Environment: Assessing the impact of forestation on global climate patterns

Large-scale forestation projects may alter the Earth’s energy balance, affecting both global atmospheric and ocean circulation patterns, suggests a modelling study published in Nature Communications. The findings indicate that massive tree planting programs, to help mitigate the effects of climate change, may have potentially unforeseen influences on global climate.

Large-scale forestation (afforestation and reforestation) projects have been proposed to mitigate climate change and its related impacts through carbon storage, and there is popular support for this idea. Both forestation and deforestation are known to affect the carbon cycle and CO2 concentrations, influencing global and local climates. There has been debate about the carbon-storage potential of forests and the local and global thermodynamic impacts of reforestation. However, due to complexity, effects on weather and climate patterns remain unresolved and are not yet considered in planning and policy.

Raphael Portman and colleagues performed multi-century coupled climate model simulations where preindustrial vegetation cover is either completely forested or deforested, and atmospheric CO2 levels are kept at constant preindustrial levels. The authors indicate that their models show that global-scale forestation and deforestation may affect the global energy balance, having opposing effects which strengthen, weaken or shift air circulation patterns, ocean currents and convection cells. In this way, both forestation and deforestation may cause changes in regional precipitation, temperature, cloud cover and surface wind patterns worldwide.

The authors caution that their findings should not be used as a general argument against forestation, as it has benefits including in relation to air quality, biodiversity and nutrition amongst others. They indicate that the design of large-scale forestation projects needs to take into account potential unforeseen influences on climate in regions far away from the forested area.