What is the Pacific Decadal Oscillation (PDO)?

The Pacific Decadal Oscillation (PDO) is a long-term climate pattern that affects the temperature of the Pacific Ocean and the weather patterns around it. The PDO is a naturally occurring phenomenon that shifts between warm and cool phases, with each phase lasting around 20-30 years. The Pacific Decadal Oscillation can strongly impact global weather and is important in long-range weather forecasting

The Pacific Decadal Oscillation – Introduction 

The Pacific Decadal Oscillation is a sea surface temperature (SST) climate cycle (or teleconnection) describing sea surface temperature anomalies over the Northeastern Pacific Ocean.  As it’s name suggests the SSTs associated with the PDO exhibit decadal variability. The PDO can influence the weather conditions across North America and the Pacific Ocean basin with characteristic patterns occurring at different times of the year. 

The PDO oscillates between positive and negative phases. The positive phase is characterized by cool SSTs north of Hawaii and warmer-than-normal sea surface temperatures along the western coast of North America. (Figure 1). The negative phase is a mirror image with warm ocean temperatures in the Central North Pacific and cooler than normal waters along the western coast of North America (Figure 2). 

Fig. 1: SST anomalies over the North Pacific Ocean during a positive Pacific Decadal Oscillation, showing a vast cool area north of Hawaii and warmer than normal waters near the North American coast
Fig. 2: SST anomalies over the North Pacific Ocean during a negative Pacific Decadal Oscillation, showing a vast warm area north of Hawaii and cooler than normal waters near the North American coast



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What is the Pacific Decadal Oscillation – Positive Phase Impacts 

Positive PDO Impacts – North American winter 

During the positive phase of the PDO in the northern hemisphere wintertime, the Southern and Eastern US is more likely to experience above normal temperatures, with below temperatures more likely in the West and Northwest (Figure 3). 

At the same time, the Northern Rockies and the Midwest are likely to be drier than normal, while Texas, the Gulf states, and the East are likely to be wetter than normal (Figure 4). 

Fig. 3: World Climate Service temperature anomaly probability map for a positive Pacific Decadal Oscillation in winter 
Fig. 4: World Climate Service rainfall anomaly probability map for a positive Pacific Decadal Oscillation in winter

Positive Pacific Decadal Oscillation Impacts – Asian Winter 

During the positive phase of the PDO in the northern hemisphere wintertime, much of Asia is usually cooler than normal, with above normal temperatures more likely over India (Figure 5). 

At the same time, China and Japan are likely to be drier than normal, while India often has a winter that is wetter than normal (Figure 6). 

Fig. 5: World Climate Service temperature probability map for a positive Pacific Decadal Oscillation in winter
Fig. 6: World Climate Service rainfall probability map for a positive Pacific Decadal Oscillation in winter

What is the Pacific Decadal Oscillation – Negative Phase Impacts

Negative Pacific Decadal Oscillation Impacts – North American Winter 

During the negative phase of the PDO in wintertime, much of the lower 48 is usually warmer than normal. The West coast and the Northwest are normally colder than normal (Figure 7). 

At the same time, many parts of the US will see drier than normal weather, but there are some notable exceptions. During a negative PDO, winter rainfall is usually above normal for the Ohio and Tennessee Valleys as well as the Northern Rockies and Plains (Figure 8). 

Fig. 7: World Climate Service temperature probability map for a negative Pacific Decadal Oscillation in winter
Fig. 8: World Climate Service rainfall anomaly probability map for a negative Pacific Decadal Oscillation in winter

Negative Pacific Decadal Oscillation Impacts – Asian Winter

During the negative phase of the PDO in the northern hemisphere wintertime, much of India and China is usually cooler than normal, But Japan has warmer than normal weather, especially in the North (Figure 9).

At the same time, Japan and Northwest China are usually wetter than normal, while Southwest China and much of India are usually wetter than normal (Figure 10).

Pacific Decadal Oscillation
Fig. 9: World Climate Service temperature probability map for a negative Pacific Decadal Oscillation in winter
Fig. 10: World Climate Service rainfall probability map for a negative Pacific Decadal Oscillation in winter

The World Climate Service provides a powerful data mining system which enables users to quickly explore the Pacific Decadal Oscillation, and many other indices, by phase for each month of the year, showing impacts on all the major weather parameters all around the globe.

El Niño/Southern Oscillation (ENSO) and the PDO

Both ENSO and the Pacific decadal oscillation are important sea surface-based phenomena that influence weather conditions in the Pacific basin. There is extensive scientific literature reviewing the interactions between ENSO events and their relationship with the PDO, which is too extensive to cover here. We present in Figure 11 a well-known relationship between the two phenomena.

Figure 11. The three months rolling averaged ENSO multi-variate index (MEI) vs. the three months rolling averaged PDO index from 1941-2022.

Figure 11 shows that when ENSO is in the El Niño phase (positive MEI), the PDO is also positive. This has occurred in 32% of the time since 1941. Likewise, when ENSO is in the La Niña phase (negative MEI) the PDO tends to be negative and has occurred approximately 35% of the time.



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Pacific Decadal Oscillation and Long Range Forecasting

The Pacific Decadal Oscillation typically remains in a given phase for many years or even decades (Figure 12), but there can be some variation within a given decadal phase. 

Pacific Decadal Oscillation
Figure 12: The PDO climate index history from 1990

At the turn of the century, the PDO entered a long-term negative phase, but there was a positive hiatus between 2014 and 2019. Owing to the long-lasting phases of the PDO and their impact on Northern Hemisphere climates, this climate index is very useful for seasonal prediction.

Pacific Decadal Oscillation: Current Phase

As of May 2023, the Pacific decadal oscillation is in a negative phase with the index reaching approximately -2.0. The negative phase started in late 2019 and reached its nadir in late 2021 with an index value of approximately -2.9, as shown below in the graphic of daily PDO values. The PDO has been in a negative phase for about 2.5 years.

Figure 13: The PDO climate index history from 2019 to May 2023

Pacific Decadal Oscillation Forecast: 2023

As of November  2023, the Copernicus Climate Change Service seasonal climate forecast models are predicting the Pacific decadal oscillation to increase over the next 5 months to near neurtral.  The graphic below is a screenshot of the World Climate Service climate index forecasting content.

Pacific Decadal Oscillation Forecast
Figure 14: The PDO index forecast as of May 2023


The Pacific Decadal Oscillation is a cyclical variation of sea surface temperature anomalies over the North Pacific Ocean that influences weather patterns across large parts of Asia and North America. 

The Pacific Decadal Oscillation phases persist for many years which makes the PDO a prime consideration in seasonal forecasting. 

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