Last week’s United Nations’ Intergovernmental Panel on Climate Change (IPCC) report suggests we may need to remove carbon dioxide from the atmosphere to keep the global average temperature from rising to dangerous levels, but researchers warn that carbon removal has never been tested on a large scale and could do more harm than good.
The IPCC report makes for grim reading. It states that our chances of preventing the global average temperature from rising more than 2.7 degrees Fahrenheit (1.5 degrees Celsius) from pre-industrial levels over the next 20 years are very slim, “unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions.”
The report lays out five possible “illustrative scenarios" to explain how the world’s climate may change depending on the extent to which humans reduce greenhouse gas emissions.
The three more pessimistic scenarios assume temperatures would rise above 3.6 degrees Fahrenheit (2 degrees Celsius) by mid-century, an increase that would lead to frequent and widespread “extreme sea level events, heavy precipitation, pluvial flooding, and exceedance of dangerous heat.”
The likelihood of the worst two scenarios (SSP5-8.5 and SSP3-7.0) is low because they assume that coal, the most polluting fossil fuel when it comes to carbon emissions, will make a big come back, something that is extremely unlikely given that solar and wind energy are growing strongly because of their low costs.
The two most optimistic scenarios (SSP1-1.9 and SSP1-2.6) assume the world would limit warming to around 2.7 degrees Fahrenheit (1.5 degrees Celsius)—a threshold scientists say could potentially allow us to prevent some of the worst effects of climate change.
The SSP1-1.9 scenario assumes humans would be able to stabilize the climate if we reach net-zero emissions by midcentury. In addition to net-zero, to have a strong chance of keeping temperatures from rising above 2.7 degrees Fahrenheit (1.5 degrees Celsius), we need to keep future emissions below 400 million metric tons of carbon dioxide. To put that into perspective, the world last year emitted 34.1 million metric tons of carbon dioxide, so we’re talking about 12 years of emissions, at current levels, probably less since emissions are forecast to increase over the next few years.
If, as expected, we fail to keep within the carbon budget or reduce emissions to zero, we would need to rely on carbon dioxide removal (CDR) technologies to extract carbon from the atmosphere and store it in reservoirs, the report says. And if we surpass the carbon budget by a large margin, we may need to use CDR at an even larger scale “to lower surface temperature.”
James Temple from Technology Review says in order to create the SSP1-1.9 scenario we will need to figure out a way to remove at least 5 billion tons of carbon dioxide a year by midcentury and 17 billion by 2100.
More harm than good?
These “technologies and techniques” would include mainly bioenergy carbon capture and storage (BECCS), which implies growing crops to suck up carbon from the atmosphere, using these crops as biofuels to produce energy, and capturing the greenhouse gas emissions resulting from producing that energy. The captured carbon would need to be stored in geological formations such as depleted oil and gas reservoirs or saline aquifers.
In addition to that, we would need to deploy “natural climate solutions”—a term used to describe the planting of trees to remove carbon dioxide from the atmosphere.
If that sounds complicated is because it is. Climate scientists say the large-scale implementation of CDR would be a huge challenge.
“The technologies to do this are still largely untested at anything close to the scales required,” noted Zeke Hausfather, a climate researcher working for the Breakthrough Institute.
Furthermore, although estimates vary, according to an analysis by Princeton students, large-scale deployment of BECCS would require up to 40% of global cropland.
“This means half the land of the United States would be needed simply for BECCS. This amount of land could lead to biodiversity loss and less food availability. Less food availability could lead to other negative impacts, such as the price of food increasing,” the analysis says.
We could potentially use other CDR techniques, such as hacking seawater through an electrochemical process so that it sequesters more carbon dioxide or using carbon sucking machines, but none of these methods have been tried on a large scale and some of them would require large energy inputs.
Ultimately, CDR techniques are largely untested, expensive, technically difficult, and could do more harm than good — the IPCC report warns that CDR may potentially have negative effects on “biodiversity, water, and food production.”
At least for now, it seems there are no shortcuts when it comes to tackling climate change and CDR is no replacement for slashing emissions.
“The urgency is, and has always been, stopping emissions first. A second line of solutions should include carbon removal, but equipped with a healthy dose of skepticism,” tweeted Dr. Jonathan Foley, the executive director of Project Drawdown.
