California is now five years deep into one of its most severe droughts on record, and scientists are continually probing the different factors that affect the state’s climate, and how much those are related to the overall warming of the globe. Increasingly, this means looking back into the past for clues about how the region has changed over the last few thousand years and what influences might shape its future. In this connection, new research published Thursday in the journal Scientific Reports suggests the Pacific Ocean may play a bigger role than anyone thought — and an unexpected one.