Direct CO2 Capture Machines Could Use ‘a Quarter of Global Energy’ in 2100
By Simon Evans
Machines that suck CO2 directly from the air could cut the cost of meeting global climate goals, a new study finds, but they would need as much as a quarter of global energy supplies in 2100.
The research, published Monday in Nature Communications, is the first to explore the use of direct air capture (DAC) in multiple computer models. It shows that a "massive" and energy-intensive rollout of the technology could cut the cost of limiting warming to 1.5 or 2 C above pre-industrial levels.
But the study also highlights the "clear risks" of assuming that DAC will be available at scale, with global temperature goals being breached by up to 0.8 C if the technology then fails to deliver.
This means policymakers should not see DAC as a "panacea" that can replace immediate efforts to cut emissions, one of the study authors tells Carbon Brief, adding: "The risks of that are too high."
DAC should be seen as a "backstop for challenging abatement" where cutting emissions is too complex or too costly, says the chief executive of a startup developing the technology. He tells Carbon Brief that his firm nevertheless will "continuously push back on the 'magic bullet' headlines."
The 2015 Paris agreement set a goal of limiting human-caused warming to "well below" 2 C and an ambition of staying below 1.5 C. Meeting this ambition will require the use of "negative emissions technologies" to remove excess CO2 from the atmosphere, according to the Intergovernmental Panel on Climate Change (IPCC).
This catch-all term covers a wide range of approaches, including planting trees, restoring peatlands and other "natural climate solutions." However, model pathways developed by researchers rely most heavily on bioenergy with carbon capture and storage (BECCS). This is where biomass, such as wood pellets, is burned to generate electricity and the resulting CO2 is captured and stored.
The significant potential role for BECCS raises a number of concerns, with land areas up to five times the size of India devoted to growing the biomass needed in some model pathways.
One alternative is direct air capture, where machines are used to suck CO2 out of the atmosphere. If the CO2 is then buried underground, the process is sometimes referred to as direct air carbon capture and storage (DACCS).
The new study explores how DAC could help meet global climate goals with "lower costs," using two different integrated assessment models (IAMs). Study author Dr. Ajay Gambhir, senior research fellow at the Grantham Institute for Climate Change at Imperial College London, explains to Carbon Brief:
"This is the first inter-model comparison … [and] has the most detailed representation of DAC so far used in IAMs. It includes two DAC technologies, with different energy inputs and cost assumptions, and a range of energy inputs including waste heat. The study uses an extensive sensitivity analysis [to test the impact of varying our assumptions]. It also includes initial analysis of the broader impacts of DAC technology development, in terms of material, land and water use."
The two DAC technologies included in the study are based on different ways to adsorb CO2 from the air, which are being developed by a number of startup companies around the world.
One, typically used in larger industrial-scale facilities such as those being piloted by Canadian firm Carbon Engineering, uses a solution of hydroxide to capture CO2. This mixture must then be heated to high temperatures to release the CO2 so it can be stored and the hydroxide reused. The process uses existing technology and is currently thought to have the lower cost of the two alternatives.
The second technology uses amine adsorbents in small, modular reactors such as those being developed by Swiss firm Climeworks. Costs are currently higher, but the potential for savings is thought to be greater, the paper suggests. This is due to the modular design that could be made on an industrial production line, along with lower temperatures needed to release CO2 for storage, meaning waste heat could be used.
Overall, despite "huge uncertainty" around the cost of DAC, the study suggests its use could allow early cuts in global greenhouse gas emissions to be somewhat delayed, "significantly reduc[ing] climate policy costs" to meet stringent temperature limits.
Using DAC means that global emissions in 2030 could remain at higher levels, the study says, with much larger use of negative emissions later in the century. This is shown in the charts, below, for scenarios staying below 1.5 C (left panel, shades of blue) and 2 C (right, green).
Pathways without DAC are shown in darker shades. For example, the solid dark blue line shows results from the "TIAM" model, with emissions peaking around 2020 and falling rapidly to below zero around 2050.
In contrast, the light blue solid line shows a pathway where DAC allows a more gradual decline, reaching zero in the 2060s and with negative emissions of around 30 billion tonnes per year (Gt/yr) by the 2080s. This is close to today's annual global emissions of around 40GtCO2/yr.
Global CO2 emissions from fossil fuels (Gt/yr) in model pathways consistent with limiting warming this century to 1.5 C (left panel, blue) or 2 C (right panel, green). Results from two different IAMs – TIAM and WITCH – are shown with solid and dashed lines, respectively. The various lines show scenarios that use direct capture ("DAC," darker shades) and those that do not ("NoDAC," lighter), as well as pathways to 2 C without negative emissions of any sort ("NoNET," darkest green). Source: Realmonte et al. (2019).
"The results of both models are surprisingly similar," says Dr. Nico Bauer, a scientist at the Potsdam Institute for Climate Impacts Research (PIK), who was not involved in the study. He tells Carbon Brief: "This increases the credibility about the main conclusions that the DACCS technology can play an important role in a long-term climate change mitigation strategy."
The use of DAC in some of the modeled pathways delays the need to cut emissions in certain areas. The paper explains: "DACCS allows a reduction in near term mitigation effort in some energy-intensive sectors that are difficult to decarbonise, such as transport and industry."
Steve Oldham, chief executive of DAC startup Carbon Engineering says he sees this as the key purpose of CO2 removal technologies, which he likens to other "essential infrastructure" such as waste disposal or sewage treatment.
Oldham tells Carbon Brief that while standard approaches to cutting CO2 remain essential for the majority of global emissions, the challenge and cost may prove too great in some sectors. He says:
"DAC and other negative emissions technologies are the right solution once the cost and feasibility becomes too great … I see us as the backstop for challenging abatement."
Even though DAC may be relatively expensive, the model pathways in the new study still see it as much cheaper than cutting emissions from these hard-to tackle sectors. This means the models deploy large amounts of DAC, even if its costs are at the high end of current estimates.
It also means the models see pathways to meeting climate goals that include DAC as having lower costs overall ("reduce[d]… by between 60 to more than 90%").
Gambhir tells Carbon Brief: "Deploying DAC means less of a steep mitigation pathway in the near-term, and lowers policy costs, according to the modeled scenarios we use in this study."
However, the paper also points to the significant challenges associated with such a large-scale, rapid deployment of DAC, in terms of energy use and the need for raw materials.
The energy needed to run direct air capture machines in 2100 is up to 300 exajoules each year, according to the paper. This is more than half of overall global demand today, from all sources, and despite rising demand this century, it would still be a quarter of expected demand in 2100.
Gambhir tells Carbon Brief:
"Large-scale deployment of DAC in below-2°C scenarios will require a lot of heat and electricity and a major manufacturing effort for production of CO2 sorbent. Although DAC will use less resources such as water and land than other NETs [such as BECCS], a proper full life-cycle assessment needs to be carried out to understand all resource implications."
There are also questions as to whether this new technology could be rolled out at the speed and scale envisaged, with expansion at up to 30% each year and deployment reaching 30GtCO2/yr towards the end of the century. This is a "huge pace and scale," Gambhir says, with the rate of deployment being a "key sensitivity" in the study results.
Professor Jennifer Wilcox, professor of chemical engineering at Worcester Polytechnic Institute, who was not involved with the research, says that this rate of scale-up warrants caution. She tells Carbon Brief:
"Is the rate of scale-up even feasible? Typical rules of thumb are increase by an order of magnitude per decade [growth of around 25-30% per year]. [Solar] PV scale-up was higher than this, but mostly due to government incentives … rather than technological advances."
Reaching 30GtCO2/yr of CO2 capture – a similar scale to current global emissions – would mean building some 30,000 large-scale DAC factories, the paper says. For comparison, there are fewer than 10,000 coal-fired power stations in the world today.
If DAC were to be carried out using small modular systems, then as many as 30m might be needed by 2100, the paper says. It compares this number to the 73m light vehicles that are built each year.
The study argues that expanding DAC at such a rapid rate is comparable to the speed with which newer electricity generation technologies such as nuclear, wind and solar have been deployed.
Climeworks greenhouse © Climeworks / Julia Dunlop
The modeled rate of DAC growth is "breathtaking" but "not in contradiction with the historical experience," Bauer says. This rapid scale-up is also far from the only barrier to DAC adoption.
The paper explains: "[P]olicy instruments and financial incentives supporting negative emission technologies are almost absent at the global scale, though essential to make NET deployment attractive."
Carbon Engineering's Oldham agrees that there is a need for policy to recognize negative emissions as unique and different from standard mitigation. But he tells Carbon Brief that he remains "very very confident" in his company's ability to scale up rapidly.
(The new study includes consideration of the space available to store CO2 underground, finding this not to be a limiting factor for DAC deployment.)
The paper says that the challenges to scale-up and deployment on a huge scale bring significant risks, if DAC does not deliver as anticipated in the models. Committing to ramping up DAC rather than cutting emissions could mean locking the energy system into fossil fuels, the authors warn.
This could risk breaching the Paris temperature limits, the study explains:
"The risk of assuming that DACCS can be deployed at scale, and finding it to be subsequently unavailable, leads to a global temperature overshoot of up to 0.8°C."
Gambhir says the risks of such an approach are "too high":
"Inappropriate interpretations [of our findings] would be that DAC is a panacea and that we should ease near-term mitigation efforts because we can use it later in the century."
"Policymakers should not make the mistake to believe that carbon removals could ever neutralise all future emissions that could be produced from fossil fuels that are still underground. Even under pessimistic assumptions about fossil fuel availability, carbon removal cannot and will not fix the problem. There is simply too much low-cost fossil carbon that we could burn."
Nonetheless, professor Massimo Tavoni, one of the paper's authors and the director of the European Institute on Economics and the Environment (EIEE), tells Carbon Brief that "it is still important to show the potential of DAC – which the models certainly highlight – but also the many challenges of deploying at the scale required."
The global carbon cycle poses one final – and underappreciated – challenge to the large-scale use of negative emissions technologies such as DAC: ocean rebound. This is because the amount of CO2 in the world's oceans and atmosphere is in a dynamic and constantly shifting equilibrium.
This equilibrium means that, at present, oceans absorb a significant proportion of human-caused CO2 emissions each year, reducing the amount staying in the atmosphere. If DAC is used to turn global emissions net-negative, as in the new study, then that equilibrium will also go into reverse.
As a result, the paper says as much as a fifth of the CO2 removed using DAC or other negative emissions technologies could be offset by the oceans releasing CO2 back into the atmosphere, reducing their supposed efficacy.
Reposted with permission from our media associate Carbon Brief.
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The COVID-19 pandemic in the United States is the deepest and longest period of malaise in a dozen years. Our colleagues at the University of Vermont have concluded this by analyzing posts on Twitter. The Vermont Complex Systems Center studies 50 million tweets a day, scoring the "happiness" of people's words to monitor the national mood. That mood today is at its lowest point since 2008 when they started this project.
The Hedonometer measures happiness through analysis of key words on Twitter, which is now used by one in five Americans. This chart covers 18 months from early 2019 to July 2020, showing major dips in 2020. hedonometer.org<p>These same tweets also indicate a potential salve. Before pandemic lockdowns began, doctoral student <a href="https://scholar.google.com/citations?user=0P0ZYbIAAAAJ&hl=en" target="_blank">Aaron Schwartz</a> <a href="https://doi.org/10.1002/pan3.10045" target="_blank">compared tweets before, during, and after visits to 150 parks, playgrounds and plazas</a> in San Francisco. He found that park visits corresponded with a spike in happiness, followed by an afterglow lasting up to four hours.</p><p>Tweets from parks contained fewer negative words such as "no," "not" and "can't," and fewer first-person pronouns like "I" and "me." It seems that nature makes people more positive and less self-obsessed.</p><p>Parks keep people happy in times of global crisis, economic shutdown and public anger. Research has also shown that transmission rates for COVID-19 are <a href="https://www.sfchronicle.com/news/article/Is-risk-of-coronavirus-transmission-lower-15287602.php" target="_blank">much lower outdoors than inside</a>. As scholars who study <a href="https://scholar.google.com/citations?user=yFzb2EUAAAAJ&hl=en" target="_blank">conservation</a> and how nature <a href="https://scholar.google.com/citations?user=CCnUeN8AAAAJ&hl=en" target="_blank">contributes to human well-being</a>, we see opening up parks and creating new ones as a straightforward remedy for Americans' current blues.</p>
Park Visits Are Up During the Pandemic<p>According to the Hedonometer, sentiments expressed online started trending lower in mid-March as the impacts of the pandemic became clear. As lockdowns continued, they registered the lowest sentiment scores on record. Then in late May, effects from George Floyd's death in police custody and the following protests and police response once again could be seen on Twitter. May 31, 2020 was the saddest day of the project.</p><p>Recent surveys of park visitors around the University of Vermont have shown people <a href="https://osf.io/preprints/socarxiv/sd3h6" target="_blank">using green spaces more</a> since COVID-19 lockdowns began. Many people reported that parks were highly important to their well-being during the pandemic.</p>
<div id="4c7e4" class="rm-shortcode" data-rm-shortcode-id="bc0ac146ab2a94228f32d973fc2ab272"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1289428912879964160" data-partner="rebelmouse"><div style="margin:1em 0">#Goldengatepark #sf #quarantinemood https://t.co/9l3ufnbkt6</div> — Suvd (@Suvd)<a href="https://twitter.com/Suvd19486406/statuses/1289428912879964160">1596258783.0</a></blockquote></div><p>The powerful effects of nature are strongest in large parks with more trees, but smaller neighborhood parks also provide a significant boost. Their impact on happiness is real, measurable and lasting.</p><p>Twitter records show that parks increase happiness to a level similar to the bounce at Christmas, which typically is the happiest day of the year. Schwartz has since expanded his <a href="https://arxiv.org/pdf/2006.10658.pdf" target="_blank">Twitter study</a> to the 25 largest cities in the U.S. and found this bounce everywhere.</p><p>Parks and public spaces won't cure COVID-19 or stop police brutality, but they are far more than playgrounds. There is growing evidence that parks contribute to mental and physical health in a range of communities.</p><p>In a 2015 study, for example, Stanford researchers sent people out for one of two walks: through a local park or on a busy street. Those who walked in nature showed <a href="https://doi.org/10.1016/j.landurbplan.2015.02.005" target="_blank">improved moods and better memory performance</a> compared to the urban group. And a team led by <a href="https://penniur.upenn.edu/people/eugenia-gina-south" target="_blank">Gina South</a> of the University of Pennsylvania showed in a 2018 study that greening and cleaning up blighted vacant lots in Philadelphia <a href="http://dx.doi.org/10.1001/jamanetworkopen.2018.0298" target="_blank">reduced local residents' feelings of depression, worthlessness and poor mental health</a>.</p>
Creative Strategies<p>It isn't easy to create new parks on the scale of San Francisco's Golden Gate Park or the Washington Mall, but smaller projects can expand outdoor space. Options include greening vacant lots, closing streets and investing in existing parks to make them safer, greener and shadier and support wildlife.</p><p>These initiatives don't have to be capital-intensive. In the University of Pennsylvania study, for example, renovating a vacant lot by removing trash, planting grass and trees and installing a low fence cost only about US$1,600.</p><p>Urban green space is most needed in neighborhoods that have lacked funding for parks, especially given <a href="https://www.nytimes.com/2020/04/08/nyregion/coronavirus-race-deaths.html" target="_blank">COVID-19's disproportionate impact on Black and Latinx people</a>.</p><p>Cities can also create parklike spaces by <a href="https://theconversation.com/with-fewer-cars-on-us-streets-now-is-the-time-to-reinvent-roadways-and-how-we-use-them-140408" target="_blank">closing streets to cars</a>. Many cities worldwide are currently retooling their transportation systems for the post-COVID-19 world in order to <a href="https://thecityfix.com/blog/bicycles-slower-speeds-livable-city-paris-mayor-anne-hidalgo-plans-ambitious-second-term-dario-hidalgo/" target="_blank">reallocate public space</a>, widen sidewalks and make more space for nature.</p><p>Urban designers, artists, ecologists and other citizens can play a direct role, too, creating pop-up parks and green spaces. Some advocates <a href="https://www.bloomberg.com/news/articles/2017-09-15/a-brief-history-of-park-ing-day" target="_blank">transform parking spaces into mini-parks</a> with grass, potted trees and seating for just the time on the meter, to make a larger point about turning so much public space over to cars.</p><p>Or cities can invest a little more. Minneapolis, Cincinnati and Arlington, Virginia, have won <a href="https://www.tpl.org/parkscore" target="_blank">national recognition</a> for their ambitious investments in public park systems. These areas could serve as models for neighborhoods that lack access to parks.</p>
<div id="25fd0" class="rm-shortcode" data-rm-shortcode-id="383f0d2df0237e9359c30dcce6cd6c42"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1276558744835379201" data-partner="rebelmouse"><div style="margin:1em 0">Looking to safely get outside? Check out the best parks for social distancing in this year's top ten ParkScore citi… https://t.co/HJjEtDsrTD</div> — The Trust for Public Land (@The Trust for Public Land)<a href="https://twitter.com/tpl_org/statuses/1276558744835379201">1593190296.0</a></blockquote></div>
A New Park Deal?<p>The United States has historically driven economic recovery with major infrastructure investments, like the New Deal in the 1930s and the 2009 <a href="https://www.investopedia.com/terms/a/american-recovery-and-reinvestment-act.asp" target="_blank">American Reinvestment and Recovery Act</a>. Such investments could easily include nature-positive spaces.</p><p>Parks are not panaceas, as evidenced by the widely publicized <a href="https://www.nytimes.com/2020/07/06/nyregion/amy-cooper-false-report-charge.html" target="_blank">racist confrontation between a white woman and a Black birder</a> in New York's Central Park in early July. But Hedonometer data add to a <a href="https://advances.sciencemag.org/content/5/7/eaax0903?utm_source=miragenews&utm_medium=miragenews&utm_campaign=news" target="_blank">growing body of evidence</a> that they provide <a href="https://doi.org/10.1073/pnas.1807504116" target="_blank">clear mental health benefits</a>. Creating and expanding parks also <a href="https://www.nrpa.org/contentassets/f568e0ca499743a08148e3593c860fc5/economic-impact-study-summary.pdf" target="_blank">generates jobs and economic activity</a>, with much of the money spent locally.</p><p>We believe investments in nature are well worth it, offering both short-term solace in difficult times and long-term benefits to health, economies and communities.</p>
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