Pacific coral may predict next spike in global temperatures

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Photo: pacific trade winds
In the equatorial atolls of western Kiribati, a coral record reveals the importance of Pacific winds in modulating global temperatures.

In the middle of the vast Pacific Ocean, somewhere between Hawaii and Australia, sits a tiny island that most people have never heard of, but which may hold a key to understanding why global temperatures rise and fall.

It’s called Tarawa and more than two decades ago, scientists collected a sample of coral from the atoll’s lagoon to study changes in ocean temperature and salinity. The coral wound up in a box, 5,000 miles away at the University of Arizona.

That's where Diane Thompson found it. She's now a post-doctoral fellow with Boulder’s National Center for Atmospheric Research and opening the box with a new question: could the coral be useful for studying climate change?

The answer is "yes."

Thompson says the coral helps gauge the patterns of Pacific trade winds. Corals form growth bands, much like the rings of a tree, and when manganese levels go up and down it signals changes in those winds.

By drilling into the coral and seeing its growth bands, scientists say they can determine when significant changes in the Pacific winds have occurred. Scientists found that periods of high winds coincided with lower rates of global warming.

What appears to be happening, Thompson says, is that the ocean absorbs excess global heat when the winds blow strong. The heat is blown into the depths of the ocean.

At the moment, the trade winds are helping keep the earth from warming at a faster rate than it might otherwise be, according to a study Thompson and her co-authors published today in the journal Nature Geoscience.

“Strong winds in the tropical Pacific are playing a role in the slowdown of warming over the past 15 years,” Thompson says.

She adds that temperatures have not risen significantly since 2001, despite well-documented annual rises in pollution that could contribute to warming around the globe. The good news won't last forever, though.

“When the winds inevitably change to a weaker state, warming will start to accelerate again," she says.

Thompson cannot say by how much temperatures will rise when the winds slow again, but, as a reference, her research indicates that between 1910 to 1940 the globe warmed by 0.4 degrees Celsius as Pacific trade winds slowed considerably.

That doesn’t sound like a significant amount, but it's about a third of the global warming over the past century. Thompson adds that even small changes in temperature can profoundly affect ecosystems. She also notes that prior period of warming came before "massive accumulation of greenhouse gases in the atmosphere."