The current rate of atmospheric CO2 increase is 10 times faster than at any other point in the past 50,000 years. This is according to scientists who did a detailed chemical analysis of ancient ice in the Antarctic.

The conclusions were published in the Proceedings of the National Academy of Sciences.

"Studying the past teaches us how today is different,” commented Kathleen Wendt, assistant professor in Oregon State University's College of Earth, Ocean and Atmospheric Sciences and the lead author of the research.

“The rate of CO2 change today really is unprecedented," she added.  

"Our research identified the fastest rates of past natural CO2 rise ever observed, and the rate occurring today, largely driven by human emissions, is 10 times higher," she continued.

In the past, carbon dioxide levels have varied because of ice age cycles and other natural causes. Today they are accelerating because of human emissions.

Ice sheets that were created in the Antarctic over millennia include ancient atmospheric gases trapped in air bubbles. Scientists use ancient ice samples, collected by drilling cores up to 2 miles (3.2 kilometres) deep, to analyse the trace chemicals and build records of past climate, according to Phys.org.

During the most recent Ice Age, ending around 10,000 years ago, there were several periods where CO2 levels seemed to accelerate at higher than the average rate, according to previous research. But those measurements were not that detailed, limiting scientists' ability to understand what was occurring, Wendt wrote in Phys.org.

"You probably wouldn't expect to see that in the dead of the last ice age," she said. "But our interest was piqued, and we wanted to go back to those periods and conduct measurements at greater detail to find out what was happening."

Using samples from the ice core of the West Antarctic Ice Sheet Divide, Wendt and colleagues probed what was occurring at those times. They found that these escalations in CO2 occurred when there were North Atlantic cold intervals, or as Heinrich Events, associated with abrupt climate shifts globally.

"These Heinrich Events are truly remarkable," said Christo Buizert, an associate professor in the College of Earth, Ocean and Atmospheric Sciences and co-author of the study. "We think they are caused by a dramatic collapse of the North American ice sheet. This sets into motion a chain reaction that involves changes to the tropical monsoons, the Southern hemisphere westerly winds and these large burps of CO₂ coming out of the oceans."

During the largest of the natural jumps, CO2 increased by around 14 parts per million in 55 years. The rapid increases occurred about once every 7,000 years or so. At today's rates, that magnitude of increase takes only five to six years.

Evidence suggests that during past periods of natural CO2 rise, the westerly winds that help the circulation of the deep ocean were also becoming stronger, leading to a fast release of CO₂ from the Southern Ocean.

Other research has suggested that these westerlies will strengthen over the next 100 years because of climate change, Wendt wrote in Phys.org.

If that occurs, it will reduce the Southern Ocean's capacity to absorb human-generated CO2, said the researchers, basing their view on the new research.

"We rely on the Southern Ocean to take up part of the carbon dioxide we emit, but rapidly increasing southerly winds weaken its ability to do so," said Wendt.