Coral shows signs of global warming, providing a clear visual record of climate change, new research reveals.

University of Arizona (UA) and National Center for Atmospheric Research (NCAR) researchers examined chemical changes in coral, allowing investigators to read a record of trade winds in the Pacific Ocean.

Pacific trade winds shifted during the 20th Century, greatly influencing global temperatures, a process that could also be contributing to current climate measurements. Weak trade winds from 1910 to 1940 contributed to warming during that period, researchers found, while stronger air currents between 1940 and 1970 caused temperatures to moderate.

Some climatologists believe that strong trade winds in recent years could be responsible for a global warming hiatus since the turn of the millennium. This new study of coral lends additional evidence to this idea, possibly explaining the mechanism behind a slowdown of global warming. Once trade winds again die down, researchers warn, temperatures will once again start to rise.

"Strong winds in the tropical Pacific are playing a role in the slowdown of warming over the past 15 years. When the winds inevitably change to a weaker state, warming will start to accelerate again," Diane Thompson, a postdoctoral scientist at NCAR, said.

Human activities have poured vast amounts of carbon dioxide and other greenhouse gases into the atmosphere since the year 2001, yet global temperatures have not risen, on average, since that time. This has left climatologists scrambling to understand where the excess heat is going. Researchers in this study believe heat may be carried into the subsurface ocean by powerful trade winds, racing across equatorial regions of the Pacific. This process brings colder water up to the surface, removing heat from the atmosphere. Rising global temperatures can be temporarily negated by these actions, but the process could reverse once Pacific trade winds die out once again.

Strong trade winds kick up sediment and material from the sea bottom in shallower bodies in the Pacific. A piece of coral, living in a lagoon near a small island, absorbed greater concentrations of manganese during times of high winds than at other periods. That specimen was examined to reveal the record of Pacific winds.

"Mother Nature is always going to inject little ups and downs along our path to a warmer world. We're trying to understand how those natural variations work so that scientists can do a better job of predicting the actual course of climate change into the future," Julia Cole of the University of Arizona, and co-author of an article announcing the results of the study, said.

The role of Pacific trade winds in moderating global warming was profiled in the journal Nature Geoscience.