The World Meteorological Organization says there is a 60% chance that the disruptive weather phenomenon known as El Niño will become fully established between now and August.
In its previous update, issued in April, the agency noted that there were signs that El Niño could occur, but it didn't put a specific number on the likelihood of it happening. It is now more certain that El Niño will develop, based on data collected by climate agencies in the U.S., U.K., France, Japan and elsewhere.
"If you go by historical frequency, there's a 25% chance of El Niño to occur at any time," said Rupa Kumar Kolli, climate scientist at the WMO, a Geneva-based agency of the United Nations. "Now we have 60%—which is more than double the historical probability."
El Niño is a natural cyclical event that gets triggered when winds in the equatorial Pacific slow down or reverse direction. That warms the water and can disrupt weather patterns around the world.
The impact can be severe. El Niño is associated with local droughts and floods. The Indian monsoon rainfall tends to be less than normal, which affects crops. Storms also tend to be more vigorous in the Gulf of Mexico and along the southeast coast of the U.S., which leads to wetter-than-normal conditions in that area.
Altered weather patterns have big effects, especially on activities such as agriculture and mining. Thus, in the past, El Niño has triggered price increases for a range of commodities, including soybeans, coffee and nickel. The last El Niño was in 2009-2010.
In recent years, researchers have become increasingly concerned that El Niño may amplify the effects of long-term global warming.
The main reason is that in El Niño years, the global mean temperature tends to be slightly higher than normal, a conclusion that is based on data collected over more than a half-century. Some researchers worry that when the El Niño effect on temperature is added to the longer-term pattern of increased temperature, the weather in El Niño years could get more disrupted than usual.
Government-run climate agencies in the U.S. and Japan have independently reported that average global temperatures in the month of May were the highest on record, even without an El Niño.
"If you couple high temperatures with a full-blown El Niño, things could get worse," said Dr. Kolli.
So far, the models suggest that this year's potential El Niño will be of moderate strength. The data shows that while the sea-surface and subsurface temperatures have reached the threshold states in parts of the Pacific, the overlying atmosphere in those regions haven't reached the conditions that would trigger El Niño.
In typical El Niño years, surface sea temperatures in the central and eastern Pacific are substantially warmer than temperatures in the western Pacific. This year, though, the western Pacific is warmer than usual—one possible reason why El Niño has yet to form.
But, as with many things climate-related, predictions can only go so far. In 2012, for example, U.S. researchers issued an "El Niño Watch" when chances became as high as 75% that El Niño would form. It never did.
http://online.wsj.com/articles/el-nino-said-to-have-60-chance-of-occurring-through-august-1403797546