As we confront the sobering reality that 2024 marked the first year global temperatures exceeded the 1.5 °C threshold established by the Paris Agreement, recognizing the vital role of forests and trees in climate regulation has never been more crucial.
The cooling power of trees
Trees provide essential shade, reducing ground-level temperatures by 2–8°C in urban areas and up to 15°C in rural settings. This direct shading effect is particularly significant in mitigating the urban heat island effect, where cities typically experience temperatures 1–3°C higher than surrounding rural areas.
Evapotranspiration, the process by which water evaporates from leaves and surrounding soil, also contributes to cooling. As water changes from liquid to vapour, it absorbs heat from the surrounding air, effectively lowering the local temperatures. A mature tree can transpire up to 400 litres of water daily, creating a natural air- conditioning effect. This process absorbs significant amounts of heat energy, with studies showing that a single large tree can provide a cooling effect equivalent to 10 room-sized air conditioners operating for 20 hours per day.
The albedo effect of forests also plays a vital, albeit complex, role in temperature regulation. Tropical and temperate forests have low albedo compared to other land cover, meaning they absorb more solar radiation and contribute to cooling. Boreal forests, with their darker canopies, present a unique case where deforestation may lead to cooling due to strong surface albedo effects. In cold conditions, the snow-vegetation albedo effect dominates, causing boreal forests to warm the climate.
A view of the forest in Central Kalimantan. Photo by Nanang Sujana / CIFOR-ICRAF
Research has also highlighted the role of forests in generating biogenic volatile organic compounds, which can lead to aerosol formation. These aerosols can influence cloud formation and precipitation patterns, indirectly affecting both local and global temperatures.
Healthy forests serve as vital carbon sinks, with global forests currently absorbing approximately 7.6 billion tonnes of CO2 annually, equivalent to about 20% of human emissions. Tropical forests alone store an estimated 250 billion tonnes of carbon in their biomass. The capacity of forests to sequester carbon varies by age and type, with mature tropical forests absorbing about 2.4 tonnes of carbon per hectare annually.
Unfortunately, deforestation and climate change increasingly threaten the temperature-regulating effects of forests. Global forest loss not only reduces these cooling benefits but can create a feedback loop where higher temperatures lead to increased forest stress and mortality, potentially converting some forests from carbon sinks to carbon sources.
The impact of deforestation on global temperatures has been severe and well-documented. Between 2000 and 2023, the world lost over 130 million hectares of tropical forest. This devastating loss has contributed significantly to rising global temperatures, with deforested areas showing temperature increases of up to 4°C (and reduced rainfall… but this is another story) compared to nearby forested regions.
As temperatures rise, many forests face increased stress from drought and fires, potentially converting them from carbon sinks to carbon sources. For example, the 2019-2020 Australian bushfires released an estimated 830 million tonnes of CO₂, demonstrating how climate change can trigger devastating feedback loops.
The science is clear: forests and trees represent one of our most powerful natural tools for regulating global temperatures and mitigating climate change impacts.
Urgent action is needed on multiple fronts:
- Protect the remaining intact or near-intact forests
- Promote sound reforestation and afforestation initiatives
- Implement sustainable forest management practices
- Integrate forest protection and restoration into climate policies
- Support Indigenous forest communities as stewards of the land
The 2024 breach of the 1.5°C threshold should serve as a stark reminder that we must act decisively to protect and expand our forest resources. Their role in temperature regulation and carbon sequestration makes them indispensable allies in our fight against climate change.
Global forest cover has declined steadily since 2000, with primary forest loss particularly acute in tropical regions. While some countries have made progress in reforestation efforts, the net loss of primary forests continues at an alarming rate of approximately 3.8 million hectares annually. This loss correlates strongly with the accelerating increase in global temperatures, contributing to the breach of the 1.5°C threshold in 2024.
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