Climate policy increasingly relies on techniques to remove CO2 from the environment as a supplement to cutting emissions: counter-balancing residual emissions in ‘net-zero’ and reducing atmospheric concentrations of CO2 to safer levels. In this talk, Duncan will survey how cities are engaging with carbon removal – reviewing the realistic scope of possibilities such as carbon negative building materials, and carbon removal through urban waste management; and suggest ways in which urban carbon removal could be governed to contribute to goals of justice and sustainability.
About the speaker
Duncan McLaren is currently a Research Fellow with the Institute for Responsible Carbon Removal at American University. His research examines the politics and implications for justice of novel technologies, particularly using public engagement methods. Prior to his PhD studies, completed in 2017, Duncan worked as an environmental researcher and campaigner, most recently as Chief Executive of Friends of the Earth Scotland from 2003 to 2011. He has advised and consulted for research and financial institutions, government departments, philanthropic donors and non-governmental bodies on energy, climate, urban and sustainable development issues. Duncan can be found on Bluesky @duncanmclaren.bsky.social, and at www.duncanmclaren.net.
Watch the video of From City to Sink: Urban Carbon Removal as Promise and Practice with Duncan McLaren
Transcript for From City to Sink: Urban Carbon Removal as Promise and Practice with Duncan McLaren
0:00:07.8 Tom Llewellyn: Welcome to another episode of Cities@Tufts Lectures where we explore the impact of urban planning on our communities and the opportunities designed for greater equity and justice. This season is brought to you by Sharable and the Department of Urban and Environmental Policy and Planning at Tufts University with support from the Barr Foundation. In addition to this podcast, the video, transcript and graphic recordings are available on our website shareable.net just click the link in the show notes. And now, here’s the host of Cities@Tufts, Professor Julian Agyeman.
0:00:40.2 Professor Julian Agyeman: Welcome to our Cities@Tufts virtual Colloquium. I’m Professor Julian Agyeman and together with my research assistants Amelia Morton and Grant Perry, and our partners Shareable and the Barr foundation, we organize Cities@Tufts as a cross disciplinary academic initiative which recognises Tufts University as a leader in urban studies, urban planning and sustainability issues. We’d like to acknowledge that Tufts University’s Medford campus is located on colonized Wampanoag and Massachusetts traditional territory. Today, we’re delighted to host Dr. Duncan McLaren. Apart from being a good old friend of mine, Duncan is currently a Research Fellow with the Institute for Responsible Carbon Removal at American University. His research examines the politics and implications for justice of novel technologies, particularly using public engagement methods. Prior to his PhD studies completed in 2017, Duncan worked as an environmental researcher and campaigner, most recently as Chief Executive of Friends of the Earth Scotland from 2003 to 2011. He’s advised and consulted for research and financial institutions, government departments, philanthropic donors and non governmental bodies on energy, climate, urban and sustainable development issues. Duncan’s talk today is From City to Sink: Urban Carbon Removal as Promise and Practice. Duncan, a zoomtastic. Welcome to Cities@Tufts.
0:02:16.4 Dr. Duncan McLaren: It’s a real pleasure to be with you, Julian, and to renew our association in the city space. Shall I just get kicked off?
0:02:28.1 Professor Julian Agyeman: Okay, go straight away, thanks. Yep, yep.
0:02:31.9 Dr. Duncan McLaren: Great. So, thanks for the invitation and as Julian says, I’m talking about urban carbon removal. There’s a lot to get through. So here we go. So, first I’m going to introduce carbon dioxide removal and its purposes and limits. I’ll then outline some past CDR promises before exploring some urban CDR prospects with a library of examples offering an estimate of practical urban CDR potential in the light of the politics around it, highlighting particularly questions of justice, before ending with some policy recommendations and conclusions. So first, what is CDR and what is it not? Well, CDR techniques are human interventions that remove CO2 from the environment, place it into long term stable storage. They are both anthropogenic and intentional, not incidental. The CO2 must come from the atmosphere or the wider environment, not from flue gases or other point sources, and be stored for centuries to millennia and not re-released. CDR does not include the natural operation of biological or geological sinks on land or water. There are some blurry boundaries however. So looking a bit deeper into the terminology, carbon dioxide removal is often shortened to carbon removal, sometimes broadened to include other greenhouse gases may also be described as negative emissions techniques or technologies.
0:04:08.8 Dr. Duncan McLaren: It’s often mixed up with other things. By contrast, carbon capture and storage is typically an adjunct to fossil fuel use, capturing perhaps 90% of the emissions at a point source and shipping them for storage or utilization. Carbon utilization can be in durable materials, but is more often in chemicals, short lived plastic products or even synthetic fuels. So typically therefore it is at best a form of emissions abatement, not carbon removal. Sequestration Carbon sequestration refers to locking away carbon dioxide but with no concern about what source it’s come from. And while EOR or enhanced oil recovery might sequester some carbon dioxide, it does so by using it to force more oil or gas from old wells. One of the big issues here is that deliberate conflation of these different techniques under the rubric of carbon management allows the fossil industry and petrostates, to justify continued fossil fuel extraction. Such discursive tricks exacerbate the big policy challenges facing CDR. These are additionality ensuring that CDR would not that that CDR would not have happened anyway durability ensuring that the storage is long term and without significant leakage and avoiding mitigation deterrence where promises of future removal enable delay in cutting emissions.
0:05:50.3 Dr. Duncan McLaren: So getting into what these methods look like this schematic indicates the main techniques involved in CDR proposals. It’s not a comprehensive set, but hopefully enough to note the principal routes of capture and storage in CDR techniques. The options in the orange shaded box have clear urban applications and I’ll say a little more about how these might work as I run through the examples later. Here I’ve added one potentially important urban option for CO2 storage in building materials using carbon sourced from biomass, Biochar or direct CO2 capture.
0:06:32.3 Dr. Duncan McLaren: Before discussing particular techniques though, a reminder of why we’re talking about carbon dioxide removal. Typically, it’s seen as having three functions in climate policy. First, accelerating progress towards net zero, then counterbalancing recalcitrant residuals at net zero, and finally reversing overshoot through net negativity after net zero. To deliver any of these functions, CDR must be additional to emissions cuts not a substitute. But so far in practice, most CDR, primarily from forestry and a little from soils and biochar, is traded in offset markets, so does nothing to accelerate progress. And all those forms of biological CDR are vulnerable to reversal by wildfire or drought, for example. So such traded substitution could ultimately make things worse.
0:07:35.2 Dr. Duncan McLaren: And in exchanging emissions reductions now for future CDR, adding to overshoot in the hope of reparation, we’re gambling on the effective delivery of that future CDR. Here, of course, by we I mean humanity in general. Though of course such a simplification is unfair to those not involved in these choices. Nonetheless, modeling suggests that limiting global temperature rises to 1.5 or even 2 degrees Celsius seems impossible unless CDR is deployed. Scenarios from the IPCC project CDR being used at rates of 6 to 11 gigatons a year in and after 2050. That’s in comparison to current emissions of around 40 to 45 gigatons a year. So about big big share and a vast increase from current levels of CDR, which are around 1.3 million tonnes, four orders of magnitude smaller. Analysis of nationally determined contributions and low emission development strategy pledges suggests countries are currently anticipating that CDR will reach 8 to 10 gigatons by 2050 to deliver net zero with around 20% of current emissions remaining. Much of the anticipated CDR is land based, with pledges accounting for over a billion hectares of land dedicated to CDR. That’s equivalent to 2/3 of all arable land. Delivery of such projected increased levels of CDR would likely transgress sustainability limits, harm human rights and exacerbate injustice.
0:09:27.8 Dr. Duncan McLaren: Experience so far suggests such modeled promises are exaggerated and dangerous. Inherent model features such as discounting future costs mean that CDR displaces early mitigation action. But the models then only square carbon budgets through huge future projected CDR capacity. That is likely impractical and almost inevitably socially and environmentally harmful. Early modeling presumed use of bioenergy with carbon capture and storage until it was shown that the levels projected would require three times the land area of India to provide biomass, creating real threats to food security. Now modeling often assumes direct air capture, which would involve energy demand nine times India’s primary energy use or around 2/3 of current world primary energy use, suggesting similar threats to energy security. Some advocates have suggested that marine CDR might prove more fruitful, but the implications there are as yet little understood and some companies in the space have already failed. So could urban CDR help fill the gap? Some research and advocacy reports suggest potentials for urban CDR of between 5 and 20 gigatons per year. However, I’m going to pour cold water on this and argue that it’s too good to be true and risks fuelling further climate procrastination. Exaggerated promises of CDR contribution don’t come out of nowhere.
0:11:06.3 Dr. Duncan McLaren: So noted already models discount future costs of CDR. They also overlook sustainability limits and tend to exaggerate the costs of near term mitigation. But there are other sources too. In the neoliberal model of venture capital funded innovation, such technologies need to promise both scale and profits if they are to obtain investment. Developers therefore project lower than realistic costs and where these businesses get funded, VC works by shunting aside the scientific founders and installing business managers to find the earliest profitable exit. The prospect of inclusion of removal credits in carbon markets risks undermining climate purposes too. Carbon traders want more products and more credits to trade, and for them, higher continued emissions means more opportunities to profit from trading, a perverse incentive for them to big up CDR’s potential. CDR also acts as a promissory technology for the oil and gas industry to legitimate its operations and protect otherwise stranded assets.
0:12:28.5 Dr. Duncan McLaren: Here there may be some hope of delivery. The oil and gas companies think they can get paid by the public for transmission storage of CO2, even if they then use it for enhanced oil recovery. But overall, this means that even if CDR could be massively scaled and net zero achieved by balancing two carbon elephants rather than two mice, huge harms would remain from continued fossil extraction and combustion. This all leaves us facing something of a dilemma. Exaggerated promises of CDR undermine essential immediate action to mitigate and phase out fossil fuels. But without removals, we’ll likely exceed carbon budgets and impose substantial additional harms on future generations.
0:13:11.1 Dr. Duncan McLaren: Delivering large scale CDR could have serious implications for justice right now, not least for other species, but also through competition for agricultural land and clean energy. We can’t afford to have a carbon tunnel vision and disregard human rights, food security and biodiversity. But nor can we reject CDR out of hand. We need policy mechanisms that can support it in just and sustainable forms and scales while weeding out the false and exaggerated promises. In the next section of the talk, I’ll sketch out existing practice on urban CDR and explore the realistic prospects, highlighting some of the misleading promises about specific techniques and possible scales which CDR methods show particular promise for cities well thinking about urban functions in procuring, managing and regulating buildings, cities have opportunities to promote carbon storage and building materials, incorporate direct air capture in buildings as operators and regulators of energy systems and buyers of energy for buildings and transport systems. Cities offer opportunities for bioenergy with CCS, perhaps including biogas and biofuel production.
0:14:30.5 Dr. Duncan McLaren: Cities also operate and regulate solid and wastewater management with more opportunities for BECCS, biochar and capture of biogenic carbon from wastewater, possibly even incorporation of enhanced weathering or alkalinity enhancement into water treatment. And of course, cities own and manage land with opportunities for biochar, both biomass supply and biochar use in parks, urban forestry and so forth. Maybe enhanced weathering through rock dust use or carbon storage in trees and soil. There are also some niche CDR opportunities that I won’t talk more about that some cities might share, like desalination, sea defences and beach replenishment. I’m going to run through this library of cases quickly and maybe skip some if we run short of time. So timber construction is generally positive in climate terms.
0:15:37.3 Dr. Duncan McLaren: Timber buildings are better in earthquake zones that don’t increase fire risks. They’re lighter, requiring less deep foundations. Using timber in construction means that carbon accumulated by the trees prior to felling is kept out of the atmosphere for at least the lifespan of the building. Recent advances in mass or composite timber mean even large buildings up to 18 storeys high can be constructed entirely from timber. On average, mass timber construction stores about 380 kilograms of carbon dioxide per meter square of floor area, but costs less up to $150 per meter squared less to construct than concrete and steel.
0:16:16.0 Dr. Duncan McLaren: So Boston’s Mass Timber Accelerator provided development teams with technical assistance and funding grants to assess and integrate low carbon mass timber building practices into their projects. It supported 10 projects over three years involving buildings up to nine storeys high. If they all come to completion, there’ll be 48 buildings over 10 million square feet of total floor area and around 350,000 tonnes of carbon dioxide stored.
0:16:51.6 Dr. Duncan McLaren: However, net gains in carbon storage in the building and built environment from timber may be at least partly offset by net losses in forest carbon. One estimate suggests mass timber use could average 2 gigatons per year of carbon dioxide, but notes that the forest pool is already declining at 0.7 gigatons a year. Highlights that potential increase in demand for timber for building materials threatens to intensify deforestation and illegal logging. Given that current timber supply would only cover about a third of estimated 2050 demand for construction if it was all shifted to timber, that means pressures on forests would grow dramatically. For this technique, lifespan and end of life issues are critical. Will these buildings remain in use for centuries or just decades? If construction waste can then be reused or become feedstock for BECCS or biochar, then storage might be meaningfully prolonged to really climatically meaningful timescales.
0:18:00.8 Dr. Duncan McLaren: There are also several methods been explored for storing carbon in concrete buildings. These include enriching concrete with carbon dioxide in the curing process, using alternative minerals such as magnesium carbonate that absorb more CO2 in the curing, and directly incorporating carbon rich aggregate to biochar in concrete up to 15% by waste wait. The Four Corners Carbon Coalition partnership of several US cities provides grants to accelerate CO2 removal projects and in 2023 it awarded nearly $400 million to 4 billion businesses incorporating carbon removal in concrete, cement, synthetic limestone and insulation materials. However, claims in this field are likely exaggerated, perhaps in defense of the interests of a major energy intensive industry. Most alleged removal of storage in this sector is not enough to even offset the emissions involved in the production of cement and concrete. Accelerating carbon uptake in concrete curing is of questionable additionality as it largely merely replaces carbon dioxide that would be absorbed over some years from the atmosphere. Accelerating curing using CO2 from fossil sources as is happening in New York is therefore likely counterproductive in CDR terms.
0:19:29.0 Dr. Duncan McLaren: CDR promises here seem likely to help lock in the use of energy intensive concrete and steel where alternatives timber or building refurbishment would be environmentally preferable. Adding biochar or carbonaceous aggregate in residual concrete uses, however, would remain sensible. Direct air capture delivers carbon removal by the selective chemical capture of carbon dioxide from air passing over a contactor. Once saturated with CO2, the contactor is moved into an enclosed space and regenerated by temperature, pressure or humidity swing techniques. The collected CO2 would be pressurized and shipped to geological storage or utilization. Direct air capture uses a lot of energy for moving large volumes of air and regenerating the sorbent. Integrating DAC into building HVAC systems, as Solitaire Power are doing in pilot projects, should increase its capture efficiency by using air enriched with CO2 from respiration as the source, and it should reduce energy demand by utilizing the HVAC airflow.
0:20:46.9 Dr. Duncan McLaren: The pilot in Aarhus promises 15 tonnes a year of removals for this one office building with no confirmed destination for the CO2 as yet. The costs are also unspecified, but described as adding 5 to 14% to rental and operational costs. At the lowest end. This implies over $1,000 a ton of carbon dioxide despite the efficiency savings. Whereas centralized DAC currently costs perhaps 400 to $600 a tonne in urban settings, collection transport costs will likely be higher too.
0:21:23.0 Dr. Duncan McLaren: However, there are potentially significant health benefits from reducing CO2 concentrations indoors. Perhaps the poster child for urban CDR is Stockholm BECCS project. BECCS Bioenergy with Carbon Capture and Storage works in theory by capturing up to 90% of the carbon dioxide from flue gas from biomass combustion, it counts as CDR because the biomass is considered carbon neutral. BECCS typically uses a chemical amine capture agent through which the flue gas is filtered. The amine is then regenerated to separate the captured CO2 which is then purified and compressed for storage, typically in a geological reservoir. Overall, this takes carbon dioxide that’s originally captured in photosynthesis into long term geological storage. But in practice most existing BECC’s plants do not result in net removals because they capture CO2 from biofuel fermentation with an overall capture rate only around 50% as the remainder of the carbon ends up in the fuel and they sell the captured carbon dioxide for enhanced oil recovery, which can lead to 150% or higher rebound in emissions.
0:22:45.9 Dr. Duncan McLaren: At least the Stockholm Beck’s proposal is better than those. It’s a form of biomass combustion generates heat and or electricity. Some 20% or so of the energy generated has to be used to run the capture system, which means that overall biomass use in a retrofit like this is increased. So Stockholm Exergy is retrofitting its Vertan biomass cogeneration district heating plant and the retrofit is scheduled to begin operations in 2028. The plant relies on importing biomass about 60% from elsewhere in Sweden and will export compressed CO2 by ship for storage. EXIGEE has won EU innovation funding of $180 million and Swedish government support of around $160 a ton for 800,000 tonnes of capture per year for 15 years. It’s also selling removal credits 3.3 million tonnes already sold in advance to Microsoft and around $50 million worth via Frontier to various buyers.
0:24:04.0 Dr. Duncan McLaren: This means much of the CDR benefit will be offset by emissions legitimated elsewhere. And intriguingly, EXIGEE has lobbied the EU in efforts to ensure that the Green Claims Directive doesn’t undermine the business logic of such credit sales. I’m going to skip this, as methanol production is a form of biofuel BECCS, which is at best a highly inefficient form of CDR. More biogenic emissions remain than are captured and a full life cycle analysis might not demonstrate net negativity. However, it was highlighted as a significant source of potential in the Amsterdam Region report commissioned by Carbon Traders South Pole, which I’ll mention later.
0:24:49.1 Dr. Duncan McLaren: Even for cities using biofuel or biogas for buses, electrifying the transit and directing biomass to more efficient CDR techniques would seem a better approach. In Trondheim we have another form of BECCs here, rather than using virgin biomass, it’s being put on a waste incinerator which incinerates mixed waste. Treating the biogenic component of mixed waste as carbon neutral by definition and thus capturing the emissions from its combustion cancer CDR. The potential here is around 300,000 tonnes per year capture from mixed waste in synergy of which about a third is fossil. The big downside here is that it creates incentives to increase or maintain waste production rather than avoid reuse or recycle or, as has already happened in Sweden, end up importing waste from other countries to feed the incinerators. Health risks from emissions make incineration unpopular in many countries, so tying CDR to such technologies might make it harder to promote.
0:26:04.4 Dr. Duncan McLaren: Turning to biochar. Biochar is the pyrolysis of biogenic materials, often waste such as forestry residues at high temperatures in the absence of oxygen. This generates a carbon rich solid character, the biochar and combustible gases and or oils. Burying the char in soil can result in stable storage of carbon for centuries.
0:26:32.5 Dr. Duncan McLaren: Nova Carbon’s biochar park, the third I think of four they’ve developed so far at Grevesmühlen, captures around 3,200 tons of carbon dioxide per year. The cost per ton are unclear, but biochar in general is estimated to cost a little under $200 per ton. The biochar may then be used in agriculture or urban landscaping. Char is believed to benefit soil stability, water retention and fertility in most settings.
0:27:13.7 Dr. Duncan McLaren: But concerns have been raised about contamination arising from waste feedstocks, especially if there’s things like heavy metals that survive the high temperatures involved. That might limit the use of such char to landscaping in relatively undisturbed areas. There are other possible biochar synergies in dry and wildfire risk areas. Incorporation of biochar might usefully enhance soil moisture retention, thus helping restrain fire spread. And there is a need to collect biomass. Harvest biomass for fire suppression purposes, which can then be supplied to the biochar facility like BECCS Biochar as CDR rests on the assumption that biomass is carbon neutral. Collection, transport and processing emissions are typically accounted for, as are emissions from any gaseous or oil fraction produced in the pyrolysis process. In this case, Nova Carbon claimed that the carb capture in char fully offsets process, energy use and the gaseous fraction.
0:28:12.7 Dr. Duncan McLaren: But they’re also selling carbon credits and it’s not clear whether the net result would be some double counting once the emissions legitimated by the credits are included. Moving to Wastewater treatment this is the first of two different approaches in wastewater treatment. At Wood Huxley Sewage Treatment plant in Zurich, CCS is being installed on a sewage sludge incineration facility aiming to abate 20,000 tons of carbon dioxide a year at a cost of over $1,000 per ton. So this is another form of BECCS here, though the process is unlikely to generate surplus energy given the energy costs of drying sludge, so several questions are generated there. I’m going to skip on more innovative approach in New Haven, Crude carbon, a spinoff from Yale, is adding alkalinity to microbial wastewater treatment. This captures carbon dioxide as bicarbonate for export to the ocean via the plant outflow. Crew Carbon claims its pilot operations have demonstrated 4,000 tons a year removals and on this basis they have made advanced sales of carbon credits for 72,000 tonnes over the period 2025 to 2030 at a cost of around 450 tonnes at $450 per ton. Unlike BECCS, DAC or even Biochar, the total quantity of carbon captured here is difficult to measure directly and monitoring reporting verification standards become critical, especially if removals are to be marketed as credits.
0:30:02.2 Dr. Duncan McLaren: A more conventional form of carbon removal has been practiced in Yokohama. Seagrass meadows and salt marshes are amongst the most effective biological carbon sinks with per hectare rates several times greater than forests. Since 2011 Yokohama has supported projects planting and protecting eel grass and seaweed beds which are generally being lost and degraded faster. But since 2015 they’ve been turning the carbon gains into tradable credits and as of 2019 total removals were just 80 tons.
0:30:45.7 Dr. Duncan McLaren: Such projects have valuable co benefits for fisheries, but the carbon removals are marginal at best and may even be double counting as these would be previously unmanaged spaces. Perhaps a bit of a niche as the this depends on a coastal location, but the Captura process uses electrodialysis, an energy consuming process to separate seawater into acid and alkali streams. The acid stream is first added to contain seawater, forcing out dissolved inorganic CO2 and the alkali stream is returned and mixed and the now CO2 depleted water returned to the ocean where it re equilibrates by drawing down atmospheric CO2. Captura have a 100 ton per annum pilot plant at the port of LA and are developing 1000 ton per annum plant In Hawaii, costs are currently estimated at perhaps $2,000 a ton and need to be cut significantly to make it competitive.
0:31:46.4 Dr. Duncan McLaren: Finally, Freetown in Sierra Leone is using reforestation tree planting to accumulate and store carbon in living biomass. Following the loss of over 500,000 trees each year from 2011 to 2018 and devastating mudslides killing over a thousand people in 2017, the city is aiming to plant 20 to 25 million trees by 2050. Motivated primarily by climate resilience benefits, stabilizing slopes and providing shade, citizens have been mobilized to plant and maintain trees through a digital app and micropayments. Funding has been raised in part through the sale of digitized tokens for corporate social responsibility purposes and plans to sell carbon credits. The project is deliberately targeted informal settlement areas for equity reasons. However, the long term durability of these carbon stores must be questioned as the land involved is in a growing urban area and policies on land use can change quickly.
0:32:58.1 Dr. Duncan McLaren: So the bottom line, how much carbon could cities remove? All these projects have generated only small numbers, none of them more than a million tons a year, some of them down in the level of tens of tonnes. Putting it together, there are a few reports that have made estimates, but there’s huge variation in the estimates and the amounts and even in the techniques considered.
0:33:28.0 Dr. Duncan McLaren: This quick survey of the literature suggests a range from less than half a gigaton to 5 or even perhaps 13 gigatons. Those upper figures appear to me hugely over optimistic in terms of the credibility of the techniques that we’ve just looked at, the sustainability of supplies for them and the uptake levels that would be likely achieved in practice. So amongst the reports, the Mercator Institute’s estimates of 0.3 to 1.2 gigatons seem perhaps most responsible in this respect. But these exclude waste management routes. So my best guess, adding some potential for waste management to the Mercator estimates is a maximum of around 2 gigatons. That builds an estimate for waste treatment based on BECCS and 3.8 gigatons of municipal solid waste in 2050, around 70% of it urban and around 20% biogenic carbon. Even this, allowing an ambitious coverage of 50% of waste treated that way, would give the figure of 0.9 gigatons. So we’ve got an overall aggregate figure that’s certainly well worth pursuing in the light of the IPCC’s estimates of a need for 6 to 11 gigatons, but not something that’s a silver bullet. There’s lots of positives being raised in the cases that I’ve suggested and lots of questions outstanding.
0:35:15.2 Dr. Duncan McLaren: So we need much more rigorous assessment of the promises of such proposals. It’s not to say such pilot projects are bad, but we should free them from the pressures and distortions of venture capital and carbon trading, providing instead public funding and public accountability based on radical transparency and public intellectual property. Rejecting offsetting for CDR is a first step towards addressing these problems, but also critical in moving away from continued magical thinking and the promises that go on contributing to mitigation, deterrence and climate procrastination CDR advocacy is riddled with magical thinking, notably expectations of technological fixes, a belief in technological wizardry to evade material and environmental limits, often coupled with financial wizardry, a belief that venture capital and novel financial instruments in constructed markets will somehow make these technologies effective and affordable.
0:36:20.9 Dr. Duncan McLaren: These combine to generate exaggerated expectations and facilitate delay and mitigation. Taking CDR into the public realm as a vital future shared utility might also seem magical thinking, especially at the current moment in US politics. But if any group of actors in the CDR space could lead such a move, then it might be cities focusing development of CDR on techniques with co-benefits for their existing services and facilities.
0:36:57.5 Dr. Duncan McLaren: Doing that will need careful navigation of a host of political currents and interests that want to turn CDR into a marketable commodity, deliberately substituting for mitigation efforts including finance, oil and gas, airlines and others. But there may be potential to win support from other sectors like the development sector as well as from the broader public. Key to public support is likely to be the question of justice and fairness, and taking account of all such issues is likely to further reduce practical potential for urban CDR.
0:37:45.5 Dr. Duncan McLaren: I think leaving an impression of perhaps half to 1 gigaton per annum by 2050 as the possible practical contribution would be responsible and realistic. David Morrow and his friends and his colleagues have suggested these guiding principles for climate justice with respect to CDR. Play the long game, support CDR as reparation, avoid carbon tunnel vision, account for all impacts, split, don’t lump measure and manage different techniques separately, and don’t bet the house on the models. Those are all useful guidance, I think for cities. More specifically, urban CDR could exacerbate injustice through several routes, notably via the location and impacts of pollution, odour, truck movements and so forth of energy and waste facilities.
0:38:37.0 Dr. Duncan McLaren: CDR doesn’t make energy generation or waste management magically clean, also via the effects of CDR in construction materials on relative housing costs and availability. Thirdly, through competition for land elsewhere for any additional BioMass to supply BECCS or biochar and finally through the many injustices in offsetting and carbon trading, such as intermediaries extracting the value, the wealthy purchasing offsets and the poor suffering project impacts. So with urban CDR cities must beware exporting impacts. BECCS and Biochar may still rely on land outside the city.
0:39:23.1 Dr. Duncan McLaren: CDR is not exempt from the risks of green colonialism. Overall as well, we should remember that environmental justice is not necessarily served by every entity individually reaching net zero. Net zero is a global goal. Cities may well do more to cut emissions and less CDR, while rural areas might have more sustained emissions from agriculture and transport, but do much more in absolute terms to generate removals. Delivering environmental justice in CDR requires careful attention to historical and continuing inequalities, failures of recognition and uneven capabilities and vulnerabilities. Coming to conclusions. Some preliminary recommendations for urban CDR policy. Keep CDR subsidiary to mitigation and adaptation. Look for the co benefits for example in waste management, district heating, air quality and health, wildfire suppression, urban greening, shade and resilience.
0:40:35.0 Dr. Duncan McLaren: Focus any BECCS or biochar on genuine residual waste generated by the city and not on imported biomass. Integrate CDR in municipal functions, states management, waste management, building regulations and planning rules, for example, and avoid buying CDR offsets. Minimize selling removals that are generated by public utilities. For brief conclusions so urban CDR has lots of potential worth exploiting even at the total half to 1 gigaton level. But cities have far greater prospects to cut emissions and eliminate fossil fuel use. Those must be the priority. In climate policy terms, urban CDR can be part of a CDR portfolio. But neither urban CDR nor CDR as a whole is a silver bullet for the climate and cities exploring in this space must beware misleading and illusory promises from CDR promoters, especially those who are seeking to sell credits. And in working with CDR, cities must attend to justice Implications CDR is not a magic wand that will erase social and environmental side effects. Thanks so much for your attention and let’s move over to the question and discussion section. I’ll be making the slides available and there’s some extra slides with links.
0:42:21.7 Professor Julian Agyeman: Well, thank you so much Duncan for that. Fascinating. And you did cover some serious ground there. It’s a lot to take in and if you just stop the screen share then we can get a picture of everybody. There we go. Well, we’ve got a lot of questions and let me just go through them. So Venkata asks, what are the challenges and support systems for alkalinity enhancement in coastal cities that also provide some level of resiliency support for local corals against ocean acidification.
0:43:06.3 Dr. Duncan McLaren: If I caught that correctly, the question is would these sort of alkalinity measures be good for protecting coral reefs and so forth? That’s one of the functions that I think researchers in the space are exploring. What’s not clear at the moment is whether a process like the Captura one would provide alkalinity in the right places and in weight in forms that reef organisms could make use of. I think there is… It’s an area that’s definitely worth thinking about, a very clear possible co-benefit here. And as I said, most of these things need co-benefits to become affordable for a start because they’re otherwise very expensive. And focusing on the co-benefits is a good way of deciding which techniques are most appropriate in the relevant location.
0:44:12.9 Professor Julian Agyeman: Great, thanks, Duncan. A very practical question from Michael. What are the super accessible interventions that cities and cities and groups can pursue in their cities? What’s the equivalent of eat less beef for citizens and city dwellers?
0:44:32.7 Dr. Duncan McLaren: I don’t think there’s anything quite as simple as that. There’s nothing… There was a study that I looked at during preparing for this that looked at biochar incorporation in residential yards and the average result was 10kg of carbon a year. You do better than that by taking the train once instead of driving. So really personal carbon removal is probably not in the big picture. But at the city level, the shift to shifting at the margin of new build into timber buildings and using biochar in city parks and urban public spaces, those would seem to be probably the early win wins and there are probably some other no regrets in terms of the management of land, whether that be urban forests or urban coastal lands.
0:45:41.3 Professor Julian Agyeman: Is Edith in the room? Because she has a quite a long question, very detailed question, and I’d rather she ask Duncan directly. Edith, are you in the room?
0:45:54.4 Edith Kutz: Yes, I am. Can you hear me? Hi. Hi. Hi. This was a great presentation. I went to one yesterday that was… Doesn’t even compare because you really hit. You really made it practical. You were critical and you also included policies. So anyhow, I just wanted to let you know, I mean, to ask you if you’re aware of. I’ve been following carbon collect. They are a direct air capture machine, let’s say, and it uses ambient air and it doesn’t use fans. So it doesn’t require huge sources of energy. And it has a proprietary transfer mechanism to absorb and release the carbon dioxide. And the carbon dioxide can be reused in carbon Manufacture concrete, like through the carbon cure method. So it’s like this win, win for a city. I mean, because you could get a circular economy going. And it’s a modular and a really attractive, the most attractive DAC mechanism that I have come across thus far. It’s not like Climeworks or some of the others. So I just wanted to suggest that because as a landscape architect, I’ve been trying to find out ways to bring DAC right into the city in parks and in places. I mean, I work with natural bay solutions also, but I’ve been really trying to find the application for mechanical ones within a city, which is why I found your presentations really very interesting and really good.
0:47:20.8 Dr. Duncan McLaren: Well, thanks, Edith. I was at the same webinar as you yesterday. Appreciated your contributions in the chat. I haven’t heard of Karma Collect specifically as you describe them. They’re not dissimilar to solitaire that I did include in the, in the talk.
0:47:39.7 Edith Kutz: No, no, no, no. Solitaire is connected to buildings, right? Yeah, no, this is a freestanding.
0:47:47.6 Dr. Duncan McLaren: Right.
0:47:48.6 Professor Julian Agyeman: Just Google Carbon Collect. You’ll see it as Mechanical Tree.
0:47:53.2 Dr. Duncan McLaren: Immediately, I would worry a little about the embodied capital cost of doing something that uses ambient air, at least in, in places that aren’t very windy. If you’ve got wind generating a good airflow, then then in theory you can get the efficiency high enough. And in general, I think DAC does have a lot of limitations because we look at photovoltaics and we think that’s brilliant. We have this dispersed, decentralized system which does away with or limits the amount of infrastructure we need because it supplants having such an intensive energy grid. DAC’s the opposite. If you make it modular and dispersed, then you have to have more infrastructure or more costly, less efficient ways of collecting up the CO2 to get it to permanent storage. And that’s partly because I’m more skeptical of the concrete reuse. So in concrete, I think incorporation of biochar is a better route than accelerated curing with DAC CO2 and more broadly, reuse of buildings. And timber buildings are better than concrete buildings.
0:49:22.5 Edith Kutz: Well, I think you ought to take a look at Carbon Collect’s site, because I’ll bring that question up to them. I’ve been in contact with them regarding their technology, but I think that the ambient air thing is not inefficient. So anyhow, I think you ought to check it out.
0:49:39.6 Dr. Duncan McLaren: And it’s a long standing debate in the in the DAC field about the potential for use of ambient air. It will probably have a niche. It will probably not be the only way to do DAC or necessarily the best way to do CDR in cities.
0:49:57.6 Edith Kutz: Okay, Well, a few… I agree. There’s going to be a mosaic of all kinds of different application technologies.
0:50:04.8 Professor Julian Agyeman: Yeah, great. Thanks for your question, Edith. Patricia Lacacia, what are smart technologies and policies that can enhance urban resilience in the face of climate disasters such as the increased frequency of hurricanes?
0:50:20.6 Dr. Duncan McLaren: That’s a huge question, Patricia. And there are. What I’ll try and do is think if there are any contributions from CDR practices specifically. There are of course, many, many other ways in which cities should be building resilience. Starting from probably the biggest and most sweeping, increasing social equity as a way to build resilience amongst the population. That always seems to me the biggest and most overlooked way of preparing for these sort of disasters. In the CDR space, there may be possibilities for coastal cities in the way that coastal defenses and beach replenishment are done. I mentioned that as niches there are carbon removal techniques that involve putting pebbles or rocks on beaches where the wave action helps accelerate the carbon uptake, using particular basaltic rocks.
0:51:32.1 Dr. Duncan McLaren: And if cities need those for to improve the defense of the city against storm surges or whatever, one could see a synergy there. That’s a very marginal thing, I think, or a niche thing in the overall resilience. Hurricanes obviously also tend to bring excess water. So anything that’s improving the permeability of urban areas is good. And here again at the margin, use of biochar in public parks and lands could be improving the ability of those parks to absorb and retain water. CDR wouldn’t be my go to technique or set of technologies for building disaster resilience in cities. I think I’d start from the other end.
0:52:24.7 Professor Julian Agyeman: Thanks, Duncan. Roger? Roger Hickman, are you still in here? For those of you who don’t know, Roger actually worked at Friends of the Earth in the in London around the same time as Duncan was there. Roger, are you in the room?
0:52:47.8 Roger Hickman: Yeah, I am in the room. Nice to see you both and it’s great to see you both working together, which is why I came really more than anything else. But excellent presentation, Duncan. You just thoroughly exhaustively researched and great and albeit a bit depressing. I just in New England, but you know, a lot of British cities, we’re right next to Dartmoor territory and I’m wondering about sort of what potential is there and what the sort of carbon abatement is there.
0:53:17.8 Dr. Duncan McLaren: Thanks Roger, you broke up a bit. It’s a real pleasure to hear from you, but I got the gist that you were asking about peatland enhancement as a climate tool. Really? And yes, I didn’t mention it in the list of techniques because there’s rarely peatland managed by the city within the city boundaries. This would fall into the category of the rural areas doing more CDR and cities doing more emissions cuts in that cities should stop using peat in their gardens and urban public spaces because the extraction of peat from peatlands is a big carbon emitter because it ends up drying out the carbon comes out of it and protecting peatlands re wetting them is indeed a potentially valuable carbon removal tool.
0:54:25.3 Dr. Duncan McLaren: Peatlands can be more rapid and more dense sinks than forests. However, rewetting peatlands also does tend to increase methane emissions from and getting a net balance that is Capturing more carbon or in greenhouse gas terms is carbon negative rather than carbon positive will depend on the particularities of the location and the age of the peatland in particular. But broadly, yes, intervene to re-wet and restore growth in peatlands and stop digging them up and turning them into gardens.
0:55:08.6 Professor Julian Agyeman: Great. Thanks Duncan. I’m afraid that’s all we’ve got time for. Can we give a warm Cities@Tufts round of applause for Dr. Duncan McLaren? Our next Cities@Tufts colloquium is on March 12th, when we have Hessann Farooqi, who is the ED of Boston climate Action Network talking about local leadership for climate change. Thank you for coming and see you on March 12th. Thanks again, Duncan.
0:55:37.1 Dr. Duncan McLaren: It’s been a pleasure.
0:55:39.2 Tom Llewellyn: We hope you enjoyed this week’s presentation. Click the link in the Show Notes to access the video, transcript and graphic recording or to register for an upcoming lecture. Cities@Tufts is produced by the Department of Urban and Environmental Policy and Planning at Tufts University in shareable with support from the Barr foundation, shareable donors and listeners like you. Lectures are moderated by Professor Julian Agyeman and organized in partnership with research assistants Amelia Morton and Grant Perry. Light Without Dark by Cultivate Beats is our theme song and the graphic recording was created by Jess Milner. Paige Kelly is our co producer, audio Editor and Communications manager. Additional operations, funding, marketing and outreach support are provided by Allison Huff and Bobby Jones, and the series is co-produced and presented by me, Tom Llewellyn. Please hit subscribe, leave a rating or review wherever you get your podcasts and share with others so this knowledge will reach people outside of our collective bubbles. That’s it for this week’s show.
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