Current levels of the greenhouse gases carbon dioxide and methane in the atmosphere are higher now than at any time in the past 650,000 years.
That is the conclusion of new European studies looking at ice taken from 3km below the surface of Antarctica.
The scientists say their research shows present day warming to be exceptional.
Other research, also published in the journal Science, suggests that sea levels may be rising twice as fast now as in previous centuries.
The evidence on atmospheric concentrations comes from an Antarctic region called Dome Concordia (Dome C).
By Richard Black
Environment Correspondent, BBC News website