Are Negative Emissions the Only Path to 2 Degrees?

September 19, 2016


Record pretty shaky on current approaches to “carbon negative”.

Climate Central:

The negative emissions technology that exists today is in its infancy. Much more research on carbon dioxide removal is necessary, and understanding the costs is paramount because the technology will take time to develop and scale.

Mounting research suggests that negative emissions may have to be a major part of any global strategy to stabilize the climate because simply slashing carbon dioxide emissions likely won’t be sufficient. That’s something that the Intergovernmental Panel on Climate Change acknowledged when it factored negative emissions into some of its climate stabilization scenarios in its Fifth Assessment Report in 2014.

A National Center for Atmospheric Research study published in July showed that halting global warming at 2°C is likely to require carbon dioxide to be removed from the atmosphere on a large scale by the second half of this century.

But researchers say the world would benefit by developing negative emissions technology as soon as possible.

“I think we should not make the mistake to only look at the second half of the century,” said Sabine Fuss, a climate change mitigation researcher at the Mercator Research Institute on Global Commons and Climate Change in Berlin. “We’re talking about a huge infrastructure that needs to be developed in time and we need to be in a position to make use of it, too, because if we continue to emit as much (carbon dioxide) as we do currently, then negative emissions won’t help us either to achieve ambitious climate targets.”

Scientists are studying many different ways of carbon dioxide removal, including growing trees for biomass electric power production and then capturing and storing the resulting emissions. Other strategies involve planting large forests across the globe, and altering soil management to increase the amount of carbon it can store.

Mark Barteau, director of the University of Michigan Energy Institute and co-founder of Beyond Carbon Neutral, said the one of the biggest challenges to developing negative emissions technology is overall lack of research funding and only recent recognition that it may be necessary at all.

With the global emphasis on emissions cuts, scientists need to think more strategically about how to generate interest in negative emissions so the technology can be developed sooner — the primary goal of Beyond Carbon Neutral, Barteau said.

Researchers at Beyond Carbon Neutral are developing both negative emissions technology and thinking about ways it could be implemented on a broad scale.

Supekar’s model, for example, focuses on what it might look like to build large “negative power plants” — renewable energy-powered installations that would directly remove carbon dioxide from the atmosphere and store it someplace.

He said the model suggests that many thousands of negative power plants would be needed globally, requiring a massive new electric power and carbon storage infrastructure whose cost could range into the quadrillions of dollars.

“Removing emissions using direct air capture as a large-scale mitigation approach is likely to be more expensive by at least two to three orders of magnitude relative to preventing our emissions in the next 10 years,” Supekar said.

Beyond Carbon Neutral scientists are also researching ways that forests can be enhanced to store more carbon dioxide.

Forests can only create negative emissions if they increase the rate at which they absorb carbon dioxide from the atmosphere and keep it locked up in the ecosystem’s roots, tree trunks and soil, said John DeCicco, a University of Michigan climate mitigation researcher and co-founder of Beyond Carbon Neutral.

From a carbon cycle perspective, once plant leaves have removed carbon dioxide from the atmosphere through photosynthesis and stored it in tree trunks and roots, “we are as ahead of the game as we can ever be with respect to the atmosphere,” he said.

So the key may be to enhance the rate at which forests absorb carbon — something Beyond Carbon Neutral scientists are studying on private forestlands in northern Michigan.

The solution is simple: “Grow more trees better and keep them parked longer, DeCicco said.

In the U.S., the more than 500 million acres of federal public lands also present a major opportunity for negative emissions, DeCicco said.

With the federal government as the single land manager of such a vast area of land, ecosystems could be optimized for enhanced carbon storage, he said.

“Instead of a big effort to promote biofuels, that should be completely abandoned from a scientific point of view and we need to be making a full-court press to protect and preserve and expand forests, wetlands, natural grasslands and natural ecosystems that are carbon sinks,” DeCicco said.

Barteau said there are many unanswered questions about how carbon can be removed from the atmosphere, but it’s urgent that those questions be answered sooner than later.

“Start now,” he said. “We may wish we could throw a switch in 2040 or 2050 to turn it on. We may not be able to do that until 2080.”

Carbon Brief:

Most carbon capture projects (and there aren’t many) are attached to power plants or industrial units, capturing the CO2 released by burning fossil fuels or making products. In an ideal world, at least, this would make these processes carbon neutral.

But the project in Decatur goes further than this. The fact that it captures emissions released by fermenting corn, which absorbs CO2 when it grows, means that, overall, the process also captures CO2 from the atmosphere.

This process is known as bioenergy with carbon capture and storage — more commonly known by its acronym, BECCS.

With the UN’s new deal on climate change, the world has signed up to keeping global temperature rise to “well below” 2C, and to 1.5C if possible. A recent study has shown that this half a degree makes a world of difference when it comes to the impacts, such as coral bleaching, sea level rise and heatwaves.

The trouble is that meeting this 2C goal is already looking like a challenge. Even with the recent round of climate pledges drawn up as part of the UN deal, countries are set to emit enough CO2 to push the planet well beyond this target, possibly to 3.7C higher than pre-industrial levels.

This is a cloud over the most vulnerable nations, such as small island states, who are counting on the 1.5C target to ensure their survival.

But there is a glimmer of a silver lining. Even if countries overshoot the 2C target, there is some hope that the planet can subsequently get back down to this level, if humans are able to remove carbon dioxide emissions from the atmosphere.

This is a process known as “negative emissions”, or “carbon dioxide removal”. As Carbon Brief explained in detail earlier this year, there are various ways of going about it, ranging from the bizarre to the plausible.

None of them are without drawbacks, but BECCS is considered one of the more feasible methods of achieving this on a large scale.

The Intergovernmental Panel on Climate Change (IPCC) says that most scenarios that return a likely chance of staying below 2C rely on the “widespread deployment” of BECCS in the second half of the century — removals of around 616 gigatonnes of CO2 (GtCO2) by 2100.

Despite this, the technology remains untested and uncertain, and climate campaigners are increasingly raising risks such as land grabs and food security, as witnessed at the latest round of UN climate negotiations.

So far, there are currently around 15 pilot projects around the world. But 2016 could be a milestone. Before the year is out, ADM is hoping that its corn processing plant in Decatur could be the first to start using the technology on a large scale.

At the ethanol plant

As part of US efforts to reduce its CO2 emissions, the Department of Energy (DoE) is funding three CCS projects that will reduce emissions from industrial sources.

ADM’s ethanol plant was selected from 12 initial proposals to enter the design, construction and operation phase, receiving $141m in funding. Private sources have contributed the remainder of the total $208m.

One reason why this particular plant is viewed as a good bet for the DoE’s money is that ADM had already succeeded in sequestering a million tonnes of CO2 over three years during a one-off pilot project (all tonnes are metric).

Between 2011 and 2014, CO2 was injected at a rate of 1,000 tonnes per day into the Mount Simon sandstone. But a million tonnes of captured CO2 is a trifle in the grand scheme of global emissions. A typical medium-sized 500 megawatt coal-fired power plant emits around three million tonnes every year.

The Mount Simon sandstone has proved ideal for CO2 storage during this experiment. It is very porous, meaning that CO2 can be stored in tiny holes in the rock, while lying beneath three layers of dense shale, which effectively cap the reservoir and prevent it from leaking.

The next part of the project is to scale it up to a commercial level. Together with the existing facilities, ADM’s ethanol plant aims to capture and store 2.26m tonnes of CO2 (MtCO2) over a period of 2.5 years, at a rate of around 0.9MtCO2 a year. After years of delay, this process is expected to begin some time before the end of 2016.

However, the Decatur facility, which is largely powered with natural gas, cannot be considered net carbon negative as a whole. The facility not only processes corn, but also a number of other products, including vitamin E, soybean and glycols. These other plants are not fitted with CCS technology.

According to figures reported to the US Environmental Protection Agency by ADM, the Decatur facility as a whole emitted more than 5MtCO2 equivalent (CO2e) in 2014.

Taking this as a rough proxy for its emissions in the near future (noting that ADM does not have an absolute emissions reduction target, only an intensity reduction target), the facility will emit 12.7MtCO2 in the 2.5 years that emissions are sequestered at the plant.

During the injection period, 2.27MtCO2 will be captured and buried. The process of capturing this CO2 will itself emit an additional 173,000tCO2, according to the EPA’s Environmental Assessment of the project. The fermentation element is only part of the process — additional CO2 will be released when the ethanol itself is burnt.

This takes the net total of sequestered CO2 to 2.1Mt, reducing the overall CO2 emissions of the plant by around 14%. This means that the plant as a whole will continue to emit around 10.5MtCO2e over the three years of the project, or around 3.5MtCO2e per year. This is almost four times as much as the amount sequestered.

It is also worth noting that the motivations for the project are not entirely environmental. A project factsheet produced by the DoE says: “Successful implementation of this project could facilitate exploration of long-term CO2 utilization options, such as enhanced oil recovery, in the Southern Illinois Basin.”

Using the captured CO2 to extract previously out-of-reach oil reserves would temper the net emissions reductions achieved, according to analysis by the International Energy Agency.


7 Responses to “Are Negative Emissions the Only Path to 2 Degrees?”

  1. Sir Charles Says:

    => Survivable IPCC projections are based on science fiction – the reality is much worse

  2. Julian Bond Says:

    Time and scale; We’re not good at them. 616 GtCO2 sequestered by 2100 is 7.3 GtCo2 pa. Which is roughly 4 orders of magnitude bigger than the Decatur plant. M’kay?

  3. Hansen argues in “Assessing Dangerous Climate Change” (12/2013) that reforestation and improved agricultural practices (soil has a great carbon storing capacity) are the most practical option and can deliver 100 Gt of Carbon drawdown this century, but must be undertaken before it’s too late, i.e., 2C may be a tipping point beyond which our efforts may be futile.

    Reforestation and Soil Carbon
    Of course fossil fuel emissions will not suddenly terminate. Nevertheless, it is not impossible to return CO2 to 350 ppm this century. Reforestation and increase of soil carbon can help draw down atmospheric CO2. Fossil fuels account for ,80% of the CO2 increase from preindustrial time, with land use/deforestation accounting for 20% [1,170,172–173]. Net deforestation to date is estimated to be 100 GtC (gigatons of carbon) with +/-50% uncertainty [172].

    Complete restoration of deforested areas is unrealistic, yet 100 GtC carbon drawdown is conceivable because: (1) the humanenhanced atmospheric CO2 level increases carbon uptake by some vegetation and soils, (2) improved agricultural practices can convert agriculture from a CO2 ource into a CO2 sink [174], (3) biomass-burning power plants with CO2 capture and storage can contribute to CO2 drawdown.

    Forest and soil storage of 100 GtC is challenging, but has other benefits. Reforestation has been successful in diverse places [175]. Minimum tillage with biological nutrient recycling, as opposed to plowing and chemical fertilizers, could sequester 0.4–1.2 GtC/year [176] while conserving water in soils, building agricultural resilience to climate change, and increasing productivity especially in smallholder rain-fed agriculture, thereby reducing expansion of agriculture into forested ecosystems [177–178]. Net tropical deforestation may have decreased in the past decade [179], but because of extensive deforestation in earlier decades [170,172–173,180–181] there is a large amount of land suitable for reforestation [182]. Use of bioenergy to draw down CO2 should employ feedstocks from residues, wastes, and dedicated energy crops that do not compete with food crops, thus avoiding loss of natural ecosystems and cropland [183–185]. Reforestation competes with agricultural land use; land needs could decline by reducing use of animal products, as livestock now consume more than half of all crops [186]. Our reforestation scenarios assume that today’s net deforestation rate (,1 GtC/year; see [54]) will stay constant until 2020, then linearly decrease to zero by 2030, followed by sinusoidal 100 GtC biospheric carbon storage over 2031–2080. Alternative timings do not alter conclusions about the potential to achieve a given CO2 level such as 350 ppm.

  4. webej Says:

    People love carbon capture and sequestration, capital intensive, energy intensive snazzy technology. It is expensive and will presumably always be out of reach on the scale we need, but coupled to power plants it garners the most interest.
    We need to lever natural processes: nature’s way of squestering CO² after volcanic build up is rock weathering, eventually moving the carbon back under the earth’s crust where it started out. It unfortunately takes too long, but there is a lot of interesting work in affordable options to help the process along and give a hand. It holds a lot more promise than carbon capture and injection.

  5. toddinnorway Says:

    Hi webej, I have worked for over 10 years to advance CO2 capture and storage (CCS) to the point that it is a viable emissions reduction option. I still however do not “love CCS”. It is like taking out the trash. Nobody loves doing it, but at some level, most of us realize that if we do not do it, the resulting mess will be worse than taking it out in a timely fashion.

    Strangely, the fossil fuels industry does not love CCS either, even though it would give them a possibility to fix most of their greenhouse gas emissions, and perhaps, secure a role for them in the future. They have been allowed to “throw their trash for out the window” for 200 years, down to a hillside dump where they do not see it. Why should they now start taking the trash out to the rubbish bin?

    As mentioned in the article, BECCS could do an even better job of removing CO2 from the atmosphere. In a related article in The Guardian, the forests of North America are dying at an accelerating rate due to heat stress, drought stress and attack from new and more effective pests. So we must re-think re-forestization in the context of a changed climate. Trees that used to thrive at certain latitudes and altitudes, will no longer do so. These dead trees will burn up, either on their own, or we could harvest them, burn them in BECSS, and at least reduce some of the CO2 load that the coming global temperate forest death will cause. Then plant something more hot-dry-pest resistant where the once mighty temperate forests dominated.

  6. A couple of points …

    Recent research has found (contact for reference) that only “old growth forests” sequester CO2 over the long term. This was based upon research done in Europe. New growth forests eventually will, but in the meantime they release essentially all the CO2 they sequester back to atmosphere on the order of decades.

    There are technologies available, like those of Klaus Lackner, which could work to grab and sequester CO2 via clear air capture, but, even at scale, these are horribly expensive, between $300-$1000 per tonne of CO2.

    Also, what most people seem to miss is that for any of these technologies to be effective, we need to STOP emitting the greenhouse gases. It is wholly unrealistic to think these technologies will not only draw down CO2 but will also compensate for CO2 still being dumped into atmosphere at prodigious amounts. Realize that agriculture itself, setting completely aside the emissions of machinery needed to grow, harvest, and process foodstuffs, produces something like 2 GtCO2 annually and globally. That’ll be a challenge on its own. So the cost will be the cost of zeroing emissions anyway PLUS the cost of mounting this huge industry of extracting CO2 from an atmosphere where it occurs at less than one part per thousand.

    Finally, even if emissions are stopped, it will take a couple of centuries for natural systems to bring down CO2, and then those concentrations plateau for 1000 years or longer. (It’s something like a 20% decrease over 2 centuries, I believe.) This plateau happens because CO2 is also dissolved in oceans, and these release the CO2 once atmospheric concentrations get lower, although the process is slow.

    Meanwhile, global temperatures will continue to rise, overshooting whatever mark humanity cares to set for a nominal point.

    Again, contact me if references are sought. That can be done at my blog.

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