The question of how do forests affect climate is a nuanced one influenced by a number of factors.
Through vegetation, plant biomass, wood, trees and organic soils, forests play a key role in regulating the climate. The IPCC (The Intergovernmental Panel on Climate Change) has identified them as a key factor in climate change mitigation efforts3, and understanding what they do helps to see why.
Forests, Carbon Sinks and the Climate
Firstly, forests act as carbon sinks. A carbon sink is a reservoir that can absorb and store the atmosphere’s carbon by using biological mechanisms. Forests store carbon as biomass in trunks, branches, foliage, roots, and soils. However, it does not end there. They absorb carbon dioxide during the process of photosynthesis, which reintroduces oxygen into the atmosphere4.
However, the ability of forests to act as carbon sinks is no longer safe for the long term. Tropical forests are removing less carbon dioxide from the atmosphere as a result of deforestation, reducing their ability to act as carbon sinks. Instead, forests like the Amazon could turn into a source of carbon in the next decade. This is due to the damage caused by loggers, farming interests5 and the impacts of the climate crisis, new research has found6. The ability of forests to act as carbon sinks is under threat from other climate impacts such as droughts. Evidence of this can be seen in Borneo7.
Forests, the Albedo Effect and the Climate
Secondly, forests can have an albedo effect on the environment8. An albedo effect refers to the amount of incoming solar radiation that is reflected by an object. Objects that are dark in colour typically absorb heat, whereas lighter objects reflect heat while reducing surface temperature.
Therefore, dark green forest cover has a low albedo and absorbs more sunlight. Research is currently looking into how large the albedo effect is on the Earth’s climate. In the northern forests, seasonality of albedo is largely due to the snow cover which can shift the albedo from 7% to 80%9. This shows how location and seasonality are also factors in how forests affect the climate.
How Do Forests Fit into Mitigation Efforts?
The IPCC10 recognises the role forests play in mitigation efforts. They outline several ways that the forest has the potential to help offset the effects of climate change. For example, reforestation and maintenance is a way of preventing the loss of carbon sinks. The halting of forest loss and promotion of restoration is needed to meet the Paris Climate Agreement11. If we do this, forests have the potential to contribute to over one-third of the total climate change mitigation required by 2030, according to scientists12.
Reforestation and the planting of new forests are cost-effective ways to mitigate the impacts of climate change, according to studies13. This is why several countries are exploring these methods to help meet climate goals. The low costs associated with afforestation are lower than other carbon removal technologies (e.g. bioenergy with carbon capture and storage) making them much more attractive14.
However, large scale afforestation is hard to implement globally. Its effectiveness differs depending on the location, making its application unfavourable in some regions. Expansion of forest in the tropics results in cooling, while afforestation in the boreal zone might have a limited effect or might even result in warming, according to research 15 using earth system models.
Therefore, many factors must be considered in answering the question of how forests affect climate. These include scaling ability, cost, CO2 absorption, and albedo. Scientists and policymakers need to address this multifaceted issue to ensure global 2030 climate goals are met 16. It must also be considered that felling large trees to allow smaller ones to grow back is not a good ecological approach. It will release more of the carbon that was stored in fossil fuels and roots into the atmosphere. It is therefore important to protect existing forests rather than focusing on planting new trees.
- Forests play a key role in the global carbon cycle and climate change, Michigan State University, 3 May 2012
- Deforestation in Brazil could significantly increase local surface temperatures, Newscenter, 20 March 2019
- Landmark IPCC report urges world to halt deforestation, Environmental Investigation Agency, 9 August 2019
- What IS Photosynthesis? Live Science, 15 October 2018
- Why is the Amazon Rain Forest Disappearing? Time, date unknown
- Asynchronous carbon sink saturation in African and Amazonian tropical forests, Nature, 4 March 2020
- Long-term carbon sink in Borneo’s forests halted by drought and vulnerable to edge effects, Nature Communications, 2017
- “Albedo effect” in forests can cause added warming, bonus cooling, Oregon State University, 19 October 2011
- Albedo matters for the climate, and forestry can have an impact on it, Phys.org, 4 December 2019
- Special Report on Climate Change and Land; Summary For Policymakers, IPCC
- New research shows why forests are absolutely essential to meeting Paris Climate Agreement goals, Mongabay, 9 November 2017
- Issues brief: Forests and climate change, International Union for Conservation of Nature (IUCN)
- Afforestation for climate change mitigation: Potentials, risks and trade‐offs, Jonathan C. Doelman, 26 October 2019
- Plant trees to mitigate climate change, urge scientists, European Scientist, 6 July 2019
- Afforestation to mitigate climate change: impacts on food prices under consideration of albedo effects, Ulrich Kreidenweis, 27 July 2016
- United Nations strategic plan for forests, 2017-2030, United Nations