EnviroLink Forum

Trees produce oxygen and absorb carbon dioxide. This balance is now threatened:

Ahead of us we have the possible destruction of forests, vital in maintaining oxygen levels necessary for life, in the control of carbon dioxide, and in water cycle balances. Notably, the concentration of oxygen in the atmosphere has dropped from 35 to 21 percent from prehistoric times to now, and the carbon dioxide has increased in part by the human growth pollution in cities with high oxygen levels, which often comprises only 15 percent of total air. So at this rate it is obvious that in these cities we will render the “air” unbreathable. Diana Beresford-Kroeger, a botanist, says, “the abuse of forests and pollution of the oceans has caused them to produce only half the oxygen (they produced) 10,000 years ago.”** We must also consider that in the last 30 years this process has accelerated the deterioration or the collapse of almost all living systems.

This paragraph really stuck out, so I began to research the facts. Are cities really losing their oxygen?

Yes.

Dangerously low levels of oxygen are now being reported in cities around the world. Increased carbon dioxide levels are displacing oxygen in the atmosphere.

We are losing three oxygen molecules in our atmosphere for each carbon dioxide molecule that is produced when we burn fossil fuels. Studies of ice cores and recent data from direct atmospheric sampling have shown that there has been a 30% increase in carbon dioxide since the beginning of the industrial age. Atmospheric Oxygen Levels Fall As Carbon Dioxide Rises

Yeah, you're right about the math but I would add one qualifier, according to the article one unit of CO2 added to the atmosphere removes 3 units of O2. Taking another tack I'm wondering what happens if we lose a serious amount of photosynthetic capability due to forest clear cutting and increasing ocean dead zones etc.

The present atmosphere would not exist without the biosphere. In order to put oxygen into the air, there had to be plants, which take in carbon dioxide and release oxygen in the process of photosynthesis. This resulted from an exceedingly complex series of evolutionary developments from anaerobic, or non-oxygen-breathing, single-cell life-forms to the appearance of algae. As plant life evolved, eventually it put more and more oxygen into the atmosphere, until the air became breathable for animal life. Thus, the atmosphere and biosphere have sustained one another.

The constant re-arrangement of continents by plate tectonics influences the long-term evolution of the atmosphere by transferring carbon dioxide to and from large continental carbonate stores.[24] Free oxygen did not exist in the atmosphere until about 1.8 billion years ago during the Great Oxygenation Event and its appearance is indicated by the end of the banded iron formations. Before this time, any oxygen produced by photosynthesis was consumed by oxidation of reduced materials, notably iron. Molecules of free oxygen did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials. This point signifies a shift from a reducing atmosphere to an oxidizing atmosphere. O2 showed major ups and downs until reaching a steady state of more than 15% by the end of the Precambrian.[25] The following time span was the Phanerozoic eon, during which oxygen-breathing metazoan life forms began to appear.

The amount of oxygen in the atmosphere has varied over the last 600 million years. Around 280 million years ago the amount of oxygen peaked around 30%, significantly higher than today's 21%. Two main processes govern changes in the atmosphere: Plants use carbon dioxide from the atmosphere, releasing oxygen. Breakdown of pyrite and volcanic eruptions release sulfur into the atmosphere, which oxidizes and hence reduces the amount of oxygen in the atmosphere. However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen. The exact cause of the variation of the amount of oxygen in the atmosphere is not known. Periods with much oxygen in the atmosphere are associated with rapid development of animals. Today's atmosphere contains 21% oxygen, which is high enough for this rapid development of animals.