- Studies of the deepest ice core ever
taken reveal an ancient record of Earth's climate over the last 420,000
years that suggests current levels of greenhouse gases are at historical
- An international team analyzed the nearly
12,000-foot-long core taken from Russia's Lake Vostok. Their findings,
published in this week's journal Nature, indicate the Earth has gone through
an ice age about four times in the past 420,000 years.
- Only about 11 degrees Fahrenheit of change
in temperature generated such dramatic shifts, the team says.
- Researchers reached their conclusions
by analyzing the hydrogen in water molecules from the ice for changes in
the abundance of different isotopes, or elements with slightly varying
- Levels of hydrogen isotopes vary according
to the temperature at the time the water falls as snow, creating a kind
of historical record. Remarkably, the low temperatures for all four glacial
periods differed by only about 2 degrees Fahrenheit.
- The team also measured carbon dioxide
and methane -- key greenhouse gases -- in bubbles trapped in the ice core.
- Increases in these gases were tightly
linked with the rises in global temperature that led to the warmer periods,
according to glaciologist Jean Robert Petit, lead author of the study.
- The team reports that increases in greenhouse
gases were probably responsible for about half of the temperature increase
during climate cycles.
- However, the researchers didn't speculate
on what may have triggered the hike in greenhouse gases in ancient times.
- The ice cores also revealed that, at
least during the 420,000 years, methane and carbon dioxide levels have
never been as high as they are now, the researchers say.
- All of the findings confirmed previous
ice core research, which only went back through two climate cycles.
- "Extending the record to four climactic
cycles is very important," says Bernhard Stauffer, an ice core specialist
at the University of Bern in Switzerland. With only two cycles, he says,
it was difficult to say whether findings indicated general rules or exceptions
in the Earth's history.