Researchers have stated that a phenomenon called the Pacific Decadal Oscillation or PDO, is causing an apparent ‘pause’ or ‘slowdown’ in the warming of the planet’s surface since 2000.
PDO is a naturally occurring wobble in the planet’s climate system that involves the burial and release of heat by the Pacific Ocean.
These ocean winds have natural cycles of waxing and waning. The researchers have stated that the last 15 to 20 years have seen strong trade winds forcing heat down into the ocean depths. They added that this has forced surface heat deep beneath the ocean, which has resulted in a slowdown in warming over surrounding land surfaces. However, the slowdown is only temporary.
For their study, the researchers used a large number of climate change model simulations to investigate the apparent ‘pause’ in surface warming of late. They also ran multiple climate model simulations to capture how external ‘forcings’, or factors like human-induced carbon dioxide emissions, were expected to drive an overall climate warming trend in recent years. Then they discarded this forced aspect of warming from the actual history of recent temperatures, and sought to identify natural or internal modes of climate variability that could explain the difference between the two.
They found that PDO was responsible for the ‘pause’ or ‘slowdown’. They also found that it was a temporary phase.
Aiguo Dai, associate professor of Atmospheric Sciences at the University at Albany-SUNY, and the lead author of the study, said, “During a cold or negative PDO/IPO phase, the tropical Pacific remains in relative cold condition while the central North Pacific is warm, but the global-mean temperature tends to be lower during the negative phase, as shown in our study. Because of this, phase changes of the PDO/IPO have implications for the global warming rate.”
The findings were published in the Nature Climate Change journal.