Forests are one of the most powerful tools we have to combat climate change. By absorbing carbon dioxide from the atmosphere, providing crucial ecosystem services, and influencing regional and global climate patterns, forests can help us avoid the worst impacts of a warming planet. This article dives into the science behind how forests mitigate climate change and what we can do to protect and restore these vital ecosystems.
How Do Forests Absorb Carbon Dioxide?
At the heart of forests’ climate change mitigation potential is their ability to absorb carbon dioxide (CO2) from the atmosphere through photosynthesis. Here’s how it works:
- Trees and other plants take in CO2 and water, using energy from sunlight to convert it into sugars for growth.
- Some of the absorbed carbon is stored in leaves, branches, trunks and roots, while some is transferred to the soil.
- The oxygen created as a byproduct of photosynthesis is released back into the air for us to breathe.
- This continuous CO2 removal makes forests carbon “sinks” – they absorb more carbon than they release.
Globally, forests absorb a net 7.6 billion metric tons of CO2 per year, about 1.5 times the annual emissions from the U.S. This carbon sequestration service is a key reason why protecting and expanding forests is critical for meeting climate goals.
What Happens to the Carbon Stored in Forests?
The carbon absorbed by forests doesn’t just sit there – it’s constantly cycling through different “pools” within the ecosystem:
- Leaves and branches: Carbon stored in foliage is released relatively quickly as leaves drop and decay.
- Wood: Carbon in woody biomass can remain locked up for decades or even centuries in standing trees.
- Soils: Root growth and leaf litter transfer carbon into soils, where it can remain for a long time.
- Atmosphere: Respiration and decay release some carbon back into the air, but it’s exceeded by the amount forests absorb.
When trees are cut down or burned, they release much of their stored carbon back into the atmosphere. But if forests are allowed to keep growing, they continue to accumulate carbon over time, acting as an ever-larger carbon sink.
How Else Do Forests Influence Climate?
Beyond pulling CO2 out of the air, forests influence climate in several other important ways:
- Evapotranspiration: Forests release moisture that forms clouds and precipitation, cooling the air and influencing rainfall patterns.
- Albedo: Forests are darker than bare land and absorb more sunlight, but this warming effect is outweighed by their carbon storage and evapotranspiration.
- Aerosols: Trees emit chemicals that form tiny particles in the atmosphere, which can have both cooling and warming effects.
- Surface roughness: The uneven structure of forest canopies affects how air moves and mixes, influencing local temperature and moisture.
These biophysical effects vary by region and forest type, but globally they reinforce the climate benefits of forests’ carbon sequestration. Tropical forests in particular are critical regulators of Earth’s climate system.
Can Planting Trees Help Stop Climate Change?
Planting trees is often touted as an easy climate solution, but the reality is more nuanced:
- Reforestation (planting trees where they previously existed) can restore lost carbon stocks and ecosystem services.
- Afforestation (planting trees where they didn’t previously grow) can create new carbon sinks but may have unintended ecological consequences.
- Tree planting is not a replacement for protecting existing forests, which store far more carbon than new seedlings.
- Planting the wrong trees in the wrong places can actually reduce biodiversity and water availability.
When done properly and at sufficient scale, tree planting can definitely help mitigate climate change. But it’s important to approach it thoughtfully, as part of a broader strategy to protect and restore natural ecosystems.
Why Are Tropical Forests Especially Important Carbon Sinks?
Tropical forests, like those found in the Amazon, Congo Basin, and Southeast Asia, have an outsized role to play in mitigating climate change:
- High productivity: Year-round warmth and rainfall allow tropical trees to grow faster and absorb more carbon than other forests.
- Vast carbon stocks: Tropical forests store about 250 billion tons of carbon, more than 7 times the annual emissions from fossil fuels.
- Rich biodiversity: Tropical forests house an estimated 50% of Earth’s terrestrial species, many of which are found nowhere else.
- Biophysical cooling: Intense evapotranspiration from tropical forests helps cool regional and global climate.
Despite their importance, tropical forests are disappearing rapidly due to agriculture, logging, mining and other human pressures. Stemming this loss is one of the most urgent priorities for climate action.
How Bad is Deforestation for the Climate?
Deforestation – the permanent removal of forests for other land uses – is a major driver of climate change:
- Emissions: Clearing and burning forests releases their stored carbon as CO2, accounting for about 10% of annual greenhouse gas emissions.
- Foregone sequestration: The carbon absorption that would have occurred if the forest had remained standing is also lost.
- Biophysical effects: Deforestation alters local and regional climate patterns, often leading to warming and drying.
- Vicious cycle: These climatic changes, along with edge effects and habitat fragmentation, can lead to further forest loss.
The tropics are ground zero for deforestation, with an area of forest the size of Greece lost each year. Brazil, Indonesia, and the Democratic Republic of Congo saw the highest rates of loss in 2020. Halting and reversing this trend is crucial for meeting the Paris Agreement goal of limiting warming to 1.5°C.
What Role Do Temperate and Boreal Forests Play?
While tropical forests get the most attention, temperate and boreal forests also have important roles to play:
- Carbon density: Temperate forests store a lot of carbon per hectare in trees and soils, due to their dense wood and cooler temperatures that slow decomposition.
- Vast extent: The boreal forest is the largest intact forest on Earth, forming a ring around the northern hemisphere that stores nearly as much carbon as the tropics.
- Albedo effects: The seasonal presence of snow in these forests complicates their warming and cooling effects, as snow-covered bare ground reflects more sunlight than evergreen trees.
Climate change itself is a major threat to these forests, as warming temperatures increase risks of pest outbreaks, fires and drought stress. Managing temperate and boreal forests for resilience is therefore key to preserving their long-term climate benefits.
What Can We Do to Maximize Forests’ Climate Mitigation Potential?
Unlocking the power of forests to fight climate change will require protecting what we have, restoring what we’ve lost, and improving how we manage working forests:
- Stop deforestation, especially in the tropics, through stronger policies, enforcement and economic incentives to keep forests standing.
- Restore degraded forests through active planting and natural regeneration, aiming to bring back native species and ecological functions.
- Manage working forests to optimize carbon storage alongside other values like timber, recreation and biodiversity, using practices like longer rotations and selective harvesting.
- Reduce the climate impact of forest products by increasing recycling, using wood in place of concrete and steel, and sourcing from responsibly managed forests.
- Support the land rights of indigenous peoples and local communities, who are the most effective stewards of the world’s forests.
These actions are not easy, but they are necessary. Forests are already doing a lot to fight climate change – imagine what they could do if we gave them the protection and support they need.
Forests Are a Climate Change Mitigation Powerhouse
Let’s review the key points on why forests are such an important climate change solution:
- Forests absorb a huge amount of CO2 from the atmosphere through photosynthesis, acting as carbon sinks
- Forests influence regional and global climate through evapotranspiration, albedo, aerosols and surface roughness effects
- Tropical forests are especially critical carbon sinks due to their high productivity, vast carbon stocks and rich biodiversity
- Deforestation is a major source of greenhouse gas emissions and destroys the climate benefits of forests
- Temperate and boreal forests also store a lot of carbon, but face increasing threats from climate change itself
- We can maximize forests’ climate mitigation potential by stopping deforestation, restoring degraded forests and improving management of working forests
The case for protecting and restoring the world’s forests has never been stronger. With the climate crisis accelerating and time running out to prevent catastrophic impacts, we can no longer afford to overlook these incredible natural allies. Investing in forests today is investing in a safer, healthier and more resilient world tomorrow.