With 2024 being on record as the hottest year, the first year global temperatures exceeded the 1.5 degrees centigrade (°C) threshold established by the Paris Agreement, scientists have recognised the vital role of forests and trees in climate regulation.

Global warming, climate change, drought, floods and destruction of forests today constitute the greatest challenges to humanity and nature. Few stories are more urgent – and global – than the destruction of the planet’s tropical rainforests.

Trees provide essential shade, reducing ground-level temperatures by 2-8°C in urban areas and up to 15°C in rural settings, according to the scientists. But how do forests protect us from climate extremes?

“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,” according to the Centre for International Forestry Research and World Agroforestry (CIFOR-ICRAF).

Writing in the CIFOR-ICRAF newsletter, Forest News, CIFOR Director-General Robert Nasi says evapotranspiration, the process by which water evaporates from leaves and surrounding soil, also contributes to cooling.

Cooling effect

“As water changes from liquid to vapour, it absorbs heat from the surrounding air, effectively lowering the local temperature. A mature tree can transpire up to 400 litres of water daily, creating a natural air-conditioning effect,” he explains.

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.

What Nasi describes as 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.

Also known as taiga or snow forests, boreal forests are the world’s largest land biome, characterised by cold, harsh winters and short, cool summers. They are dominated by coniferous trees like pine, spruce and fir. Boreal forests play a crucial role in regulating the global climate and are home to a diverse range of wildlife.

Research highlights forests’ role 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.

Scientists have also established that healthy forests serve as vital carbon sinks, with global forests currently absorbing approximately 7.6 billion tonnes of carbon dioxide (CO₂) annually, equivalent to about 20 per cent 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, says Nasi, adding: “Unfortunately, deforestation and climate change increasingly threaten the temperature-regulating effects of forests. Global forests loss not only reduces these cooling benefits but 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 forests.

This devastating loss has contributed significantly to rising global temperatures, with deforested areas showing temperature increases of up to 4°C compared to nearby forested regions. These regions have also recorded reduced rainfall.

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, according to the CIFOR chief. 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.
First, humanity must protect the remaining intact or near-intact forests. Second is to promote sound reforestation and afforestation initiatives, and third to implement sustainable forest management practices.

Indispensable allies

Fourth, there is urgent need to integrate forest protection and restoration into climate policies, and fifth to 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,” Nasi emphasises.

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.

Meanwhile, the fate of forests of the Amazon, the Congo Basin, and Southeast Asia continues to occupy the hearts and minds of researchers, journalists, communities, and ordinary people around the world.

Concerned, and at the very least, intrigued, the Rainforest Investigations Network (RIN) continues to seek answers to the challenge of how we live in harmony with the life that exists in these forests.

According to RIN Director of Environmental Investigations Gustavo Faleiros, this interest doesn’t always take into account the economic centrality that these regions occupy in our lives.

“We depend on the forests for food, comfort, and prosperity. Global production chains – such as soy, meat palm oil and rare minerals – have deep roots in tropical rainforests, affecting biodiversity and Indigenous communities,” Faleiros says.

In the year of COP30, he says, the first United Nations climate change summit to be held in the Amazon, in Belém, Brazil, it is likely that the significance of protecting the forest will finally get the attention it deserves.

RIN has announced another cohort of nine investigative journalists as fellows for the next 12 months covering topics such as the impacts of public policies that encourage the sustainable use of natural resources or, on the contrary, turbocharge the destruction of native forests.

More than 60 fellows and 300 grantees have been supported through RIN to keep the future of forests well-monitored.

Documenting forests

The complexity and interdependence of these rainforest ecosystems and other landscapes, including urban ones, are becoming increasingly evident and vital.

Scientists remind us that few stories are more urgent – and global – than the destruction of the planet’s tropical rainforests. RIN seeks to create an ecosystem of collaboration among journalists to follow the money and the many illegal practices and legal loopholes that enable industrial-scale deforestation.

RIN seeks to harness investigative reporting and cross-border collaboration to tackle stories at the intersection of climate change, corruption, and governance in the world’s three main tropical rainforest regions – Amazon, Congo Basin and South East Asia.