This week, Gothenburg in Sweden played host to the first international conference on “negative emissions”.

The three-day event brought together around 250 researchers at Chalmers University of Technology to discuss the different ways to remove CO2 from the atmosphere and store it on land, underground or in the oceans.

The topics presented and debated ranged from “natural” solutions to the technologically advanced, through to the potential limitations and risks. Running parallel to the scientific discussions was a focus on the policy challenges.

Eva Svedling, Sweden’s secretary of state for development and climate, marked the occasion by launching a public enquiry into the potential for forests, soil and bioenergy to provide carbon removal for the country. Sweden already has a legally binding target to reach net-zero carbon emissions by 2045.

Carbon Brief was at the conference to watch the 11 keynote speeches, 140 presentations and three panel debates. A range of presenters, such as Dr James Hansen and Dr Sabine Fuss, was asked on camera (see below) what they each think is needed for negative emissions to become a reality at scale.

Keynotes

Dr James Hansen, former director of the NASA Goddard Institute for Space Studies and current director of the climate science, awareness and solutions programme at Columbia University’s Earth Institute, kicked things off in a cautionary tone. Hansen explained that he was “sceptical, but open-minded” about the role that negative emissions can play in tackling climate change.

Hansen emphasised the importance of reducing emissions rapidly and that negative emissions technologies (NETs) should not provide a “get-out-of-jail-free card to policymakers”. However, he also pressed upon the audience the full extent of the risks of climate change and the need to cut emissions rapidly.

In particular, Hansen argued in favour of nuclear energy, lamenting the lack of research and development into “advanced nuclear power” in recent decades. Its potential should have been researched in the same way as the “appropriate” research into NETs today, he said.

Dr James Hansen setting out the "potential injustices" of climate change at #NegCO2 pic.twitter.com/jyC6ePxdpS — Leo Hickman (@LeoHickman) May 22, 2018

Following Hansen, Prof Anders Lyngfelt from Chalmers University of Technology – who conceived the idea for this conference – argued that NETs are both “a dangerous game” and “necessary for the climate”. NETs are dangerous if they are “seen as the primary solution to the climate problem”, he said, expanding on a theme of “balance”, but it is “totally irresponsible not to start using negative emissions”.

at #NegCO2 @Anders_Lyngfelt calls negative emissions "a dangerous game" *if* it is use as the primary climate solution, to continue fossil fuel emissions, to pass burden of climate action to future generations, or as excuse for slow climate action today — Noah Deich (@TheCarbonSink) May 22, 2018

The day-one keynotes rounded off Tuesday afternoon with presentations from Mike Monea, CEO of the International CCS Knowledge Centre, and Prof Sally Benson of Stanford University.

Monea used to run the world’s first large-scale carbon capture and storage (CCS) facility, which is attached to a coal plant in Saskatchewan, Canada. The “Boundary Dam” project can capture one million tonnes of CO2 per year, explained Monea, the bulk of which is used for “enhanced oil recovery” in nearby oil fields. But you cannot just have one or two plants trying to clean up a fossil fuel, argued Moned, “you need thousands”.

Benson’s talk, meanwhile, focused on the options for geological storage for captured CO2, pointedly noting that long-term storage should be the aim for negative emissions, rather than recovering oil.

"If we are interested in negative emissions, we probably shouldn't be looking at enhanced oil recovery" mic drop at #negco2 from Prof Sally Benson — Duncan McLaren (@mclaren_erc) May 22, 2018

The second day of keynotes began with Dr Sabine Fuss presenting the findings of a new three-part literature review of negative emissions published in Environmental Research Letters (ERL). Fuss, who is based in Berlin at the Mercator Research Institute on Global Commons and Climate Change, began by showing how the various NETs have featured throughout the Intergovernmental Panel on Climate Change (IPCC) assessment reports. There has been an “explosive growth, but little systematic review” in the literature since the late 2000s, she noted.

Other than ocean fertilisation, Fuss said all NETs show “relevant potentials” for helping to meet the Paris goals, but that a “portfolio of multiple NETs each deployed at modest scale reduces the risk of side effects”. She concluded by repeating a familiar theme at the conference, namely, there needs to be “an open societal discussion” about the trade offs and feasibility of the various NETs.

Day 2 of #negCO2 has started with keynote by Sabine Fuss from @MCC_Berlin highlighting the huge growth in literature on negative emissions. Big task for @IPCC_CH AR6 to assess them all… pic.twitter.com/GfoheNxZFY — Leo Hickman (@LeoHickman) May 23, 2018

Prof Detlef van Vuuren’s keynote focused on explaining how and why bioenergy with carbon capture and storage (BECCS) features so prominently in the integrated assessment models (IAMs), particularly those which show pathways to keeping global warming “well below 2C”. As Carbon Brief’s BECCS timeline shows, Van Vuuren, who is based at the PBL Netherlands Environmental Assessment Agency, has been a key figure over the past 15 years for introducing BECCS into the modelling.

Glossary Integrated Assessment Models: IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to help decision-making. For climate research, specifically, IAMs are typically used to project future greenhouse gas emissions and climate impacts, and the benefits and costs of policy options that could be implemented to tackle them. Integrated Assessment Models: IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to help decision-making. For climate research, specifically,… IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to help decision-making. For climate research, specifically,… Read More

Most models, he said, only tend to include the NETs which can “easily be compared in a cost-optimisation regime”. These tend to be BECCS and afforestation. By contrast, they do not focus on “societal constraints”, such as diet change.

However, in a recent paper (covered by Carbon Brief) he showed for the first time how the 1.5C Paris goal could be achieved with a “greatly reduced amount of BECCS”. He said “this would require significant lifestyle changes”. For example, beef could only be eaten “once a fortnight”.

His keynote drew some criticism from the floor. Tim Kruger of the Oxford Martin School scolded Van Vuuren, saying these “prescriptive, unfalsifiable” models are a “profoundly misleading and dangerous influence on policies”. Van Vuuren responded: ”I disagree. They are a useful tool, as long as you know the limitations.”

Wednesday’s keynotes concluded with Dr Oliver Geden, head of the EU research division at the German Institute for International and Security Affairs in Berlin. Geden began by summarising a recent paper (about which he co-wrote a Carbon Brief guest post with Dr Glen Peters) on a common talking point at the conference – who should actually “deliver” negative emissions? Why should it be left for the EU to be the “frontrunner”, he posed? Is that “fair”? If not the EU, then who?

The keynotes on the final day highlighted the breadth of the NETs available. Dr Jennifer Wilcox from the Colorado School of Mines started out by explaining how direct air capture (DAC) “scrubs” CO2 out of the air, which can then be stored or used elsewhere. And it is this subsequent use – and the purity of the required CO2 – that will define how cost effective the technology is.

Wilcox highlighted a couple of examples, including the Petra Nova DAC facility in Texas, where CO2 captured from a coal power plant is used for enhanced oil recovery, and the Climeworks plant in Switzerland, which captures CO2 from a waste incinerator and sells it to local fruit and vegetable growers for use in greenhouses. (Carbon Brief visited the Climeworks facility when it opened last year.)

But the amount of energy needed for DAC means it essentially needs to be sited next to a power plant, noted Wilcox, which means “it’s a misconception that you can put DAC anywhere”.

“It’s not true that you can put DAC anywhere,” says Wilcox. “It’s a misconception” #NegCO2 pic.twitter.com/Ho5g0nLH3R — Robert McSweeney (@rtmcswee) May 24, 2018

In a change of pace, the next keynote – by Prof Pete Smith from the University of Aberdeen – outlined the contribution that soils could make to negative emissions. Adding biochar – carbon-rich charcoal made from biomass – to soils and maximising soil carbon sequestration (SCS) are both forms of NETs.

Their key benefit, explained Smith, is that you can continue to use the land while you’re working with the soil – and adding biochar or replenishing carbon can make the soil more productive. While this makes them relatively “no regret” NETs options, Smith said, they have their limitations as well. That said, SCS could be deployed “immediately and at scale”, and biochar “shows potential” despite needing further research.

“So, if SCS and biochar are so fantastic, why aren’t we doing them?” asks Smith They have some caveats, he says: saturation (after 20-50 years), permanence (gains in C easily lost), leakage/displacement (are we storing C or just moving it about?) #negco2 — Robert McSweeney (@rtmcswee) May 24, 2018

Responding to a question from Lancaster University’s Dr Duncan McLaren on how to roll out these NETs in agriculture, Smith suggested incentives for improving soil carbon in the UK could be implemented in a similar way to existing ones for improving biodiversity on farmland.

The biodiversity theme continued with Prof Almut Arneth of the Karlsruhe Institute of Technology in Germany, speaking on afforestation, bioenergy and ecosystem services. Her main takeaway was that all research into large-scale land-based mitigation indicates “huge trade-offs for land area, water use, pollution and food [production]”.

Can we have our cake and eat it too? Modelling shows plenty of solutions for feeding the world (blue lines), but no solutions for meeting food demands, keeping within safe limits for croplands and having small amounts of bioenergy, says Arneth #negco2 pic.twitter.com/Nn7WoY4iFz — Daisy Dunne (@daisydunnesci) May 24, 2018

In the final keynote of the conference, Dr Phil Renforth from Cardiff University presented on enhanced weathering (EW) – speeding up the natural CO2-absorbing rock weathering process by crushing and spreading rocks on land.

The potential for enhanced weathering (EW) is “almost unlimited”, says @phil_renforth. “It’s a resource optimisation issue; we’re not going to run out of material” #negco2 — Robert McSweeney (@rtmcswee) May 24, 2018

Renforth lamented that EW was often “singled out for problems of scale”, yet “we’re already doing many of core components” of EW – such as coastal-sand nourishment and adding pulverised limestone to farmland:

“I find it hard to believe that we can’t sequester 1-10 gigatonnes of CO2 per year by the end of the century.”

Costs of EW could also be minimised by linking up with other NETs, Renforth added. CO2 captured from BECCS or DAC could be used in the process, he suggested, as the gas is combined with pulverised rock and water to form a carbonate for spreading onto land.

New research suggests that you do not need pure CO2 for this process, Renforth explained, which would, for example, make DAC cheaper if it supplied the CO2.

Video interviews

A common theme in the keynotes – and the conference as a whole – was how NETs could be scaled up from the relatively few projects around the world to make a significant contribution to tackling climate change. In the video below, Carbon Brief puts that question to:

Policy

A core theme running through all three days of the conference was the open question of how scientists working on negative emissions can “best serve the needs of policymakers”.

The “feasibility” of negative emissions was routinely raised by presenters and questions from the floor. Policymakers, if they are to implement regulations and incentives enabling NETs to be rolled out at the scale the modellers indicate are required, need to know answers to some key questions: which NETs work best? How much will they cost? Where should they be located? What are the trade-offs and side-effects? How can societies be persuaded they are required? How can their performance be monitored and verified?

On Tuesday, the first policy session began with Dr Glen Peters from CICERO in Norway highlighting a problem with the targets that NETs are supposedly meant to be helping the world to meet. Peters said he was surprised that, since the Paris Agreement was adopted in late 2015, there still had not been enough clarification on exactly what “well below 2C” actually means.

“We’re always 5 minutes to midnight,” he said. This could be the situation for “decades to come”, with the combination of fuzzy targets and negative emissions. “Paris is still possible forever. When can you ever say that Paris has failed?” This could allow policymakers to keep saying that the Paris goals are still within reach and, therefore, delay immediate action.

Is is always possible to keep below 2°C? Even if we delay aggressive mitigation to 2030, 2°C is still possible (blue). The new 1.5°C scenarios (purple) are more aggressive, suggesting 2°C will still be alive in 2040! My presentation at #negco2…https://t.co/u1l12zDgLf pic.twitter.com/8yTHTLuHsl — Glen Peters (@Peters_Glen) May 22, 2018

Dr Silke Beck from Germany’s Helmholtz Centre for Environmental Research highlighted another factor for policymakers to consider. She said that public support for NETs could quickly be eroded if campaigners started to target them negatively. This is already starting to happen, she said, with some environmental NGOs, who have previously long supported IPCC science, now criticising the sustainability and feasibility of BECCS.

Dr Duncan McLaren continued this theme with a presentation warning of the “hype curve”. We are now primed, he said, to expect hype to be followed by disappointment. This could play out with NETs, he warned. “BECCS has emerged at the perfect time to take over from failed CCS,” he added. NETs risk being seen as “geoengineering in waiting”, with the “moral hazard” that they act as a “mitigation deterrent”.

Again, this point was repeatedly made by presenters throughout the conference, although some pointed out that the term “moral hazard” was itself misunderstood and ill-defined.

There seems to be a lot of interest in moral hazards at #NegCO2. A problem is everyone seems to define "moral hazard" differently. With @KevinClimate, we defined in reference to the expected "optimal" future pathway with BECCS "at scale". https://t.co/0TylSqkd3R pic.twitter.com/NmqSz43iO2 — Glen Peters (@Peters_Glen) May 23, 2018

If NETs are to win public acceptance, there are lessons to be learnt from the polarisation of climate change, said Dr Rebecca Colvin from the Australian National University’s Climate Change Institute.

Echoing McLaren’s point, she said that if they are viewed as a “subset of geoengineering” they will likely suffer from public’s “fear of the technofix”. She added that is was “worrying” that the UK government views negative emissions as being under the umbrella of geoengineering. (The UK government updated its “view” on negative emissions this week.)

Colvin said she is already witnessing the “nascent polarisation” of negative emissions. It is, therefore, vital that NETs avoid “ideological bundling”, namely, they should not be “of the Left or the Right”. One potential option might be to frame them as “natural climate solutions” (see Carbon Brief’s recent article on NCS), which is a “very clever approach”. If this is done, NETs will “have an easier ride through the policy system”.

Tim Kruger presented the preliminary findings of the two-year GRIP project (Greenhouse gas Removal Instruments and Policies). It is examining what policies will help to “accelerate, slow down or stop” the deployment of various NETs.

In total, 34 key stakeholders in the UK were interviewed for the project. They ranged from civil servants and politicians through to representatives from industry and NGOs. Kruger said there was broad agreement that there needs to be research into NETs. (The world’s first NETs research programme was launched in the UK last year.) The only NET to attract a broadly negative reaction was ocean fertilisation.

However, echoing the point made by Colvin, he said that the respondents had reflected an “appeal to naturalness”, with “land-use change, afforestation and peat-bog restoration seen as benign and socially acceptable”.

Fascinating results from Tim Kruger's GRIP project at @oxmartinschool which interviewed 34 key stakeholders in UK about negative emissions… Respondents reflected an "appeal to naturalness"#NegCO2 pic.twitter.com/yxtjohIK1R — Leo Hickman (@LeoHickman) May 23, 2018

Wednesday saw a panel session dedicated to policy. It was dominated by a sometimes fraught discussion about the utility – or otherwise – of the IAMs and, in particular, the way they “prescribed” the use of NETs, such as BECCS.

Detlef van Vuuren again defended his modelling: “We can trust the models, for what they are designed for. Models are confronted with uncertainty. They are not designed to provide a reliable forecast.”

Prof Christian Azar of Chalmers University of Technology said the models should be clear whether they are “prescriptive, descriptive or proscriptive”. He added: “BECCS is not a silver bullet. It will only be a minor share.”

Sabine Fuss said the models need to better reflect that “costs are dynamic”, with costs falling for many technologies.

But a questioner from the floor again challenged the “falsifiability and feasibility” of the models’ reliance on NETs. Dr Mark Workman from Imperial College London’s Energy Futures Lab said the “way we are presenting this data is unconstructive”, adding that the “ecology of black box models is impenetrable, with no attempt to assess how realistic they are or to discuss publically what the trade offs are or their plausibility”.

Finally, as Dr Gregory Nemet of University of Wisconsin at Madison pointed out in a side session, there is a still a very large gap between research and development of NETs and their actual deployment. Nemet, a lead author on the new ERL review on negative emissions presented by Fuss in her keynote, said their work highlighted that the scientific literature “did not reflect the urgency of NETs adoption that is reflected in the IAMs”.

If we’re saying we need a lot of R&D, we need to demonstrate how to get from R&D to widespread deployment (quickly), says @greg_nemet #NegCO2 — Robert McSweeney (@rtmcswee) May 22, 2018

BECCS

Away from policy discussions, some researchers presented on the technical challenges of deploying BECCS on a large scale.

On Thursday, Andreas Krause, a PhD student at the Karlsruhe Institute of Technology, presented his results looking at how effective large-scale BECCS – as well as other types of land mitigation – could be at storing CO2. Using modelling, he found that BECCS could store CO2 effectively – but valuing how much CO2 it could store remains difficult.

One reason for this is that models that simulate how vegetation responds to changes in climate tend to project a much lower carbon uptake from the land than those based on land use alone. Overall, he told the conference, “relying on land-based negative emissions is a high-risk strategy”.

Andreas Krause @KITKarlsruhe sums up his research on carbon uptake of land-based mitigation. One “disturbing” finding is the vegetation models predict “much lower” carbon uptake than land-use models, he says #NegCO2 pic.twitter.com/OPK8GxSMho — Daisy Dunne (@daisydunnesci) May 24, 2018

The potential for BECCS to contribute to mitigation was also assessed by Dr Naomi Vaughan, from the Tyndall Centre for Climate Change Research. Presenting the results of her recent paper, Vaughan told the conference that BECCS could be threatened by poor governance, which could lead to carbon loss through soil erosion and land use change.

Her research also suggests that the need for biomass could be met by using plant residues from forestry and agriculture and from growing dedicated bioenergy crops on abandoned farmland. Doing this would ensure that green spaces and land dedicated to food production would be left untouched, she told the conference.

. @nemvaughan presents model results showing expected growth of bioenergy from energy crops and agroforestry residues. Growth expected even in a “no climate action” scenario #NegCO2 pic.twitter.com/4j6qfkAbmn — Daisy Dunne (@daisydunnesci) May 24, 2018

Elsewhere, researchers discussed potential sites for BECCS deployment across the world. On Tuesday, in a session titled, “BECCS – regional examples”, delegates heard of plans to use BECCS in the US, UK and Germany.

Caspar Donnison, a postgraduate research student at the University of Southampton, presented his research outlining the challenges facing BECCS deployment in the UK. According to his results, the most likely candidates for BECCS power plants include the coastal towns of Peterhead, Barrow and Easington – which are all close to proposed offshore CO2 storage sites.

However, on Wednesday, Oliver Munnion, from the campaign group Global Forest Coalition, spoke out against the deployment of BECCS in the UK. During a talk titled, “the risks of large-scale biosequestration in the context of Carbon Dioxide Removal”, he voiced objection to energy company Drax’s plans to pilot BECCS at its biomass plant in north Yorkshire. He told the conference:

“For me, this highlights what our fears are about large-scale BECCS deployment.”

Natural climate solutions

Another subject capturing interest among delegates was the potential of “natural climate solutions” to contribute to negative emissions – a topic covered recently by Carbon Brief. These methods typically aim to enhance the existing carbon uptake of soil and vegetation, which currently soak up around 40% of CO2 emissions from human activity.

One way this could be achieved is by replenishing degraded forests (reforestation), or by creating new forests (afforestation). Recent research suggests that, out of all of the natural climate solutions, afforestation and reforestation have the largest potential for storing carbon. However, this potential is likely to be largely influenced by what trees are planted, according to Dr Charlotte Wheeler from the University of Edinburgh.

On Wednesday, she presented her results looking at the carbon sequestration potential of tropical forest restoration. Under the Bonn Challenge, 43 countries have pledged to bring back 292m hectares of tropical forest – either by restoring natural forest, planting agroforests or creating monoculture plantations (using eucalyptus, for example).

Land committed to forest restoration, from Charlotte Wheeler @EdinburghUni Restoration = plantations, natural restoration and agroforestry #NegCO2 pic.twitter.com/JvtsnsLDa2 — Daisy Dunne (@daisydunnesci) May 23, 2018

Using modelling, Wheeler finds that restoring natural forests would be the best way to replenish carbon stocks under the Bonn Challenge. In fact, her results show that, in a scenario of mixed land-use, natural forests are likely to cover 34% of the land, but store 90% of its carbon. In contrast, plantations are expected to cover 45% of the land area, but store just 2.5% of the total carbon. She told the audience:

“Plantations have very limited carbon sequestration potential due to their rapid removal on a cyclical basis, which means that the carbon is never actually stored on the land for very long periods of time.”

However, even if all of the land pledged under the Bonn Challenge is dedicated to natural forest generation, it is still unlikely to make a sizeable contribution to mitigation efforts, she said:

“In our upper carbon estimates from the natural regeneration scenario, we have 42Pg [42bn tonnes] of carbon stored by the end of the century, which is only four years of current fossil fuel emissions.”

Forest carbon storage discussions continued on Thursday, when Pierre Taillardat, a PhD student from the National University of Singapore, presented his research on the mitigation potential of “blue carbon” – the carbon stored in marine ecosystems, including mangroves, seagrasses and kelp forests.

Pierre Taillardat talks us through the global importance of “blue carbon” stored in mangrove forests #NegCO2 pic.twitter.com/GOv8hTbbGO — Daisy Dunne (@daisydunnesci) May 24, 2018

His research finds that, while blue carbon only makes a small contribution to global forest carbon storage (around 1%), it could be important to countries rich in mangroves, such as Indonesia, Myanmar and Nigeria. Protecting mangroves – which are threatened by deforestation – could help these countries to offset around 1-10% of their annual fossil fuel emissions, his research suggests.

The potential of enhancing soil carbon stocks was another widely discussed theme across the talks. On Tuesday, Prof Claudia Kamman of Hochschule Geisenheim University made the oft-repeated observation that an advantage of applying biochar to cropland is it can increase soil carbon while boosting crop yields.

On Wednesday, Constanze Werner, a PhD student at the Potsdam Institute for Climate Impacts Research, presented her research modelling the impacts of using biochar to meet the goals of the Paris Agreement. Her research shows that limiting global warming to 1.5C using biochar alone would require it to be spread over 300-1,500Mha of land. This would likely bring significant threats to agriculture and biodiversity, she said.

Limiting global warming to 1.5C using biochar alone would require 300-1500Mha of land, causing issues for biodiversity and agriculture, says Werner #negco2 — Daisy Dunne (@daisydunnesci) May 23, 2018

Another intriguing idea for enhancing soil carbon storage was presented by Dr Jennifer Pett-Ridge from Lawrence Livermore National Laboratory. Pett-Ridge told the conference that a large and underestimated driver of soil carbon loss has been modern agriculture’s penchant for using crops with shallow roots. Swapping current crops for perennials – which have roots stretching up to 15 metres down into the earth – would increase stability and, therefore, carbon storage, she told the conference.

These perennials have some seriously long roots… and could enhance soil carbon storage #negco2 pic.twitter.com/x3WVxmu81T — Daisy Dunne (@daisydunnesci) May 22, 2018

Other NETs

As well as the more well-known negative emissions options, such as BECCS and reforestation, the conference covered the range of available NETs – partly in the keynotes, but particularly in the parallel sessions.

For example, two talks on EW emphasised how the technology could be applied today.

Dr Filip Meysman from the University of Antwerp and Delft University of Technology argued that crushed rocks could be applied to coastal areas in a similar way to how beaches are topped up with sand to counteract erosions.

“Essentially we don’t need innovation,” says Meysman, describing how much of the infrastructure (e.g. mining and distribution) for applying enhanced weathering in coastal areas is already in place #negco2 — Robert McSweeney (@rtmcswee) May 24, 2018

Prof David Beerling, director of the Leverhulme Centre for Climate Change Mitigation, presented his findings on the application of EW to croplands to sequester CO2 and boost crop yields at the same time.

Early field trials in the US found that spreading crushed basalt when growing maize increased yields by 15%, Beerling said, and reduced nitrous oxide emissions from the soil by 40%. Because of the co-benefits for improving topsoil, EW should be considered “even if you think [it] is a really bad idea for carbon dioxide removal”, he said.

Beerling wrote a Carbon Brief guest post on his research earlier this year.

Talks also focused on some of the more esoteric options for NETs. Dr Stefano Caserini of the Polytechnic University of Milan, for example, presented on a patented process to store liquid CO2 in glass capsules on the deep seabed.

Some lesser-known #negCO2 technologies being presented here, including submarine storage of CO2 in glass capsules See paper: https://t.co/Zwq4T2If4a — Robert McSweeney (@rtmcswee) May 22, 2018

Other unconventional options included research by Dr John McDonald-Wharry of the University of Waikato in New Zealand on sequestering CO2 in biochar and then combining it with a plastic to form a solid, usable material. And Dr Renaud de Richter of the Institute Charles Gerhardt, Montpellier describing two ways – the “iron salt aerosol” method and using giant “solar chimneys” – to sequester greenhouse gases other than CO2.

John McDonald-Wharry of @waikato now presenting on sequestering carbon in solid materials: "If a tree falls in the woods, is it worth converting into biochar?”#negco2 — Robert McSweeney (@rtmcswee) May 22, 2018

The conference closed with the announcement that it will not be the only one. A follow-up is planned for around 18 months’ time, with a view to the conference becoming a regular event.