New technology offers hope for storing carbon dioxide underground

Dom Wolff-Boenisch, Curtin University

To halt climate change and prevent dangerous warming, we ultimately have to stop pumping greenhouse gases into the atmosphere. While the world is making slow progress on reducing emissions, there are more radical options, such as removing greenhouse gases from the atmosphere and storing them underground.

In a paper published today in Science my colleagues and I report on a successful trial converting carbon dioxide (CO₂) to rock and storing it underground in Iceland. Although we trialled only a small amount of CO₂, this method has enormous potential.

Here’s how it works.

Turning CO₂ to rock

Our paper is the culmination of a decade of scientific field and laboratory work known as CarbFix in Iceland, working with a group of international scientists, among them Wallace Broecker who coined the expression “global warming” in the 1970s. We also worked with the Icelandic geothermal energy company Reykjavik Energy.

The idea itself to convert CO₂ into carbonate minerals, the basis of limestone, is not new. In fact, Earth itself has been using this conversion technique for aeons to control atmospheric CO₂ levels.

However, scientific opinion had it up to now that converting CO₂ from a gas to a solid (known as mineralisation) would take thousands (or tens of thousands) of years, and would be too slow to be used on an industrial scale.

To settle this question, we prepared a field trial using Reykjavik Energy’s injection and monitoring wells. In 2012, after many years of preparation, we injected 248 tonnes of CO₂ in two separate phases into basalt rocks around 550m underground.

Most CO₂ sequestration projects inject and store “supercritical CO₂”, which is CO₂ gas that has been compressed under pressure to considerably decrease its volume*. However, supercritical CO₂ is buoyant, like a gas, and this approach has thus proved controversial due to the possibility of leaks from the storage reservoir upwards into groundwater and eventually back to the atmosphere.

In fact, some European countries such as the Netherlands have stopped their efforts to store supercritical CO₂ on land because of lack of public acceptance, driven by the fear of possible leaks in the unforeseeable future. Austria went even so far as to ban underground storage of carbon dioxide outright.

The injection well with monitoring station in the background.
Dom Wolff-Boenisch, Author provided

Our Icelandic trial worked in a different way. We first dissolved CO₂ in water to create sparkling water. This carbonated water has two advantages over supercritical CO₂ gas.

First, it is acidic, and attacks basalt which is prone to dissolve under acidic conditions.

Second, the CO₂ cannot escape because it is dissolved and will not rise to the surface. As long as it remains under pressure it will not rise to the surface (you can see the same effect when you crack open a soda can; only then is the dissolved CO₂ released back into the air).

Dissolving basalt means elements such as calcium, magnesium, and iron are released into pore water. Basaltic rocks are rich in these metals that team up with the dissolved CO₂ and form solid carbonate minerals.

Through observations and tracer studies at the monitoring well, we found that over 95% of the injected CO₂ (around 235 tonnes) was converted to carbonate minerals in less than two years. While the initial amount of injected CO₂ was small, the Icelandic field trial clearly shows that mineralisation of CO₂ is feasible and more importantly, fast.

Storing CO₂ under the oceans

The good news is this technology need not be exclusive to Iceland. Mineralisation of CO₂ requires basaltic or peridotitic rocks because these types of rocks are rich in the metals required to form carbonates and bind the CO₂.

As it turns out the entire vast ocean floor is made up of kilometre-thick oceanic basaltic crust, as are large areas on the continental margins. There are also vast land areas covered with basalt (so-called igneous provinces) or peridotite (so-called “ophiolitic complexes”).

The overall potential storage capacity for CO₂ is much larger than the global CO₂ emissions of many centuries. The mineralisation process removes the crucial problem of buoyancy and the need for permanent monitoring of the injected CO₂ to stop and remedy potential leakage to the surface, an issue that supercritical CO₂ injection sites will face for centuries or even millennia to come.

On the downside, CO₂ mineralisation with carbonated water requires substantial amounts of water, meaning that this mineralisation technique can only succeed where vast supplies of water are available.

However, there is no shortage of seawater on the ocean floor or continental margins. Rather, the costs involved present a major hurdle to this kind of permanent storage option, for the time being at least.

In the case of our trial, a tonne of mineralised CO₂ via carbonated water cost about US$17, roughly twice that of using supercritical CO₂ for storage.

It means that as long as there are no financial incentives such as a carbon tax or higher price on carbon emissions, there is no real driving force for carbon storage, irrespective of the technique we use.

*Correction: The sentence has been corrected to note that gas volume rather than density decreases when it is compressed. Thankyou to the readers who pointed out the error.

The Conversation

Dom Wolff-Boenisch, Senior Lecturer, Western Australian School of Mines, Curtin University

This article was originally published on The Conversation. Read the original article.


Removing CO2 from the atmosphere won’t save us: we have to cut emissions now

Pete Smith, University of Aberdeen and Pep Canadell, CSIRO

Over 190 countries are negotiating in Paris a global agreement to stabilise climate change at less than 2℃ above pre-industrial global average temperatures.

For a reasonable chance of keeping warming under 2℃ we can emit a further 865 billion tonnes of carbon dioxide (CO2). The climate commitments to reduce greenhouse gas emissions to 2030 are a first step, but recent analyses show they are not enough.

So what are the options if we cannot limit emissions to remain within our carbon budget?

Emitting more than the allowance would mean we have to remove carbon from the atmosphere. The more carbon we emit over the coming years, the more we will need to remove in future.

In fact, out of 116 scenarios consistent with 2℃ published by the Intergovernmental Panel on Climate Change, 101 scenarios require the removal of CO2 from the atmosphere during the second half of this century. That’s on top of the large emission reductions required.

So how do we remove carbon from the atmosphere? Several technologies have been proposed to this effect. These are often referred to as “negative emissions technologies” because the carbon is being removed from the atmosphere (in the opposite direction to emissions).

In a study published today in Nature Climate Change, which is part of a broader release by the Global Carbon Project, we investigate how big a role these technologies could play in halting global warming.

We find that these technologies might play a role in climate mitigation. However, the large scales of deployment currently used in most pathways that limit warming to 2℃ will be severely constrained by environmental and socio-economic factors. This increases the pressure to raise the level of ambition in reducing fossil fuel emissions now.

Smith et al. 2015, Nature Climate Change

How to pull carbon out of the atmosphere

The technologies range from relatively simple options, such as planting more trees, which lock up CO2 as they grow, or crushing rocks that naturally absorb CO2 and spreading them on soils and oceans so they remove CO2 more rapidly.

There are also higher-tech options such as using chemicals to absorb CO2 from the air, or burning plants for energy and capturing the CO2 that would otherwise be released, then storing it permanently deep below the ground (called bioenergy with carbon capture and storage).

Bioenergy with carbon capture and storage.
Canadell & Schulze 2014, Nature Communications

We examined the impacts of negative emission technologies on land use, greenhouse gas emissions, water use, earth’s reflectivity (or albedo) and soil nutrient loss, as well as the energy and cost requirements for each technology.

One major limitation that we identified is the vast requirements for land.

About 700 million hectares of land are required to grow biomass for bioenergy with carbon capture and storage at the scale needed in many 2℃ pathways. This would remove more than 3 billion tonnes of carbon from the atmosphere every year and would help to compensate an overshoot in emissions earlier this century.

The area required is close to half of current global arable land plus permanent crop area. If bioenergy with carbon capture and storage were deployed at this scale there would be intense competition with food, water and conservation needs.

This land requirement has made other negative emissions technologies attractive, such as direct air capture. However, current cost estimates for such technologies are between US$1,600 and US$2,000 per tonne of carbon removed from the atmosphere. In contrast, the majority of emissions with a carbon price in 40 national jurisdictions have a cost of less than US$10 per tonne of carbon dioxide.

The study shows that there are many such impacts that vary across technologies. These impacts will need to be addressed and should determine the level at which negative emission technologies can play a role in achieving climate mitigation goals.

Plan A: reduce fossil fuel emissions

We conclude that, given the uncertainties around large-scale deployment of negative emissions technologies, we would be taking a big gamble if actions today were based on the expectation of heavy use of unproven technologies tomorrow.

The use of these technologies will likely be limited due to any combination of the environmental, economic or energy constraints we examined. We conclude that “Plan A” must be to reduce greenhouse gas emissions aggressively now. A failure to initiate such a level of emissions cuts may leave us with no “Plan B” to stabilise the climate within the 2℃ target.

The technologies of today are not the technologies of tomorrow. However, a prudent approach must be based on the level of climate abatement required with available technologies, while strongly investing in the research and development that might lead to breakthroughs that will ease the formidable challenge ahead of us.

The Conversation

Pete Smith, Professor of Soils and Global Change, University of Aberdeen and Pep Canadell, CSIRO Scientist, and Executive Director of Global Carbon Project, CSIRO

This article was originally published on The Conversation. Read the original article.

We may have to suck up CO2 to prevent planet from frying, U.N. says


The climate situation is so dire that we may have to resort to geoengineering to keep the planet livable, according to a leaked draft of a forthcoming report from the U.N. Intergovernmental Panel on Climate Change.

The New York Times reports:

Nations have so dragged their feet in battling climate change that the situation has grown critical and the risk of severe economic disruption is rising, according to a draft United Nations report. Another 15 years of failure to limit carbon emissions could make the problem virtually impossible to solve with current technologies, experts found.

A delay would most likely force future generations to develop the ability to suck greenhouse gases out of the atmosphere and store them underground to preserve the livability of the planet, the report found. But it is not clear whether such technologies will ever exist at the necessary scale, and even if they…

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Plants will reach point where they couldn’t possibly take another bite of our CO2


Plants love carbon dioxide. It’s their oxygen. That’s why forests, meadows, and the like are called carbon sinks — they help draw a fraction of our CO2 emissions back out of the atmosphere and into the soil.

But we can’t expect plants to clean up after us forever.

After running computer simulations, European and Japanese scientists concluded that plants that haven’t been bulldozed, poisoned, burnt up, or attacked by invasive pests will continue to absorb more carbon as atmospheric carbon levels rise. But they found that rising temperatures could eventually prevent vegetation from absorbing any more of our CO2 pollution.

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Deserts Growth Spurt

The link below is to an article that reports on the growth explosion in deserts due to the increase in CO2.

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China Leads the Way in CO2 Emissions Battle

The link below is to an article reporting on China leading the world in greenhouse gas reductions.

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