The Hot Zone

Catch a cold

Posted by Alison Hawkes on June 21, 2010
Category : Climates of the Past, The Oceans

Climate change has made apparent the interconnectedness of Earth systems. That sometimes doesn’t match with our human experience of the vastness of the world, where we dump trash elsewhere, fish the oceans without limit, and send pollutants into the atmosphere thinking nothing will ever come back at us.

Yet a study published in a recent journal of Science is a reminder of how change in one place can ripple to the far reaches of the globe. Data from as far back as 3.5 million years ago shows that when the polar ice sheets grow and recede, tropical waters far to the South get nippier and warmer as well.

Models predict that the direct effects of large ice sheets would extend some 2,000 km, but not far enough to alter tropical water temperatures.

Greenland ice sheet. Photo from NASA.

Greenland ice sheet. Photo from NASA.

“What surprised us is that the tropics seemed to shiver when the polar latitudes get cold, and they warm up when the ice ages pass,” said Timothy Herbert of Brown University and a lead author of the paper.

The link between the oceans, researchers believe, has to do with carbon dioxide levels. The polar oceans absorb a lot of it and can draw down atmospheric levels by as much as 30 percent.

The changes in CO2 impact the tropical oceans, which have a powerful influence over global climate conditions. Warm tropical oceans produce water vapor, which drives global rainfall patterns and is a potent greenhouse gas warmer.

The researchers examined the remains of plankton in sediment cores under tropic waters to establish surface sea temperature going back in time from the onset of the Earth’s ice age oscillations. There have been 45 separate ice ages since 2.7 million years ago.

They found a near perfect match between ice sheet expansion/ retraction and tropical surface water temperatures over time.

“We think the best explanation that would connect these changes so far away from each other is a dominant role for carbon dioxide to help coordinate changes between different parts of the climate system,” said Herbert. “That’s the best explanation for why we see these patterns.”

The odd thing is that the CO2 feedback seems to be strengthening.

“It’s like those movies of a bridge that starts shaking and then shakes more and more wildly as time goes on,” says Herbert. “As we come toward today the ice age cycles and the carbon dioxide effects become bigger and bigger. We don’t understand why that’s changed over time.”

Modern day climate conditions don’t escape these influences.

“We don’t understand human activity as we affect the globe, how those are going to cascade or show up in other parts of the system,” Herbert said. “From our study we can say that the areas that don’t directly feel climate change will sooner or later almost certainly feel a very strong change.”

-Alison Hawkes

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