A nearly two-mile-long core of ice – the oldest frozen sample ever drilled from the underbelly of Antarctica – shows that levels of two greenhouse gases, carbon dioxide and methane, have not been as high as they are today for 650,000 years.

The research, published in the November 25 issue of the journal Science, describes the content of the greenhouse gases within the core and shows that carbon dioxide levels today are 27% higher than they have been in the last 650,000 years and levels of methane, an even more powerful greenhouse gas, are 130% higher, said Thomas Stocker, a climate researcher at the University of Bern and senior member of the European ice-coring team that wrote two papers based on the core.

The work provides more evidence that human activity since the Industrial Revolution dramatically has altered the planet’s climate system, scientists said. “This is saying, ‘Yeah, we had it right.’ We can pound on the table harder and say, ‘This is real,'” said Richard Alley, a Penn State University geophysicist and expert on ice cores who was not involved with the analysis.

Previous records, from an ice core drilled at the Russian Antarctic station Vostok, extended back 440,000 years. Extracting and analyzing that core was a major achievement, but the core stopped short of a time period scientists are anxious to study because it was like today’s.

Ice cores are plugs drilled from glaciers and ice sheets. They are composed of tens of thousands of layers of fallen snow and air bubbles that become compressed over time. Ice cores are among the most powerful tools available to climate scientists. The chemistry of the ice reveals what temperatures were in the distant past, while bubbles within the ice are minuscule time capsules that capture samples of air and greenhouse gases as they existed hundreds of thousands of years ago.

The ice core was drilled by the European Project for Ice Coring in Antarctica from a high plateau in East Antarctica called Dome C that rises about two miles above sea level. It is one of driest, coldest parts of the icy southern continent, where summer temperatures can fall to 50 degrees below zero Fahrenheit. Temperature records from the core were published in a paper in 2004, and scientists have been waiting for an analysis of the core’s gases.

The last time carbon dioxide levels were as high or higher than today was probably tens of millions of years ago, Alley said. Over millions of years, carbon dioxide levels shift because of slow geological processes, such as weathering of rocks, swallowing of crust into subduction zones and the release of gases from volcanoes. But these processes are much slower and more gradual than the current rapid increase of carbon dioxide into the atmosphere from the burning of fossil fuels, Alley said.

Scientists are enthusiastic about the ice core because it includes about eight full glacial cycles. The Vostok sample had four. Glacial cycles occur roughly every 100,000 years and include long periods of cold, when ice ages occur, and brief, warm interglacial periods, such as the current one. The cycles are controlled by shakes, wobbles and tilts in the Earth’s orbit around the sun that determine the amount of sunlight falling on and warming the planet.

The Vostok core showed that warm interglacial periods lasted about 10,000 years. Because the current temperate interglacial period has lasted about 12,000 years, many scientists had speculated that the planet was overdue for an ice age.

But the new core shows that the interglacial period of 440,000 years ago, when the Earth’s position relative to the sun was very similar to what it is today, lasted nearly 30,000 years and was not ended by natural decreases in carbon dioxide, Stocker said. The work suggests that the next ice age is about 15,000 years away.