Carbon Dioxide Passes Symbolic Milestone for First Time in Recorded History

About 3.6 million years ago, the Earth was a far warmer place than it is today. The Arctic possessed little in the way of ice, and was instead carpeted with trees. Even sea levels were higher, swamping what are now coastal areas. While our planet may have looked different, though, it did share something in common with today's climate--it had the same levels of carbon dioxide.

Researchers have found that for the first time in human history, the concentration of climate-warming carbon dioxide in the atmosphere has passed the milestone level of 400 parts per million (ppm). The only time that these levels have been higher was when the Arctic was ice-free a few million years ago. The consequences of this increasing level of carbon dioxide could be devastating on today's environment.

These carbon dioxide measurements were actually made by the Keeling Lab in Hawaii, which has the longest continuous measurement of the greenhouse gas. The gas itself is regarded as one of the most important of the manmade greenhouse gases, so it's crucial to keep tabs on it. A product of burning fossil fuels such as coal, oil and gas, carbon dioxide is known for its ability to warm temperatures as it mixes with our atmosphere.

How do we know that these measurements compare to the ones associated with warmer temperatures a few million years ago? Researchers study sediment and ice cores, which trap gas bubbles. These cores actually lay out the climate history of our Earth, and allow scientists to examine exactly what the ancient atmosphere of our planet was like.

"It is symbolic, a point to pause and think about where we have been and where we are going," said Ralph Keeling, who oversees the carbon dioxide measurements at the lab in Hawaii, in an interview with The Guardian. "It's like turning 50: it's a wake up to what has been building up in front of us all along."

It's not likely that the measurements will stay at 400 ppm, though. At the Hawaiian lab, it's normal to see the CO2 concentration rise in winter months and then fall again as the northern hemisphere growing season kicks in and pulls some of the gas out of the atmosphere. In the next few weeks, it's likely that the measurement will drop back down below the historic number, according to BBC News.

That's not to say that we're out of the woods, though. The fact that measurements actually made it up to 400 ppm means that the Earth currently has historic levels of carbon dioxide in its atmosphere. In fact, carbon dioxide is now rising about 75 times faster than in pre-industrial times, according to The Guardian. It could show that our planet is passing a point where climate change, warmer temperatures and an ice-free Arctic are inevitable.