With the first in-depth analysis of the air bubbles trapped in the ice core of east Antarctica, scientists have discovered that today's atmospheric carbon dioxide levels are the highest in 650,000 years.
The analysis highlights the fact that today's rising atmospheric carbon dioxide concentration, at 380 parts per million by volume, is already 27 percent higher than its highest recorded level during the last 650,000 years, reported scientists in two papers in the Nov. 25 issue of the journal Science.
One study chronicles the stable relationship between climate and the carbon cycle during the Pleistocene (650,000 to 390,000 years ago). The second paper documents atmospheric methane and nitrous oxide levels over the same period.
Carbon dioxide and methane, known as greenhouse gases, are blamed for global warming. Scientists believe that humans have been accelerating the global warming trend by emitting more greenhouse gas through industrialization.
The ice core from Antarctica, containing hundreds of thousands of years-worth of atmospheric air samples within tiny bubbles trapped in the ice, adds to this argument by extending Earth's greenhouse gas record by 210,000 years.
The new records should help scientists better understand climate change and the nature of the current warm period on Earth, and may also aid researchers in reducing uncertainty in predictions of future climate change, said the researchers.
"We have added another piece of information showing that the timescales on which humans have changed the composition of the atmosphere are extremely short compared to the natural time cycles of the climate system," Thomas Stocker, senior author for both studies, said in a statement.
The new studies confirm the stable relationship between the Antarctic climate and greenhouse gases carbon dioxide and methane during the last four glacial cycles.
The ice core analysis also extends this relationship back another two glacial cycles, to a time when the warm "interglacial" periods were milder and longer than more recent warm periods, according to the researchers.
The new atmospheric and climate records from the ice core also indicate that the response of the natural carbon cycle to climate warming remains the same over time, explained the researchers.
The new ice core analysis provides insights on our present interglacial warm period through a glimpse into Antarctic climate and greenhouse gas concentrations during the most recent warm period that is relatively similar to our current warm period. Known as Marine Isotope Stage 11 or MIS 11, this analog warm period occurred between 420,000 and 400,000 years ago.
The similarities between our current warm period and MIS 11 are primarily due to a similar configuration of the orbits of the Earth around the Sun: the relative positions of the Earth and Sun are thought to be the key driver of ice age cycles.
"MIS 11 shows us that the climate system can indeed reside in a warm period for 20,000 or 30,000 years, something that we can't say based on the last three warm phases which are no longer than about 10,000 years each," said Stocker.
The greenhouse gas record also provides indirect evidence for abrupt climate change in the past, the researchers found. This suggests that abrupt climatic events on time scales relevant to societies may be common features of the last climatic cycles.