Final answer:
The greatest effect of a cold ocean current on Los Angeles' temperature occurs in summer, with the cold California Current moderating temperatures. Ocean currents significantly influence weather patterns and local economies, such as commercial fishing.
Step-by-step explanation:
The season in which the proximity to a cold ocean current has the greatest effect on Los Angeles' temperature is summer. During summer, the cold California Current off the west coast of North America helps to moderate the temperatures in coastal areas including Los Angeles. The ocean's capacity to retain its temperature from the previous winter means that it cools the air throughout the summer months. Similarly, in the winter, the ocean releases heat absorbed during the summer, leading to milder winter temperatures. The phenomena of El Niño events and their impact on global weather patterns underline the significant influence of ocean currents and temperatures on regional climates.
It is noteworthy, too, that such currents, along with the overall oceanic influence, play a critical role in climate moderation in other aspects. For instance, ocean temperature affects marine life, productivity, and can have secondary effects on industries such as commercial fishing. A cool ocean temperature stimulates the growth of plankton, which in turn supports a robust marine food chain and affects activities such as salmon fishing.