How oxygen levels impact the climate

Take a big deep breath. That oxygen you’re inhaling? It’s not just a gas that’s vital for life. Oxygen has also impacted our planet’s climate, according to University of Michigan climate scientist Chris Poulsen, lead author of a 2015 study published in Science. While oxygen does not play a role in any change of today’s climate, oxygen levels help explain the az’s past climates and how life on this planet has evolved. Poulsen and his team found that oxygen currently represents about 21% of the gases in the Earth’s atmosphere, but that over the past 500 million years the oxygen percentage has varied between 10% to 35%.  “Because O2 is not a greenhouse gas, often this variability has not been considered in studies of climate change,” he writes. Poulsen says there is an undeniable link between oxygen levels and climate when you study the geological timescales.

Let’s take a brief trip back in time. 

Oxygen’s role in the history of the Earth

If we look at the known history of the earth, the oxygen level was very low at the beginning. Based on scientific studies, it was cyanobacteria — more commonly known as blue-green algae — that started pumping oxygen into the atmosphere around 2.5 billion years ago as a waste product of photosynthesis. This period is known as The Great Oxygenation Event and the earth faced a rise in oxygen level. That oxygen rise changed the atmosphere from a reducing state to an oxidizing state and, subsequently, new forms of life evolved, which further increased oxygen levels. What do the fluctuations in oxygen levels mean?

Poulsen and his team found that low levels of oxygen helped to thin the earth’s atmosphere, which allowed more sunlight to reach the surface of the planet. When more sunlight reached the earth, it evaporated more moisture and increased the amount of water vapor in the atmosphere. These vapors trapped heat, and the evaporation also resulted in a high humidity level. The result: decreased oxygen levels led to substantial increases in global precipitation rates and temperature. But over time, as the level of oxygen increased, the atmosphere thickened, allowing less sunlight to reach the earth and scattering most of the sun light that did hit the surface. The consequences of a high oxygen level were lower vaporization and less production of water vapors, resulting in a decrease in temperature.  

What does it all mean?

Considering the role played by oxygen in the geological history of the earth helps explain some of the climate variations. By including oxygen in studies, scientists will have better models of our planet’s past. As for how oxygen impacts us today: the levels are dropping at very slow rate, so it doesn’t much affect today’s climate. "Oxygen concentration can help explain features in the paleoclimate record not accounted for by variations in carbon dioxide levels, and it must be considered if we are to fully understand past climates," Poulsen said. "However, variations in oxygen levels are not an important factor in present-day climate change." That is not to say oxygen should be ignored. Understanding the past informs the future so knowing oxygen’s role in climate is a critical finding.

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