New research in Antarctica shows CO2 follows temperature "by a few hundred years at most"

The question of “which comes first, the temperature or the CO2 rise?” has been much like the proverbial “which came first, the chicken or the egg?” question. This seems to settle it – temperature came first, followed by an increase in CO2 outgassing from the ocean surrounding Antarctica.

“Our analyses of ice cores from the ice sheet in Antarctica shows that the concentration of CO₂ in the atmosphere follows the rise in Antarctic temperatures very closely and is staggered by a few hundred years at most,” – Sune Olander Rasmussen

From the University of Copenhagen – Rise in temperatures and CO2 follow each other closely in climate change

The greatest climate change the world has seen in the last 100,000 years was the transition from the ice age to the warm interglacial period. New research from the Niels Bohr Institute at the University of Copenhagen indicates that, contrary to previous opinion, the rise in temperature and the rise in the atmospheric CO₂ follow each other closely in terms of time. The results have been published in the scientific journal, Climate of the Past. 

In the warmer climate the atmospheric content of CO₂ is naturally higher. The gas CO₂ (carbon dioxide) is a green-house gas that absorbs heat radiation from the Earth and thus keeps the Earth warm. In the shift between ice ages and interglacial periods the atmospheric content of CO₂ helps to intensify the natural climate variations.

It had previously been thought that as the temperature began to rise at the end of the ice age approximately 19,000 years ago, an increase in the amount of CO2 in the atmosphere followed with a delay of up to 1,000 years.

“Our analyses of ice cores from the ice sheet in Antarctica shows that the concentration of CO₂ in the atmosphere follows the rise in Antarctic temperatures very closely and is staggered by a few hundred years at most,” explains Sune Olander Rasmussen, Associate Professor and centre coordinator at the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen.

Deep-sea’s important role

The research, which was carried out in collaboration with researchers from the University of Tasmania in Australia, is based on measurements of ice cores from five boreholes through the ice sheet in Antarctica. The ice sheet is formed by snow that doesn’t melt, but remains year after year and is gradually compressed into kilometers thick ice. During the compression, air is trapped between the snowflakes and as a result the ice contains tiny samples of ancient atmospheres. The composition of the ice also shows what the temperature was when the snow fell, so the ice is an archive of past climate and atmospheric composition.

“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,” explains Sune Olander Rasmussen.

He explains that one of the theories is that when Antarctica warms up, there will be stronger winds over the Southern Ocean and the winds pump more water up from the deep bottom layers in the ocean where there is a high content of CO₂ from all of the small organisms that die and fall down to the sea floor and rot. When strong winds blow over the Southern Ocean, the ocean circulation brings more of the CO_2-rich bottom water up to the surface and a portion of this CO₂ is released into the atmosphere. This process links temperature and CO₂ together and the new results suggest that the linking is closer and happens faster than previously believed.

Climatic impact

The global temperature changed naturally because of the changing solar radiation caused by variations in the Earth’s orbit around the Sun, the Earth’s tilt and the orientation of the Earth’s axis. These are called the Milankowitch cycles and occur in periods of approximately 100,000, 42,000, and 22,000 years. These are the cycles that cause the Earth’s climate to shift between long ice ages of approximately 100,000 years and warm interglacial periods, typically 10,000 – 15,000 years. The natural warming of the climate was intensified by the increased amount of CO₂ in the atmosphere.

“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,” explains Sune Olander Rasmussen adding “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.”

• The article in the Climate of the Past >>

Tightened constraints on the time-lag between Antarctic temperature and CO₂ during the last deglaciation

J. B. Pedro^1,2, S. O. Rasmussen³, and T. D. van Ommen^2,4

¹Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia

²Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia

³Centre for Ice and Climate, University of Copenhagen, Copenhagen, Denmark

⁴Australian Antarctic Division, Kingston, Tasmania, Australia

Abstract. Antarctic ice cores provide clear evidence of a close coupling between variations in Antarctic temperature and the atmospheric concentration of CO₂ during the glacial/interglacial cycles of at least the past 800-thousand years. Precise information on the relative timing of the temperature and CO₂ changes can assist in refining our understanding of the physical processes involved in this coupling. Here, we focus on the last deglaciation, 19 000 to 11 000 yr before present, during which CO₂ concentrations increased by ~80 parts per million by volume and Antarctic temperature increased by ~10 °C. Utilising a recently developed proxy for regional Antarctic temperature, derived from five near-coastal ice cores and two ice core CO₂ records with high dating precision, we show that the increase in CO₂ likely lagged the increase in regional Antarctic temperature by less than 400 yr and that even a short lead of CO₂ over temperature cannot be excluded. This result, consistent for both CO₂ records, implies a faster coupling between temperature and CO₂ than previous estimates, which had permitted up to millennial-scale lags.

Final Revised Paper (PDF, 463 KB)   Discussion Paper (CPD)

Citation: Pedro, J. B., Rasmussen, S. O., and van Ommen, T. D.: Tightened constraints on the time-lag between Antarctic temperature and CO₂ during the last deglaciation, Clim. Past, 8, 1213-1221, doi:10.5194/cp-8-1213-2012, 2012.