Recent Ice Core Carbon Dioxide Measurements Lean On Thin Ice

Ice cores are cylindrical samples from large glaciers sometimes going thousands of feet deep that can help paint a picture of the climate hundreds of thousands of years in the past.

As snow falls on top of snow over time, the weight compresses the snow into a type of ice called firn that traps gasses like carbon dioxide, oxygen, and others in bubbles. Those trapped bubbles can then be analyzed to get an approximation of atmospheric gas at that time.

More specifically, they’ve been used to gauge how anomalous the current climate is from past eras. One of the first prominent ice core projects from the Antarctic Volstok station established by Russian researchers in 1957 would show the alternating pattern of carbon dioxide in the atmosphere between 182 and 298 parts per million with a frequency of about 100,000 years. The findings at Vostok would be repeated by other similar projects, like the European Project for Ice Coring in Antarctica (EPICA) at Dome C.

Data from those projects would all show the oscillation of carbon dioxide peaking at close to 300 ppm in the last 20,000 years.

But instead of going down from its peak, more recent ice core projects like that of Law Dome and the West Antarctic Ice Sheet (WAIS) would take much shallower ice core extractions and show carbon dioxide levels going far beyond the regular peak in the last two centuries. Not only was carbon dioxide not declining as part of its regular oscillation, it was increasing beyond prior maximums.

Shallow Measurements

Historic ice core measurements were aimed at understanding long-term trends in carbon dioxide and other gases to compare against the Paleolithic era. They didn’t get close to approximating measurements in the current day.

Vostok and EPICA measurements both started around 150 meters depth, which equates to measurements around 2,690 years before the current day—approximately 733 B.C—nothing close to the last two centuries and the industrial revolution.

The highest carbon dioxide estimate from Vostok over the course of hundreds of thousands of years was 298.6 parts per million (ppm) over 300,000 years ago.

Law Dome data shows a maximum of 359.5 ppm in the last 20 years based on ice cores at less than 16 meters depth—very shallow ice measurements above the firn.

The depth at which firn begins in Antartica is regularly assumed to be around 70 to 100+ meters. To approximate carbon dioxide levels in the last 50 years would require measurements at depths less than 50 meters.

Instead, WAIS and Law Dome samples are taken from “near surface firn” and the effects of firn densification are compensated for with approximations.

The implication of the WAIS and Law Dome measurements is that current carbon dioxide levels are far beyond natural variation seen in historic trends.

The WAIS and Law Dome measurements also make it seem like the growth in carbon dioxide came suddenly at the earliest stages of what might be called the industrial revolution—the early 1700s—as if human contributions to carbon dioxide were negligible before then despite population growth for centuries but exploded with the earliest days of steel production.