Final answer:
Scientists indicate changes in the onset of an El Niño by observing changes in Sea Surface Temperature (SST). A significant rise in SST in the equatorial Pacific Ocean signals the onset of an El Niño event.
Step-by-step explanation:
Scientists use changes in Sea Surface Temperature (SST) to indicate changes in the onset of an El Niño event. El Niño, a climate cycle in the Pacific Ocean, has a strong influence on global weather and climate patterns. The sea surface temperatures in the equatorial Pacific Ocean rise significantly during an El Niño, and this deviation from the average conditions signifies its onset. This variable is key since the increase in SST directly impacts atmospheric conditions like air pressure and wind patterns, making it an essential part in predicting the occurrence of El Niño.
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