15 Apr 2014

El Nino event possible in coming months

Today, the World Meteorological Organization issued a press release that detailed the possible onset of an El Nino event in the coming months.

El Nino is a naturally occurring ocean-atmosphere phenomenon that is characterised by unusually warm surface water temperatures in the central and eastern Pacific.

It is important because it has a significant impact on the climate in many parts of the world, with a warming influence on global temperatures. global_sst_NOAA_wp

Whilst El Nino is noted for its warming affect, the opposite, La Nina, has a cooling effect. It is these two, along with neutral conditions (when neither is taking place), that make up something called the El Nino-Southern Oscillation (ENSO) indicators.

ENSO indicators consist of tropical Pacific sea surface temperatures, sea level pressure, cloudiness and trade winds. How each of these behave determine whether conditions are considered as El Nino, La Nina or neutral.

Signs of warming

Since the second quarter of 2012, ENSO conditions have generally remained at neutral levels.

asia_global_g_wpHowever, since February, there have been two strong westerly wind events and an overall weakening of the trade winds in the tropical Pacific.

The result of this has been a significant warming of the waters below the surface of the central Pacific, which has historically been a precursor to an El Nino event occurring.

Whilst there is no guarantee that an El Nino event will occur, for June to August, two-thirds of prediction models suggest that El Nino thresholds will be reached. The remaining third of models suggest that neutral conditions will persist.

Even though there is some skill in predicting the onset of El Nino events, the ability to predict their strength remains unreliable.

What effects does El Nino have on global climate?

The most notable effect that El Nino has on the climate is a warming influence on global average temperatures – something that was observed during a strong El Nino in 1998.

However, it should be noted that no two El Nino events are ever the same and its effects will work with other drivers that influence the world’s climate system.

Nevertheless, historical data shows that the effects of El Nino can be felt far and wide – much like dropping a pebble in a pond and the ripples extending outwards.

Effects of El Nino regionally

El Nino during summer tends to have the following effects;

– Abnormally dry weather for northern Australia, Indonesia and the Philippines

– Drier than normal over south eastern Africa and northern Brazil

– Indian monsoon rainfall lower than normal – especially in north west India

– Wetter than normal along the west coast of tropical South America, and at subtropical latitudes of North America (Gulf Coast) and South America (southern Brazil to central Argentina)


El Nino during winter tends to result in the following;

– Mid-latitude low pressure systems tend to be more vigorous than normal in the region of the eastern North Pacific. These systems pump abnormally warm air into western Canada, Alaska and the extreme northern portion of the contiguous United States.

– Storms also tend to be more vigorous in the Gulf of Mexico and along the southeast coast of the United States resulting in wetter than normal conditions in that region.


What about the UK?

The effects of El Nino on the UK directly are generally considered to be tenuous, however there are suggestions that more blocked, drier and colder conditions can be experienced in a winter following an El Nino event.

There are also hints that it tends to be wetter than normal to the south of the UK, across France, Spain and Portugal during late-summer and autumn.

It’ll be interesting to see if El Nino does indeed occur in the coming months. I’ll keep you updated here on my blog, as well as on Twitter – @liamdutton

Images: Met Office, NOAA


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