Researchers used a novel method of analyzing chemical changes in coral to demonstrate that weak Pacific trade winds are linked to global warming in the early 20th century.
The findings suggest these Pacific trade winds are helping prevent global temperatures from rising despite increases of greenhouse gas, but this process will most likely resume if the winds weaken, the National Center for Atmospheric Research (NCAR) reported.
"Strong winds in the tropical Pacific are playing a role in the slowdown of warming over the past 15 years," said lead author Diane Thompson, a postdoctoral scientist at NCAR. "When the winds inevitably change to a weaker state, warming will start to accelerate again."
Despite clear increases in atmospheric greenhouse gases, the global surface temperature has not significantly risen since 2001. A past study suggested the phenomenon could be linked to Pacific trade winds driving heat deep into the ocean and bringing cold water to the surface.
The recent study focused on the early 20th century, when a third of the century's global warming took place before greenhouse gas accumulation was even an issue. The research team looked at an old core taken from a coral skeleton from the ocean off a western tropical Pacific island in order to determine Pacific wind patterns between 1894 and 1982.
When strong winds blow in from the west they can stir up manganese in sediment at the bottom of the ocean, these types of winds usually occur when trade winds from the east are especially weak. The local coral cores took up the manganese in their skeletons as they grew, giving the scientists clues to wind behavior during that time period.
The analysis revealed spiked in the manganese-to-calcium ratio from about 1910 to 1940, which is when the Earth experienced significant warming. The team also compared manganese-to-calcium ratios and wind observations in the 1960s, and found a link between this phenomenon and weaker trade winds.
The team noted wind changes are only one contributing factor to the leveling off, of global warming, and influences such as increased industrialization and emissions of sunlight-blocking particles were most likely also involved.
"This research shows that the influence of winds on climate is not anything new. These mechanisms have been at work earlier," Thompson concluded. "We believe this is a significant contribution to understanding the role of natural processes in modulating global temperature change."
The findings were published in a recent edition of the journal Nature Geoscience.
