In the collective imagination, trees slow down global warming by storing CO2 emitted by humans into the atmosphere. But, more and more scientific work suggests that things might not be so simple.
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For limit global warmingwe must reduce our emissions of CO2. The challenge is big. Because, despite the threat, our society is struggling to review its consumption patterns. So, some imagine solutions based on the capture of CO2 atmospheric. By planting a large number oftrees, especially. Trees meant to absorb carbon dioxide. Indeed, they need it to live. By photosynthesis, they transform CO2 in energy. But they also use it to make wood and roots, a way of storing atmospheric carbon dioxide for several decades. Especially since a 2011 study claims that trees absorb more carbon than they emit through respiration and decomposition.
For the first time in 2015, the Paris agreement provided that countries should strive to offset their carbon emissions, not only by protecting their existing forests, but also by planting new forests. China plans to to plant trees over an area four times the size of the UK. And in California, forest owners can sell credits to CO emitting companies2. In 2017, a study estimated that the world’s forests could contribute more than a third of the “emissions reduction” needed to keep warming below 2°C by 2030.
Conflicting study results
Nevertheless, some scientists urge caution. According to them, forests have climate impacts which remain uncertain. Researchers have known for a long time that the leaves of trees absorb more light from Sun than fields or bare ground. Forests therefore reflect less solar energy back into space, which leads to global warming. A phenomenon that is mainly observed at high latitudes and in mountainous or dry regions.
Furthermore, it now seems certain that trees constantly exchange with theatmosphere. And they emit a host of chemicals, some of which could contribute to global warming. Data collection campaigns should shed light on the subject. But one study, for example, points to theisoprene who, by reacting with the nitrogen oxides of the’aircan formozonea powerful greenhouse gas. Isoprene is also found to extend the life of atmospheric methane. However, it must also be recognized as having a cooling effect when it blocks sunlight by promoting the production of aerosols. Thus, the study concludes that the transformation of forests into land agriculture during the industrial era would have had little overall impact on the weather.
Uncertainties to remove
Other work published in 2017 stirred up confusion by reporting that trees also emit large amounts of methane. Half of the total emissions of the Amazon. However, these results still need to be clarified.
The debate, however, is on, and researchers are turning to increasingly large and comprehensive computer models and datasets in hopes of determining the impact of forests on the global climate. In Europe, a study concluded in 2018 that no forest management scenario could have a significant impact. In the United States, on the other hand, it could be interesting to plant trees on the west coast and in the regions east of the Mississippi in particular.
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