Does carbon capture and use reduce emissions?
If the latest IPCC report has taught us anything, it’s that it’s time to tackle climate change now. And while it’s absolutely crucial to reduce the amount of fossil fuels we use, there’s no doubt that some of the carbon dioxide in our atmosphere will have to be sucked out one way or another. This is where carbon capture and sequestration comes in.
Carbon capture and sequestration, often referred to as CCS, is the process by which CO2 can be drawn in by sources such as power plant smokestacks or, in some cases, even by the atmosphere through direct air capture. Then the carbon is permanently locked up, often underground, by sequestration.
However, there is another potential way to capture carbon dioxide: to reuse it for another product. And in a world where circular economies based on the reuse of as much material as possible are needed, many are exploring a second life for greenhouse gas emissions.
“Carbon capture is definitely a way to remove CO2 of the atmosphere,” says Daniel Sanchez, associate cooperative extension specialist in the Department of Environmental Science, Policy, and Management at UC Berkeley. “We can do a lot more with this, though. We can reduce emissions and we can recycle emissions.
But there are still many questions about how carbon dioxide can be reused and whether it is really worth it for the climate.
Carbon Capture and Utilization, Explained
In 2017, a group of researchers found that to stay below a 2 degree Celsius rise above pre-industrial temperatures by 2050, the world would need to avoid emitting about 800 gigatonnes of carbon over the next three decades. Even with emission reductions, a piece of about 120 to 160 gigatonnes of CO2 will have to be sequestered until 2050, and even more so after that.
However, there aren’t many economic incentives to bury loads and loads of carbon deep under the land or sea. Enter carbon capture and utilization (CCU), which turns these released gases into products salable.
There are several ways to commercialize and reuse captured carbon, starting with direct use or non-conversion. This is a method in which the carbon dioxide is not chemically modified. Some common forms of direct use are channeling the gas into greenhouses, concentrating it as a fertilizer, and turning it into a solvent for decaffeination or dry cleaning.
But the most common way to reuse carbon dioxide without conversion is through enhanced oil recovery. Enhanced Oil Recovery (EOR) is the process by which carbon dioxide is injected into an existing oil field to, through increased pressure, expel even more oil. (The world produces 500,000 barrels of oil every day using this method, according to a 2018 analysis.) Theoretically, if some of the carbon dioxide stays underground and the rest is collected and re-injected into the process, the oil could to be “carbon negative. Of course, burning oil always releases carbon dioxide into the atmosphere, so the balance depends on where the gas originated in the EOR process and who gets the credit for the storage .
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Beyond just using carbon dioxide as is, emissions can be converted into products like methane, methanol, gasoline, plastic polymers, cement, and concrete. In some cases, the carbon captured in these products can be held out of the atmosphere for, theoretically, up to centuries.
But regardless of how the captured carbon is used, those emissions will likely one day return to the atmosphere, leading to much debate about whether and how these technologies should be used against climate change.
The debate over the use of CCU against climate change
Last month, a study published in the journal On earth broke down the emissions lifecycle and technology readiness of dozens of different CCU pathways to determine if any of them could potentially meet global targets to halve carbon emissions by 2030 and reach net zero by 2050. After considering where the carbon dioxide came from (atmospheric, biogenic, or naturally occurring from plants, fossil fuels, or a combination of biogenic and fossil fuels) and what it has become (direct use, fuels and chemicals, mineral carbonates and building materials, or enhanced oil recovery), only a handful of met the terms of the 2030 Paris Agreement. Only one would work with the reference 2050.
What researchers have found is that technologies that align with the 2030 goals use carbon dioxide from a biogas plant to enrich agricultural greenhouses, biogenic carbon dioxide to make building materials , the combustion gases captured directly to, again, make building materials and basic oxygen. furnace gas to produce urea, which can be used in fertilizers and commercial products. The EOR, on the other hand, only achieves the Paris objectives in the very specific circumstances where the CO2 is used directly and that no more than two barrels of oil are produced per tonne of carbon injected.
“There are only very few of these CCU routes that are compatible in 2030, or because they are not ready in time,” says Kleijne de Kleijne, author of the study and doctoral student at Radboud University in Nijmegen in the Netherlands. “They are still at a low level of technological readiness.”
Jump to the Paris Agreement vision for 2050, and only one type of CCU makes the difference: building blocks using a purified stream of biogenic CO2. “Because CO2 is not permanently stored in fuels or chemicals, these products can only be strictly compatible with Paris when the CO2 is of biogenic or atmospheric origin and no emissions are associated with capture and conversion processes,” the authors write.
But Paris’ goals are incredibly difficult to achieve, says Sanchez. Considering how difficult it will be for the world to keep climate change below a 1.5 degree Celsius rise, and how far off track we are currently, the bar is extremely high.
“[CCU] can substitute for other fossil-intensive alternatives. It can help us reduce emissions, but it doesn’t remove carbon from the atmosphere,” Sanchez says. “It keeps the carbon in the economy.” Without long-term storage, he notes, achieving zero emissions is nearly impossible.
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There are two other major arguments in favor of powering up the CCU. The first is that by recycling carbon dioxide for purposes for which we would typically turn to fossil fuels, we are keeping more fossil fuels buried deep under the ground and out of the atmosphere.
With so many industries struggling to decarbonize quickly, it seems all the more important to find ways to keep the economy alive without all the environmental degradation that comes with extracting more fossil fuels. A study in the journal Nature last year has shown that to have even a 50/50 chance of meeting the Paris Agreement goals, 58% of the world’s oil, 59% of fossil gas and 89% of coal must stay in the ground. “Additional investments in the extraction of fossil fuels are not compatible [with mitigating climate change]as this research shows,” said Steve Pye, co-author and energy systems researcher at University College London. PopSci in September.
The second reason is that even if we were able to convert the world’s energy to near net zero overnight, we would still likely depend on carbon capture and sequestration to extract existing carbon from the atmosphere in order to to control the climate (the current atmospheric CO2 levels are 419.03 parts per million, compared to pre-industrial levels of around 260 to 270 parts per million). In some cases, CCU can be used as a stepping stone to more permanent carbon sequestration technologies.
“There is a really interesting and more nuanced conversation to be had around [CCU]“says Sanchez. “Maybe the net of all positive emissions and all negative emissions must be less than or equal to zero. But not all [technology] must be zero.