El Niño and La Niña conditions occur when abnormally warm or cool waters accumulate in tropical latitudes of the central and eastern Pacific Ocean. The Oceanic Nino Index is the tool NOAA scienitsts use to watch for these temperature changes.
The total amount of water on Earth isn’t increasing, but the volume of liquid that fills the ocean is growing as ice and snow on land melt. The water is also getting warmer, which makes it expand.
This map shows where temperatures in March 2013 were warmer or cooler than the long-term average temperature from 1981-2010. Shades of red indicate where temperatures were warmer than average; shades of blue show where it was cooler than average. The darker the color, the larger the difference from average.