Climate change stands as one of humanity’s greatest challenges, with melting ice caps, rising sea levels, and extreme weather events, such as droughts and hurricanes, becoming increasingly widespread. The blame for this lies with the rising greenhouse gases, which insidiously absorb and trap the sun’s heat radiating from the surface, preventing it from reflecting into space and causing global warming.
Trees excel at sequestering carbon dioxide – a form of greenhouse gas – in the atmosphere and locking it away in their biomass, which they then use to turn into sugars to create energy for their survival. Tree-planting has thus undoubtedly gained traction as a strategy to combat global warming over the years. Many initiatives are in place to ambitiously mobilize efforts for mass tree-planting, such as The Bonn Challenge, which commits to restore 350 million hectares of land by 2030 alongside 61 committed countries, and The Northern Forest, which seeks to plant 50 million trees around five cities in the UK, including Sheffield.
However, the study led by Dr James Weber from the University of Sheffield’s School of Biosciences and published this year on February 22nd in the Journal Science, casts doubt on the efficacy of relying on tree-planting endeavors to fix our warming Earth.
By utilizing high-performing computational technology to stimulate global forest expansion, the study sheds light on two important issues that undermine the effectiveness of tree-planting initiatives.
Firstly, trees have dark hues – or at least relative to snow and grassland – which tend to absorb heat and diminish the Earth’s surface reflectivity, or albedo. This effect is particularly pronounced in places with temperate climates, such as the UK, Western Europe, Canada, and certain parts of the US, which would normally already have high albedo because of the seasonal snow cover. Tropical regions that experience perpetual warmth are less affected by this phenomenon.
Secondly, trees emit volatile organic components (VOCs), which can influence atmospheric methane and ozone, both of which are greenhouse gases. VOCs increase methane levels by suppressing a powerful agent known as hydroxyl radical, while their influence on ozone depends on regional factors such nitrous oxide (NO) availability, with ozone being produced at sufficient levels of NO and destroyed at high levels. However, VOCs can also undergo chemical changes to form scattering aerosols, which help reflect the sun’s radiation and influence cloud formation, partially offsetting the albedo effect.
These combined issues, statistically speaking, have the potential to nullify the impact of carbon emissions reduction by tree-planting by as much as a third and result in a net increase in temperature.
Nevertheless, Dr Weber and his team highlighted that integrating tree-planting with other measures, like reducing carbon emissions and pollutants, can negate its negative effects. This study thus emphasizes the importance of a holistic approach, including accounting for regional discrepancies, to maximize the effectiveness of large-scale tree planting in mitigating climate change.