It is a well-established fact that forests play a key role as major global carbon sinks and are key to climate change mitigation. They are the largest land-based absorbers of carbon, removing around 7.6 billion tonnes of carbon dioxide (CO2) from the atmosphere annually. Therefore, can planting trees help us reach net zero?
However, the way we utilise forests is also a significant cause of climate change, with compound effects. Deforestation accounts for roughly 12.5% of all global emissions, simultaneously reducing the trees available to absorb CO2.
Restoring degraded forest areas is part of the solution, as is sustainable forestry. This industry ensures areas always have trees growing, while substituting wood for other raw materials reduces emissions and sequesters carbon in end products.
Forests are not only important in terms of carbon sequestration though. They provide a host of climate benefits.
For one thing, rainforests are integral to keeping the planet cool. They remove CO2 from the atmosphere, slowing the effects of climate change, and have additional cooling impacts including evaporation and evapotranspiration. A 2022 study by the World Resources Institute notes that evapotranspiration processes “function as natural air conditioning, cooling Earth’s surface and near-surface air”.
The study details how forest removal increases local temperatures and disrupts rainfall patterns, compounding the local effects of global climate change. This is so pronounced in the tropics, says the study, that conserving tropical forests can have a 50% larger impact on reducing global temperatures than when considering only the amount of carbon they absorb.
Additionally, the unevenness of forest canopies affects wind speed and creates turbulence, lifting heat and moisture away from Earth’s surface with a cooling effect. Pollen and other aerosols (tiny particles) released by forest trees, meanwhile, interact with the atmosphere in complex ways.
The study highlights that non-carbon forest-climate interactions illustrate how climate change is not just about greenhouse gas emissions and global average temperatures. It emphasises that the additional cooling effects of forests “must be integrated into governments’ climate policies to fully reflect what forests do for the planet”.
A stabilising effect
Forests stabilise the climate in many ways, acting as storehouses for biodiversity (which guards against disease and species extinctions) and stabilising rainfall. They also buffer the impacts of increasingly severe storms and floods. Tree canopies can, for example, slow storm rainfall, trapping up to 30% of the water to decrease the impact of flooding and reduce the risk of landslides. This water then evaporates back into the atmosphere.
Forests also help to regulate river ecosystems that supply drinking water to human populations.
Mangrove forests are highly effective at sequestering carbon and provide a host of ecosystem benefits. They are also critical in protecting tropical coastlines from storm damage.
The increasing importance of urban forests
Urban forests can impart multiple benefits to city populations.
Satellite data has shown that trees reduce the summer surface temperature of some central European cities by up to 12°C, compared to a negligible effect from green spaces without trees.
Trees not only provide shade, but their impressive cooling powers are reinforced at nighttime. This is because they reduce solar radiation absorption and the heat retained in built structures to keep temperatures lower.
The cooling effects of urban forests have a secondary benefit: they reduce the energy required and carbon emitted to cool indoor spaces.
Urban forests also increase the flood resilience of cities, as trees provide more permeable land to absorb rainwater, improve soil integrity, and break up large areas of impermeable concrete, tarmac, and paving.
Healthy forests’ ability to remove harmful airborne and waterborne pollutants and reduce the bioaccumulation of contaminants is yet another boon.
Lining the path to net zero with trees
Trees will clearly be crucial to offsetting the effects of climate change. Afforestation, reforestation, and natural forest regeneration will significantly aid the quest to reach net zero emissions.
Reducing deforestation and promoting sustainable forestry activities are also essential to the process. Halting the loss and degradation of natural systems and promoting their restoration can potentially contribute over one-third of the total climate change mitigation required by 2030.
Both larger forested areas and larger trees provide increased benefits, so it is vital to conserve our great ancient forests. We should also be greening our cities with urban forests and incorporating vegetation into urban architecture. Community tree planting also actively contributes to efforts and educates people on the benefits of trees.
In these ways, we can line the path to net zero with trees, and spend the journey enjoying the shade, clean air, and cooling effects of forests.