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Carbon, trees and forests

Carbon (C) is a chemical element that, when burned with oxygen (O2), combines to make carbon dioxide (CO2). It is found in all organic materials whether alive or dead.

Carbon is released as CO2 when we burn fossil fuels such as coal, oil and gas. It is also produced when animals and plants use oxygen to release energy from food or when they die.

Carbon dioxide and climate change

Most of our atmosphere is made up of nitrogen (78 per cent by volume) and oxygen (21 per cent by volume). The remaining one per cent of the atmospheric gases are known as trace gases because they are present in such small concentrations. Despite their relative scarcity, the most important trace gases in the Earth's atmosphere are the greenhouse gases (GHGs).

Carbon dioxide (CO2) which accounts for 380 of every million molecules (ppm) in the air, is the most abundant of the six greenhouse gases identified under the Kyoto Protocol. The other five are Methane (CH4), Nitrous oxide (N2O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), and Sulphur hexafluoride (SF6). Despite being present in such small concentratons, carbon dioxide and the other greenhouse gases help to keep the Earth 33°C warmer than it would otherwise be without an atmosphere. The level of CO2 in the air stabilised at a fairly constant 270-280ppm for hundreds of years until the Industrial Revolution. Since then it has steadily increased and is now about 380ppm and is continuing to rise at between one and two ppm per year. 

Whilst ozone behaves like a greenhouse gas in the troposphere, in the stratosphere where its abundance is most significant within the ozone layer, it helps to filter out the incoming ultraviolet radiation from the Sun, protecting life on Earth from its harmful effects.

CO2 in the atmosphere

It is estimated that there is around 3000 gigatonnes of CO2 in the air. Each year humans add about 26 gigatonnes of CO2, mainly by burning fossil fuels. The rate of CO2 emissions varies depending on economic activity. However, the total amount of CO2 in the air has risen every year since we started to measure it in the 1950s.

We are able to measure the amount of CO2 that is in the atmosphere each year. The results show that about half of the carbon that enters the atmosphere stays there. The oceans absorb 25 per cent and the remaining 25 per cent must be absorbed by land-based ecosystems such as forests.

Carbon and trees

 Movie: carbon sequestration

Trees use energy from sunlight to convert CO2 from the air into sugars. This is the process of photosynthesis. These sugars fuel tree growth and wood production. When trees die most of the stored carbon is returned to the atmosphere, although some of it may be locked up in the soil.

Young forests grow rapidly and soak up carbon more quickly than mature forests. In mature forests the carbon balance may reach a steady state as carbon storage is matched by decomposition. At this point the forest becomes a vast carbon reservoir. When mature trees die the carbon stored is released back into the atmosphere. By harvesting trees before they die we can ensure that the carbon is locked up for longer in recyclable wood products. We can ensure that the system will continue to provide environmental benefits for future generations by replacing the felled trees with new ones.

Growing wood to use as a fuel is carbon neutral and provides a sustainable alternative to burning fossil fuels.

Wood also provides a versatile and lower carbon alternative to brick, concrete and steel in house building and construction. Wood has the technical qualities for a wide range of domestic and industrial uses.

Forests provide many other valuable benefits: they act as reserves of biodiversity; they provide protection to soil and people from extreme weather events; they provide food and opportunities for recreation.

Last updated: 18th December 2014