Despite being a promising and widely considered approach, a new study finds that forestation of Earth’s vast drylands would do little to slow climate change, researchers report. The findings show that although smart dryland forestation can be an important tool in some respects, its limited short-term climate benefits argue that it cannot be a substitute for rapidly reducing emissions. Growing forests sequester carbon. Leveraging this ability through forestation, which includes both afforestation to create new forests where there was no previous tree cover and reforestation to restore depleted forests, has been widely proposed as a promising approach to counteract increasing carbon emissions to mitigate ongoing global climate change. However, the actual climatic benefits of forestation are uncertain because increased tree coverage reduces the landscape’s albedo or its ability to reflect solar energy, which, depending on the scale, could result in local or global warming effects. This is particularly true for the dryland regions covering nearly 40% of the global land area where the albedo warming effect of afforestation could strongly outweigh any cooling effect from carbon sequestration as reflective desert land is converted to darker energy absorbing forest cover. To better understand the possible climatic benefits for dryland forestation, Shani Rohatyn and colleagues performed a high-resolution spatial analysis of global drylands and simulated the climatic effects of afforestion in these regions. Through their investigation, Rohatyn et al. identified 448 million hectares suitable for forestation and sequestration potential of more than 32 billion tons of carbon over the next 80 years. However, the authors found that this would do little to slow our warming climate. Accounting for the significantly decreased albedo in these regions, the authors show that the cooling effect of forestation of this vast area would only amount to that of a decrease of about 1% of projected greenhouse gas emissions under medium-emissions and business-as-usual climate scenarios. Despite this, Rohatyn et al. note that carefully planned and implemented dryland afforestation could provide other, more local benefits and potentially longer-term climate mitigation beyond their 80-year evaluation period.
Limited climate-change mitigation potential through forestation of the vast dryland regions
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