Earth's orbit can drastically affect our planet's climate. In fact, the wobbly nature of its path can cause our planet's ice ages. Now, though, scientists are uncovering a little bit more about the Northern Hemisphere's last ice age. It turns out that Antarctic warming began at least two, and perhaps four, millennia earlier than we previously thought.

Previous research indicated that the Northern Hemisphere's last ice age ended about 20,000 years ago. Most evidence in the Southern Hemisphere seems to show that its ice age ended about 2,000 years later. This suggests that the south was responding to warming in the north. Yet a new ice core seems to show that warming in West Antarctica was well underway 20,000 years ago.

The core was taken from the West Antarctic Ice Sheet Divide, an area where there is little horizontal flow of the ice. This way, the scientists knew that the data were from a location that remained consistent over long periods. More than two miles deep, the core covers more than 68,000 years of climate history.

The scientists analyzed this core by running two electrodes along the ice to measure high electrical conductivity associated with each summer season. This allowed the researchers to identify the annual layers in the core. Evidence of greater warming turned up in layers associated with 18,000 to 22,000 years ago, the beginning of the last deglaciation.

"Sometimes we think of Antarctica as this passive continent waiting for other things to act on it," said T.J. Fudge, one of the researchers, in a news release. "But here it is showing changes before it 'knows' what the north is doing."

It's likely that the warming in West Antarctica 20,000 years ago was due to how the sun's energy was distributed over the region. It not only warmed the ice sheet, but also warmed the Southern Ocean that surrounds Antarctica, particularly during summer months when more sea ice melting could take place.

The findings reveal a little bit more about the Earth's climate history and also might show a little bit more about future climate changes. That said, it's unlikely that changes in Earth's orbit today are an important factor in the current rapid warming. While Earth's orbit changes on a scale of thousands of years, current levels of carbon dioxide are changing on the scale of decades.

The findings are published in the journal Nature Geoscience.