Trees & Carbon Dioxide (CO2): All the Facts

The typical diet of a Westerner leads to the cutting down of four trees every year.¹ Felling trees is a major contributor to climate change.² Global warming, trees and carbon dioxide (CO2) are closely related.

If we are to prevent a disastrous increase in average global temperatures, we must stop deforestation now.³

Do trees release carbon dioxide when they are cut down?

Simply put, yes. Trees release carbon dioxide when they are cut down.⁴ They also emit this greenhouse gas when they are burned or left to rot.⁵ CO2 in the Earth’s atmosphere increases global warming by preventing heat from escaping into space.⁶ Consequently, tree cover loss is responsible for eight per cent of all annual carbon emissions.⁷

Tropical deforestation is causing more emissions per year than 85 million cars over their entire lifetime.⁸ If tree felling in the tropics was a country, it would rank third in the world for CO2 emissions.⁹ Cutting down trees releases significant quantities of CO2. This has serious consequences for our planet.

What do trees do to carbon dioxide?

Trees and other plants absorb carbon dioxide as they grow.¹⁰ They capture it directly from the air through the process of photosynthesis.¹¹ A typical mature tree will take up about 22 kilograms of CO2 from the atmosphere each year.¹² They combine carbon with water and use energy from sunlight to make food, enabling plants to grow. The process also releases the oxygen we need to breathe as a byproduct.¹³

Carbon in soil and leaf litter

Excess carbon is stored in the trunks, branches and leaves of a tree.¹⁴ Trees also store about 48 per cent of their captured carbon in nearby leaf litter and soil. As a result, a healthy forest ecosystem sequesters much more CO2 than trees can individually.¹⁵

Which trees absorb the most carbon dioxide?

Trees absorb more carbon as they mature.¹⁶ Forests of tall, old trees – such as the temperate rainforests of North America’s Pacific coast – are some of the world’s biggest carbon sinks.¹⁷ Slower-growing species can also store the most carbon, thanks to their longer lifespans. For this reason, it is better to leave existing trees standing than to cut them down and plant new trees.¹⁸

How do trees reduce carbon dioxide?

Trees reduce the amount of carbon dioxide in the atmosphere by absorbing it and storing it for extended periods. Long-lived trees, including high elevation pines and other high-northern conifers, can store carbon for many centuries.¹⁹

By pulling CO2 from the air, trees lower the amount of greenhouse gas in the atmosphere. Therefore, deforestation increases the amount of CO2 in two ways:

• The act of cutting them down releases stored CO2
• The trees are also unable to absorb any further carbon

How do trees release carbon dioxide?

As plant matter breaks down, it recycles the stored carbon back into the atmosphere as CO2.²⁰ This happens naturally as trees and carbon dioxide are an important part of the carbon cycle.²¹ It also occurs as a result of human activities.

Cutting a tree down causes the premature release of CO2 that the tree has absorbed. Decreasing the number of trees in a tropical forest also affects the health and uptake of CO2 of the remaining trees.²²

Many trees store CO2 in the heartwood of their trunk. The amount can be significant, especially in long-lived species like the California redwood. Research shows that these trees store 63 to 77 per cent of their aboveground carbon in the heartwood. This means that the carbon remains stored in the wood until it is burned or rots, even if it is chopped down for timber or pulped for paper.²³

Planting trees and carbon dioxide

Does planting trees remove CO2?

Planting more trees can help remove more CO2 from the atmosphere. One study has claimed that our planet could support continuous forest on an additional 0.9 billion hectares of land.²⁴ This would store 25 per cent of the current carbon in the atmosphere.²⁵ It would negate about 20 years of human-produced carbon emissions.²⁶

How do we remove more CO2 from the atmosphere and help to mitigate climate change?

It is important to note that tree planting alone cannot prevent climate change. The Intergovernmental Panel on Climate Change (IPCC) has warned that we must limit global warming to 1.5°C above pre-Industrial levels.²⁷ For this to happen, global greenhouse gas emissions must be 55 per cent lower by 2030 than in 2017.²⁸ Planting trees can help us reach this target. But, it will be impossible to achieve unless we stop burning fossil fuels and cutting down our existing forests.

Which trees are more efficient at cleaning our air?

Young trees absorb far less CO2 than mature trees.²⁹ It can take decades for them to absorb large quantities of CO2. Scientists have found that “in more than 30 years, the regrowth of secondary forests in the Brazilian Amazon has offset less than 10 per cent of emissions from the loss of old-growth forests”.³⁰ The carbon offset that old-growth trees provide cannot be quickly and easily replaced simply by planting new seedlings.

Protecting our trees for better air quality

This demonstrates the importance of protecting and enhancing our existing forests to ensure they continue to serve as carbon sinks. The world’s standing forests currently absorb a net 7.6 billion tonnes of CO2 per year.³¹ Without them, it will be impossible to prevent global warming exceeding 1.5°C.³²

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