A satellite image shows plumes of dust blowing east from East Asia toward the Pacific Ocean. Photo by SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE
Jan. 6 (UPI) -- New analysis of dust grains dredged from the bottom of the North Pacific suggests the westerlies moved toward the poles during the warmest stretches of the Pliocene, between 3 and 5 million years ago.
Scientists on Wednesday published their findings in the journal Nature.
The westerlies, sometimes called the anti-trades, are a series of prevailing winds blowing from west to east across the middle latitudes.
Over the last several decades, scientists have noticed the winds slowly migrating away from the equator, inching into higher and higher latitudes.
"Much of the work that has been done in describing changes to the westerlies over the last several decades suggests that warming caused by greenhouse gases may be a major contributor to this movement of the westerlies," lead study author Jordan Abell told UPI in an email.
"In addition, some scientists hypothesize that the ozone hole may also be important," said Abell, a grad student at Columbia University's Lamont-Doherty Earth Observatory.
Scientists were pretty sure about what they were seeing play out across short time-scales that span the last 30 or 40 years. But they were less certain about how the prevailing westerlies might behave as atmospheric carbon levels continue to rise.
To find out, Abell and his research partners looked at layers of marine sediment sourced from the bottom of the ocean.
More specifically, the team of Lamont scientists sought out tiny dust grains blown eastward from East Asia's drylands a few million years ago.
By comparing the dust concentrations at different times and latitudes, they were able to determine that Earth's prevailing westerlies moved away from the equator and toward the poles during the warmest portion of the Pliocene.
Temperatures were several degrees warmer than today. Interestingly, atmospheric CO2 levels during the Pliocene were lower than they are today.
Researchers used two different dating techniques to match sediment layers from cores collected from different parts of the Pacific.
"For our cores, the ages of the sediments were determined either using oxygen isotopes, which allow for very accurate determination of ages, or well-known reversals in Earth's magnetic field that have previously been identified in marine sediments," Abell said.
The findings suggest the poleward shift of the westerlies is likely to continue as human-induced warming continues unabated.
The prevailing westerlies are known to influence everything from ocean circulation to precipitation patterns, and the long-term migration could have big implications for weather patterns across shorter time-scales, researchers said.
"If the winds continue to move poleward, then it is likely that mid-latitude precipitation belt may move poleward as well," study co-author Gisela Winckler told UPI.
Scientists hope their latest findings will help today's climate models more accurately simulate the relationship between climate change and the prevailing westerlies.
"We hope that our work will draw attention from both the modern and paleoclimate modeling communities, and provide further data to test model simulations against," said Winckler, a physicist and isotope geochemist at the Lamont-Doherty Earth Observatory.
"The most effective way to move this forward is likely through direct interaction between modeling and observational communities, and we are trying to do this," Winckler said.