Carbon Dioxide Removal Approaches: Long-Term Implications And Requisite Societal Commitments

In recent years, a number of climate change commentators, non-governmental organizations, and intergovernmental organizations have discussed the potential need for so-called “negative greenhouse gas emissions” strategies. It is also anticipated that Working Group III of the Intergovernmental Panel on Climate Change will include a discussion of this approach in its upcoming report pursuant to its contribution to the Fifth Assessment Report. The rationale advanced for focusing on negative emissions approaches are usually the threat posed by burgeoning emissions, which could result in exceeding of critical climatic thresholds in a few decades, as well as system inertia, which could lock in temperature increases associated with radiative forcing for many centuries. The processes that could effectuate permanent removal carbon dioxide from Earth’s atmosphere include air capture, bioenergy and carbon capture and storage, ocean iron fertilization and soil mineralization, and are usually classified as carbon dioxide removal (CDR) geoengineering approaches.

In my next few postings on the site, I’d like to highlight some of the excellent peer-reviewed literature on carbon dioxide removal strategies that has been released in the past few years. In 2010, Stanford professors Long Cao and Ken Caldeira published a study in the journal Environmental Research Letters (open access) that sought to assess both the long-term consequences and level of commitment required to effectuate massive removal of carbon dioxide from the atmosphere. The researchers employed a coupled-climate carbon cycle model, initially integrated under a fixed pre-industrial atmospheric concentration of 278ppm for 5000 years. The model was subsequently integrated under prescribed historical carbon dioxide concentrations between 1800-2008, and then forced with carbon dioxide emissions from 2009-2049 following the IPCC’s A2 emissions scenario. The study then simulated cessation of carbon dioxide emissions and two extreme carbon dioxide scenarios, one in which carbon dioxide was instantaneously set to its pre-industrial level of 278ppm at the beginning of 2050 by removing all carbon dioxide from atmosphere, with carbon dioxide levels in the atmosphere permitted to evolve freely thereafter, and the other scenario in which carbon dioxide was set at 278ppm in 2050 and then held at that level thereafter. In both scenarios, integration of the simulations was continued until 2500.

Among the study’s conclusions:

1.     Following an extreme one-time removal of all anthropogenic carbon dioxide from the atmosphere, atmospheric concentrations are restored under the simulation to pre-industrial levels of 278ppm.

a.     However, due to efflux of carbon from land associated with responses of net primary production and soil respiration, as well as releases of carbon from oceans, atmospheric concentrations experience an overshoot, with a peak concentration of 362ppm 30 years after the removal.  Overall, 27% of removed carbon returns to the atmosphere. Thus, if society would wish to maintain atmospheric concentrations of carbon dioxide at a specified level, it would have to commit itself to long-term removal of carbon dioxide released from land and ocean sources;

b.     A one-time removal of anthropogenic carbon dioxide also reduces warming by a little less than 50% at the time of removal, and radiative forcing by two-thirds on centennial timescales.

2.     If atmospheric concentrations of carbon dioxide were restored to 350ppm, it would result in surface warming of 1.2°C, which would last for several centuries;

3.     The simulated reduction in temperatures in the study yields a cooling of 0.16°C for every 100 PgC CO2 removal. The conclusion that the concept of proportional temperature change to cumulative carbon dioxide emissions is apposite to carbon dioxide removal has implications for assessing the potential effectiveness of such approaches.

4.     The study also contains a cautionary note: if effective heat capacity should prove to be less than estimated in the study, or the carbon dioxide degassing timescale proved longer, it could result in temperature overshoots in which initial temperature decreases are reversed when carbon dioxide re-accumulates in the atmosphere. However, the research concluded that they did not observe this result in their simulations.

Of course, it is not likely that deployment of negative emissions approaches would, or in the case of most prospective technologies, could, follow what the researchers themselves characterize as an “extreme” scenario, i.e. a one-time removal of all carbon dioxide at a discrete point. Moreover, it’s far from clear that society would seek to return to pre-industrial climatic conditions, even if that could be effectuated. And, of course, the study did not address issues associated with feasibility, However, this study is very valuable for a number of reasons. First, it provides a preliminary estimate of anticipated reductions in temperatures per 100 PgC CO2, providing a guide to policymakers who might contemplate more limited uses of negative emissions strategies than contemplated in this study. Second, the study provides a pointed reminder of the fact that a negative emissions strategy would likely necessitate a multi-generational societal commitment, with all of the implications that this would hold for governance, ethics and practical logistics. Finally, the study could provide students with an excellent window into the methods, as well as challenges, of simulating the climatic impacts of geoengineering strategies with climate models.

Assessment of Efforts to Reform the European Union’s Emissions Trading System

In January, the European Commission published its proposal for the Climate and Energy Package 2030, which is slated for submission to the European Council this week. An important component of the proposed package is several changes to the European Union’s beleaguered Emissions Trading System (EU-ETS) For instructors who include a discussion of the EU-ETS, or more generally, emissions trading, in their courses, check out a new study by Paris-Dauphine University’s Climate Economics Chair. The study employed a model that sought to simulate supply and demand for emissions allowances (European Union Allowances or “EUAs”), year after year, incorporating the measures proposed by the Commission to date, including “backloading” allowances during the third phase of EU-ETS implementation and ratcheting up the linear annual emissions reduction factor from 1.74% to 2.2% from 2021 onward. It also focuses on the establishment of a market stability reserve (MSR) mechanisms, which, if implemented, will establish two triggering thresholds based on the quantity of allowances in circulation: a “high threshold” that triggers removal of 12% of the allowances in circulation when the quantity of allowances in circulation is greater than 833 Mt., and a “low threshold” that removes 100 Mt of allowances when the quantity of allowances in circulation is less than 400 Mt.

The study’s primary findings are as follows:

  1. If EU-ETS market participants’ expectations lead to early reductions in emissions from 2021 onward and high banking of allowances (keeping allowances for future use) (designated in the study as a “high scenario”), then prices for EUAs may reach 50 euros per ton in 2021 and remain above price levels in the baseline scenario until 2030. By contrast, under a “low scenario,” in which participants don’t consider it necessary to immediately reduce emissions or hold many allowances for banking purposes, prices rise to lesser degree than under the high scenario and fall below the reference price when the MSR leads to additional allowances being injected into the market;
  2. The MSR introduces greater price volatility into the market compared to a reference scenario without this mechanism. The reason is that the MSR lacks provisions to account for and respond to fluctuations in participants’ needs for allowances related to factors e.g. the evolution of abatement costs, relative energy prices, changes in technology and weather and economic conditions;
  3. While banking in emissions trading systems is generally recognized as salutary, as it permits participants to reduce emissions in the most economically manner possible, the establishment of the MSR may scupper this result. The reason for this, argues the authors of the study, is that if agents decide to purchase allowances with the intention of banking them for future use, this could ease triggering of the MSR, “which … would go against their interests as an equivalent quantity would be withdraw from auctions.” Similarly, if agents decide they don’t need to purchase allowances currently, this would result in a lower number of allowances in the system, resulting in a release of additional allowances into the system from the MSR. This would also vitiate the economic efficiency of the system.

Among the in-class discussion questions that this study brings to mind are:

  • Given what you know about the state of the European economy and its energy markets, what is the likelihood that the “high scenario” cited by the study will occur in 2021 and beyond? How about the “low scenario?” What are the implications for different allowance prices in terms meeting the objectives of the EU-ETS?
  • Does the MSR vitiate the operation of the EU-ETS as a “market-based” mechanism? If yes, is that problematic?
  • Given the fact that many believe that volatility in allowance prices can severely undercut investment in technologies to de-carbonize the economy, could there be ways to revise the MSR to avoid the potential price volatility cited in this study?


Effects of Feed-In Tariffs on Renewable Energy Generation

Feed-in tariffs (FITs) have become a widely used instrument to seek to drive market penetration of renewable energy sources. A recent study concluded that FITs have been implemented in 63 countries and 26 regional jurisdictions. In the United States, FITs have been adopted in twelve states and numerous municipalities. However, the impacts of FITs remain contested. A new study on the effects of FITs would make a good student reading in graduate courses with students with good quantitative skills.

The study used instrumental variables to estimate the causal effect of FITs on renewable electricity generation in 26 industrialized countries in the period of 1979-2005. The study employed two different instruments, a spatial instrument based on average FIT in neighboring countries (argued to be a strong predictor of a country’s FIT) and a 4-year lag of a country’s own FIT (argued to be a strong predictor of a country’s current FIT).

The researchers concluded that increasing the FIT by one cent U.S. per kilowatt hour increases the percentage change of renewable energy’s share in the electricity mix by 0.11%. Over a decade, a FIT of 10 cents would thus increase a country’s renewable energy share of electricity production by approximately 12%, with this share exceeded in several studies countries, including Austria and Portugal.

Among the in-class discussion questions that would be pertinent to this study include the following:

  1. Are the results here pertinent to developing countries?
  2. Are FITs the optimal instrument to incentivize renewable energy market penetration? How do we compare the instrument’s effectiveness vis-a-vis other approaches, e.g. renewable portfolio standards or net metering?;
  3. Some countries have begun to scale back FITs on the grounds of costs and maturation of some renewable energy technologies. How does society engage in the cost-benefit analysis to determine optimal levels of FITs?

Interactive Climate Exercises

The folks at the website Simple Climate have posted a really good set of exercises to guide those interested in learning more about climate change science. The exercises includes an excellent method to calculate one’s carbon footprint, an interactive map on the Keeling curve, and NASA’s Global Equilibrium Energy Balance Interactive Tinker Toy ((GEEBITT). There is also an excellent app for Apple platforms to guide users on how scientists construct and use global circulation models to predict climate change.

Climate Geoengineering Timeline

As part of my work with the Washington Geoengineering Consortium (WGC), I have established a timeline of key geoengineering events. The site facilitates viewing the timeline in several formats, including visual timetable, “Flipbook,” which focuses on each event on the timeline, and as a list. The timeline also includes pertinent links to many primary and secondary sources on climate geoengineering.

Assessment of Fast-Start Finance

A report published last year by the European Capacity Building Institute on the record of fast start financing by developed countries under the UNFCCC is well worth consulting by instructors who include an adaptation component in their courses. The report, which builds on assessments by the authors in previous years of reports filed by parties to the UNFCCC, seeks to determine “whether wealthy nations transparently contributed a fair-share of the $30 billion dollar pledge, while balancing adaptation and mitigation funding, sourcing funds through UNFCCC channels, and without reverting to debt-inducing loans in the place of grants.”

The assessment sought to answer nine pertinent questions. The first question was whether the amount of fast-start financing provided by developed countries was adequate. While concluding that developed States had exceeded the fast-start finance pledge of $30 billion for the period of 2010-2012, the authors contend that a large percentage of this funding was either not new or additional (see below for further analysis of this issue). Moreover, they noted that some analyses had concluded that as much as $200 billion would be necessary for mitigation and adaptation initiatives by 2030. The second proffered question focused on transparency of financing, including indicia eg. project-level reporting and the division of funding between mitigation and adaptation. The study found more countries woefully inadequate in this context, with even the top country, Switzerland, only scoring 67%.

The third question focused on equitable considerations, i.e. what developed countries were deemed to have contributed their “fair share” based on criteria of responsibility for the problem of climate change (defined as historical carbon dioxide emissions between 1960-2008) and capability, based on national income. The authors found that Norway and Japan had contributed far above their fair share, with New Zealand and Canada close to meeting this criteria, while all other developed States had contributed below fair levels. The fourth question centered on the balance of funding between adaptation and mitigation initiatives, given the mandate in the Copenhagen Accord to approximate an even division of funding between these two prongs of responding to climate change. In this accord, the authors found fast-start funding clearly lacking, with only approximately 18-25% allocated to adaptation projects.

The fifth question assessed the percentage of fast-start funds provided as grants vs. loans, the latter of which were deemed by the authors to be particularly inappropriate for adaptation projects because this form of funding can exacerbate the economic impacts of climate change and because it’s usually a response to damage caused by the very countries that might now be offering only loans. Question 6 of the assessment focused on whether funds are being delivered, per the Copenhagen Accord, through effective, transparent, and representative institutions, e.g. the Green Climate Fund, the Special Climate Fund, the Adaptation Fund and the Least Developed Countries Fund. The study concluded that only 4% of funding was directed through these channels.

One of the most critical questions is whether mitigation and adaptation funding is “new and additional,” or rather reallocation of foreign assistance from other sectors, e.g. health and education. The study concludes that there are serious problems in this context. First, a recent Oxfam study found that only 33% of fast start funding can be considered “new.” Moreover, the study notes that if all fast-start contributions were truly new and additional, overseas development assistance should be increasing by $10 billion annually. However, given the fact that all forms of overseas development assistance only increased by $11.7 billion annually between 2008-2011, the authors concluded that it was highly unlikely that almost 90% was concentrated in the climate sector.

UNFCCC negotiations have called for the needs of particularly vulnerable populations to be prioritized. The study deemed fast-start funding to be disappointing in this context also. For example, while LDCs have estimated that they would need $5 billion to meet their most pressing adaptation needs, as identified in National Adaptation Plans of Action, to date only $603 million has been pledged for such purposes. The study also cites a lack of transparency in reporting by developed countries as to whether they are seeking to meet the objective of focusing funding on the needs of the most vulnerable States and sectors.

The final question was whether pledges of fast start funds was actually translated into disbursement of funds. While most developed countries fail in their reporting to disclose such figures, a recent study suggested that only approximately a third of pledged funds had actually been delivered, while another concluded that perhaps only 10% of originally pledged climate funds make it to recipients!

The final section of the report provides some helpful suggestions on how to improve the process moving forward (a critical consideration as we move toward 2020, at which point contributions should reach $100 billion annually). These include improving the efficiency of the GEF project cycle, proving direct access to developed countries instead of through intermediary multilateral development institutions, and improved transparency, including standardized reporting that includes project mapping and progress tracking.

This report is certainly not a good portent for long-term financing of adaptation and mitigation initiatives in developing countries. While some of the more process-oriented issues, e.g. reporting requirements and structuring of priorities seem relatively easily rectified, more fundamental issues, e.g. the level of funding commitments (especially given the much higher funding requirements that will be necessary in the future) and the division of funding between grants and loans may prove far more challenging.

Among the discussion questions that might be pertinent if this study is used as a student reading include the following:

  1. Are there certain potential funding sources that might help to facilitate adequate levels of finance for mitigation and adaptation in developing countries over the next few decades, i.e. that are more politically viable?;
  2. Should adaptation and mitigation funding be viewed, as some developing countries argue, as a form of “reparations,” justifying very few constraints on disbursement, or a form of assistance in which “donors” are entitled to ensure that funds are used wisely?;
  3. What other considerations, beyond funding of adaptation, should be studied, i.e. how do we prioritize adaptation and mitigation projects, and how do we measure “effectiveness?”

Broecker on Air Capture Geoengineering

For instructors who cover climate geoengineering, Columbia University Professor Wally Broecker has recently published a thoughtful opinion piece (open access) on the judiciousness and potential of air capture geoengineering. The piece appears in the new journal Elementa: Science of the Anthropocene.

At the outset, Broecker develops the theme that drives most of the support for geoengineering research in contemporary society, despair over feckless climate policymaking, or as Broecker characterizes it “nibbles by developed countries … swamped by increased energy demand in traditionally poor countries.” After portraying albedo modification geoengineering approaches as only a “band aid” that could help ameliorate climatic impacts until we found permanent solutions, Broecker focuses on air capture as such a potential permanent solution.

Broecker notes that while there are three private groups in the U.S. and one in Switzerland that have launched air capture projects, none have garnered sufficient funding to build and test a complete and automated prototype. This has left us with highly variable estimates of project costs, ranging from Klaus Lackner’s claim that air capture could be effectuated for less than $100 per ton of carbon dioxide to more than $1000 in a 2011 study, as well as the American Physical Society’s estimate of about $600 per ton.

Broecker nicely summarizes the approach of Lackner, who contemplates the development of mass production of modular air capture units that would be shipped to sites of deployment. If each such unit were to capture one ton of carbon dioxide per day, then Broecker estimates that 100 million units would be required to capture the 32 billion tons of carbon dioxide produced annually from fossil fuel combustion. As each unit is estimated to require the amount of materials required to produce an automobile, he argues that it is within the capacity of a society that currently produces 80 million automobiles annually.  However, he also notes that 400 million additional units would be required if we wished to bring carbon dioxide down by 10pm annually. Given resource constraints, he concludes this might require the simultaneous use of albedo modification approaches in a time of climatic crisis.

Broecker also outlines several potential advantages of air capture over carbon capture and sequestration (CCS), including the potential to sequester carbon dioxide on-site rather than piping it over long distances, the need to only strip out a relatively small percentage of carbon dioxide from the air (30%), and the potential for mass production of units instead of custom design of CCS units for existing facilities. He also suggests that air capture could contribute to de-carbonizing the transportation sector by permitting us to combine hydrogen produced by water electrolysis with captured carbon dioxide to produce liquid fuels. Moreover, an air capture initiative could produce a substantial number of jobs since it would create an industry 10-20% of the size of the energy sector. Finally, it would raise the price of fossil fuels, helping to level the playing field for renewable energy options.

Broecker concludes by calling for a government-funded program, with “Manhattan Project”-like targets and time tables. This is necessary, he contends, given the fact that industry and venture capitalists view the prospects of air capture as too remote to justify substantial investment.

Broecker’s piece poses some interesting questions. In poo-poing concerns that a commitment to air capture research might create a “moral hazard” scenario in which pressure will be reduced to pursue a transition to renewable energy, he argues that air capture will take many decades to ultimately deploy. However, this sidesteps the question of whether there are substantial opportunity costs in pursuing a full-throated air capture R&D program. Thus, it would be important to assess costs of ramping up such a program over the next few decades, and the potential implications for crowding out renewable energy R&D and deployment. Also, as Broecker himself points out, if the ultimate cost of air capture is in the range of $600-1000, it will not prove viable. While he embraces Lackner’s much lower estimates, it would be interesting to know why he thinks such estimates are more reasonable. Finally, absent from Broecker’s analysis is a consideration of the implications of seeking to store up to 34 billion tons of carbon dioxide annually in terrestrial or ocean-based facilities, including the imposing environmental and health risks associated with potential leakage, and the huge “NIMBY” battles that may ensue in areas where such facilities might be sited.

However, at the end of the day, it’s hard to disagree with Broecker that air capture is an option that must be seriously considered given the continued dithering of the world community in addressing climate change.

Oxford Online Short course

The University of Oxford is delighted to announce that enrolment is open for the seven-week advanced online short-course Constructing and Applying High Resolution Climate Scenarios to commence Monday 17 February 2014.

This course draws upon the world-class climate science expertise at the University of Oxford and the UK MET Office, and is taught online by Dr Friederike Otto and Dr Pete Walton at the Oxford Environmental Change Institute.  It is designed to enable policy-makers and other professionals to gain the skills and scientific understanding necessary to support organisations in climate change policy and practice.


The course provides a detailed investigation of regional climate modelling, examining how global climate change information can be ‘downscaled’ to regional levels, how this information can produce climate scenarios appropriate for input to impacts models, and how results from regional climate modelling systems can be interpreted and utilised.  The course will also be of significant benefit to users of PRECIS.

As an online course, it can be taken from anywhere in the world and is attractive to an international community.  Participants are able to interact with one another and the course tutor online via our dedicated Virtual Learning Environment.  For more information and enrolment please visit:

Additionally, the University also offers a free online untutored course An Introduction to the Science of Climate and Climate Change.  This course provides an introduction to climate science and current issues surrounding the use of model projections of climate change.  It will be of great value to those wishing to learn about the basics of climate science and modelling, such as volunteers or students, and how to go about interpreting the results of modelling experiments.  For further information and registration please visit:

For full details of all of our climate change science and policy courses please visit or contact the course team on or +44 (0)1865 286953. 

Kind regards,

Chris Thompson


Administrative Officer (Environment & Sustainability)

Continuing Professional Development Centre

Department for Continuing Education

University of Oxford


Tel: +44 (0)1865 286952

Fax: +44 (0)1865 286934

New Courses from the GHGMI

Dear colleagues:

The Greenhouse Gas Management Institute (GHGMI) is developing* a new series of online courses based on the 2006 IPCC guidelines for greenhouse gas inventories. The curriculum in these courses is the definitive “source code” for carbon accounting at all scales: from national inventory estimation down to corporate footprinting.

The first course in this series, “501 IPCC: Introduction and Cross-Cutting Issues,” is now open for enrollment. This course teaches the techniques fundamental to compiling an inventory of greenhouse gas emissions and removals.

This spring, we will be launching a series of sectoral online courses also based on the 2006 IPCC Guidelines, including:

511 IPCC: Energy
521 IPCC: Industrial Processes and Other Product Use
531 IPCC: Agriculture
541 IPCC: Forestry and Other Land Uses
551 IPCC: Waste

For more information and registration details for the “501 IPCC: Introduction and Cross-Cutting Issues” course or other GHGMI curriculum please email or visit:

World Energy Outlook 2013

The International Energy Agency has released its World Energy Outlook 2013. Because I cannot afford the heftily priced full version, I am going to discuss the Executive Summary below. This would be an excellent student reading to provide a snapshot of the current state of global energy consumption and production and projections over the next few decades.

Among the findings in the report:

  1. China is poised to become the world’s leading oil importer by the early 2020s and India, the leading importer of coal. The U.S. may meet all of its energy needs from domestic sources by 2035;
  2. Energy-related carbon dioxide emissions are still slated to rise by 20% through 2035 even under the study’s “Central Scenario,” which includes policy interventions in the United States, China and Japan. As a consequence, the world is on a trajectory for long-term temperatures to increase 3.6C above pre-industrial levels;
  3. Two-thirds of potential economically viable energy efficiency gains remain on the table despite substantive changes in policy recently to facilitate efficiency improvements;
  4. By 2035, oil consumption will be concentrated in two sectors, transport and petrochemicals;
  5. Brazil is an extremely dynamic actor in the energy sector in 2035, with oil production tripling, natural gas production increasing five-fold, and biofule production tripling. At the same time, the country is projected to see an 80% increase in energy use during this period.