Over time, warming events in Greenland and the North Atlantic were followed by gradual cooling. These changes correlate well with the concentration of nitrous oxide found in ice core samples. Antarctic temperature variations, on the other hand, were smaller and more gradual. They correlate highly with carbon dioxide (CO2) concentrations found in ice core samples. They also show warming during the Greenland cold phase and cooling while the North Atlantic was still warm.

Scientists believe abrupt changes in the Atlantic meridonial overturning circulation, the dominant north-south ocean circulation current in the Atlantic, caused the observed abrupt climate changes in the North Atlantic. Climate modelers from Oregon State University have modeled an episode of abrupt climate change that shows remarkable agreement with observed concentrations of greenhouse gases. They concluded that ocean circulation changes were primarily responsible for driving CO2 and nitrous oxide fluctuations during glacial periods on millennial time scales.

Ultimately, the model’s agreement with ice core sample evidence lends credibility to the hypothesis that ocean circulation modulates variations in greenhouse gases. This knowledge may also help scientists postulate a solution for climate change.