El Niño is monitored using sea surface temperature data from a specific area in the eastern Pacific known as the ENSO 3.4 region. Meteorologists compare these temperatures to historical averages to determine the strength of an event. Strong El Niño events can significantly influence global temperatures, with some years becoming the warmest on record due to its effects. Observing trends in this region helps scientists predict the potential impacts of El Niño on weather patterns.