Avoided Conversion - American Farmland Trust

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Protecting farmland, protecting the climate

What we’re doing

Illinois case study

AFT partnered with The Conservation Fund to estimate the avoided greenhouse gas emissions from an agricultural easement on a 103-acre farm in central Illinois.

Climate change mitigation refers to reducing climate change by minimizing greenhouse gas emissions or enhancing the storage of carbon dioxide in soils, forests, and oceans. The Climate and Farms Under Threat teams at American Farmland Trust are working to estimate the mitigation benefits of conservation easements on agricultural lands that are under threat of development to non-agricultural uses and part of a buffer zone around already developed areas, e.g., “Saving Farmlands, Growing Cities.”

We studied an Illinois farm under an agricultural conservation easement with our partners at The Conservation Fund using modified methodology from the California Air Resources Board (CARB). We estimated that placing the 103-acre Illinois farm under an agricultural conservation easement potentially avoids (mitigates) over 19,000 metric tonnes (t) of carbon dioxide equivalents (CO2e ) in its first 30 years, equivalent to avoiding over 100 railcars’ worth of coal burned. The easement also avoids about 8 t of non-greenhouse gas air pollutant emissions in the same time period. The case study brief and full report are available here. Now, we are developing a calculator for estimating the climate benefits of past and future permanently protected farmland in the contiguous U.S.


Why this work matters

The agricultural sector is both vulnerable to and a potential solution for climate change. One way that communities can reduce greenhouse gas emissions is by protecting farmland.

Farmland converted to low-density residential use tends to be more energy intensive per household than smart growth urban development. This applies to agricultural conservation easements on properties that are under pressure of being converted to non-agricultural uses and are part of a buffer zone supporting in-fill (i.e., compact development in already developed areas). These easements protect the land that sustains us and help avoid the excess greenhouse gas emissions associated with low-density residential development.

Furthermore, agricultural conservation easements may help reduce pressure to convert grasslands to croplands. Between 2008 and 2016 about 1 million acres of U.S. land was converted to croplands every year, 88% of which was grasslands. Converting grasslands to croplands is detrimental to people and the environment in many ways including loss of habitat (above and below ground), infiltration and water storage capacity, and flood and drought mitigation capacity. In terms of climate change, grassland conversion to cropland means greater decay and loss of soil organic carbon and perennial root biomass carbon, meaning CO2e emissions. Avoided grassland conversion to cropland in the U.S. could mitigate 55-188 million metric tonnes of carbon dioxide equivalents (CO2e) per year, which is the equivalent of 9%-32% of the U.S. ag sector’s emissions in 2020.

Satellite imagery of interfacing farmland and development in Illinois (left), Colorado (middle), and Oregon (right). Source: Google Maps.

This work builds on a legacy of innovation at AFT

Researchers at the University of California, Davis published a report in 2013 showing developed land in Yolo County, California emitted about 70 times the greenhouse gases per acre compared to emissions from irrigated cropland. A 2015 study by AFT found that acre for acre, developed land in California emits about 58 times the greenhouse gases emitted by cropland. These studies led the CARB to make farmland protection through agricultural conservation easements part of their greenhouse gas mitigation strategy. In 2017, AFT published a similar report focused on farmland vulnerable to development in New York, which found that New York’s developed land emits about 66 times the greenhouse gases per acre emitted by farmland. These studies led CARB to make farmland protection through agricultural conservation easements part of their greenhouse gas mitigation strategy.

How it works

To quantify the climate benefit of an agricultural conservation easement, AFT adapted CARB’s Agricultural Lands Conservation Easement Quantitative Methodology (2020), which was updated in 2022. The CARB method takes a refined approach to quantifying the climate benefits of easements compared to the studies mentioned above. The previous studies compared the per-acre greenhouse gas intensity of agricultural to developed land uses. The CARB and AFT methods look at the difference between the transportation and energy use efficiencies and soil organic carbon loss between in-fill of cities and low-density residential development on the easement site. You can read more about the methodologies from CARB and the 2022 AFT case study.

Not all agricultural conservation easements have quantifiable climate benefits. The CARB methodology assumes that protecting farms on the urban fringe will result in more compact development without reducing the number of housing units built. Climate benefits will only be realized if the avoided development that occurs when protecting agricultural land does not then occur on a different undeveloped property. The CARB and AFT methods thus look at the climate benefit from easements supporting in-fill of already developed areas.

A farm neighboring a housing development in New York. Photo by Jim Newton for AFT.


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