Pacific Ocean winds may be the cause behind a global warming hiatus recorded by environmentalists since the turn of the century. The slowdown in rising temperatures could be driven by a change in circulation patterns, which began in 1999 in the world's largest ocean.
The Pacific Decadal Oscillation (PDO) alters temperatures in the northern and southern Pacific Ocean. This effect is similar to the more-familiar El Niño Southern Oscillation.
Researchers examined records dating back to 1791, which revealed that the PDO entered a cool phase just prior to the start of the global warming hiatus. This resulted in equatorial waters becoming cooler, as polar regions warmed. These effects were felt 2,300 feet beneath the surface of the water in subtropical regions, researchers report.
Extra atmospheric heat which would normally would have raised global temperatures was, instead, channeled into oceans, leading to a slowdown in rising global temperatures.
"Because the ocean is in contact with the atmosphere, there's heat exchange between the atmosphere and the surface ocean. It seems that about 90 percent of the heat that should be in the atmosphere right now with all that extra CO2 [humans have emitted since 1999] has gone into the ocean," said Braddock Linsley from the Lamont-Doherty Earth Observatory at Columbia University.
The PDO is one facet of the circulation of wind and water around the Pacific, known as the Interdecadal Pacific Oscillation.
Data collected during the 224 years examined in the study is inconsistent, especially prior to 1950, adding to challenges examining how the PDO could affect the reduction of rising global temperatures over the last 15 years. Researchers developed a historical model of the PDO since 1791, utilizing coral fossils to determine past conditions. They found that the PDO fluctuates on a semi-regular basis, once every 20 to 25 years.
This schedule would suggest that if a cooling period began 15 years ago, the world may quickly be heading into a warming period. Researchers believe warming may have started in April 2014. That year was the warmest on record, and many areas along the East Coast of the United States experienced record snowfalls. If the Pacific Ocean does quickly warm during a reversal of the PDO, global warming could enter a new, more dangerous, phase.
Future research could examine further physical records of temperatures going back thousands of years to better understand the effect of the cyclical processes.
Analysis of the PDO and the effect of the atmospheric condition on rising global temperatures since the year 2000 was detailed in the journal Geophysical Research Letters.
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