Relationship with North American climate

Fig. 7. Winter (DJF) SAT in Detroit and PDO indices smoothed by 11-yr running averages, with the SAT leading PDO by 22 years. Years on the abscissa are those of the PDO.

An oscillation with the period of 65-70 years can also be found in North American climate (Schlesinger and Ramankutty, 1994). A good example of the presence of this cycle in surface temperature is a time series of winter SAT in Detroit. The correlation between this time series and the winter PDO index (both smoothed by 11-yr running averages) reaches -0.8 when the SAT is leading by 22 years. As shown in Fig. 7, not only the phases of the 70-yr cycle in the SAT, but even smaller-scale variations, such as cooling in the 1960s, coincide with similar variations in the PDO. A strong warming trend in the Midwest in the past 30 years suggests that the PDO will continue to decline through 2025, possibly reaching record low values. The mechanism of this relationship, however, is unknown.