We’ve all been hearing a lot more about carbon in our news feeds, at field days, and at the coffee shop. A lot of the focus is on what individual farmers can do with their soils and how that contributes to the nation’s greenhouse gas footprint.
But in between the individual and national levels, we can also look at how communities and watersheds can be a part of solving climate change.
American Farmland Trust, where I am a scientist, has developed the Carbon Reduction Potential Evaluation (CaRPE) Tool in collaboration with USDA Agricultural Research Service to help communities and states set achievable targets for climate change mitigation from their ag sectors. CaRPE pulls together the best available science on greenhouse gas emissions, reductions, and soil organic carbon sequestration on US farmland to produce carbon reduction estimates – such as this recent estimate at the national scale – and guide investments in climate-smart agriculture.
For those of us who think global and act local, CaRPE provides county-specific estimates of past and future greenhouse gas mitigation potentials from the adoption of soil health conservation practices in cropping and grazing systems – practices that often also have benefits for water.
CaRPE pairs two publicly available datasets. The first is the US Census of Ag, conducted every five years, which provides county-based data on acres in different production systems and the adoption of cover crops and reduced- and no-tillage.
The second is COMET-Planner, which provides county-level estimates of the carbon sequestration and greenhouse gas impacts of the adoption of NRCS conservation practices. (If you’re interested in estimating the greenhouse gas and soil carbon footprint of an individual farm or ranch rather than a whole county, COMET-Farm is the tool for you.)
These estimates are practice-specific and account for differences in soils, climate, and production systems. CaRPE uses the practice adoption acreages from the Census and the climate impacts from COMET-Planner to calculate estimates for the climate impacts of current and future practice adoption for your county.
As you can see, these values are provided at the county level rather than at the watershed level, which I know is going to be a sticking point for The Confluence readers! I have some thoughts on that, which I will share later.
Let’s look at an example of how to use CaRPE. Let’s say we want to explore how cover crops in Iowa County, Wisconsin could help mitigate carbon emissions.
The most recent Ag Census for which data are available was in 2017. In 2017, 7.9% of cropland acres in Iowa County had a cover crop, which is greater than the state rate of 6% adoption. Assuming 10% of the cover crops were legumes and 90% were non-legumes, CaRPE estimates that those cover crops in Iowa County reduced carbon emissions by about 1700 metric tonnes of carbon dioxide equivalents (t CO2e) per year, the equivalent of avoiding about 9 railcars’ worth of coal burned (EPA 2022).
That’s nice, but how much could we reduce carbon emissions if we reached a 30% adoption rate in Iowa County? According to CaRPE, that would be about 6,470 t CO2e per year or about 35 railcars’ worth of coal not burned.
With CaRPE, a county-based organization, such as a Farm Bureau chapter or a Soil and Water Conservation District, could set a data-driven climate mitigation goal and date for achieving that goal.
Looking ahead, this spring we plan to provide a video tutorial on how to use CaRPE. Look for that here. We’re also submitting a proposal to host a professional development session on CaRPE at this year’s Soil and Water Conservation Society conference in August.
In 2024, USDA will release the results for the 2022 Census of Ag, which will be incorporated into CaRPE.
On our wish list for the future of CaRPE are a new set of N2O emission reduction estimates for conservation practices, including more precision nitrogen management scenario options. Currently, CaRPE includes some N2O estimates but mainly focuses on carbon (as you can tell from its name!). This addition might also allow us to estimate nitrate leaching, which would help tie together the climate and water quality co-benefits of soil health practices.
Also on our wish list is incorporating annual, county, and watershed scale measurements of cover crop and reduced- and no-tillage adoption using data from publicly available remote sensing imagery via OpTIS (Operational Tillage Information System).
If you have questions about using CaRPE, suggestions for improvement, or an example of putting CaRPE estimates to use, I’d love to hear from you: email@example.com.
I also encourage you to check out these two-page briefs on climate mitigation potential for several states, including Illinois and Michigan, that AFT has developed to get a sense for how CaRPE results could be used locally to advocate for climate-smart agriculture goals.
Header photo by Rebecca Drobis for American Farmland Trust.