In April 2019, Environmental Entrepreneurs (E2) hosted a farming carbon capture webinar and then, in conjunction with The Energy Mix, published a report on the proceedings. The premise is straightforward. Better farming techniques with potentially some additional biotechnology will increase the capacity of tilled soil to retain carbon.
The promise is not so straightforward. Their claim of a potential 130 billion tons of CO2 or roughly 65 ppm is surrounded by so many stated and unstated provisos that while it will get hopeful headlines, it’s not a good claim to repeat.
E2 is a Washington DC-based “national, nonpartisan group of business leaders, investors, and professionals from every sector of the economy who advocate for smart policies that are good for the economy and good for the environment.” The Energy Mix is a “Canadian non-profit that promotes community awareness of, engagement in, and action on climate change, energy, and post-carbon solutions.” Both are credible organizations doing valuable work; this is not a slight on their efforts in any way.
The 130 billion tons pertains the amount of CO2 lost from the soil due to excessive tillage practices since the beginning of industrialized agriculture per good quality research. That number isn’t in doubt, and it does equate to 65 ppm.
The report gets more nuanced the more you read it as well. They aren’t always overstating the potential. A key message is somewhat buried near the end of the summary:
This is the catch-and-release problem of all biological capture mechanisms. While biological processes do eventually sequester CO2 permanently, the majority is released in a variety of ways back into the atmosphere.
The pathway to permanent sequestration using standard soil mechanisms is glomalin:
Glomalin is a glycoprotein produced abundantly on hyphae and spores of arbuscular mycorrhizal (AM) fungi in soil and in roots. Glomalin was discovered in 1996 by Sara F. Wright, a scientist at the USDA Agricultural Research Service. The name comes from Glomales, an order of fungi.
The challenge with the glomalin pathway is that it’s slow. Radiocarbon dating of soil carbon has found that it’s six times older than previously thought. If the majority of CO2 comes out of the soil rather than being sequestered, and it takes hundreds or thousands of years for the process to sequester the excess, this is too slow.
It’s worth looking at agriculture’s emissions in more detail. The UN’s Food and Agriculture Organization (FAO) performed a wide-ranging study published in 2014. It’s worth looking at where emissions come from in agriculture and whether soil carbon capture is the low-hanging fruit.
The analysis shows increases in emissions of agriculture (from 4.6 to 5.0 Gt CO2 eq yr-1 in 1990s and 2000s; 5.3 Gt CO2 eq yr-1 in 2011), decreases in deforestation rates (from 4.6 to 3.8 Gt CO2 eq yr-1 in 1990s and 2000s; 3.7 Gt CO2 eq yr-1 in 2010), and decreases in forest sinks, albeit with a reversal since the mid-2000s (from -2.9 to -1.9 Gt CO2 eq yr-1 in 1990s and 2000s values; -2.1 Gt CO2 eq yr-1 in 2010).
We’re at about 5 gigatons of CO2-e per year, but 785 megatons of that are solely from energy used for transportation and electricity.
That’s a 16% reduction in emissions that’s viable with today’s technology, and some of it is already occurring with widespread deployment of wind and solar generation. A very large portion of agricultural emissions could be eliminated annually, which is better than trying to draw down CO2 very, very slowly after it’s emitted.
Similarly, there’s another chart from the FAO report worth considering.
There is a reason why people talk about beef consumption as a concern when it comes to climate change. That sector alone is responsible for over 50% of emissions. A great deal of this is subject to reductions simply by pasture-raising animals instead of using feedlots, along with commensurate consumption taxes on high-CO2e beef. But a great deal of that involves changing human behavior, so it’s unlikely to be popular or occur quickly. The energy use is a better lever for reductions.
The last point to be concerned about is the ethanol example. In the USA, that turned into a very large subsidy for a limited reduction model with downsides. While recent studies show that emissions are at 39% to 43% of gasoline emissions — much better than the 21% reduction that’s dominated policy discussions since roughly 2010, electric vehicle emissions are much lower. The energy used to create ethanol, if used as electricity in an EV instead, would carry it much further for lower emissions.
If farming carbon capture approaches are incented solely on the catch-and-release model, then only a small value will be achieved, likely at a significant expense. It’s quite likely that this will be a popular policy regardless in democracies, as rural votes have significantly more power than urban votes in the large majority of democratic countries, and buying votes is a time-honored tradition in politics.
Present projections of the Earth’s capacity to naturally sequester carbon suggest that in 2-3 centuries all but 20% of emitted CO2 would be eliminated if we stopped contributing now. That last 20% will be intransigent however, so increasing how else we can draw down CO2 will be important, and the time frame may not be as critical. Farming carbon capture approaches have value beyond CO2 as they also tend to reduce soil erosion and depletion, so they are well worth pursuing.
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