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Why We Need CCS, Part 4: Carbon Negative Solutions

Schalk Cloete's picture
Research Scientist Independent

My work on the Energy Collective is focused on the great 21st century sustainability challenge: quadrupling the size of the global economy, while reducing CO2 emissions to zero. I seek to...

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  • Jul 1, 2014


  • The economic growth ambitions of the developing world combined with the very tight carbon budget prescribed for the 2 ᵒC scenario could potentially demand a very large deployment of carbon negative solutions from the middle of the 21st century.
  • CCS is the best candidate for achieving negative CO2 emissions – both in the form of bio-energy with CCS and direct air capture. 
  • Extensive modelling studies performed by the IPCC show that removal of this option makes the achievement of the 450 ppm scenario much more expensive or even impossible. 


As discussed in a previous post, CCS is likely to play a very important role if climate science is eventually proven correct and long-term atmospheric CO2 concentration levels of ~450 ppm are confirmed as a top global priority. The possible role of CCS retrofits to the very young fleet of fossil-fueled industry currently being built in the developing world was discussed as a medium-term possibility in the case where CO2 prices rise very rapidly in the next decade. Given the massive coal-fired push towards economic growth in the developing world and the very tight CO2 budget related to the 450 ppm scenario, however, this is unlikely to be sufficient.

Indeed, with every passing year of much climate talk and little climate action, various agencies around the world adjust their 2 ᵒC scenarios towards something that looks even more unrealistic than the previous iteration. The most recent of these scenario analyses comes from the IPCC where it was flatly stated that many models could not achieve the 450 ppm scenario if CCS is eliminated as an option. And a substantial portion of the projected CCS impact comes in the form of carbon negative solutions resulting in net-negative emissions from the electricity sector starting mid-century (see below).

IPCC 450 scenarios

Carbon negative solutions

Taking CO2 from the air is quite a lot more difficult than putting it there, but, as shown in the figure above, almost all 450 ppm scenarios require large net-negative emissions from the electricity sector towards the end of the century. The IPCC assigns this responsibility to bio-energy with CCS (BECCS), but also mentions direct air capture as an option.

Naturally, there is great uncertainty tied to BECCS, primarily related to the feasibility and impact of building out bio-energy on such an enormous scale. However, if it eventually turns out that the 450 ppm scenario is indeed a vitally important target for the future of the planet, we will have little choice other than making this work.

CCS rollout

The amount of emissions mitigated by CCS in various scenarios producing long-term CO2 concentrations in the range of 430-530 ppm is shown below. A rapid upscaling is clearly visible with the storage rate in the year 2100 being close to the entire energy-related emission rate of today – a rather incredible expectation.

CCS deployment

The ~3 GtCO2/yr storage rate in 2030 might not look very impressive in comparison, but the enormity of this upscaling effort becomes evident when compared to the large subsidy-driven renewable energy rollout in recent years. For example, wind energy has expanded at a very impressive 30% CAGR over the past 15 years, but, as shown below, currently avoids only about 0.235 GtCO2/yr – more than an order of magnitude less than is expected from CCS within a similar timeframe under the 430-530 ppm scenario. (CO2 mitigation from wind is calculated under the assumption that wind displaces natural gas at 0.45 tCO2/MWh and that additional emissions associated with embodied energy, fossil fuel balancing and the rebound effect are negligible.)

Growth in CO2 abatement from wind

Cost implications

The IPCC details several mitigation scenarios which deviate from the “all of the above” baseline case. The difference in total mitigation costs relative to the baseline scenario for these different scenarios is given on the left in the figure below.

Cost implications of non-ideal mitigation paths


It is clear that the “No CCS” scenario results in the biggest cost increase among 450 ppm scenarios, followed by the “Limited Bioenergy” scenario. It should also be noted that many of the “No CCS” model runs could not achieve the 450 ppm scenario.

One of the reasons given for the substantial cost increase caused by these two mitigation scenarios is the absence of BECCS (negative emissions) in the second half of the century. In comparison, the “Nuclear Phase Out” and “Limited Solar/Wind” scenarios show very small cost increases relative to the baseline because they are limited to the electricity sector and cannot achieve negative emissions.

It should also be noted that the above-left figure is generated under highly idealistic assumptions of a global least-cost climate change mitigation effort starting immediately. Under more realistic assumptions regarding delays in climate action and regional differences in ambition, mitigation costs increase further (as shown on the right in the figure above) and model predictions become increasingly dependent on large negative emissions from CCS in the second half of the century.


The role of CCS is increasingly becoming more clearly defined as an insurance policy against the scenario where climate science actually turns out to be correct. This climate insurance can potentially be claimed through retrofits to the enormous new fleet of fossil-fueled infrastructure still being rapidly deployed in the developing world and through the carbon negative solutions of bio-energy with CCS and direct air capture.

Even though the existence of this insurance policy can make the potentially catastrophic longer-term effects of climate change appear less daunting, it should not be relied upon too heavily. An enormous push towards carbon negative solutions towards the middle of the century is likely to be unnecessarily expensive and potentially environmentally destructive due to the enormous amounts of bio-energy that will be required. We can make things a lot easier for ourselves by establishing a true technology-neutral CO2 mitigation policy framework sooner rather than later.

Ed Dodge's picture
Ed Dodge on Jun 30, 2014


I continue to agree. The arithmetic is pretty clear. In a world of growing energy demand there is no way to meet carbon emissions goals by midcentury without CCS. Expensive or not we need CCS and the best way to bring costs down is to deploy it.

Roger Arnold's picture
Roger Arnold on Jun 30, 2014


BECCS is the only carbon-negative approach considered in the IPCC report you cite, but it is not the only one out there.  Even if one discounts the Direct Air Capture (DAC) approaches advocated by Dr. Klaus Lackner and others as too expensive, there are at least two other promising candidates that I know of.

One of those is direct capture and sequestration through alkaline minerals.  There are (literally) trillions of tons of naturally alkaline clay and trona deposits in the Great Basin areas of Nevada and western Utah.  They were created over the last few million years from weathering of granite and other rocks after the rapid uplift of the Sierra Nevada mountains.  The runoff containing the weathering products evaporated in the basin that the uplift created, never making  it to the sea.  The high content of soluble carbonates in those deposits, when dissolved in water, forms a strongly alkaline solution.  The solution serves as a natural “sponge” for CO2. 

Using cheap solution-mined minerals avoids two big costs of other approaches to DAC: the need to regenerate the sorbant used to capture CO2 from the air; and the need to sequester the gaseous CO2 that results from sorbant regeneration.  Instead, the CO2 is captured and stored as bicarbonate mineral content in the wet clay.  This is the approach championed by David Newell on this site.

The other approach is carbon-negative hydrogen from saline electrolysis. There are other approaches to carbon-negative hydrogen, but they’re based on pyrolysis of biomass, creating bio-char.  Those approaches are fine as far as they go.  However, they fall into the category of BECCS, and are subject to the same limitations of land use, low productivity, and limited scalability that beset most forms of energy from biomass.  The electrolytic approach appears (to me) more scalable.  It integrates well with hydrogen production for energy storage and dynamic balancing of power from wind and solar.  Greg Rau was the lead scientist on the LLNL team that published the referenced paper on the concept.

Max Kennedy's picture
Max Kennedy on Jun 30, 2014

CCS is and will remain a potential disaster.  CCC,  conversion to a solid like a plastic, is the long term stable solution.Instead of another partial solution leading to potential catastrophic release.  We have a chance to do it right instead of taking half measures, lets see if we have the wisdom.

Schalk Cloete's picture
Schalk Cloete on Jul 1, 2014

Could you find any solid cost estimates for these alternatives in your studies? I would be very much interested to take a look at these if they exist.

Schalk Cloete's picture
Schalk Cloete on Jul 1, 2014

Once we have a meaningful price on CO2, pure CO2 streams will be much more readily produced and the free market will be incentivised to come up with all kinds of innovative ways in which to deal with these large CO2 streams. If more technically, economically and politically feasible alternatives to traditional underground storage exist, they will be found and deployed in a very natural way soon after the CO2 economy takes off.

As you can see from the second graph in the article, the amount of CO2 that must be stored (in some way or another) is truly gigantic and keeps on increasing all the way to the end of this century. We therefore have a lot of volume and a lot of time which can be used to advance CO2 utilization and storage technology.

Engineer- Poet's picture
Engineer- Poet on Jul 1, 2014

Pure CO2 streams are like liquid toxic waste; they can be dumped accidentally or deliberately and wind up exactly where they’re not supposed to go.

I suspect that there’s much greater potential in the conversion of biomass to forms which are unavailable to decomposers over the short term.  Biochar is one such form.  If we could catch a substantial fraction of the carbon that’s fixed during the northern hemisphere growing season (the annual dip in the Keeling curve), we could force the YoY variations downward even at current levels of FF use.

Engineer- Poet's picture
Engineer- Poet on Jul 1, 2014

Fascinating link, Roger.  The scheme seems analogous to the Naval method of saltwater electrolysis with CO2 evolution to produce raw material for fuel synthesis.

One side-effect of the acid dissolution of silicates is the production of silicic acid, no?  If released into the ocean, it would favor the growth of diatoms.  It’s a pity that the news item didn’t link the paper’s abstract or detail any specific minerals suitable for the process.

Roger Arnold's picture
Roger Arnold on Jul 1, 2014

I believe that Klaus Lackner and David Keith have both published cost estimates for their respective versions of direct air capture.  Both have at least some financial backing and have fielded limited prototypes.  But their estimates are controversial and discounted by other researchers.  The consensus seems to be that whatever DAC may cost, it’s bound to be a lot more than point source capture.  So it’s pointless to even think about it before we have serious emissions pricing in place and point source capture has been broadly implemented. I have doubts about that — I think DAC could be economical — but that seems to be the thinking among most researchers.

As to the two alternative approaches that I mentioned, neither has been developed to the point that “solid” cost estimates could be developed.  The only costing work that I know of is the work that I’m doing myself, and that’s “back of the envelope” stuff.  

The carbon-negative hydrogen approach is the easier one to get a handle on.  The laboratory version of the electrolysis cell that the LANL team used to validate the concept is not a practical model for production use.  However, I worked out a design that I think would be practical, and found that the features needed to produce separate acid and base output streams come virtually “for free”.  If stacks were produced in volume, production of acid and base streams should add only pennies per kilogram to the cost of the hydrogen produced.  That leaves the cost of neutralizing the acid by pumping it through a bed of crushed mafic rock, and the cost of transporting the base solution (NaOH) to the ocean, diluting it down, and broadcasting it to the surface waters at concentrations that won’t harm sea life.  Those costs are hard to estimate.

Roger Arnold's picture
Roger Arnold on Jul 1, 2014

Now there’s a fine doomsday scenario for you!  Some anonymous research group, concluding that too little is being done to address global warming, decides to take matters into their own hands.  They genetically engineer a virus that is supposed to knock off a few decomposer microbes and slow down the release of CO2 from dead biomass.  But they miscalculate, and their virus is overly effective.  Around the world, decomposition slows to a crawl.  CO2 levels plummet, and the earth enters a new “snowball earth” phase.

Hopefully not possible.  There should be enough diversity in decomposers that no single virus could do much damage.  But if’s something to worry about, for those who somehow can’t fine enough real and immediate problems to lose sleep over.

Ed Dodge's picture
Ed Dodge on Jul 1, 2014

Pure CO2 is a commodity. Supercritical CO2 has a wide variety of beneficial uses. I don’t know why you would say it is toxic waste. We inject CO2 into beverages every day for soda, hardly evidence that it is toxic. CO2 is only toxic at elevated concentrations where it is an ashphyxiant, but it is true of virtually all substances that they are toxic in elevated doses. Water kills too you know.

Finding beneficial uses for CO2 that financially incentivize the capture and needed pipeline infrastructure is one of the best things we can do to keep CO2 emissions out of the atmosphere.

Engineer- Poet's picture
Engineer- Poet on Jul 1, 2014

The process of capturing, purifying and liquefying CO2 costs both money and energy.  I suspect that any truly successful scheme is going to bypass as many of those steps as possible, and the alternative is simply not to convert fixed carbon into CO2 in the first place.

Engineer- Poet's picture
Engineer- Poet on Jul 1, 2014

I don’t know why you would say it is toxic waste.

How dare you put words in my mouth.  I said it is like toxic waste, and stated exactly how.  Waste haulers not far from me have dumped benzene-laden fraccing effluent onto county roads, when they were supposed to be spraying dust-suppression brine.  This was only possible because it was a liquid that could simply be dumped, just like CO2 is a liquid that can simply be dumped.

If you think CO2 is non-toxic I will be happy to let you breathe 30% O2, 60% N2 and 10% CO2 for an hour and then tell me your revised opinion.

Speaking of water,  I think I am going to go paddle on the millions of cubic meters of the stuff off the edge of my yard.

Ed Dodge's picture
Ed Dodge on Jul 1, 2014

You reiterated precisely what I said. CO2 is only harmful as an asphyxiant at highly elevated doses, aside from that it is beneficial. And water is also pretty destructive at highly elevated doses, but we need it for life in the proper amounts. Its all about finding the right balances.

As for dumping CO2 on the ground (presumably illegally), that doesn’t make sense when it is a valuable commodity once it has been purified, pressurized and loaded onto a truck. Just because someone, somewhere commits an environmental crime with some other chemical from some other process does not correlate out to the discussion we are having about what to do with CO2.

Max Kennedy's picture
Max Kennedy on Jul 1, 2014

The order of magnitude increases you suggest will increase the risks exponentially.  None of what you’ve said is either unknown to me or provides any confidence the process will be safely managed., All I have to do is look at the so called “safe fracking practices” and the methane leaks which so far entirely negate the so called “lower carbon” aspect of that fuel.  If not here then elsewhere business will cut corners and the so called “safe” practice will fail catastrophically.  Same cannot be said for a material transformed into a solid.which can replace other materials in many uses such as housing, consumer products, automotive etc. or transformed into a liquid fuel to replace what is derived from fossil fuels.  Hardly a “small” fraction of the need for removal.

Ed Dodge's picture
Ed Dodge on Jul 1, 2014


Todd is correct that there are orders of magnitude differences between the potential demand for CO2 used for EOR versus CO2 plastics or synthetic fuels. While I hope all of these applications move forward and all have promise CO2-EOR is far and away the big player on the CO2 demand stage with gigatons of potential demand and forty years of successful operational experience.

Zero-risk is not an appropriate threshold for moving forward. Nothing in life is risk free, you could get food poisoning next time you go to a restaurant. We need good goverance and oversight to manage risks in an appropriate way. And of course government corruption undermines this effort which is seen throughout the developing world where environmental management really is a tragedy. 

We need to be realistic that hydrocarbon resources are simply not going away, either in supply or demand. We need to make continuous efforts to minimize the damages and maximize the benefits we gain from them.

Schalk Cloete's picture
Schalk Cloete on Jul 1, 2014

The IPCC included biochar (objectively) in the wide range of AFOLU impacts considered in the material discussed in this article. It is therefore already included in the general conclusion that the 450 ppm scenario will be much more expensive or even impossible without CCS.

Max Kennedy's picture
Max Kennedy on Jul 1, 2014

Sorry but that statement is inherintly wrong.  Since the vast majority of the excess CO2 comes from fuel use there cannot be “orders of magnitude difference” in demand when synthetic fuels are included.  They would simply displace current fuel use.  What that is is a reflection of the use and dispose mentality that keeps current corporations in profits.  This is just snother argument for business as usual and is unacceptable.  You’ll have to present concrete numbers with reliable references to back up such a patently ludicrous statement.  What you really mean is it wouldn’t provide enough profits. 

Ed Dodge's picture
Ed Dodge on Jul 1, 2014

Making synthetic fuels from CO2 (which I think is a great idea) is basically an energy storage exercise, its not a resource. The equation that describes it is:

C02 + H2O + energy input -> CO-H2 + O2

It is reverse combustion and it provides synthesis gas and pure oxygen as outputs. It requires significant energy inputs which can be heat and/or power. I don’t have the exact figures in front of me, but the process is well documented by chemists. It is also described as electrolysis of CO2 and H2O.

NewCO2fuels is an Israeli company working on this process using industrial waste heat that can be  found in gasification plants or steel manufacturing. I think it is very promising especially when done at gasification plants because the oxygen can be recycled back in as an input and is very helpful in the overall energy efficiency because it replaces some of the demand on the Air Separation Units.

While this all very cool and interesting, scalability and cost are serious issues. But it is a way to recycle some portion of waste CO2.

DNV has done detailed research on CO2 utilization, you can wade through their numbers. DOE has a program also.

I am 100% in favor of CO2 utilization. I have written on CO2 fuels and CO2 plastics, I have samples of CO2 plastics on my desk.  Zero Waste is my guiding principle in all of my research and writing. But CO2 is a tough nut to crack. If it was easy we would be doing it already.

Engineer- Poet's picture
Engineer- Poet on Jul 1, 2014

You still don’t get it.  NItrogen is an asphyxiant.  Freons are asphyxiants.  Added to air, they displace oxygen.  They have no other effects at sea-level pressure.

CO2 is a toxin even at elevated levels of O2.

Robert Bernal's picture
Robert Bernal on Jul 2, 2014

Is there a way to capture CO2 from the oceans? It would seem that the density of the liquid would make it easier than direct air capture.

Robert Bernal's picture
Robert Bernal on Jul 2, 2014

How much energy is required to (and how do we) make biochar and could enough be made to offset the need to sequester about 500 billion tons of excess CO2 in either geologic or mineral form?

Schalk Cloete's picture
Schalk Cloete on Jul 2, 2014

At elevated concentrations (~10 vol%), CO2 is a toxic in the sense that it disrupts blood chemistry. This source gives the following reactions to increasing concentrations of CO2:

2-3% – Shortness of breath

5% – Heavy breathing, sweat, pulse quickens

7.5% – Headaches, dizziness

10% – Impaired hearing, nausia, loss of consciousness

30% – Coma, convulsions, death

At 30% concentration, unconsciousness sets in within 1 minute, implying that this can be very dangerous. However, the likelihood of CCS activities resulting in 1 minute of exposure to 30% CO2 concentrations are very low. Pipeline ruptures are probably the most risky element, but this risk can easily be mitigated through well-established best practices.

donough shanahan's picture
donough shanahan on Jul 2, 2014

In principle it is a nice idea but the concnetration is probably too low. That is why stack exhausts are targeted rather than the general atmosphere by most.

Rick Engebretson's picture
Rick Engebretson on Jul 2, 2014

Without criticism of CCS, I do agree “biochar” or other soil carbon sequestration is a double winner.

We live in a part of Minnesota where glaciers pushed the topsoil to Iowa. Years of frustrating gardens were transformed to unbelievable gardens by raised beds and synthetic black dirt trucked in. We get similar results in hay fields allowed to enhance organic content.

This is old soil science well understood in the 1950s. Further, Carbon without the O2 isn’t “500 billion tons” anymore.

Photosynthesis is VERY greedy for CO2. After all, we are worried about parts per million of CO2. Yet we barely give a thought to the Pacific Ocean wildlife eating plastic. Maybe California rain patterns are a different problem?

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