Removing Carbon Dioxide from the Atmosphere

In October 2018 the Intergovernmental Panel on Climate Change (IPCC) issued a Special Report updating the occurrence of weather and climate extremes since 2014.  It compared the effects of an increase in the long-term global average temperature of 2°C (3.6°F) with that of a 1.5°C (2.7°F) increase, referenced to the pre-industrial climate, on humanity and the natural world.  Its conclusions emphasized the necessity of limiting warming to the more stringent goal of 1.5°C to avoid severe harms to our planet by later in this century.

In its models the Report used four climate scenarios.  All the scenarios admit that global emission rates, to greater or lesser extents, will not be reduced adequately, or fast enough, to limit the temperature increase without deployment of technologies to remove carbon dioxide (CO₂), a principal greenhouse gas, from the atmosphere.  CO₂ results from humanity’s burning of fossil fuels.  CO₂ removal, also called “negative emissions”, would compensate for any failure to reduce direct emission rates of greenhouse gases from their original sources.  An example of one of the scenarios is shown here:

Net emission rates per year throughout the remainder of the 21^st century (Blue line), representing the result of the following contributions.  Grey shading , annual CO₂ emission rates from burning fossil fuels; Brown shading , annual CO₂ emission rates or reductions from agriculture and forestry;  Gold shading , annual CO₂ reduction rates from bioenergy with carbon capture and storage.

Source: IPCC Special Report, Summary for Policymakers https://www.ipcc.ch/site/assets/uploads/sites/2/2018/07/SR15_SPM_High_Res.pdf

 

Large scale CO₂ removal is considered in an article by Lu and coworkers, entitled “Gasification of coal and biomass as a net carbon-negative power source for environment-friendly electricity generation in China”, released April 9, 2019 in Proceedings of theNational Academy of Sciences.

 

As an aside, the importance of scrutiny of scientific reports by anonymous peer reviewers is brought out in this article, for the authors thank “…the reviewers for valuable and constructive suggestions. We are particularly grateful to one of the reviewers for her/his painstaking efforts to critique several versions of the manuscript and for questions raised that contributed to an important improvement in the final presentation.”  Peer review remains the gold standard for assessing the worthiness of scientific reports.

 

The authors recognize the wide availability of plant waste in China.  In Combination with the widespread use of coal already in place in the country, the authors model using various mixtures of agricultural Biomass with coal in an efficient technology for generating Electricity, coupled with use of process heat to drive CO₂ Capture and Storage (CBECCS).  The model extends over the long-term lifetime of such equipment. 

 

The authors find:

• Crop waste proportions greater than 35% mixed with coal would yield net-zero emission of CO₂ evaluated over the service lifetime, moving toward significant levels of negative emissions as the crop waste proportion increases;
• The cost of generating electricity over the lifetime, including the equipment costs, is US$ 0.092/kwh (kilowatt-hour);
• As China moves toward a national policy of imposing a price on carbon in the near future, a cost of US$52/ton would render CBECCS competitive with China’s current pulverized coal power plants; and
• Conventional pollutants widely acknowledged to arise from coal-fired electricity generation and vehicle exhaust (oxides of sulfur, oxides of nitrogen, black soot and PM_2.5 aerosols (2.5-micrometer or smaller particles detrimental to human health)) are significantly reduced by CBECCS. Severe urban smog in China has been a major driver to curb use of fossil fuels because they produce high levels of these pollutants.  CBECCS would contribute significantly to improving public health in the country.

CBECCS is especially feasible in China at the scale needed because the country is endowed with a very large geological storage capacity for the CO₂ produced in the carbon capture and storage portion of the technology.  The model projects that only 0.036% of known geological formations suitable for storage would be needed each year; this capacity is widely distributed geographically across China.

The article lists barriers to implementing CBECCS technology at scale, including

• Deploying and integrating the many component advanced technologies to ensure smooth operation, and to extend it on a scale needed to make a significant contribution to reducing net emission rates;
• Implementing infrastructure to enable delivery of waste biomass to the CBECCS facilities at the scale and regularity needed; and
• Infrastructure and operating costs evaluated for CBECCS are more than double those for current coal generation. These costs can become competitive as China’s carbon pricing regime becomes operational as planned in 2020.

CO₂ Removal from the atmosphere (ambient air) in a pilot project in Canada.

The New York Times published a report on April 8, 2019 describing new technology for CO₂ removal from ambient air and preparing it for geological storage underground.  The company doing this work, Carbon Engineering, has attracted funding from oil companies Chevron and Occidental Petroleum, and the large Australian mining company BHP, as well as others.  Recently the company raised US$68 million.  The oil companies, sensitive to enterprise risk as renewable energy threatens to displace gasoline for transportation, are interested in carbon removal technologies such as being developed by Carbon Engineering as a way potentially to offset CO₂ emissions due to use of their products.  Fiona Wild, BHP’s vice president for sustainability and climate change states “This is about recognizing that climate change poses significant risk to all economic sectors.  Climate change is … a business risk that requires a business response.”  Similarly, Dieter Helm, professor of energy policy at Oxford University, says “If money is being spent on research and development to develop ways to sequester carbon, that is a good thing.”

A schematic flow diagram of Carbon Engineering’s technology is shown here:

Flow diagram for capturing the dilute CO₂ gas present in ambient air (1, left), and preparing it as pure CO₂ (upper arrow at stage 3, Calciner) for storage underground or for use in chemical processes to synthesize fuels.  The fan units include an alkaline solution that serves to absorb most of the ambient CO₂.  As shown at the right, the alkaline substance needed to absorb the CO₂ is regenerated and ultimately fed back to absorb more CO₂ in the fan units.

Source: New York Times, https://www.nytimes.com/2019/04/07/business/energy-environment/climate-change-carbon-engineering.html.

 

So far, according to the report, the pilot plant has produced the calcium carbonate pellets in stage 2.  Calcium carbonate is the mineral limestone.  If heated to a high temperature in the calciner the limestone would release pure gaseous CO₂ for collection.  

 

Discussion

 

An alarming impression of fossil fuel consumption by humanity since the beginning of the industrial revolution is shown here:

Global annual use of the three fossil fuels (gray, coal; orange, crude oil; teal, natural gas) shown from 1800 (before the industrial revolution) to 2017, in energy units of terawatt-hours.  For 2017 the energy from each fuel translates to approximately 5.4 billion metric tons/yr of coal; 30 billion barrels/yr of oil; and 122 billion cubic feet/yr of natural gas (using conversions provided at https://www.unitjuggler.com/convert-energy-from-kgSKE-to-Wh.html). Source: https://ourworldindata.org/fossil-fuels

 

These fuels, when burned, yield man-made CO₂ in comparably large amounts.  Since planetary warming is determined by the total amount of CO₂ that we have added to our atmosphere, one need only look back to this graphic and in her mind’s eye estimate the total area under the curve shown.

 

This result should impress the reader about the daunting task facing implementation of negative emission technology.  Even achieving fractional depletion of added CO₂, as suggested in the first graphic above, is a huge challenge.  A mitigating factor is that humanity has perhaps 1-2 decades to begin carbon removal at scale; in the first graphic above significant negative emissions (Gold shading) aren’t apparent until about 2040.

 

Carbon capture and storage technology at a less sophisticated level than presented here by Yu and coworkers has been known for more than a decade.  Even so, there are only a handful of such projects, operating as pilots, around the world.

 

Occidental Petroleum, and other petroleum extracting companies, already use CO₂, injecting it into operating oil wells to pressurize the crude oil and enable extracting more.  Thus CO₂ is being injected underground to produce more oil, which when refined and burned produces fresh CO₂!  Occidental believes this cycle could help make its operations carbon-neutral.

 

Carbon Engineering, and Chevron, in contrast, envision using CO2 to synthesize fuels, a process that requires the input of at least as much energy as was released when a fossil fuel was burned and yielded CO₂. Carbon Engineering plans to use renewable energy to generate hydrogen gas needed for making the synthetic fuel.  Thus a competition is implied, wherein a choice must be made between using renewable energy to serve the public directly versus using it in industrial processes to regenerate a carbon-containing fuel. 

 

As with the CBECCS process described by Lu and coworkers, the hurdle to achieve operation of the direct CO₂ removal at scale, as envisioned by Carbon Engineering, is high.  A single Carbon Engineering plant could remove 1 million tons of CO₂ per year.  This is a tiny fraction, about 0.003%, of the CO₂ produced by humanity around the world per year.

 

Both technologies described here are believed by the protagonists to become price competitive as the scale of operations increases and as use of fossil fuels falls due to market pressure if and when a meaningful price on carbon fuels is implemented.  In the meantime governmental resources and the private sector will drive the development of these technologies.

© 2019 Henry Auer

Summer Heat Waves, Carbon Storage and Natural Gas

Summary.  Man-made emissions of greenhouse gases are producing higher long-term global average temperatures.  A New York Times Op-Ed discusses a new normal of increased average global temperature accompanied by more, and more serious, extreme weather events with damaging consequences.  An editorial in the New York Times describes how a pilot project for CO₂ underground storage, which could reduce emissions, lost U. S. federal funding because of Congressional inaction.  A display ad by Chesapeake Energy, and its web site, describe the company’s new funding for projects to develop natural gas as a domestic American fossil fuel to replace imported oil.

Analogies are presented to illustrate that even if mankind stopped emitting new CO₂ now, the present level of warming and its attendant spawning of extreme weather events would still be with us.  A peer-reviewed article by Davis and coworkers concludes that even if mankind ceased putting new fossil fueled equipment into service, fuelling the existing equipment would still lead to increased atmospheric CO₂ with its attendant harmful weather consequences.  It is concluded that we must move toward a zero-emissions energy economy as soon as possible.

Introduction.  An overwhelming majority of the world’s climate scientists support the conclusion that man-made emissions of greenhouse gases are producing higher long-term global average temperatures.  This increase leads to more occurrences of short-term extreme weather events, carrying with them significant financial, humanitarian and societal harms.

In this post we consider first, an Op-Ed article by the climate scientist Heidi Cullen; second, an editorial describing termination of U. S. federal support for a pilot project whose goal had been developing viable technology to store the greenhouse gas CO₂ underground for geologically long time periods; and third, an effort announced by Chesapeake Energy to produce natural gas domestically in the U. S. as a replacement for imported petroleum based fuels.

In an Op-Ed in the New York Times of July 20, 2011, Heidi Cullen of Climate Central summarizes a recent report of the U. S. National Oceanic and Atmospheric Administration (for a preliminary version, see here).  The report redefines “normal” temperatures upward as a result of higher temperatures recorded over the last 30 years in the U. S.  It finds that the last 10 years in the U. S. were about 1.5ºF warmer than in the 1970s.  Furthermore, the U. S. National Center for Atmospheric Research found that heat waves and damaging rainfall could cause as much as US$485 billion in losses from crop damage, construction delays and disrupted travel.

Ms. Cullen continues that climate scientists, using a statistical method intended to identify causes, have determined that mankind’s burning of fossil fuels that yield greenhouse gases has led to the warming of the climate, and, just as importantly, to the occurrence of extreme events such as the severe 2003 European heat wave.  It is expected that this trend will continue.

Our earlier post entitled “Global Warming Is Responsible For Extreme Rainfall” summarizes two reports in the journal Nature in February 2011 that apply similar methods to ascribe unambiguously, for the first time, extreme rainfall events and flooding that occurred in 2000 and earlier directly to the effects of man-made global warming.  In addition, a report entitled “The Hot Summer of 2010: Redrawing the Temperature Record Map of Europe”  published in the journal Science (see Note 1) in April 2011 concluded that extreme heat waves such as experienced over 50% of Europe in 2003 and 2010 exceeded 500 year old temperature records.  Similar events are predicted in the future using climate models that include a “scenario” of increasing greenhouse gas levels.  In view of the scenario, the predicted behavior can be directly attributed to increases in atmospheric greenhouse gases arising from fossil fuels.

Also in the New York Times of July 20, 2011 an editorial entitled "Blame Congress” discusses the termination of a commercial pilot project on underground storage of CO₂ at an American coal-burning electricity plant.  Burning coal produces more CO₂ per unit of heat obtained than does the burning of other fossil fuels.  Therefore it would be important to find a way to capture the CO₂ and store it permanently underground in suitable geologic formations, instead of releasing it to the atmosphere.

This project originally received significant funding from the U. S. Department of Energy.  Energy legislation that would have provided economic incentives for innovative projects such as this has recently failed in Congress.  As a result, no funding is available any more, and the project is held up.  The industry relies on federal funding for such development projects aimed at reducing  greenhouse gas emissions.

Chesapeake Energy.  In the same issue of the Times, Chesapeake Energy displays a full-page advertisement on American energy independence.  The company announced three initiatives that it says will reduce America’s dependence on imported oil.  These are 1) extracting 50% more oil and natural gas domestically using horizontal drilling and hydraulic fracturing; 2) providing a US$150 million investment in Clean Energy Fuels Corp. to install liquefied natural gas fueling capability in filling stations in the U. S.; and 3) providing a US$155 million investment in Sundrop Fuels, Inc. to produce nonfood biomass-based alternative gasoline fuel derived from natural gas and waste cellulosic material.

The company will divert 1-2% of its annual drilling expenditures to these projects for the next 10 years.  It intends to stimulate acceptance of natural gas and gas-to-liquid fuels in the U. S.   Burning natural gas in place of diesel and gasoline  reduces CO₂ emissions by about 40% (still, burning natural gas, a carbon-containing fossil fuel, does not totally eliminate greenhouse gas emissions).

Analysis.

Atmospheric concentration of CO_2.  Worldwide the burning of fossil fuels for energy continues to increase.  The atmospheric concentration of CO₂ accordingly continues to increase as well, by about 2 parts per million (ppm; parts by volume of CO₂ gas per million parts by volume of air total) per year, and presently stands at 391 ppm. The increase in CO₂ from 1958, measured at Mauna Loa in Hawaii, is shown below (the red line is the averaged curve from monthly data).

Source: Wikipedia http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmosphere

It should be noted that, rather than being a straight line, the curve actually bends upward because emissions are increasing each year.

Ms. Cullen’s Op-Ed article emphasizes the need to minimize new emissions of greenhouse gases, indeed to reduce them to zero, as soon as possible.  This is because the atmosphere retains the CO₂ released for very long times, on the order of 100 years or more.  (See Note 2)  Essentially all the gas released today will still be in the atmosphere a century from now.  There is no natural mechanism known that depletes CO₂ from the atmosphere once released into it.

The CO₂ bathtub.  A simple model for atmospheric CO₂ is a bathtub containing CO₂.  Its faucet continues filling the tub with more CO₂ (from continued burning of fossil fuels), but the drain mechanism is essentially plugged, so virtually no CO₂ leaves the bathtub (our atmosphere).  As a result, the CO₂ level has increased from about 280 ppm

Source: http://warmgloblog.blogspot.com/2010/10/co2-bathtub.html 

before the industrial revolution began to 390 ppm today.  Even if no further CO₂ is added, by turning off the faucet, the earth’s atmosphere already has an elevated level of CO₂ which has already increased the average global temperatur and produced extreme weather events.  These would not cease even if mankind stopped now to emit all new CO₂. Although this ideal cessation  is not possible, it behooves mankind to minimize new CO₂ emissions as soon as possible. (See Note 3)

The fiscal analogy.  Another analogy to global climate change is drawn from the the current U. S. budgetary drama.  In fiscal terms, the analog of yearly increases in atmospheric CO₂ levels is the yearly deficit in the budget of the U. S. federal government.  Each year’s deficit is added to the total deficits accumulated over the preceding years; this accumulated deficit is the U. S. national debt.  The national debt is the analog of the total concentration of CO₂ already in the atmosphere.  Even if the deficit were reduced to zero next year (no new emissions), the total national debt (atmospheric CO₂) would still be there. 

These analogies indicate that the people of the world should be striving to bring new emissions of CO₂ close to zero as soon as possible. 

Global average temperature will increase due to existing fossil fuel-burning installations. In 2010 in Science, Davis, Caldeira and Matthews (see Note 1) assessed the future production of atmospheric CO₂ and its effect on global temperature from only fossil fuel-burning equipment already in place.  Their analysis predicts that atmospheric CO₂ will increase from the present 390 ppm, to a predicted maximum of about 412 ppm at about 2037.  After 2037 the predicted CO₂ concentration falls slightly to about 408 ppm by 2060. (See Panel C from Fig. 1 of Davis and coworkers below). 

  

© American Association for the Advancement of Science.  The upper and lower line projections relate to upper and lower bound estimates by Davis and coworkers for the reduction in CO₂ emissions over the time period to 2060.

Source: http://www.sciencemag.org/cgi/content/full/329/5997/1330

The current average global temperature is about 0.7ºC (1.3ºF) higher than it was in preindustrial times due to increased atmospheric CO₂ emitted since 1850.  Davis and coworkers predict that as a result of the continued emission of CO₂ from only existing installations (Panel C above) the average global temperature will continue to rise slowly over the next 50 years, reaching 1.3ºC (2.3ºF) above average preindustrial temperature by 2060, according to the Middle scenario. (See Panel D from their Fig. 1, above).  Thus even if we were to cease building new power plants and cars, global temperature would continue rising.  This scientific assessment by Davis and coworkers amplifies the simple bathtub and fiscal analogies presented above.

The U. S. has no national energy policy in place, as detailed in the New York Times editorial described above.  This void is currently filled by various state and regional greenhouse gas reduction initiatives, including California’s plan, the Western Climate Initiative, the Midwest Greenhouse Gas Reduction Accord, and the New England and mid-Atlantic Regional Greenhouse Gas Initiative.  These programs have varying levels of coverage and differing terms of duration.  In the absence of federal legislation governing energy policy, the Obama administration is implementing various policies by executive and administrative actions.

Is Natural Gas A Long-Term Solution?   The energy industry is promoting natural gas as a way to achieve American independence from reliance on imported petroleum, and as a “clean” fuel.  (See the earlier post “Producing More Natural Gas in the U. S.: The Pickens Plan”. )  Coal is the worst of the fossil fuels, producing the most CO₂ for a given amount of heat energy released.  Natural gas is the most efficient of the fossil fuels, emitting the least CO₂ for the amount of heat energy obtained.  It is called “clean”-burning for this reason, and because it emits no mercury and sulfur dioxide as pollutants, in contrast to coal. Nevertheless, natural gas still emits large amounts of CO₂ on burning. 

Natural gas is an abundant domestic fuel resource, especially with the development in recent years of hydraulic fracturing technology (“fracking”) to extract it from gas-containing shale formations that occur widely in the U. S.  At least one major oil company, Shell, is actively producing natural gas as a supplement to extracting crude oil.  In 2012 the company will produce more natural gas than petroleum. 

Problems with Natural Gas. The problems with natural gas are two-fold.  Natural gas (i.e., methane) is itself a greenhouse gas which is 25 times as potent a greenhouse gas as CO₂.  The New York Times on April 11^th, 2011 reported that natural gas wells, especially those using hydraulic fracturing, leak significant amounts of methane into the atmosphere.  These wells therefore worsen the global warming conundrum, rather than help it.

Also, fracking uses toxic chemicals in water to get the gas out.  Unfortunately the chemicals, as well as toxic substances (metals, radionuclides) leached from the shale, may contaminate ground water and may be released into surface waste water. 

The Pickens Plan for Use of Natural Gas in Transportation.  T. Boone Pickens, a oil and gas businessman, recognizes the disadvantage that the U. S. has with its energy economy, transferring about $220 billion a year to the Organization of Petroleum Exporting Countries alone.  Pickens has responded to this situation with a plan to develop natural gas and alternative energy domestically in the U. S. in order to reduce our dependence on imported petroleum.  He believes that natural gas can serve as a bridge fuel that is more advantageous than using gasoline and diesel made from imported crude oil.

Mr. Pickens has promoted the New Alternative Transportation to Give Americans Solutions Act of 2011 (H.R. 1380).  The bill offers tax credits to promote domestic production and distribution of natural gas, as well as the production and purchase of vehicles capable of using it.

Chesapeake Energy seeks to expand use of domestically produced natural gas instead of imported petroleum based fuels such as diesel and gasoline in transportation.  It will commit 1-2% of its drilling budget to the projects itemized above, amounting to at least US$1 billion over 10 years.  This means that its expected drilling budget overall will be US$50-100 billion, a very large expenditure indeed, over this period.  Contrary to Mr. Pickens, Chesapeake Energy appears, at least in its press release, not to view its new investments as a step along a transitional path to abandoning fossil fuel use.  This may be true for Shell as well.  Commitment to major investments in new gas wells likely is not undertaken with a view to phasing them out before the end of their useful lifetimes.

Conclusion.  Increases in the average global temperature, arising from mankind’s burning of fossil fuels for energy since the onset of the industrial revolution, is upon us.  The rate of burning fossil fuels has been increasing, as has the corresponding increase in the concentration of atmospheric CO₂. 

Heidi Cullen’s Op-Ed spotlights the need for world-wide action to curb further emissions of CO₂ and other greenhouse gases.  She emphasizes the occurrence of extreme weather events, whose frequency is projected to increase with the increase in atmospheric greenhouse gases.   The New York Times laments the cessation of a federally-subsidized pilot project that might have led to a technology for constraining emissions of CO₂.

The energy industry is rapidly developing natural gas contained in shale formations.  In the U. S. development of domestic energy resources is intended to eliminate dependence on imported petroleum.  It is not clear whether this new drilling activity is viewed as an interim phase which will be phased out as we move more comprehensively to renewable sources of energy.

Yet the work of climate scientists such as Davis and coworkers clearly shows the necessity of attaining a worldwide energy economy that is free of greenhouse gas emission as soon as possible.  The analogies provided by the bathtub model and the budget model help drive home this urgent need.  Since natural gas produces major amounts of CO₂ when burned, it should not be considered to be a long-term solution, but at best only a temporary crutch to lean on as the world progresses to a fully renewable and alternative energy economy.

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Note 1. Abstract available free; full article available online for a fee or through personal or institutional subscription.  Many public libraries, and university libraries open to the public, receive the journal.

Note 2. About 30% of released CO₂ dissolves in the oceans; this fraction essentially does not change.  Thus the comments presented here refer to the remaining 70% which stays in the atmosphere.

Note 3. It would be beneficial to be able to remove CO₂ already in the atmosphere in order to reduce its concentration.  Currently there is no engineering solution that would succeed in accomplishing this worthy objective.  Reforestation is one way of achieving this objective.

© 2011 Henry Auer