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Friday, April 11, 2014

Trees and Oxygen

A recent letter to the editor, in our local paper, complained that we should be careful not to cut down trees, because we need them to provide Oxygen for us. The author was, no doubt, well-intentioned, but wrong.

It is true that photosynthesis, carried out by trees and other green plants, releases Oxygen. But, as the Wikipedia article on the Atmosphere of Earth tells us, about one-fifth of the earth's atmosphere is Oxygen. As this article tells us, it would take about 2,000 years for us to use up all the Oxygen in the atmosphere, if no more were released by photosynthesis. (We would become extinct much sooner than that, if photosynthesis ceased, because we would run out of food.) The article also tells us that the Oxygen released by forests is almost entirely used up by those same forests. This is because, to obtain energy from stored plant material, most organisms use cellular respiration, which takes up Oxygen, and generates Carbon Dioxide. Even trees use cellular respiration to release the energy they store through photosynthesis..

The letter might much better have warned us that indiscriminate tree-cutting would be expected to mean that less Carbon Dioxide was taken up by photosynthesis, and, hence, the amount of CO2 in the atmosphere would increase. The result would be that the atmosphere would be less likely to allow heat radiation to pass through it, which would contribute to global warming. (See this Wikipedia article on Carbon Dioxide in the atmosphere.) Burning fossil fuels is the main culprit in the recent increases in CO2 in the atmosphere, but cutting forests is the second largest contributor.

Thanks for reading. Be glad that there is Oxygen enough to breathe, and be careful to save as many green plants as possible, so that global climate change can be slowed down.


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