The greatest climate change in the last 100,000 years was the shift from ice age to the warm interglacial period 19,000 years ago. New research showed temperature rise was closely followed by a rise in carbon dioxide during this shift. Scientists previously thought there was a gap of about 1000 years; new evidence suggested the time delay was just a few hundred years.
The research was carried out by scientists from the Niels Bohr Institute at the University of Copenhagen and the University of Tasmania in Australia. The researchers analyzed ice cores from ice sheets in Antarctica to study the interaction between temperature change and atmospheric carbon dioxide.
Ice sheets act as a blueprint of the atmospheric composition of the past. It is formed by snow that does not melt, but builds up year after year until it is compressed into kilometers of thick ice. During the compression, air is trapped between the snowflakes. As a result, ice contains tiny pockets of ancient atmosphere. The composition of the ice also shows what the temperature was when the snow fell. Hence, the ice is an archive of past climate as well as atmospheric composition.
Five boreholes through the ice sheets in Antarctica were analyzed. The measurements showed a nearly synchronous relationship between the temperature and the atmospheric carbon dioxide. According to Sune Olander Rasmussen, a centre coordinator at the Niels Bohr Institute, the research results suggested processes in the deep-sea around Antarctica played a crucial role in carbon dioxide increase.
Rasmussen explains that it is possible that as Antarctica warms up, it triggers strong winds over the Southern Ocean. These winds pump water vigorously from the deep bottom layers of the ocean where there is a high content of CO2 from the degradation of aquatic organisms that die and fall down to the sea floor. When the CO2-rich bottom water rises to the surface, a portion of the gas is released into the atmosphere. This theory could explain the close link between the rise in temperature and CO2 during the climate change that ended the ice age.
The rise in CO2 also helps to intensify the natural climate variations during that period. It is a greenhouse gas that absorbs and traps heat from the sun, making the Earth warm.
The earth undergoes natural climate variations caused by changes in the earth’s orbit around the sun, the earth’s tilt and the orientation of the earth’s axis. These are called Milankowitch cycles and occur in approximately 100,000, 42,000 and 22,000-year periods. These cycles cause the Earth’s climate to shift between long ice ages of around 100,000 years and warm interglacial periods of around 10,000 to 15,000 years.
According to Rasmussen, the natural cycle of the earth’s climate change is out of balance because of human activities. The global rise in CO2 in the last 150 years is equivalent to over 8,000 years of transition from the last ice age. He asserts that it is vital we have a good understanding of the processes of climate change of the past to be better prepared for the future.
The results of this research were published in the scientific journal Climate of the Past.