.frontiersin.org April | Volume | Article | crust called peridotite. Both of these rocks can be used to store carbon dioxide and help fight climate change-I am interested in which parts we can use and where we can find them.

SELJA ÓSK SNORRADÓTTIR
My interest in preserving the natural environment from the impact of climate change sparked my interest in innovation and sustainability early on. I studied both business and sustainability science at university. Now I am working as an advisor in an environmental software company, helping cities, companies, and organizations measure their carbon footprint with real-time data and set goals on how to minimize their carbon footprint.

KÁRI HELGASON
My passion for the natural sciences was ignited by the richness of the universe. An early career in astrophysics kept me fascinated with the many planets being discovered outside our solar system. I have now shifted my attention to planet Earth and am dedicated to keeping carbon out of Earth's atmosphere by turning it into stone. So far, it is the only habitable world we know of.