Die Ozeanzyklen beeinflussen die globalen Temperaturen in starkem Maße. Ein 60-jähriger Zyklus lässt die Temperaturen in bestimmten Phasen stärker steigen, während er zu anderen Zeiten kühlend wirkt. Das gibt die typischen Wellen im Temperaturverlauf. Ein Forscherteam um Robert Wills hat nun den Effekt der Ozeanzyklen im Pazifik genau herausgerechnet. Dabei stießen sie auch auf Unterschiede in verschiedenen Sektoren des Pazifik. Der PDO-Zyklus war besonders in den mittleren Breiten auszumachen. In den Tropen hingegen schwankten die Meerestemperaturen hochfrequenter, ein Effekt des El Nino, der alle 2-7 Jahre auftrittt. Hier der Abstract von Wills et al. 2018:
Disentangling global warming, multi-decadal variability, and El Niño in Pacific temperatures
A key challenge in climate science is to separate observed temperature changes into components due to internal variability and responses to external forcing. Extended integrations of forced and unforced climate models are often used for this purpose. Here we demonstrate a novel method to separate modes of internal variability from global warming based on differences in timescale and spatial pattern, without relying on climate models. We identify uncorrelated components of Pacific sea-surface temperature (SST) variability due to global warming, the Pacific Decadal Oscillation (PDO), and the El Niño–Southern Oscillation (ENSO). Our results give statistical representations of PDO and ENSO that are consistent with their being separate processes, operating on different timescales, but are otherwise consistent with canonical definitions. We isolate the multi-decadal variability of the PDO and find that it is confined to midlatitudes; tropical SSTs and their teleconnections mix in higher-frequency variability. This implies that midlatitude PDO anomalies are more persistent than previously thought.
Aber auch die Landtemperaturen der USA werden stark von der PDO sowie von der AMO beeinflusst, wie Mermelstein 2017 zeigte:
The Effects of the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation on U.S. Regional Weather
This paper aims to identify and discuss the sensible weather trends in each of the ten climate regions of the U.S. affected by the natural oscillations representing the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-Decadal Oscillation (AMO). By finding the correlations between the natural oscillations and the sensible weather, we can create composites and learn about their tendencies to better aid in forecasting the weather. The importance of the different modes of each oscillation has been found to vary among each of the climate regions of the U.S, as defined by the National Centers for Environmental Information (NCEI) (Karl, T. R. & Koss W. J., 1984) – Northwest, West, Southwest, Northern Rockies and Plains (West North Central), Upper Midwest (East North Central), South, Ohio Valley (Central), Southeast, and Northeast. It has been found that the different regions tend to be influenced differently by each of the oscillations and their modes, thus leading to variances in the regional sensible weather experienced in each mode’s time series. The most obvious effect on sensible weather that the AMO and PDO have can be seen from the temperature curves that are quite visible on the temperature time series (Kurtz, 2015). These indicate that the 1940-1978 decrease in CONUS temperatures was caused more by the negatively trending oscillatory modes of the AMO/PDO than other factors, and the 1978-2001 increase in temperatures was caused more by the positively trending oscillatory modes of the same oscillations. The small increase, or rather stagnant nature in U.S. CONUS temps since 2001, was likely due to peaking positive modes of the AMO/PDO. In the same way that the AMO and PDO can modify the regional temperatures, we see the same types of effects on precipitation, snowfall and drought in the different regions of the U.S.