Understanding and have records through today. Scientists

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

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.

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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.
Difference PDO El Niño and La Niña
Time Decades Months
Area Mainly North Pacific but can include lower latitudes Mainly lower latitudes but can impact North Pacific
Phases Warm phase is like El Niño, whereas cold phase is like La Niña One phase only

An interesting tidbit though: when the PDO is in the warm phase, scientists believe it intensifies El Niño, and when it’s in the cold phase, it intensifies La Ni;a.So, back to that blob from the beginning of the lesson. Scientists aren’t sure if the PDO is to blame, but they’re seeing strange things as a result of this increased water temperature, such as species that are not usually found in Alaskan waters showing up, like tuna, sunfish, and pygmy killer whales.

And some species, like the copepod, which are small critters at the base of the food chain, are moving further north, which is causing problems for marine animals that feed on them. Although this ocean warming might not end up being part of the PDO, scientists did conduct a study on the PDO and how it affected salmon species. They found that the salmon did better during the cold phase, whereas they declined during the warm phase, so it isn’t a stretch to think the PDO may be having some effect on marine life.But back to the blob. In addition, this mysterious ocean warming has caused some strange weather in the Pacific Northwest, like increased thunderstorms and forest fires. And in California, there has been an increase in droughts. So, the jury is still out on whether or not the PDO is causing the ocean warming at this time, but understanding the PDO, El Niño, and La Niña will help scientists better understand the blob and what its long-term effects may be on the Pacific Ocean.

Lesson Summary

The Pacific Decadal Oscillation (PDO) is the cyclic fluctuation of surface ocean temperatures in the North Pacific and can last for decades. In addition to impacting some marine animals, like salmon, this fluctuation can cause precipitation and temperature to deviate from the average on land.There are hot and cold phases of the PDO. El Niño is similar to the warm phase of the PDO, but it is warming of surface waters near the equator of the Pacific Ocean, and it can also affect the North Pacific.

La Niña is similar to the cold phase of the PDO and is a cooling of surface ocean temperatures near the equator of the Pacific Ocean. While El Niño and La Niña are short-lived, the PDO is not. And while El Niño and La Niña mainly impact equatorial waters, the PDO’s impact is mostly in the North Pacific.

Learning Outcomes

Following this lesson, you’ll have the ability to:

  • Describe the Pacific Decadal Oscillation (PDO)
  • Explain the differences, similarities and relationship between the PDO, El Niño and La Niña

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