To keep global temperature increases below 1.5o Celsius — the threshold for avoiding the worst consequences of climate change — the world needs both rapid reductions of new climate pollution and removal of existing carbon dioxide from the atmosphere.
Increasing the amount of carbon stored in cropland soils is one pathway for carbon dioxide removal, and it has gained traction over the past several years in voluntary agricultural carbon markets and U.S. climate policy discussions. The idea is that farming practices, such as using cover crops, will add carbon to agricultural soils, and thus help slow climate change.
Scientists agree that agricultural soils can be part of the climate solution, but their estimates about when and how much carbon agricultural soils can store — and thus the magnitude of climate mitigation that soils could deliver — vary widely.
To better understand areas of agreement and disagreement, Environmental Defense Fund asked American University’s Institute for Carbon Removal Law and Policy to survey 31 soil carbon scientists working in academia, nonprofit organizations and government agencies.
Here is what they found:
1. Improving soil health is low risk, high reward
All respondents agreed that agricultural practices, such as crop rotations and conservation tillage, have the power to improve soil health.
Of the scientists surveyed, 90% agreed that managing soils to improve soil health is low risk, and EDF would argue high reward. This is a no-regrets approach that is likely to improve soil fertility and yield resilience and prepare farms to better withstand extreme and variable weather.
Policymakers and agricultural practitioners have strong scientific backing to focus on improved soil health.
2. Soil carbon accumulation remains an uncertain climate solution
For 75% of scientists, there isn’t comprehensive enough scientific understanding — across farm management practices and biophysical conditions — to accurately predict the quantity, pace and durability of soil carbon accumulation and storage in croplands.
Furthermore, survey respondents worried about the potential for trade-offs between one climate pollutant and another. For example, some interventions could boost soil carbon but also increase emissions of nitrous oxide, one of the most potent greenhouse gases. According to 85% of scientists, a singular focus on soil carbon risks causing unintended consequences for climate change and ecosystem health.
As a result, 80% of respondents recommended that agricultural economic incentives should focus on widespread and durable improvements in soil health, but should be conservative about expectations for climate change mitigation.
3. But scientists see future potential worth pursuing
Despite current uncertainties, a majority of scientists see soil carbon as a promising climate mitigation solution.
Sixty-five percent of respondents agreed that the promise of soil carbon is large enough to warrant major investment in further research and data collection about the conditions under which net greenhouse gas reductions — or soil carbon gains minus new emissions of other greenhouse gases occur.
In addition, 80% of respondents saw value in strengthening information exchange between researchers and agricultural practitioners, including landowners, to help advance efforts to protect existing soil carbon stores and accumulate new soil carbon.
Taken in total, the scientists’ responses reflect valid concerns with soil carbon as a climate mitigation strategy today and measured optimism about the role soil carbon can play in the future.
Many scientists at EDF and elsewhere are hard at work determining the realistic climate potential of cropland soils. While there isn’t yet a strong enough scientific understanding to support a robust, credible voluntary market for agricultural soil carbon, protocol developers and credit buyers have a host of other climate investment opportunities to consider.