Why Tumbling Oxygen Levels Aren't Freaking Scientists Out
Don't hold your breath.
Princeton scientists announced this week that Earth has been slowly leaking oxygen over the last 800,000 years, and they’re not exactly sure why. But these scientists are urging you to please calm down, we’ll all be fine.
The scientists, led by geochemist Daniel Stolper, looked at samples of air trapped in ice from Greenland and Antarctica, and found that oxygen concentrations had steadily declined by 0.7 percent over the period of study. That’s not alarming — you’d notice as much of a change if you took the elevator from the ground floor to the 30th in a seaside building, Stolper tells Live Science. The results were published Friday in Science.
Reality check: The slow, gradual leak is nothing compared to the oxygen depletion that humans are currently causing by fossil fuel burning, which eats up oxygen and releases carbon dioxide. In fact, the researchers ignored the most recent 200 years in order to exclude human-caused factors, which have made things get more than a little weird. Today, the rate of oxygen depletion in the atmosphere is more than 2,000 times what it was over the study period.
Oxygen falls as carbon dioxide rises, but only one of these trends will dramatically alter the planet. (Scripps O2 Program)
You’re probably wondering at this point why you hear so much about increasing levels of carbon dioxide and nothing about declining oxygen, if these things are roughly equivalent. It’s a very good question with a pretty straightforward answer.
Climate change to date has been driven by an increase in atmospheric carbon dioxide from about 280 parts per million in pre-industrial times to about 400 parts per million today. That’s more than a 40 percent increase — enough to very significantly change the gas’s heat-trapping effects. But oxygen is many hundreds of times more abundant in the atmosphere, and the flipside of this transaction is a drop in O2 levels from about 209,580 to 209,460 ppm. That’s a loss of just 0.06 percent, a negligible amount for the planet and its O2-breathing creatures, Homo sapiens included.
At least on land — the oceans are a different story. While atmospheric oxygen won’t plummet to dangerous levels anytime soon, the same cannot be for undersea creatures that depend on dissolved O2, which is less abundant and therefore more sensitive to change.
A poverty of dissolved oxygen results in frequent dead zones in the Gulf of Mexico.
Every year, localized drops in oxygen levels create ocean dead zones, which are getting worse and worse. The primary contributor to these apocalyptic scenes is fertilizer runoff from agriculture, which causes algal blooms, providing a great feast for bacteria that consume oxygen. The abundance of these bacteria cause O2 levels to plummet, and if they go low enough, organisms that need it to survive swim away or die.
Fossil fuel burning is not the primary culprit for these dead zones — although it is very likely making them worse, for at least two reasons. Warmer water can actually hold less dissolved oxygen than cooler water, so oceans will lose oxygen as global warming heats them up.
Secondly, scientists predict less mixing of the oceans in the future, as surface waters become warmer and less salty than deep waters below. It will be less salty because of more freshwater runoff from melting glaciers, and warmer because of the extra atmospheric heat. These factors compound to increase the difference in density between higher and lower layers, which will make it harder for them to mix. This could spell disaster for O2-consuming creatures that hang out in the deep, and decrease the amount of oxygen in the seas overall.
Basically, don’t worry about any climate change-induced shortness of breath for the foreseeable future. The same can’t be said for the seafood you like to eat, unfortunately.
