Unit 2 - The Environment Importance of Forests

Lesson 9: Forests Affect Climate

You probably have heard about the greenhouse effect. The carbon dioxide in the earth's atmosphere acts like the panes of glass of a greenhouse, keeping the heat inside.

The more carbon dioxide in the atmosphere, the greater the greenhouse effect. The greater the greenhouse effect, the warmer the air becomes.

To some extent, the greenhouse effect is necessary for the survival of plants and animals. If there were no greenhouse gases such as carbon dioxide, there would be no greenhouse effect. Without the greenhouse effect, all of the warmth from the sun would radiate back into space and the earth would be a very cold, inhospitable planet. However, since the Industrial Revolution, increased burning of fossil fuels and destruction of the world's forests has resulted in increased levels of carbon dioxide in the atmosphere.

As mentioned earlier, trees remove carbon dioxide from the air and incorporate carbon into their living tissues.

This carbon will only be released if the tree is burned or if it falls to the ground and decays.

As such, forest ecosystems store large amounts of carbon, hence the reason why forests are often referred to as carbon "sinks".

The diagram, to the left,  shows how trees can act as "carbon sinks".

However, despite the fact that the world's trees remove huge amounts of carbon dioxide from our air, they can no longer keep pace with the enormous amounts of carbon dioxide entering the atmosphere. That is, carbon is being released into the air faster than it can be stored by trees. The consequence of this build-up of carbon dioxide in the atmosphere is a slow but steady increase in global temperatures — a situation that could have disastrous effects for the environment.

In particular, the boreal forest plays a critical role in regulating the earth's climate. The thick layers of moss, soil, and peat of the boreal forest make up the world's largest storehouse of organic carbon. In fact, per unit area, the boreal forest stores twice as much carbon as tropical forests. On the following page you will learn about the importance of the Boreal Forest.

Besides preventing global warming by absorbing carbon dioxide from the atmosphere, forests can also affect our climate in other ways.  For example, the world's climate is greatly influenced by tropical rain forests.  Through the process of transpiration, the trees of the rain forests give off an enormous amount of water vapour.  This water vapour not only falls elsewhere in the world as precipitation, but it also keeps the air temperature at the equator lower than it might otherwise be.  Trees also lend shade, which keeps soil temperatures cooler.

Dr. Werner Kurz discusses how Canada's forests contribute to the overall carbon balance and explains how forest management and the use of forest products can promote carbon sequestration.
  Click on the Boreal Forest picture to the right to watch Dr. Kurz's video.