Are Negative Emissions the Only Path to 2 Degrees?
September 19, 2016
Record pretty shaky on current approaches to “carbon negative”.
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.”
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.”