Forests are More Than Carbon Sinks; They Stabilise the Planet

Forests, having the remarkable capacity to sequester carbon, are crucial in the battle against climate change. However, their value extends far beyond this.

A wealth of research reveals that forests engage with the atmosphere in myriad ways beyond mere carbon sequestration. They influence rainfall patterns, temperature, and local and global climates, offering a wealth of non-carbon benefits equally significant in the fight against global warming.

The World Resource Institute (WRI) article delves into four specific non-carbon processes in forests that are beneficial to the climate:

1. Albedo – a measure of how much of the sun’s energy is reflected back into space. Forests’ dark green cover absorbs more energy than snow cover, crops, or bare soil, warming the air as leaves release that heat.
2. Evapotranspiration – the trees’ process of releasing moisture into the air and producing a cooling effect akin to natural air conditioning.
3. Surface roughness—the unevenness of a forest canopy—affects wind speed and turbulence, helping lift heat and moisture away from the Earth’s surface.
4. Aerosols—released by forests, such as pollen and chemical compounds—interact with the atmosphere in complex ways, changing ozone and nitrate concentrations and affecting the colour of clouds.

Studies show the effects of urban forest and tropical forest cooling

The transformation of urban areas into green spaces can effectively combat the urban heat island (UHI) effect. A study demonstrates that trees and shrubs in urban areas, known as urban forests, can significantly lower temperatures. Their finding reveals that urban forests can potentially reduce temperatures by an average of 1.6 °C, offering an effective solution to cities’ heat challenges.

According to a 2022 study published in Frontiers, tropical forests cool the world by more than 1°C and offer other benefits, like increasing rainfall and shielding people and crops from deadly heat. Tropical forests’ cooling effect comes from their capacity to capture and store atmospheric carbon, and around a third of their cooling effect comes from other processes like the release of water vapour and aerosols.

The study notes that the cooling effect of tropical forests, especially during the hottest season, should be valued, in addition to their role in curbing emissions and the direct benefits that forests offer to local communities.

Another study published in AGU in 2024 shows that a century of reforestation in the Eastern United States has averted warming, contrasting with the warming trends across North America during the same period.

The Eastern United States (EUS) has undergone extensive reforestation over the last century. At the same time, there has been no warming over a large portion of the EUS during this period, which raises the question of whether reforestation has curbed the historic pace of warming in the region.

Both ground- and satellite-based observations indicate that EUS forests cool the land surface by 1–2°C annually compared to nearby surfaces with short-stature vegetation. During midday in the growing season, surface cooling is 2–5°C, and forests aged 25–50 exhibit the strongest cooling effect. The surface cooling extends to the near-surface air, with forests reducing midday growing-season air temperature by up to 1°C.

These findings indicate that reforestation has a cooling effect on the surface and near-surface air temperature, especially during midsummer periods when high temperatures can most harm the EUS and likely contribute to the region’s slower warming pace.

However, the study notes that its findings may not apply to all temperate regions or to all strategies, such as afforestation. For instance, reforestation in boreal areas causes changes in albedo and evaporation dynamics that could lead to warming in the long term. Hence, the implementation of Nature-based Climate Solutions (NbCS), such as reforestation, must be undertaken with consideration to avoid unintended consequences that could lead to net warming.

Overall, the study provides compelling evidence of the biophysical climate benefits of reforestation in the EUS and establishes a clear relation between land-cover changes and temperature shifts observed throughout the 20th century. It also emphasises the potential for reforestation to provide local climate adaptation benefits in temperate regions such as the EUS, highlighting the importance of biophysical co-benefits of nature-based climate solutions.

As the growing body of research reveals, forests offer a range of climate services in addition to their ability as powerful carbon sinks. Forests can influence local and global weather and climate, which, when effectively harnessed, have the potential to stabilise the climate, which is critical as we face the growing threats from climate change.

The WRI offers some practical tips on how policymakers can take full advantage of the full range of forest climate services by integrating them within existing mandates and policies.  For example, countries in the tropics can incorporate the benefits of forests and non-carbon cooling into their NDCs. The UNFCCC’s Warsaw Framework for REDD+  also incentivises countries to preserve their forests and allows them to account for their avoided CO2 emissions if they don’t engage in deforestation. Forests’ ability to affect regional rainfall patterns, where deforestation in one country affects the rainfall patterns in another, can lead countries to establish a mechanism to monitor, collect data, and model the impacts of forests to inform policies.

Lastly, countries can remove deforestation from commodity supply chains in partnership with NGOs and private sectors, such as the Protect, Conserve, Include program in Mato Grosso, Brazil.