Which 1972 event marked the beginning of this trend?

St. louis, missouri, and san francisco, california, both lie around 33° north latitude. st. louis is inland, while san francisco is on the coast of the pacific ocean. which statement about these north american cities would be true? san francisco will be warmer than st. louis in the winter. san francisco and st. louis will be about the same temperature year round. san francisco will be warmer than st. louis in the summer. san francisco will be warmer than st. louis year round.