Tag Archives: Capture

New capture technology scrubs atmospheric CO2 on the cheap

A novel carbon capture technique can scrub the gas out from the air even at relatively low concentrations, such as the roughly 400 parts per million (ppm) currently found in the atmosphere.

We have a climate problem: namely, we’re making the planet hotter and hotter. This change is caused by a build-up of greenhouse gases released by our various activities, and carbon dioxide (CO2) is the single most important such gas. Tackling climate heating hinges on our ability to reduce emissions or to find ways of scrubbing them from the air. Since the former would involve at least some economic contraction, neither industry nor politicians are very keen on it. So there’s quite a lot of interest in developing the latter approach.

Most of the methods available today need high concentrations of CO2 (such as the smoke emitted by fossil fuel-based power plants) to function. The methods that can work with low concentrations, on the other hand, are energy-intensive and expensive, so there’s little economic incentive for their use. However, new research from MIT plans to change this state of affairs.

Convenient cleaning

“The greatest advantage of this technology over most other carbon capture or carbon absorbing technologies is the binary nature of the adsorbent’s affinity to carbon dioxide,” explains MIT postdoc Sahag Voskian, who developed the work during his PhD.

“This binary affinity allows capture of carbon dioxide from any concentration, including 400 parts per million, and allows its release into any carrier stream, including 100 percent CO2.”

The technique relies on passing air through a stack of electrochemical plates. The process Voskian describes is that the electrical charge state of the material — charged or uncharged — causes it to either have no affinity to CO2 whatsoever or a very high affinity for the compound. To capture CO2, all you need to do is hook the material up to a charged battery or another power source; to pump it out, you cut the power.

The team says this comes in stark contrast to carbon-capture technologies today, which rely on intermediate steps involving large energy expenditures (usually in the form of heat) or pressure differences.

Essentially, the system functions the same way a battery would, absorbing CO2 around its electrodes as it charges up, and releasing it as it discharges. The team envisions successive charge-discharge cycles as the device is in operation, with fresh air or feed gas being blown through the system during the charging cycle, and then pure, concentrated carbon dioxide being blown out during the discharge phase.

The electrochemical plates are coated with a polyanthraquinone and carbon nanotubes composite. This gives the plates a natural affinity for carbon dioxide and helps speed up the reaction even at low concentrations. During the discharge phase, these reactions take place in reverse, generating part of the power needed for the whole system during this time. The whole system operates at room temperature and normal air pressure, the team explains.

The authors hope the new approach can help reduce CO2 production and increase capture efforts. Some bottling plants burn fossil fuels to generate CO2 for fizzy drinks, and some farmers also burn fuels to generate CO2 for greenhouses. The team says the new device can help them get the carbon they need from thin air, while also cleaning the atmosphere. Alternatively, the pure carbon dioxide stream could be compressed and injected underground for long-term disposal, or even made into fuel through a series of chemical and electrochemical processes.

“All of this is at ambient conditions — there’s no need for thermal, pressure, or chemical input,” says Voskian. “It’s just these very thin sheets, with both surfaces active, that can be stacked in a box and connected to a source of electricity.”

Compared to other existing carbon capture technologies, this system is quite energy efficient, using about one gigajoule of energy per ton of carbon dioxide captured. Other existing methods use up to 10 gigajoules per ton, depending on the inlet carbon dioxide concentration, Voskian says.

The paper “Faradaic electro-swing reactive adsorption for CO2 capture” has been published in the journal Energy & Environmental Science.

New material selectively captured CO2 molecules and turns them into useful products

Japanese researchers at the University of Kyoto have recently demonstrated a porous polymer that selectively binds to carbon dioxide molecules. It is ten times more efficient than similar other materials and is made from inexpensive materials. In the future, such a material could be incorporated into the exhausts of fossil fuel power generators or carbon capture stations. The CO2 would not only be prevented to reach the atmosphere, where it raises temperatures, it could also be turned into a useful product.

This new porous polymer has propeller-shaped molecular structures that enables selectively capturing CO2. Credit: Mindy Takamiya.

The new material belongs to a class called porous coordination polymer (PCP), also known as metal-organic frameworks (MOF). It mainly consists of zinc metal ions and an organic component, known as a ligand, with a propeller-like molecular structure.

When CO2 molecules approach the structure, the ligands rotate and rearrange themselves, thereby trapping the carbon. This results in slight changes in the molecular channels of the PCP, which basically acts as a sieve.

X-ray structural analysis revealed that the material only interacts with carbon dioxide molecules, which are captured 10 times more efficiently than other PCPs.

No energy input is required for the process to occur because it is favorable for the CO2 to bind to the zinc ions. Once bound, the CO2 molecules become activated and capable of reacting with other molecules.

“We have successfully designed a porous material which has a high affinity towards CO2 molecules and can quickly and effectively convert it into useful organic materials,” says Ken-ichi Otake, a materials chemist at Kyoto University.

The researchers claim that the CO2 can be incorporated into useful organic materials, such as cyclic carbonates which can be used in petrochemicals and pharmaceuticals.

The findings appeared in the journal Nature Communications.

Limestone.

New method of CO2 capture is cheaper, more effective, and “a key step toward closing the carbon loop”

Researchers from the University of Toronto (U of T) Faculty of Applied Science & Engineering plan to make CO2 capture even more appealing — they’ve developed a process that allows for atmospheric CO2 to be recycled into fuel or plastics for much lower costs than before.

Limestone.

Limestone, a carbonate rock. CO2 capture methods often convert the gas into similar rocks.
Image via Pixabay.

Direct-air carbon capture is an emerging technology that uses CO2 already in the atmosphere as raw material to make a range of commercial products such as fuel or plastics. It’s a promising alternative to the traditional approach, environmentally speaking, because it substitutes carbon compounds found in oil, coal, or natural gas with the one that’s floating around in (and heating up) the air we breathe. However, it’s also the more expensive approach between the two.

The team, led by Professor Ted Sargent from the U of T, aims to drive its cost down.

Cutting out the middleman

“Today, it is technically possible to capture CO2 from air and, through a number of steps, convert it to commercial products,” says Prof. Sargent.

“The challenge is that it takes a lot of energy to do so, which raises the cost and lowers the incentive. Our strategy increases the overall energy efficiency by avoiding some of the more energy-intensive losses.”

The team worked on a new electrochemical process that can capture and transform that CO2 for a fraction of the cost (compared to currently-available approaches).

Up to now, the most common approach involved pumping air through a liquid, alkaline solution. This substance dissolves CO2 in the air, chemically-tying it into carbonate compounds. To retrieve the useful carbon, these compounds need to then be turned back into CO2 gas. Commonly, chemical agents are used to convert the carbonate solution into a solid salt which is then baked at temperatures in excess of 900ºC to release the gas. This is then hoovered up and used to synthesize other carbon compounds.

It takes a lot of energy — and thus, a lot of money — to generate all that heat. And that’s just not a very effective way of doing it, the team believes. Their alternative method involves the use of an electrolyzer, a device that uses electricity to drive chemical reactions. They got the idea from previous work which involved the use of electrolyzers to produce hydrogen from water. The process, they say, does away with the heating step, allowing for the carbonate solution to be turned directly back into CO2.

The new electrolyzer also employs a silver-based catalyst that immediately turns the released CO2 into syngas. Syngas (synthesis gas) is a mixture of hydrogen, and CO, with some CO2, and is a very common feedstock material for the chemical industry. Syngas is involved in processes ranging from plastic to jet fuel production.

“We used a bipolar membrane, a new electrolyzer design that is great at generating protons,” says Geonhui Lee, co-lead author of the paper describing the technique. “These protons were exactly what we needed to convert the carbonate back into CO2 gas.”

“This is the first known process that can go all the way from carbonate to syngas in a single step,” Sargent adds.

Another advantage this process has over conventional CO2 retrieval processes is better yields and higher efficiency. Furthermore, it solves a major problem regarding existing electrolyzing technologies: these cannot actually work with carbonate.

“Once the CO2 turns into carbonate, it becomes inaccessible to traditional electrolyzers,” says Li. “That’s part of the reason why they have low yields and low efficiencies. Our system is unique in that it achieves 100% carbon utilization: no carbon is wasted. It also generates syngas as a single product at the outlet, minimizing the cost of product purification.”

Lab tests showed that the new electrolyzer can convert carbonate to syngas with an overall efficiency of 35%, with stable operations confirmed for over six days at a time. There’s still work to be done in upscaling the process to industrial scales, according to Sargent, but the proof-of-concept device shows the new method is viable.

“It goes a long way toward answering the question of whether it will ever be possible to use air-captured CO2 in a commercially compelling way,” he says. “This is a key step toward closing the carbon loop.”

The paper “CO2 Electroreduction from Carbonate Electrolyte” has been published in the journal ACS Publications.

Wall fans.

New paper proposes we use air conditioners to make fuel out of thin air

Cool down your home and the climate at the same time.

Wall fans.

Image credits Sławomir Kowalewski.

New research from the Karlsruhe Institute of Technology and the University of Toronto wants to put your air conditioning unit to work on fighting climate change. The idea is to outfit air conditioners — devices which move huge amounts of air per day — with carbon-capture technology and electrolyzers, which would turn the gas into fuel.

Crowd oil

“Carbon capture equipment could come from a Swiss ‘direct air capture’ company called Climeworks, and the electrolyzers to convert carbon dioxide and water into hydrogen are available from Siemens, Hydrogenics or other companies,” said paper co-author Geoffrey Ozin for Scientific American.

Air-conditioner units are very energy-thirsty. As most of our energy today is derived from fossil fuels, this means that air conditioners can be linked to a sizeable quantity of greenhouse emissions. It’s estimated that, by the end of the century, we’ll be using enough energy on air conditioning to push the average global temperature up by half a degree. Which is pretty ironic.

The team’s idea is pretty simple — what if heating, ventilation, and air conditioning (or HVAC) systems could act as carbon sinks, instead of being net carbon contributors? Carbon-capture devices need to be able to move and process massive quantities of air in order to be effective. HVAC systems already do this, being able to move the entire volume of air in an average office building five to ten times every hour. So they’re ideally suited for one another. The authors propose “retrofitting air conditioning units as integrated, scalable, and renewable-powered devices capable of decentralized CO2 conversion and energy democratization.”

“It would be not that difficult technically to add a CO2 capture functionality to an A/C system,” the authors write, “and an integrated A/C-DAC unit is expected to show favourable economics.”

Modular attachments could be used to add CO2-scrubbing filters to pre-existing HVAC systems. After collection, that CO2 can be mixed with water to make, basically, fossil fuels. As Ozin told Scientific American, the required technology is commercially available today.

But, in order to see if it would also be effective, the team used a large office tower in Frankfurt, Germany, as a case study. HVAC systems installed on this building could capture enough CO2 to produce around 600,000 gallons of fuel in a year. They further estimate that installing similar systems on all the city’s buildings could generate in excess of 120 million gallons of (quite wittily-named) “crowd oil” per year.

“Renewable oil wells, a distributed social technology whereby people in homes, offices, and commercial buildings all around the world collectively harvest renewable electricity and heat and use air conditioning and ventilation systems to capture CO2 and H2O from ambient air, by chemical processes, into renewable synthetic oil — crowd oil — substituting for non-renewable fossil-based oil — a step towards a circular CO2 economy.”

Such an approach would still take a lot of work and polish before it could be implemented on any large scale. Among some of the problems is that it would, in effect, turn any HVAC-equipped system into a small, flammable oil refinery. The idea also drew criticism as it could potentially distract people from the actual goal — reducing emission levels.

“The preliminary analysis […] demonstrates the potential of capturing CO2 from air conditioning systems in buildings, for making a substantial amount of liquid hydrocarbon fuel,” the paper reads.

“While the analysis considers the CO2 reduction potential, carbon efficiency and overall energy efficiency, it does not touch on spatial, or economic metrics for the requisite systems. These have to be obtained from a full techno-economic and life cycle analysis of the entire system.”

The paper “Crowd oil not crude oil” has been published in the journal Nature Communications.

Liquid cerium catalyst.

New process could capture CO2 and make it coal again

Instead of burning coal and releasing CO2, new research plans to absorb CO2 and produce coal.

Charcoal.

Image via Pixabay.

A new breakthrough could allow us to burn our coal and have it, too. Researchers from Australia, Germany, China, and the US have worked together to develop a carbon storage method that can turn CO2 gas into solid carbon particles with high efficiency. Their approach could help us scrub the atmosphere of (some of) the greenhouse emissions we produce — with a certain dash of style.

Coal idea

“While we can’t literally turn back time, turning carbon dioxide back into coal and burying it back in the ground is a bit like rewinding the emissions clock,” says Torben Daeneke, an Australian Research Council DECRA Fellow and paper co-author.

The idea of permanently removing CO2 from the atmosphere isn’t new — in fact, it’s heavily considered as a solution to our self-induced climate woes. We’ve developed several ways to go about it, but they simply aren’t viable yet. Current carbon capture technologies turn the gas into a liquid form, which is then carted away to be injected underground. However, the process requires high temperatures (which means high costs) and there are environmental concerns regarding possible leaks from storage sites.

The team’s approach, however, relies on an electrochemical technique to capture atmospheric CO2 and turn it into solid, easy to store carbon.

“To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable,” Daeneke explains. “By using liquid metals as a catalyst, we’ve shown it’s possible to turn the gas back into carbon at room temperature, in a process that’s efficient and scalable.”

“While more research needs to be done, it’s a crucial first step to delivering solid storage of carbon.”

The liquid metal cerium (Ce) catalyst has certain surface properties that make it a very good electrical conductor — the current also chemically activates the catalyst’s surface.

Liquid cerium catalyst.

Schematic of the catalytic process.
Image credits Dorna Esrafilzadeh, (2019), Nature.

The whole process starts with the team dissolving carbon dioxide gas in a liquid-filled beaker and a small quantity of the liquid metal. When charged with electrical current, this catalyst slowly starts converting the CO2 into solid flakes of carbon on its surface and promptly falls off, so the process can be maintained indefinitely.

“A side benefit of the process is that the carbon can hold electrical charge, becoming a supercapacitor, so it could potentially be used as a component in future vehicles,” says Dr Dorna Esrafilzadeh, a Vice-Chancellor’s Research Fellow in RMIT’s School of Engineering and the paper’s lead author.

“The process also produces synthetic fuel as a by-product, which could also have industrial applications.”

The paper “Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces” has been published in the journal Nature.

Corn Field.

Using land displaced by biofuels to grow trees is much better for climate, say researchers

One researcher from the University of Michigan (UE) says that growing and harvesting bioenergy crops is a poor way to fight climate change — instead, we should keep these areas wild and increase forest cover.

Corn Field.

Image via Pixabay.

Biofuels just aren’t very climate-friendly, a new opinion piece published by John DeCicco, a research professor at the UM Energy Institute. Instead of growing bioenergy crops, such as corn used to produce ethanol, which is a poor use of a limited and precious resource, we should instead nurture wild areas like forests or grassland to help naturally sequester CO2, he adds.

If it ain’t broken, don’t use it as cropland

Wild areas like forests and grasslands naturally capture carbon dioxide from the atmosphere — and they are one of our best tools for quickly scrubbing greenhouse gasses from the atmosphere, writes DeCicco. In a paper he published alongside William Schlesinger, president emeritus of the Cary Institute of Ecosystem Studies,  DeCicco urges policymakers, funding agencies, fellow academics, and industry leaders to shift the focus from bioenergy to terrestrial carbon management (TCM), and do it fast. TCM is a strategy that relies on wild area conservation and increasing tree cover to reduce CO2 levels in the atmosphere.

“The world needs to rethink its priorities about how to use the biosphere given the urgency of the climate problem and the risks to biodiversity,” DeCicco said. “Current policies advancing bioenergy contribute to the pressure to convert natural land into harvested forest or cropland,” he adds.

“But high quality land is a limited resource. For reducing atmospheric CO2, the most efficient use of ecologically productive land is to leave it alone, or reforest it. Let it act as a natural, long-term carbon sink.”

The opinion is based on DeCicco’s earlier work, which found that biofuels are not inherently carbon-neutral. It also draws roots from Schlesinger’s work in ecology and biochemistry.

The duo calls the assumption that biofuels recycle carbon a major ‘accounting error’. Because such fuels are assumed to be carbon-neutral, current assessment models (used energy policy as well as the protocols for international carbon accounting) do not accurately reflect reality, they explain. This view has also promoted major R&D investments in biofuels, which, in turn, have been assigned a key role in many climate stabilization scenarios.

The core (and wrong) assumption with biofuels is the idea that producing a biofuel and then burning it for energy moves a given amount of carbon from the biosphere to the atmosphere, and back again in an unending and stable cycle, the team writes. So, unlike fossil fuels — which only release CO2 as they burn, and not absorb it in their production process — the crops that biofuels are produced from are believed to absorb the same quantity of emissions the fuel generates while being burned.

Biofuel cycle.

However, the team writes, this assumption isn’t true. For biofuels to really be carbon neutral, the carbon flow from the atmosphere back into vegetation needs to be much faster than it actually is; in other words, the plants need to grow much faster than they do. Otherwise, it can take many decades before the “carbon debt” in the air is repaid by plant growth, they explain. A paper published by DeCicco in 2016 reported that just 37% of the CO2 released from burning biofuels was balanced out by carbon uptake in crops over the first eight years of the U.S. biofuel mandate.

In other words, biofuels acted as net carbon contributors to the atmosphere over these eight years, DeCicco claims. Whether or not this evens out over the long term isn’t important for us right now, the authors explain — because we don’t have ‘long-term’, we need to reduce greenhouse gas levels now.

“All currently commercial forms of bioenergy require land and risk carbon debts that last decades into the future. Given the urgency of the climate problem, it is puzzling why some parties find these excess near-term CO2 emissions acceptable,” the researchers write.

Increasing the rate at which trees and other plants remove CO2 from the air is a much better (and faster way) to use land, the duo writes. If no new breakthroughs are made in the field of carbon capture or bioenergy systems, protecting and nurturing carbon-rich natural ecosystems remains our best strategy for carbon dioxide reduction, they add.

“By avoiding deforestation and by reforesting harvested areas, up to one-third of current carbon dioxide emissions from fossil fuels could be sequestered in the biosphere,” the researchers write. “Terrestrial carbon management can keep carbon out of the atmosphere for many decades.”

However, many scientists disagree with DeCicco, whose 2016 paper claiming that biofuels aren’t carbon neutral was funded by the fossil fuel industry.

“This is the same study, same flawed methodology and same fallacious result that Professor DeCicco has churned out multiple times in the past,” said Geoff Cooper, the Renewable Fuels Association senior vice president, for the Detroit Free Press. “He has been making these arguments for years, and for years they have been rejected by climate scientists, regulatory bodies and governments around the world, and reputable life-cycle analysis experts.”

Argonne National Laboratory scientist Michael Wang, an expert in life cycle analyses, says the findings are questionable for a variety of different technical reasons, including the fact that DeCicco only took American farming into account. It’s thus unfair to look at CO2 released by biofuel combustion and biofuel crop carbon sequestration only, simply because CO2, being a gas, is dispersed all over the world. About 29% of San Francisco’s air pollution comes from China, for instance. All of this CO2 will be absorbed by all sorts of plants, such as trees, flowers, corn or sunflower crops, and so on — because plants don’t discriminate between differently sourced CO2. It’s the same chemistry for them.

“In the long run, there’s no question that biofuels displacing petroleum is a benefit,” said Daniel Schrag, a geology professor at Harvard who advises the EPA on bioenergy climate impacts. His views sharply oppose those of DeCicco. “It’s just a question of how long you have to wait.”

The paper “Reconsidering bioenergy given the urgency of climate protection” has been published in the journal Proceedings of the National Academy of Sciences.

Redwood National Park

Curbing climate change: carbon storage is good, forests are oft-times better

Carbon capture can definitely help our efforts of curbing climate change — but in many areas, we may be better off by simply maintaining forests, a new paper suggests.

Redwood National Park

Redwood National Park, California.
Image via Pixabay.

By now, we’re pretty well committed to a future that includes one degree (pun intended) or another of climate change. Carbon dioxide (CO2) takes a while — hundreds of years — to break down in the atmosphere. Even if we were to stop all emissions right now, future generations will still feel the effects of these gases in shifting climate, changing ocean patterns, and their ecological implications.

With this in mind, one idea has been bounced around with increasing optimism: carbon capture. The term broadly refers to technologies that can suck up CO2 and then lock it out of the atmosphere. One particular form of this tech, biomass energy with carbon capture and storage (or ‘BECCS’), has garnered a lot of optimism. BECCS-type approaches propose the use of crops to capture CO2 out of the atmosphere; these crops are later used to fuel power plants, and the resulting CO2 is stored underground, in bedrock.

It’s like having your CO2 and storing it too. Which is ideal.

However, BECCS may not be the silver bullet many people hope it to be, a new paper reports. While it sounds nice on paper, in practice BECCS power stations could end up increasing the levels of CO2 in the atmosphere, the authors warn.

Between a rock and a hot place

The study shows that for BECCS to have a meaningful impact on CO2 levels in the atmosphere, we’d need to convert massive expanses of land into fields to grow crops. In wooded areas, this ends up as a net-carbon-positive affair — replacing forests with crops would actually leave more CO2 in the atmosphere than doing nothing.

Carbon flow diagram.

Diagram stylizing carbon flow for different types of energy generation. ‘Up’ symbolizes emissions to the atmosphere, ‘down’ symbolizes storage. A forest only stores carbon.
Image credits Elrapto / Wikimedia.

With this in mind, the team reports that protecting and regenerating forests is a better option than BECCS in many cases.

“The vast majority of current IPCC scenarios for how we can limit global warming to less than 2°C include BECCS,” said lead author Dr. Anna Harper, from the University of Exeter (UoE).

“But the land required to grow biomass in these scenarios would be twice the size of India”.

The team used a cutting-edge computer model known as IMAGE to gauge how levels of greenhouse gases will evolve in the atmosphere over time. The model takes into account factors such as global vegetation and soils, but also factors such as economics, energy policy, resource availability, population dynamics, or climate change projections.

They then ran scenarios of land use that would be required to stabilize climate at less than 1.5°C and 2°C over pre-industrial levels, respectively. In areas where these crops would replace forests, BECCS-style approaches would actually increase the levels of CO2 in the atmosphere, they report.

“In some places BECCS will be effective, but we’ve found that in many places protecting or regenerating forests is much more sensible,” says co-author Dr. Tom Powell, also at the UoE.

“Carbon removed from the atmosphere through BECCS could easily be offset by losses due to land-use change. If BECCS involves replacing high-carbon content ecosystems [e.g. forests] with crops, then afforestation/reforestation and avoided deforestation are often more efficient for atmospheric CO2 removal over this century than BECCS,” the paper explains.

No universal solution

The effectiveness (or ineffectiveness) of BECCS in climate-change-mitigation relies upon the relative change in CO2 carbon capacity compared to the previous ecosystem — i.e. how much or how much less CO2 is saved this way. This, in turn, is built on several factors: the choice of crop grown for fuel, the gain or loss of carbon due to the change in ecosystem — i.e. what we do with the plants that used to grow in an area –, how well the system can store the CO2 it produces, and the level of fossil-fuel emissions it replaces from the grid.

Bituminous coal.

This chunk of bituminous coal (5.5 cm / 2 in across) was formed from ancient plants. When we burn it, we release the carbon it stores as CO2. BECCS-type installations capture and burn CO2 that’s already in the atmosphere.
Image credits James St. John / Flickr.

In other words, while it may not be the right choice for many areas now, future improvements in BECCS technology can change this. The team didn’t set out to demonize the process. Rather, they wanted to show that we need to apply some discretion in regards to which areas we devote to BECCS-type systems. And, at the same time, that we cannot rely solely on carbon capture to solve our problem.

“Our paper illustrates that the manipulation of land can help offset carbon dioxide emissions, but only if applied for certain, quite specific locations,” says co-author Chris Huntingford, a Professor at the UK Centre for Ecology and Hydrology.

“To meet the climate change targets from the Paris agreement, we need to both drastically reduce emissions and employ a mix of technologies to remove carbon dioxide from the atmosphere,” adds Dr. Harper.

“There is no single get-out-of-jail-free card.”

Which is solid advice in all areas of life, not just climate change.

BECCS and forests?

Given that BECCS-type systems scrub CO2 out of the atmosphere, and that forests store a lot more carbon than regular crops, I asked the team whether we couldn’t merge the two for a super-duper carbon removal system. In my mind, we could grow forests in lieu of crops, and then use the wood for fuel. It sounds sweet in theory, right? I thought so too.

Just as I was waiting to be handed a diploma, Dr. Harper sadly informed me that my fail-proof plan is quite fallible. Forests simply take much more time to grow compared to regular crops.

However, pre-existing forests have already scrubbed a lot of carbon while growing, she told me, so maintaining their health and integrity would effectively keep that carbon out of the atmosphere. Furthermore, fully-fledged forests contain a lot of biomass, which means there are many (and large) roots to feed. They lap up much more CO2 out of the atmosphere than a simple fuel crop could. Proper management and conservation would only see this scrubbing potential increase — and, for many parts of the world, it would simply outshine any benefits BECCS-type processes can bring to the table.

“An important point is that the carbon benefit from forests often comes from existing forests, underlining the value of maintaining present-day forests and avoiding deforestation,” Dr. Harper explained for ZME Science in an email.

“Even with more optimistic yet realistic assumptions [about the yield of crops and the efficiency of the BECCS process] there are still about 35-40% of the locations where [maintaining forests is] a better option.”

BECCS-type ventures would make sense in areas that either lack forests today, or those whose forests aren’t lush enough to capture more CO2 than a simple fuel-crop would.

BECCS-forest comparison.

The difference in total carbon stocks (including accumulated storage via BECCS) by the year 2100 on grid cells where the two scenarios have conflicting land­use change. Blue areas indicate more carbon stored with BECCS and red areas indicate more carbon stored by forests under two land use scenarios.
Image credits Harper et al., 2018, N.Comms.

There is, however, one clear advantage of carbon capture over forests — security. One of the effects of climate change is an increased rate of wildfires, spurred on by higher average temperatures and shifting patterns of precipitation. A paper recently published by researchers from the University of California, Davis suggests that this increased occurrence of wildfires effectively turned the forests of California from carbon sinks into carbon sources. Dr. Harper agrees with the point raised by the authors but, instead of giving up on forests entirely, she says we should double-down on our efforts to keep them from burning down.

“I saw that paper recently, and it’s a good point — carbon stored in forests is not guaranteed to stay there. I would say this highlights the point that we need to manage forests if they are being grown for carbon dioxide removal so we can increase the likelihood that the carbon will stay out of the atmosphere.”

“The decision between growing crops, maintaining forests, or growing new forests will always be very location-specific and there’s not one answer that applies everywhere. That study was based on California where the climate lends itself to fires (as we are seeing now, unfortunately), and in those regions it probably doesn’t make sense to invest lots of money into growing a forest,” she concludes.

Asked whether vertical farms could help provide space for fuel crops while maintaining forest integrity, Dr. Harper replied that the current paper doesn’t take such installations into consideration — but that it would be “really interesting to evaluate” their potential in this role.

The paper “Land-use emissions play a critical role in land-based mitigation for Paris climate targets” has been published in the journal Nature Communications.

Grasslands could overtake forests as the most reliable carbon sink ecosystems

In the face of unstable climate and weather patterns, grasslands may be more reliable carbon sinks than forests, a new paper suggests.

Sunset.

Image credits Rüştü Bozkuş.

Forests are key carbon sinks for our planet. All plants capture carbon atoms from CO2 gas as they grow, using them to weave together new tissues. Trees, being some of the largest plants out there, are particularly effective. Their sheer size stands as a testament to this ability — each and every square centimeter of that plant is build using carbon locked away from the atmosphere.

In recognition of this fact, forests are often considered net carbon sinks in cap-and-trade/emission trading type schemes. In this case, particularly, they’ve been included in California’s cap and trade system since the state’s Air Resources Board (ARB) adopted the U.S. Forests Compliance Offset Protocol in November 2014.

So why then don’t we just plaster the Earth in trees and spew CO2 without a care in the world? Well, first off, it wouldn’t work — trees alone can’t save us from climate change, studies have shown. Another issue is that our photosynthesizing friends also have an Achille’s heel: their ability to gobble up carbon is matched by their propensity to burn. Forest fires free stored carbon mightily fast and disrupt carbon-storing ability over many years.

Kindling not firewood

One new paper published by researchers from the University of California, Davis, shows that in the context of climate change, forests may no longer be the go-to ecosystems for carbon storage. Decades of fire suppression has left California’s forests rich with fuel while warming temperatures and drought increase the risk of wildfires. Overall, they write, the higher incidence of such fires effectively turned the state’s forests from carbon sinks to carbon sources.

Grasslands, the team surprisingly reports, are more resilient carbon sink ecosystems than forests in today’s California. The findings warrant including grasslands in the state’s cap-and-and trade market, the authors add.

“Looking ahead, our model simulations show that grasslands store more carbon than forests because they are impacted less by droughts and wildfires,” says lead author Pawlok Dass. “This doesn’t even include the potential benefits of good land management to help boost soil health and increase carbon stocks in rangelands.”

Biomass in forests is very top heavy, in that most of it is stored in wood and leaves above ground. By contrast, most biomass in grasslands is concentrated under the surface. Fires can’t draw this biomass as fuel since there’s not enough oxygen to sustain combustion below the surface. Because of this, carbon stored in underground biomass isn’t affected by wildfires — which are a serious threat in the context of climate change.

To gauge how forests and grasslands would fare as climate sinks in the future, the team ran simulations of four scenarios:

  • Warming limited to 3.06 degrees F (1.7 degrees C) of warming by 2100 as a result of a massive drop in global carbon emissions — yes, this was considered the “positive” scenario.
  • A business as usual scenario, under which carbon emissions continue unabated. This scenario sees a temperature increase of up to 8.64 degrees F (4.8 degrees C) by 2100.
  • Climate-change-induced periodic intervals of drought — similar to the weather patterns generated by La Niña/El Niño.
  • A ‘megadrought’ scenario, lasting for a century or longer.

California’s forests were more reliable carbon sinks than grasslands only under the first scenario, the team explains. It’s extremely unlikely that those conditions will ever come to pass, as the scenario requires more aggressive global greenhouse gas reductions than those called for under the Paris Climate Agreement (and we’re not even meeting those yet). As things stand now, grasslands may become the only secure net carbon sinks through to 2101, the team explains.

Grassland or forest evolution.

Grassland (A) and forest (B) evolution in response to 21st-century climate changes. Blue shows expansion while red indicates contraction. Forests retreat in all future climates except those associated with aggressive emissions reductions (RCP 2.6), the team found.
Image credits Pawlok Dass et al. 2018 Environ. Res. Lett.

The team cautions that their findings don’t mean we should cut down forests — far from it. It only goes to show that from a cap-and-trade & carbon-offset perspective, conserving grasslands and promoting rangeland practices that promote carbon sequestration could help more readily meet the state’s emission-reduction goals. While trees stay on the cap-and-trade portfolio, protecting them through strategies meant to limit and combat wildfires — prescribed burns, strategic thinning and replanting, for example — will reduce overall carbon losses.

Trees and forest provide a wealth of environmental services, and we would be wise to conserve them. Finally, while grasslands may become the more reliable carbon sinks, forests still have the ability to soak up much more carbon per unit or surface than grasslands.

“In a stable climate, trees store more carbon than grasslands,” said Professor Benjamin Houlton, a paper co-author. “But in a vulnerable, warming, drought-likely future, we could lose some of the most productive carbon sinks on the planet.”

“California is on the frontlines of the extreme weather changes that are beginning to occur all over the world. We really need to start thinking about the vulnerability of ecosystem carbon, and use this information to de-risk our carbon investment and conservation strategies in the 21st century.”

The paper “Grasslands may be more reliable carbon sinks than forests in California” has been published in the journal Environmental Research Letters.

High-resolution spectroscopy could revolutionize seawater uranium capture

New imaging techniques might revolutionize the technologies currently used to capture uranium from seawater, as researchers gain a better understanding of the way the compounds that bind the atoms interact with them.

Using high-energy X-rays, researchers discovered uranium is bound by adsorbent fibers in an unanticipated fashion.
Image via phys

A research team led by Carter Abney, Wigner Fellow at the Department of Energy’s Oak Ridge National Laboratory, used ultra-high-resolution imaging to study the polymer fibers that bind uranium from seawater. Their results, gained through collaboration with the University of Chicago and published in a paper in the journal Energy & Environmental Science, shows that these materials don’t behave the way computational models say they should.

“Despite the low concentration of uranium and the presence of many other metals extracted from seawater, we were able to investigate the local atomic environment around uranium and better understand how it is bound by the polymer fibers,” Abney said.

By looking at the polymeric absorbent materials with X-ray Absorption Fine Structure spectroscopy at the Advanced Photon Source, Argonne National Laboratory, the researchers found that the spectrum response from the polymers were very different from what they were expecting to see based on previous small molecule and computational investigations.

They concluded that for this system the approach of studying small molecule structures and assuming that they accurately represent what happens in a bulk material simply doesn’t work. What is needed is to consider the behavior of the molecules in-bulk, to take into account interactions that only start working in a large-scale setting, says Abney.

“This challenges the long-held assumption regarding the validity of using simple molecular-scale approaches to determine how these complex adsorbents bind metals,” Abney said. “Rather than interacting with just one amidoxime, we determined multiple amidoximes would have to cooperate to bind each uranium molecule and that a second metal that isn’t uranium also participates in forming this binding site.”

(Amidoximes are the chemical group attached to the polymer fibers that bind the uranium atoms.)

Armed with this knowledge, Abney and colleagues hope to develop absorbents that can efficiently harvest the vast quantities of uranium dissolved in seawater.

“Nuclear power production is anticipated to increase with a growing global population, but estimates predict only 100 years of uranium reserves in terrestrial ores,” Abney said. “There is approximately 1,000 times that amount dissolved in the ocean, which would meet global demands for the foreseeable future.”