What caused the monster El Nino in 2015?

Washington: Presence of warm water in the Pacific Ocean due to a stalled El Nino in 2014 stacked the deck for a monstrous version of the warming climate cycle to occur in 2015, a study says.

Easterly winds in the tropical Pacific Ocean stalled a potential El Nino in 2014 and left a swath of warm water in the central Pacific. This left over warm water gave the current El Nino a head start, the researchers explained.

El Nino and La Nina are the warm and cool phases of a recurring climate pattern across the tropical Pacific Ocean called the El Nino-Southern Oscillation, or ENSO. 

The warm and cool phases shift back and forth every two to seven years, and each phase triggers predictable disruptions in temperature, wind, and rain across the globe. 

During El Nino events, water temperatures at the sea surface are higher than normal. Low-level surface winds, which normally blow east to west along the equator, or easterly winds, start blowing the other direction, west to east, or westerly.

In the spring of 2014, strong westerly winds near the equator in the western and central Pacific Ocean created a buzz among scientists - they saw the winds as a sign of a large El Nino event to come in the winter of 2014, said lead author of the study Aaron Levine, a climate scientist at US National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory in Seattle, Washington.

But as the summer progressed, El Niño did not form the way scientists expected it to. Sea surface temperatures in the eastern Pacific never warmed enough to truly be called an El Nino, and the buzz fizzled out.

But then, in the spring of 2015, episodes of very strong westerly wind bursts occurred and became more frequent throughout the summer. 

Following a pattern set by previous large El Ninos, 2015 to 2016 became one of the three strongest El Ninos on record, along with 1982 to 1983 and 1997 to 1998, Levine said.

The findings will be published in a forthcoming issue of the journal Geophysical Research Letters.