The Pacific Decadal Oscillation is a variation of weather patterns, sea surface temperature and currents in the Pacific that changes back and forth over approximately one to three decades. This natural phenomenon is referred to as the "PDO" for short.
The PDO has positive and negative phases. In its positive or warmer phase, higher than normal sea surface temperatures are found stretching from the western coast of North America down through the Equatorial Pacific. This is similar to sea surface temperatures in an El Niño event, but the PDO is on a much larger scale. This phase creates lower-than-normal pressure in the Pacific, which can yield more high-pressure ridging over western North America.
In the PDO's negative or cool phase, it's the opposite of what you might imagine. Cooler sea surface temperatures are prevalent with a warm core through the north-central Pacific. This scenario is similar to a La Niña event, but again, the PDO is much larger. In this setup, there is higher pressure anomalies over the ocean, potentially leaving western North America with a trough that would create stormier and cooler weather.
The Pacific Decadal Oscillation is referred to as the "daddy" of El Niño/La Niña. Like that smaller oscillation, the PDO will influence weather events around the world, especially in North America. A positive PDO contributes to more warming of the Earth, while a negative or cold phase will slow global warming or even cool the planet.
The current PDO is negative, and this graph shows it's the strongest negative phase in recorded history. This, along with numerous other global oscillations, create different patterns across the earth and to what extreme is yet to be seen.
