Research at the California Current Ecosystem Long Term Ecological Research (CCE-LTER) site focuses on mechanisms leading to transitions over time between different states of the pelagic ecosystem. Observations from the remarkable California Cooperative Oceanic Fisheries Investigations (CalCOFI) coastal ocean time series — now in its 7th decade of sampling — demonstrate the effects of external factors in forcing alterations to this ecosystem on multiple time scales. These factors include a warming trend that has been documented over the past 6 decades, the long term warming and cooling cycles (ca. 20-30 years) represented by the Pacific Decadal Oscillation, and the year-to-year temperature fluctuations dominated by El Niño. Combinations of these processes, together with interactions among living organisms, can lead to ecosystem responses that may be manifested as relatively abrupt transitions.