A recent University study has found that oxygen levels affect the Earth’s climate.
Oxygen not only makes up 20 percent of the Earth’s atmosphere, but also has an impact on how much sunlight gets to the Earth’s surface and, consequently, the temperature of the Earth.
Throughout the Earth’s history, the amount of oxygen in the Earth’s atmosphere has varied between 10 and 35 percent. Scientists already knew greenhouse gases such as carbon dioxide, methane and water vapor change the climate, but a recent study published in Science Magazine tells how oxygen, too, affects the Earth’s climate.
The study was conducted by University Prof. Chris Poulsen, chair of the Department of Earth and Environmental Sciences, University Ph.D candidate Clay Tabor and Biology Prof. Joseph White of Baylor University.
Oxygen is not a greenhouse gas, and it doesn’t interact with long-wave radiation the way greenhouse gases do. It was therefore unknown that oxygen could have an impact on the climate. Because oxygen makes up part of the atmosphere, when the amount of oxygen in the atmosphere decreases, more sunlight shines through the atmosphere and therefore increases temperatures.
“Indirectly, it increases the greenhouse effect by decreasing the water vapor because water is a greenhouse gas,” said Poulsen. “The really novel thing about this study is that a gas that is not considered to be a greenhouse gas can have a climactic effect.”
The researchers used a climate model, a computer simulation of oxygen in the Earth’s atmosphere in the Phanerozoic period, a time period when the Earth was hot, carbon dioxide levels were high, and dinosaurs were not yet extinct.
According to Poulsen, they changed the climate simulation model by removing a portion of the oxygen in it. Reseraches began their work wondering if changes in oxygen levels may have had an effect on the climate, but they didn’t know what they would find.
“It’s not a surprise that we changed the mass of the atmosphere and that the amount of radiation would potentially increase,” Poulsen said. “When I started doing the work, it wasn’t absolutely clear to me that it would have a climactic effect. I thought that it would, and that’s why I did the study. But I wasn’t 100 percent sure.”
While the findings are not significant for today’s climate change, they do illustrate a clearer picture of the Earth’s atmosphere and climate in the past.
“This doesn’t have significant implications for modern climate change,” Poulsen explained. “The reason for this is that oxygen levels are changing, but they’re decreasing very, very slowly. However, oftentimes in order to understand modern climate, we go back and look and say, ‘Well, what was it like in the past?’”
To compare the Earth’s past climate and its climate today, the comparisons have to be accurate. With knowledge that changes in oxygen levels affect the atmosphere as well as the Earth, scientists can more clearly see how Earth’s atmosphere in the past compares to the present. The study has found when oxygen levels have gone down or up, it has forced the climate to change.
“If we’re going to look to the paleo-record, the distant past, as a way of understanding climate, we have to make sure we understand all the things that were different in the past, and this one factor had been overlooked,” said Poulsen.