Over the last few months, there have been severe wildfires in the Amazon rainforest. Many people are concerned about this, because they think the Amazon is important to the supply of oxygen that we breathe. Some people have been spreading a false fact that “the Amazon provides 20% of our oxygen”. This article will explain why this is not true, but why we should still be concerned about the fact that the rainforest is burning.
PHOTOSYNTHESIS ANY OXYGEN PRODUCTION
In photosynthesis, plants use light energy and carbon dioxide to make oxygen and carbohydrates (sugars which are most organisms’ main source of energy). 1/3 of all photosynthesis that takes place on land occurs in tropical forests, of which the Amazon is the largest.
RESPIRATION AND OXYGEN USE
Almost all of this oxygen is consumed again by the plants themselves and other organisms that feed on plant matter. Plants constantly lose dead leaves, twigs and roots, which are consumed by insects and microbes (tiny organisms like bacteria and viruses). The living plants themselves are eaten by animals. The animals, insects and microbes use up the carbohydrates contained in the dead plant parts, turning it into carbon dioxide and energy. This process is called respiration, and it consumes oxygen from the air. The cycle between oxygen production via photosynthesis, and oxygen usage via respiration, means that the net oxygen production by land plants is close to zero.
SO WHERE DOES THE OXYGEN IN THE ATMOSPHERE COME FROM?
In the ocean, tiny plants called phytoplankton can grow into huge populations. When the phytoplankton die, they sink into deeper waters and are consumed by microbes. These microbes can eat so much phytoplankton that they use up all the oxygen in the surrounding water so that there is none left for burning. Any leftover phytoplankton sinks to the seafloor and are not consumed. The oxygen that the phytoplankton produced as it grew at the surface of the water remains in the atmosphere, since it is not consumed by organisms eating the phytoplankton.
WHY DOES THE RAINFOREST BURNING MATTER?
If the rainforest disappeared, there would be less oxygen produced, but also less oxygen consumed. This is good news, as it means that the Amazonian forest fires do not put us in danger of suffocation.
However, the burning of forests does release a huge amount of carbon dioxide. Since 1900, we have almost doubled the levels of atmospheric carbon dioxide, which is causing global warming. The Amazon holds approximately 90 billion tonnes of carbon dioxide, preventing it from entering the atmosphere. Even though we don’t need to protect the Amazon for fear of lacking oxygen, we do need to stop the burning to prevent carbon dioxide levels rising further and contributing to climate change. The second-largest tropical rainforest in the world (after the Amazon) is the Congo Basin, and it is vital that we ensure this forest does not fall to the same fate.