The Pacific Decadal Oscillation & El Nino

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  • 0:02 What Is the PDO?
  • 2:44 PDO, El Nino & La Nina
  • 6:11 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Understanding the Pacific Decadal Oscillation, or the PDO, and El Niño allows scientists to better understand weather phenomenon. This lesson explores the PDO, as well as its similarities with El Niño and La Niña.

What Is the Pacific Oscillation?

Imagine a giant blob that lurks in the Pacific Ocean, killing sea birds, damaging the food chain, and causing some species to relocate. So, what is this 'blob'? An oil slick? Toxic waste? Garbage? Nope! Scientists, who actually call it 'the blob,' describe it as a giant chunk of warm ocean water that was first noticed in 2013. Estimates of its size vary, but some say it was 1,000 miles wide by 1,000 miles long by 100 yards deep in 2014, but it continues to grow.

Scientists aren't sure what is causing the blob, but some are blaming the Pacific Decadal Oscillation, or the PDO. The Pacific Decadal Oscillation (PDO) is the cycling change in the surface temperatures of the North Pacific Ocean and can be divided into the warm phase and the cold phase. Scientists started gathering data for this oscillation in 1900 and have records through today. Scientists are unsure what causes the PDO, but they do know each phase of the cycle can last for years, sometimes lasting 20 to 30 years! And the change of ocean temperature also affects winds, temperatures, and precipitation levels on land.

Let's take a moment to briefly look at each phase in the PDO, starting with the warm phase, which causes a rise in the average temperature of surface waters along the Pacific Coast all the way from Alaska to the equator. But the warming is only half of the story. While the coastline warms, the waters further away from the coast actually cool. The warm, coastal waters form a sideways U around the cooler waters.

In addition to warming the surface ocean temperatures, the warm phase of the PDO also influences temperatures and precipitation levels on land. For example, during the winter months, the warm PDO causes colder temperatures in the Southeast United States, warmer temperatures in the Northwest parts of North America, and warmer temperatures in the Northeast. Finally, there is less winter precipitation in the Northwestern parts of North America.

The cold PDO, on the other hand, causes the waters off the Pacific Coastline to cool, and these cold waters form a sideways U around warmer waters further away from the shore. And like the warm PDO, the cold PDO influences weather on land, causing colder winters in the Northwestern parts of North America and warmer winters in the Southeastern United States, as well as increased winter precipitation in the Northwestern parts of North America.

PDO, El Niño and La Niña

You may have heard of other weather phenomenon that warm and cool surface ocean waters, such as El Niño and La Niña. So, you may be wondering what the difference is between the PDO and these phenomena.

So far, we know that the PDO is a cyclic change in water temperature in the North Pacific Ocean, and it can affect winter temperatures and precipitation levels. El Niño is the warming of surface ocean waters near the equator in the Pacific Ocean. From this NASA image, you can see the warm areas as white during this El Niño year:

Warm areas are white during El Niño.
nasa image showing different temps on globe

This increased ocean surface temperature in turn causes weather changes on land. Yep, so far it does sound fairly similar to the warm phase of the PDO, doesn't it?

For El Niño, the weather changes include warmer temperatures in parts of the continent, like Western Canada and the U.S., drier conditions in the Pacific Northwest, and increased precipitation along the Gulf Coast of the U.S., just to name a few.

And it's worth noting there is a La Niña, which is the opposite of El Niño, bringing colder ocean surface temperatures in the Pacific Ocean near the equator, which, in turn, brings a change in temperature to North America. Specifically, colder winters in the Northwest and warmer temperatures in the Southeast. La Niña shares some similarities with the cold phase of the PDO.

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