Since climate forecasters declared an "El Niño Watch" on March 6, the odds of such an event in the tropical Pacific Ocean have increased, and based on recent developments, some scientists think this event may even rival the record El Niño event of 1997-1998. If that does happen, then 2015 would almost be guaranteed to set a record for the warmest year on Earth, depending on the timing of the El Niño conditions.

El Niño and La Niña events refer to fluctuations in air and ocean conditions in the tropical Pacific. El Niño events are characterized by warmer than average sea surface temperatures in the central and eastern equatorial Pacific, and they add heat to the atmosphere, thereby warming global average temperatures. They typically occur once every three to seven years and can also alter weather patterns around the world, causing droughts and floods from the West Coast of the U.S. to Papua New Guinea.

El Niño events tend to dampen hurricane activity in the North Atlantic, and some research has even linked El Niño events to civil conflicts in Africa.

When combined with global warming from greenhouse gas emissions and other sources, El Niño events greatly increase the odds that a given year will set a new global temperature record, as occurred in 1998.

Tony Barnston, the chief forecaster at Columbia University’s International Research Institute for Climate and Society (IRI), told Mashable that the odds of an El Niño event developing during the next six months have increased to about 60%, which is up from just over 50% on March 6.

Global sea surface temperature anomalies, showing milder than average conditions in parts of the tropical Pacific. Image: NOAA.

The Pacific Ocean exists in a constant state of unease, like an ocean badly in need of a mood stabilizer. Trade winds blow along and to the north of the equator from east to west, piling up warm ocean waters in the western Pacific, and causing sea levels to be higher in the west than they are in the east. Like a tipping bathtub, this setup can quickly be reversed with a reversal in trade winds and a sloshing of the warm sea surface temperatures from the western Pacific to the east, first at depth in a series of undersea waves known as Kelvin waves, and next toward the surface as the warm waters rise off the west coast of South America.

This complex chain of events, in which the atmosphere and the ocean act in concert to set up El Niño conditions, is well under way now. Starting in January of this year, there have been a series of strong bursts of winds coming out of the west in the equatorial tropical Pacific, and these have essentially replaced the typical easterly trade winds.

Partly as a result of these wind bursts, ocean buoys and satellites have detected the movement of unusually warm ocean waters from the western Pacific to the east. Ocean surface currents, which normally move westward across the Pacific basin, have reversed as well. El Niño forecasters have taken this as a further sign of a developing El Niño, and these conditions were a key reason why an El Niño Watch was issued on March 6.

Eric Blake, a hurricane specialist at NOAA’s National Hurricane Center in Miami, said conditions are changing rapidly in the Pacific, going from 50/50 odds of an El Niño, to a setup that eerily resembles the circumstances that preceded the monster El Niño of ‘97-'98.

“It’s something we haven’t really seen since the '97 El Niño,” Blake said of the westerly wind bursts and ocean observations. Instead of having trade winds blowing from the east at five to 10 mph, some locations in the western Pacific have had winds from the west blowing at up to 30 miles per hour, Blake says. This is important because it has ripple effects on the sea and below the sea surface.

“[It’s] not that we can’t step away from it, but with each passing day [an El Niño event is] becoming more likely,” Blake told Mashable.

Paul Roundy, a meteorology professor at the University at Albany, State University of New York, said that the westerly wind bursts have been extremely strong compared to historical records. Two of these events in particular, Roundy says, “were of similar amplitude to the events that preceded the 1997 El Niño.”

In addition, the warm waters moving eastward under the surface have been measured as much as nine degrees Fahrenheit above average, which is greater than similar waves observed prior to the 1997 El Niño event. “The present event is actually bigger than it was in 1997,” said Roundy.

Roundy cautioned that this doesn’t necessarily mean that the current event will be stronger than 1997-98 was, but it does raise red flags.

Map showing the TAO buoys, with buoys reporting recent data colored in yellow and those without recent data in red. Image: National Data Buoy Center

Wind patterns in the next two months will help determine whether an El Niño actually forms, and how strong it becomes. For example, even a temporary reversal of trade winds back to more typical conditions could dampen the eastward moving wave of warm water. So far, though, this hasn’t happened.

“Instead of switching to easterly winds there’s been an actual continuation of westerly winds,” Roundy said.

One problem that forecasters encounter when trying to foresee the likelihood and intensity of El Niño events is that there is limited historical data of the vast Pacific Ocean. Observational data only dates back to about 1990, Roundy says.

Making matters more difficult for forecasters is the recent degradation of a crucial buoy network used for El Niño and La Niña monitoring. Budget cuts have led to missing data, with the network known as the Tropical Atmosphere Ocean Project, or TAO array, operating at just 30 to 40% percent of capacity.

Roundy said the chances of an unusually strong El Niño event “Are much higher than average, it’s difficult to put a kind of probability of it … I’ve suggested somewhere around 80%”

“The conditions of the Pacific ocean right now are as favorable for a major event as they were in march of 1997. That’s no major guarantee that a major event develops but clearly it would increase the likelihood of a major event occurring,” Roundy says.

Barnston said any similarities of current conditions in the Pacific to those seen before the 1997-98 El Niño are an insufficient basis for forecasting an intense event. “As for the strength of the event, it is not known. Just seeing similarities with 1997 is not enough to go on," Barnston told Mashable in an email. "Unless we continue to get westerly wind events in the coming weeks, there is no guarantee that it will be a big event, and there is a 40% or so chance we will not get an El Niño at all,” he told Mashable in an email.

Roundy and Blake also urged caution about concluding that an El Niño event is nearly certain to occur, and that it will be intense. Rather, Blake said, the situation bears close watching.

“Anytime you have a non-negligible chance of something extreme happening, and you see it happening in a way that you haven’t seen in 15 to 20 years, it’s interesting,” says Blake.