Reforesting and managing ecosystems have been proposed as ways to mitigate global warming and offset anthropogenic carbon emissions. Photo by: Pixabay

 

Natural solutions have been proposed to stop and reverse the steady rise in CO2 in the atmosphere. Theses natural solutions nclude planting a tree in our back yard or buying carbon credits, that finance the planting of millions of trees and restoring ecosystems

In a new study in the journal Global Change Biology authors provide their perspective on how well plants and ecosystems sequester carbon. Their analyses is based on 1163 site-years of direct eddy covariance measurements of gross and net carbon fluxes from 155 sites across the globe. The ability of individual plants and ecosystems to mine carbon dioxide from the atmosphere, as defined by rates and cumulative amounts, are limited by laws of physics and ecological principles. “Consequently, the rates and amount of net carbon uptake are slow and low compared to the rates and amounts of carbon dioxide we release by fossil fuels combustion. Furthermore, managing ecosystems to sequester carbon can also cause unintended consequences to arise”, said Prof. Dennis Baldocchi from University of California, Berkeley.

In this opinion piece, authors articulate a series of key take-home points:

– First, the potential amount of carbon an ecosystem can assimilate on an annual basis scales with absorbed sunlight, which varies with latitude, leaf area index and available water.

– Second, efforts to improve photosynthesis will come with the cost of more respiration.

– Third, the rates and amount of net carbon uptake are relatively slow and low, compared to the rates and amounts and rates of carbon dioxide we release by fossil fuels combustion.

– Fourth, huge amounts of land area for ecosystems will be needed to be an effective carbon sink to mitigate anthropogenic carbon emissions.

– Fifth, the effectiveness of using this land as a carbon sink will depend on its ability to remain as a permanent carbon sink.

– Sixth, converting land to forests or wetlands may have unintended costs that warm the local climate, such a changing albedo and soil moisture, increasing surface roughness or releasing other greenhouse gases.

Authors point out that they do not argue that planting forests and deep-rooted perennial grasslands or restoring peatlands and wetlands should not be part of the climate mitigation portfolio. Prof. Penuelas from CREAF-CSIC Barcelona argues that “Given the urgency of reducing carbon dioxide in the atmosphere, the relatively low potential of converting solar energy to stored carbon, the vast amount of land needed to be significant carbon sinks and the risk for unintended consequences, we want the reader to consider that political capital and resources may be better aimed towards more effective and immediate solutions, like reducing and eliminating carbon emissions that are associated with fossil fuel combustion”.

 

Reference: Baldocchi, D., Peñuelas, J. 2019. The Physics and Ecology of Mining Carbon Dioxide from the Atmosphere by Ecosystems. Global Change Biology 2019