Complex sentence: The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years.
Split into simpler sentences: The Pacific Decadal Oscillation (PDO) is a pattern of change in in the Pacific Ocean's climate (see climate variability). It shifts phases on at least inter-decadal time scale, usually about 20 to 30 years.