More trees – dark…

Jakub: The notion of more trees as a measure to address climate change has been around for a while. This idea stems from the fact that trees readily absorb CO2 from the air and effectively fix it in biomass. I have thought that trees were crucial in keeping global temperatures to acceptable levels. Until I came across an article by Bala et al. (2007). ..

The authors of this study modelled the overall effects (not only photosynthesis, but also physical and other chemical properties) trees have on temperature. They found that the impact of forest on air temperature varies across latitudinal bands. Their results show that trees in high latitudes actually exacerbate rather than ameliorate climate change because of physical properties of trees. Lower albedo of trees compared to bare soil causes more solar radiation to be absorbed. This results in significant warming which is of a higher magnitude than cooling effect of photosynthesis by those trees.  They propose that further afforestation of high and mid-latitudinal bands will bring no additional benefit in terms of climate change mitigation with some high-latitude locations in Russia experiencing up to 6oC decline after the place has been deforested. Conversely, the impact of trees in tropical regions is opposite. Although deforestation would bring some benefit in terms of decreased air temperature, trees in tropics transpire to a high degree and are thus responsible for cloud cover, which has high albedo and therefore reflect large proportion of incoming insolation. This ultimately results in net cooling effect of trees in tropics.

This article was an interesting read because it confronted my previous belief that we should plant more trees wherever is possible. It showed me that it is a much more complicated topic and many more factors will therefore have to be considered when determining the role of trees in climate change mitigation, especially in specific regions.

Bala, G., Caldeira, K., Wickett, M., Phillips, T. J., Lobell, D. B., Delire, C., & Mirin, A. (2007). Combined climate and carbon-cycle effects of large-scale deforestation. Proceedings of the National Academy of Sciences, 104(16), 6550-6555.


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