In the basement of Ed Brook's lab at Oregon State University in Corvallis, Christo Buizert ducked into a freezer hovering around -11 degrees Fahrenheit in a short-sleeved shirt and Birkenstocks, emerging moments later with a disk-shaped slice of ancient ice.
It was a piece of scrap, the remnants of a sample pulled from the layer of ice that sits top Antarctica, according to Buizert, an assistant professor at the College of Earth, Ocean, and Atmospheric Sciences. The continent is so cold that even in the warmest summer months the ice layer almost never melts, and in some places it reaches roughly three miles thick. If all that ice were to melt, global sea levels would rise by some 70 meters, according to Buizert.
Now, outside the freezer, the leftover core sample was rapidly melting and pooling at Buizert's feet. If you held the ice chunk up to your ear at that moment, you would have heard the crackle of air bubbles popping as ancient gases trapped some 50,000 years ago escaped back into the atmosphere. Only in Antarctica and Greenland, where snow falls in airy flakes before being compressed into ice without first melting, are the ice layers laced with tiny bubbles of trapped air such as these.
Buizert likes to watch the bubbles escape from scrap pieces into a cool drink. "When you need a 100-meter ice core, you drill one extra meter for your drinks," he jokes.
Both Buizert and Brooks, a distinguished professor of earth, ocean, and atmospheric sciences, are interested in the levels of greenhouse gasses—carbon dioxide, methane, and nitrous oxide—trapped within these pockets, and what they might tell us about the Earth's ancient climate.
This particular ice chunk is hardly even considered "old" by Antarctica's standards. The oldest ice found so far on the continent is 2.7 million years old. To get to it usually involves drilling deep into the ice layer and extracting a cylindrical core. It can take years to drill an ice core, which is usually extracted in 10-foot sections. The deeper the drill gets, the longer it takes to pull the sample to the surface. "Imagine if you had to walk three miles only 10 feet at a time," Buizert says.
In some places, old ice layers are easier to get to. Many of the samples Brook's lab collects come from Antarctica's Taylor Glacier, where strong winds whip across the surface carrying away snow and ice so that old layers rise to the surface. "Here, you can just walk through time," Christo says.
The trickiest part of this work is getting the air out without contaminating it. To measure methane or nitrous oxide levels, Brook's lab puts small pieces of ice core into jars and then pumps out the air so that the sample sits in a vacuum. Then the ice is melted, allowing the gases, which are insoluble in water, to escape. To measure carbon dioxide levels, which would dissolve into water, Brook's team crushes the ice sample to bits instead of melting it. Once the air is separated from the ice, the researchers use gas chromatography to quantify the trace gases.
Some of their results can be seen in a poster titled "Ice Cores: Time Machines Into the Earth's Past," which leans against a wall in the hallway just outside the freezer. There's a graph in the corner that charts temperature, carbon dioxide, and methane levels going back at least 800,000 years. The gas levels and temperatures tend to spike and fall in unison, cycling through highs and lows every 100,000 years or so. Scrunched together, the peaks and troughs look like the read-out from a hospital heart rate monitor. But toward the far end, when the graph reaches the present day, the lines tracking carbon dioxide and methane levels rocket up far above any previous high recorded in the ice core. And this alarming chart is already out of date: On the poster, carbon dioxide levels are just shy of 400 parts per million—a threshold crossed just last year.
Carbon dioxide and methane are the two most potent greenhouse gases, but nitrous oxide is becoming more important, according to Brooks. The gas stays in the atmosphere for roughly 140 years, and is eventually destroyed in a process that involves ozone. As we phase out ozone-harming chemicals like chlorofluorocarbons, nitrous oxide become the most important ozone-depleting greenhouse gas. Carbon dioxide, on the other hand, will remain in the atmosphere much longer—long after we stop emitting it.
"Some fraction of the carbon dioxide we put in the atmosphere today is still going to be there 100,000 years from now," Brook says.
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