Climate change - the value of tropical forests in controlling temperature

Tropical forest - Shutterstock

Most research and published articles on forests and global warming focus on the capacity for carbon sequestration as well as current retained levels of carbon within the forests. This is particularly relevant when considering the climate effects that occur when forest cover, structure and composition change as a result of deforestation. However there are more factors to consider with the role of tropical forests than just carbon sequestration.

Scientists from the University of Virginia, USA, the Woodrell Climate Research Centre, USA and the International Centre for Tropical Agriculture, Colombia have published compelling research this year on the role of tropical forests in regulating temperature, environment and removal of CO2 emissions. Forests are responsible for much of the carbon removal together with terrestrial ecosystems which amount in total to 29 % of annual carbon emissions. As the researchers have commented "the biophysical effects of forest cover can contribute significantly to solving local adaptation challenges, such as extreme heat and flooding, at any latitude. The carbon benefits of forests at any latitude contribute meaningfully to global climate mitigation".

Key aspects of the report have found -

• forests contain over 800 PgC (petagrams of carbon) almost as much as currently stored in the atmosphere,
• tropical forests have one of the fastest carbon sequestration rates per unit land area,
• forests impact on climate directly through controls on three main biophysical mechanisms: albedo (the fraction of light that a surface reflects), evapotranspiration (ET) and canopy roughness, 
• in the tropics, where ET and roughness are dominant biophysical drivers, forests cool the lower atmosphere and provide water vapour to support cloud formation,
• forests partition incoming solar radiation between latent heat and sensible heat: "Deep roots and high leaf area make forests very efficient at moving water from the land surface to the atmosphere via ET, producing latent heat. Thus beneath the forest canopy, the sensible heat flux and associated surface temperature are relatively low especiually the gorwing season when ET is high",
• the role of forests in maintaining critical habitat for biodiversity is well known but there is now new research on extinction that "confirms the role of forests in maintaining critical climates to support biodiversity. Changes in maximum temperature are driving extinction not changes in average temperature",
• forests minimise risks due to drought associated with heat extremes. "A combination of deep roots, high water use efficiency and high surface roughness allow trees to continue transpiring during drought conditions and thus to dissipate heat and convey moisture to the atmosphere'' 

The full research article can be accessed at this link: Deforestation: biophysical effects on climate