The Temperature & PDO decrease in the 1940s needs to be explained.

Roy W. Spencer, Ph.D. , October 20, 2008 (updated December 29, 2008), “Global Warming as a Natural Response to Cloud Changes Associated with the Pacific Decadal Oscillation (PDO) at: http://www.drroyspencer.com/research-articles/global-warming-as-a-natural-response/ wrote:

Extract: 

“As Joe D’Aleo, Don Easterbrook, and others have pointed out for years, the Pacific Decadal Oscillation (PDO) has experienced phase shifts that have coincidently been associated with the major periods of warming and cooling in the 20th Century. As can be seen in the following figure, the pre-1940 warming coincided with the positive phase of the PDO; then, a slight cooling until the late 1970s coincided with a negative phase of the PDO; and finally, the warming since the 1970s has once again coincided with the positive phase of the PDO.”

PDO Characteristics: 

PDO has since been described as a long-lived El Niño-like pattern of Pacific climate variability because the two climate oscillations have similar spatial climate fingerprints, but very different temporal behavior. Two main characteristics distinguish PDO from El Niño/Southern Oscillation (ENSO): first, 20^th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months; second, the climatic fingerprints of the PDO are most visible in the North Pacific/North American sector, while secondary signatures exist in the tropics - the opposite is true for ENSO. 

(Source: http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm )

Comment :

A ENSO event duration is typically last only about one year. The persistent cooling during the 1940s can not be sufficiently explained on this basis, but should include the impact of naval war on ocean pattern in the Pacific. 

Chapter: 1_11

Book Page: 5c

File: 928e

Image: Roy W. Spencer, 10 Oct.2008