Scientists better understand climate of the past and its relationship to carbon dioxide

Climate change from a historical context was more closely linked to carbon dioxide than previously thought, according to research by the Niels Bohr Institute at the University of Copenhagen. Published in the journal ‘Climate of the Past’, the evidence from ice cores shows that during the transitions between glacial and interglacial, carbon dioxide concentrations followed the temperature very closely, with a maximum lag of only a few hundred years maximum, as opposed to previous estimates with a lag of thousands of years.

The researchers looked at Antarctica in particular, where year after year, ice does not melt, but is compacted into kilometre thick ice. Air trapped between the ice particles are effectively preserved air from the time the snow was laid down, giving the opportunity for scientists to unearth the atmospheric conditions of the past, and in particular the carbon dioxide concentrations of a given period.

"The ice cores show a nearly synchronous relationship between the temperature in Antarctica and the atmospheric content of CO2, and this suggests that it is the processes in the deep-sea around Antarctica that play an important role in the CO2 increase," says Sune Olander Rasmussen, coordinator at the Niels Bohr Institute.

The prevailing theory is that when the continent warms, stronger winds pump water up from the Southern Ocean bottom layers. These lower layers have more CO2 that is then released into the atmosphere. It is a plausible link which means carbon dioxide could increase very quickly following a change in temperatures. It means that natural variations in temperatures could be accentuated by the carbon dioxide, creating feedback effects that mean swift and sometimes drastic changes in climate.

Today, this link between carbon dioxide and the climate has been altered, with the atmospheric changes driving the climate rather than vice versa. As Rasmussen says, "What we are observing in the present day is the mankind has caused the CO2 content in the atmosphere to rise as much in just 150 years as it rose over 8,000 years during the transition from the last ice age to the current interglacial period and that can bring the Earth's climate out of balance."

"That is why it is even more important that we have a good grip on which processes caused the climate of the past to change, because the same processes may operate in addition to the anthropogenic changes we see today. In this way the climate of the past helps us to understand how the various parts of the climate systems interact and what we can expect in the future,” says Rasmussen.