There has been much speculation about what exactly caused the end of the last ice age 10,000 years ago. Some say the Earth’s orbital changes were the cause, others say it was an increase in atmospheric CO2.

But although a correlation between rising CO2 levels and deglaciation became clear from records of the past millions of years, the latter explanation seemed to have been disproven due to the fact that warming during the last ice age seemed to precede rising CO2 levels, as shown by Antarctic ice samples.

But a comprehensive study of global data now shows that the situation in Antarctica was an exception and that in fact in most parts of the world warming did follow rising CO2 levels.

As described in their paper in Nature, the Harvard research team used seven different records of past temperatures, among which ice cores, the chemical composition of fossilised microscopic life and ancient pollen. In total they collected 80 measurements from all over the world and compared them to CO2 records.

Measurement location map

Lack of data

They found an unmistakable correlation between rising CO2 levels at the end of the ice age and rising global temperatures, with the temperatures trailing CO2 levels at every location except at Antarctica.

According to the researchers the fault in previous studies was a lack of data. While CO2 levels from Antarctic ice cores are an accurate measurement for global CO2 levels, temperature records from Antarctica are not necessarily an exact representation of global temperatures.

Antarctica

The researchers also present an explanation for the lag in CO2 increase compared to rising temperatures on Antarctica: a shift in ocean current. The conveyor belt normally moves heat from south to north, away from Antarctica, which is the reason for a slightly higher average temperature of the Northern Hemisphere than the Southern Hemisphere. A disturbance or shutdown of these ocean currents that transport heat away from Antarctica would result in faster rising temperatures in the south.

As for the other hypothesis of orbital changes [although previously debunked], according to the researchers, they may have given rising temperatures a small kick start, but not nearly enough to move Earth out of the ice age.

CO2 was the real driving factor of global warming during the last glaciation. The origin of the extra CO2 however remains a mystery, although theories exist.

© Jorn van Dooren | www.bitsofscience.org