Are forests really essential for the oxygen we breathe?

There are a thousand arguments to protect our forests. They are essential for biodiversity, carbon storage, water management, ecosystem services, recreation, our well-being, etc. One argument we often hear for protecting forests is that they produce oxygen and are therefore essential for our survival. At the same time, the Amazon rainforest is also called the “green lungs” of the Earth. But it is also said that microscopic plankton in the oceans are responsible for fifty percent of our oxygen production. How does this work exactly?

Our atmosphere contains approximately 21 percent oxygen. Carbon dioxide or CO₂, the largest driver of climate change, currently has a concentration of about 0.04%. Before the industrial revolution I fluctuated Between 0.017% and 0.03% for hundreds of thousands of years. Oxygen concentration also showed differences. Over the past 500 million years, the content has fluctuated largely between 15% and 30%.

A significant peak of up to 35% occurred in the Carboniferous, the era of vast coal forests. The dead plant materials that sank in those swampy forests and which would later turn into charcoal were not broken down by microorganisms and fungi. This resulted in a net increase in oxygen. It shows how forests still contribute to oxygen production today. This is the result of an imbalance, where more organic matter must be produced than is broken down in the ecosystem.

revolution

Historically, the oceans were extremely important to the level of oxygen on Earth. Trees have only been around for 385 million years (see also: Are Sharks Really Older Than Trees?), when the oxygen content of the atmosphere easily exceeded 15 percent. At least two billion years ago, long before there were any plants or animals, single-celled cyanobacteria began photosynthesis. In what we now call the Great Oxygen Crisis, oxygen first filled the oceans and then steadily accumulated in the atmosphere. At the end of the Precambrian, the oxygen content in the atmosphere rose to more than ten percent. It was a revolution that, according to some, led to the “Cambrian explosion” about 540 million years ago, and the astonishing emergence and diversification of the many groups in the animal kingdom.

Today, the oceans are still responsible for half of oxygen production. Almost all of it is used by life in the oceans themselves. The production of oxygen in the atmosphere appears to come mainly from the Earth itself. The largest contribution comes from tropical grasslands, savannas and rainforests. Together they account for about 60 percent of oxygen production On the ground. Temperate forests contribute only eight percent. These are – from a humanitarian point of view – very slow processes. The atmosphere is a giant reservoir: oxygen production will completely stop tomorrow, We can still continue for thousands of years.

Conclusion: On the geological time scale, tropical forests are already the green lungs of Earth today. But protecting forests, even the Amazon, would have no effect on our oxygen availability on a human time scale. Of course, other reasons why they deserve our protection remain.