Whoops! I apologize, but the article included in our newsletter, Soil Carbon & Climate Change was a bit misleading in its description, although it did spark some great conversation among many of my peers. Check out one of their responses below along with a better description of the article from Science journal. Sorry about the mishap, but thanks for understanding!
Best,
Jeff
From Whendee L. Silver Professor of Ecosystem Ecology and Biogeochemistry and Rudy Grah Endowed Chair in Forestry and Sustainability, Department of Environmental Science, Policy, and Management, UC Berkeley:
The He et al. paper points out that the large models don’t yet incorporate some of the important mechanisms of ecosystem carbon cycling. The goals of the He et al. (2016) paper were to explore and test the assumptions made by Earth Systems Models (ESMs) with regard to changes in soil carbon stocks with elevated CO2 concentrations. ESMs integrate large-scale processes in the biosphere (including land, ocean, ice, and atmosphere) to predict patterns in regional and global climate using a variety of scenarios (i.e. different levels of elevated CO2). These large, complex models often as yet do not capture detailed process-level information of modeled components. The He et al. study focuses on the inability of a current suite of ESM models to capture mechanisms driving soil carbon cycling in response to elevated CO2. They focus on the worst case scenario (RCP 8.5 – the most rapid and extreme rates of greenhouse gas emissions with minimal mitigation).
The He et al. paper uses empirical soil radiocarbon (14C) data to show that the ESMs are as yet unable to accurately represent soil carbon cycling at a global scale. Soil radiocarbon analyses are a form of carbon dating that allow us to estimate the turnover time, or residence time, of carbon in the soil. It is important to note that the radiocarbon technique has its own set of assumptions and limitations, importantly that a small amount of very old carbon can bias the overall age of the material being measured, making all of it appear older than it is. The paper also assumes that the sites sampled are in steady state, which is unlikely given some of the other assumptions in the same paper.
Neither the ESMs nor the He et al. analysis consider the role of agricultural and grassland management on soil carbon storage (differentiated from land cover change such as deforestation). This is an emerging area in the modeling arena, and will undoubtedly improve the accuracy of the models.
Thus, the conclusions of He et al. have no bearing on the potential to increase soil carbon sequestration and help mitigate climate change via improved land management. It is also important to note that not all carbon needs to be stored in long-lived carbon stocks to have a positive impact on the atmosphere. As long carbon inputs exceed carbon outputs, there will be less CO2 in the air. It is possible, based on existing data and models, that the size of young and intermediate-aged pools could increase for many years, particularly as a result of improved management.
A key finding in the He et al. paper is that elevated CO2 alone may lead to smaller increases in soil carbon than previously thought. Thus mitigation of climate change requires active and rapid improvement in land management globally.
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