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An analysis of the global carbon cycle and climate for a 70,000-year period in the most recent Ice Age shows a strong correlation between carbon dioxide levels and abrupt changes in climate.

The findings, published 11 September in the online edition of the journal Science, shed further light on the fluctuations in greenhouse gases and climate in Earth’s past, and appear to confirm the validity of the types of computer models that are used to project a warmer climate in the future, researchers said.

We’ve identified a consistent and coherent pattern of carbon dioxide fluctuations from the past and are able to observe the correlation of this to temperature in the northern and southern hemispheres. This is a global, interconnected system of ocean and atmosphere, and data like these help us better understand how it works.

—Prof. Ed Brook, Oregon State University

The analysis was made by studying the levels of carbon dioxide and other trace gases trapped as bubbles in ancient ice cores from Antarctica.

In the last Ice Age, as during most of Earth’s history, levels of carbon dioxide and climate change are intimately linked. Carbon dioxide tends to rise when climate warms, and the higher levels of carbon dioxide magnify the warming, Brook said. These natural cycles provide a “fingerprint” of how the carbon cycle responds to climate change.

The level of atmospheric carbon dioxide today is about 385 parts per million, or more than double that of some of the lower levels during the Ice Age. These changes have taken place at a speed and magnitude that has not occurred in hundreds of thousands of years, if not longer. Past studies of ice cores have suggested that Earth’s temperature can sometimes change amazingly fast, warming as much as 15 degrees in some regions within a couple of decades.

Before humans were affecting the Earth, what we are finding is regular warm and cold cycles, which both began and ended fairly abruptly. This study supports the theory that a key driver in all this is ocean currents and circulation patterns, which created different patterns of warm and cold climates depending on the strength of various parts of the global ocean circulation system.

—Ed Brook

One of the primary circulation patterns is the meridional overturning circulation. When that current is moving large amounts of warm water from the equator to the north, it helps to warm the high latitude parts of the Northern Hemisphere, and particularly the North Atlantic region. When the system stops or dramatically slows, as it has repeatedly in the past, Greenland and Europe get much colder while the Antarctic regions become warmer, Brook said.

In every historic sequence we observed, the abrupt warming of Greenland occurred about when carbon dioxide was at maximum levels. And that was during an Ice Age, and at levels of atmospheric carbon dioxide that are far lower than those we have today.

—Ed Brook

Resources

• Jinho Ahn and Edward J. Brook (2008) Atmospheric CO₂ and Climate on Millennial Time Scales During the Last Glacial Period. Science DOI: 10.1126/science.1160832

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