Uncertainties and Misunderstood Natural Effects of the Pacific Decadal Oscillation and ENSO State: Out-of-Phase Dynamics and Their Implications for Local and Global Climate, Farming, and Fisheries.

Author: David I Birch

Affiliation: Independent Oceanic Researcher Date: March 24, 2025

Abstract

The Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) are dominant drivers of interannual to decadal climate variability, yet their interactions and natural effects remain poorly understood. This paper explores the uncertainties surrounding these phenomena, particularly when their phases are misaligned (e.g., negative PDO with El Niño or positive PDO with La Niña), which can dampen or obscure expected climatic outcomes. We assess the implications for local and global climate, weather patterns, temperature anomalies, and their cascading effects on agriculture and fisheries. Case studies from the North Pacific and adjacent regions, including data from 1977, 1998, and 2015–2016, illustrate these dynamics. Our analysis highlights the need for a critical re-examination of oversimplified climate narratives and improved predictive frameworks to address these complex interactions.

1• Introduction

The Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) are oceanic-atmospheric phenomena that exert profound influence on global climate systems. The PDO, characterized by decadal-scale sea surface temperature (SST) anomalies in the North Pacific (north of 20°N), oscillates between warm (positive) and cool (negative) phases, typically lasting 20–30 years (Mantua et al., 1997). In contrast, ENSO operates on shorter timescales (6–18 months), with El Niño (warm phase) and La Niña (cool phase) driving equatorial Pacific SST anomalies and atmospheric teleconnections (Trenberth, 1997). While their individual impacts are well-documented, the interplay between PDO and ENSO—especially when out of phase—introduces significant uncertainties that challenge predictive models and conventional interpretations.

Out-of-phase conditions, such as a negative PDO coinciding with El Niño or a positive PDO with La Niña, can dampen or mask the expected effects of ENSO, leading to misunderstood natural variability. This paper critically examines these dynamics, their influence on local and global climate, weather, and temperature, and their socioeconomic consequences for farming and fisheries. We incorporate case studies to ground our analysis in historical events, emphasizing the need to move beyond simplistic climate narratives.

2. Uncertainties in PDO and ENSO Interactions.

The PDO is not a singular mode of variability but an aggregate of processes, including ENSO teleconnections, stochastic atmospheric forcing, and North Pacific gyre dynamics (Newman et al., 2016). This complexity introduces uncertainty in attributing causality to observed climate shifts. Similarly, ENSO’s influence extends beyond the tropics via atmospheric bridges (e.g., Rossby wave propagation), yet its interaction with the PDO remains inadequately resolved in models (Kumar et al., 2013). A key misunderstanding lies in assuming PDO amplifies ENSO linearly, when evidence suggests out-of-phase alignments can neutralize or reverse expected outcomes.

For instance, a negative PDO features cooler SSTs along the North American coast and a weaker Aleutian Low, potentially counteracting the warm, wet conditions typically associated with El Niño. Conversely, a positive PDO, with warmer coastal SSTs and a stronger Aleutian Low, may offset La Niña’s cooling and drying tendencies. These interactions challenge the reliability of seasonal forecasts and highlight gaps in our understanding of natural variability versus anthropogenic signals.

3. Out-of-Phase Dynamics and Climatic Effects.

3.1 Local Climate and Weather.

Out-of-phase PDO and ENSO states can significantly alter local weather patterns. During a negative PDO, cooler North Pacific SSTs weaken the jet stream’s intensity, reducing storminess along the North American west coast. When paired with El Niño, this can suppress the expected increase in precipitation, as seen in California during the 1997–1998 El Niño event amid a transitioning PDO phase (Gershunov & Barnett, 1998). Conversely, a positive PDO enhances coastal warmth and moisture transport, potentially mitigating La Niña’s drought-inducing effects in the south-western United States.

3.2 Global Climate and Temperature.

Globally, these misalignments influence atmospheric circulation patterns, such as the Pacific-North American (PNA) teleconnection, which modulates temperature anomalies across continents. A negative PDO with El Niño may weaken the PNA’s positive phase, reducing warming in north-western North America and cooling eastern regions less than anticipated. During a positive PDO with La Niña, the reverse occurs, potentially tempering global cooling signals. These effects complicate attribution of temperature trends to ENSO alone, as PDO’s decadal persistence introduces a low-frequency filter.

3.3 Data Insights.

Historical PDO indices (e.g., from JISAO) and ENSO records (e.g., Niño 3.4 index) reveal frequent out-of-phase periods. From 1947–1976 (negative PDO), El Niño events were less frequent and intense, while the 1977–1998 positive PDO coincided with stronger El Niños (e.g., 1982–1983, 1997–1998). Since 1998, a predominantly negative PDO has overlapped with variable ENSO states, including the muted 2015–2016 El Niño, underscoring the dampening effect.

4. Impacts on Farming and Fisheries.

4.1 Farming.

Out-of-phase PDO-ENSO dynamics disrupt precipitation and temperature patterns critical to agriculture. In the U.S. Midwest, a positive PDO with La Niña may reduce expected drought severity, sustaining corn and soybean yields, as observed in 2011–2012. Conversely, a negative PDO with El Niño can diminish rainfall in California’s Central Valley, impacting almond and grape production, as seen in 1997–1998 when yields dropped by ~10% due to below-average precipitation (USDA data).

4.2 Fisheries.

The North Pacific’s fisheries, notably salmon, are highly sensitive to PDO-ENSO interactions. A positive PDO enhances coastal upwelling and nutrient availability, boosting salmon returns during La Niña years (e.g., 1977–1989 Alaskan salmon boom; Hare & Mantua, 2000). However, a negative PDO with El Niño reduces upwelling, depressing stocks, as evidenced by the 1997–1998 decline in Oregon coho salmon landings (~20% below average, NOAA Fisheries).

5. Case Studies.

5.1 Case Study 1: 1977 PDO Shift and El Niño (Negative PDO Transition).

In 1977, the PDO shifted from negative to positive amid a weak El Niño. Despite El Niño’s warming tendency, western North America experienced cooler-than-expected temperatures and reduced rainfall, attributed to lingering negative PDO effects. California wheat yields fell by 15% due to drought, while British Columbia salmon catches remained stable, highlighting localized dampening.

5.2 Case Study 2: 1998,Negative PDO and Strong El Niño.

The 1997–1998 El Niño, one of the strongest on record, coincided with a PDO shift to negative. California anticipated heavy rains, but precipitation was 30% below forecasts, linked to PDO-driven jet stream suppression. Fisheries off Oregon saw a 25% drop in chinook salmon, reflecting reduced ocean productivity.

5.3 Case Study 3: 2015–2016 El Niño with Negative PDO.

The 2015–2016 El Niño, during a sustained negative PDO, failed to deliver expected rainfall to the U.S. Southwest, exacerbating drought conditions. Arizona cotton yields declined by 12%, while Gulf of Alaska cod stocks plummeted due to warmer SSTs unmitigated by PDO cooling, disrupting regional fisheries.

6. Discussion.

The interplay of PDO and ENSO, particularly when out of phase, reveals significant gaps in climate science. Models often overestimate ENSO’s dominance, underrepresenting PDO’s modulating role (Seager et al., 2019). This mischaracterization affects farming and fishery management, where reliance on ENSO forecasts alone proves inadequate. The case studies underscore how natural variability can confound expectations, urging a re-evaluation of predictive tools and a deeper exploration of oceanic-atmospheric feedbacks.

7. Conclusion.

The uncertainties and misunderstood effects of PDO-ENSO interactions, especially in out-of-phase states, have profound implications for climate, weather, and socioeconomic systems. Negative PDO with El Niño or positive PDO with La Niña can dampen ENSO’s signature, altering local and global patterns in unpredictable ways. Enhanced monitoring and modelling, integrating decadal and interannual scales, are critical to refining our understanding and supporting adaptive strategies in agriculture and fisheries. This analysis challenges the establishment’s tendency to oversimplify these phenomena, advocating for a more nuanced approach.

References.

Gershunov, A., & Barnett, T. P. (1998). Interdecadal modulation of ENSO teleconnections. Bulletin of the American Meteorological Society, 79(12), 2715–2725.

Hare, S. R., & Mantua, N. J. (2000). Empirical evidence for North Pacific regime shifts in 1977 and 1989. Progress in Oceanography, 47(2–4), 103–145.

Kumar, A., et al. (2013). Does knowing the oceanic PDO phase help predict atmospheric anomalies? Journal of Climate, 26(4), 1268–1285.

Mantua, N. J., et al. (1997). A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin of the American Meteorological Society, 78(6), 1069–1079.

Newman, M., et al. (2016). The Pacific Decadal Oscillation, revisited. Journal of Climate, 29(12), 4399–4427.

Seager, R., et al. (2019). Persistent discrepancies between observed and modelled trends in the tropical Pacific Ocean. Journal of Climate, 35(14), 4571–4589.

Trenberth, K. E. (1997). The definition of El Niño. Bulletin of the American Meteorological Society, 78(12), 2771–2777.