European researchers say greenhouse gases, carbon dioxide and methane, are at their highest levels in 650,000 years.
The findings come from scientists who have analyzed air bubbles trapped for hundreds of thousands of years in Antarctic ice cores.
Analysts for the European Project for Ice Coring in Antarctica say carbon dioxide levels in the atmosphere are currently 27 percent higher than the highest levels in the past 650-thousand years. Methane gas levels are also currently at their peak.
Previously studied air bubbles dated back only 440,000 years. Scientists believe the latest data will help clarify whether human activity has altered the Earth's climate and contributed to global warming.
The research is to be published in Friday's issue of the journal Science.