Thoughts on the La Niña Summit


Michael Glantz
National Center for Atmospheric Research
Boulder, CO. USA
glantz@ucar.edu


 

Why are you having the La Niña summit now?

Recall that the title of the workshop is as follows:

“A REVIEW OF THE CAUSES AND CONSEQUENCES OF COLD EVENTS”

So, it is an attempt to review what we think we know and what we don’t know about La Niña, or the cold part of the El Niño Southern Oscillation Process (ENSO).

The subtitle is :

A LA NIÑA SUMMIT

The idea of a summit was to bring together as many key people concerned with ENSO cycle (both cold and warm events) as possible.

Early in1998 it became clear that eventually there would be a decay of the El Niño that was then in full force.We did not know when it would occur or even if it would directly follow this El Niño, but it appeared to be the right time to draw attention to the other part of the ENSO cycle.

The reality is that there are three parts of the ENSO cycle: the extreme cold part, the extreme warm part and a normal range of SSTs in the central and equatorial Pacific.

The United Nations University (in Tokyo) agreed to support a workshop on La Niña as afirst activity in a joint NCAR/UNU project on “El Niño impacts and response strategies in Pacific Rim Countries”.

Why haven’t we heard about La Niña before?

Actually, we did hear about La Niña in the summer of 1988. that was one of the hottest years on record for the globe and there was a severe drought in the US Midwest. In retrospect, researchers have calculated that it cost the US economy $40 billion [in comparison, Hurricane Andrew or the Northridge earthquake cost considerably less].

And the term, La Niña, was apparently first coined by George Philander in 1985 and is in the title of his 1990 book “El Niño, La Niña and the Southern Oscillation”. The book, however, was a technical treatise for ENSO researchers and was not targeted specifically to the general public.

There have been fewer La Niña events since the early 1970s than El Niño events: scientists say that there have been twice as many El Niño events than La Niña events.La Niña does not necessarily follow every El Niño. This challenges the view that the ENSO cycle is like a pendulum that swings back and forth producing equal but opposite effects.

Depending on the definition one uses of La Niña, there have been about four since the early 1970s: 1974, 1975, 1988-89 and 1995-96. The 1995-96 event was a mild one whereas the 1988-89 has been viewed as a major cold event.

At first the 1988 drought was associated with a human induced global warming of the atmosphere (by James Hansen, GISS). Many people questioned the global warming hypothesis and when it was suggested that La Niña was the cause of that drought, it became an alternative hypothesis that people could latch on to. Today, the connection of that drought to the 1988 La Niña is being questioned.

As a final comment on why we haven’t heard much of La Niña or the cold events before now, various funding agencies as recent as three years ago had been asked to support research on the impacts of La Niña but were apparently not interested in doing so.

With hindsight, however, it should not be surprising that we have come so late to think about the cold side of the ENSO process.
Although El Niño was first named in the early 1890s, it took us till the 1970s to show some interest in it. It took this El Niño of 1997-98 to capture the attention of the media, the general public and policy makers (one could argue that this El Niño was the El Niño of the users of El Niño information; it’s when they got interested in El Niño in a big way). The 1982-83 El Niño was the El Niño of the scientists.

So, interest in this La Niña is a spillover of interest in the 1997-98 El Niño. Had there been no interest in this El Niño, there would likely have been no interest in La Niña at this time. But - interest in La Niña is better late than never.

What can one expect to come out of this summit?

Why should we care about La Niña?

Although La Niña events have been fewer in number than El Niño in the past two decades, they too have been associated with extreme climate-related impacts around the globe. An improved forecast of the onset of La Niña could provide societies with enough lead time to take precautionary actions to mitigate the potential adverse impacts that might ensue. As has been often noted, there is a tendency toward an increase in the number of tropical storms and hurricanes during La Niña periods in the Atlantic and Gulf of Mexico region. Information such as this can prove valuable to societies that are prepared to use it.

Also, looking at La Niña along with El Niño brings us closer to realizing how important it is to improve our understanding of climate variations from one year to the next. Climate related forecasts can be used every year to enhance societal well-being and societal productivity. Rather than having to wait every four and a half years on average to respond to an El Niño forecast, societies can be alerted on shorter time periods, as ENSO forecasting improves.

Why haven’t scientists paid attention to La Niña?

A response to this question requires speculation. It seems that interest in El Niño has more or less grown in interest because of the disasters that it has generated. At first from the 1890s to the early 1970s, El Niño events were associated with torrential rains and flooding in Northern Peru and Southern Ecuador and the mass death of guano-producing birds. After the 1972-73 event, it became associated with the collapse of Peru’s anchovy fishery and a disruption in agriculture as farmers in the United States shifted their planting from wheat to soybeans, a second choice to anchovy fishmeal as a animal feed supplement. In 1982-83, El Niño became associated with droughts and famines in a variety of countries around the globe, especially in sub-Saharan Africa. El Niño has thus been associated primarily with “bad news”. Meanwhile, little attention was given to any other part of the ENSO cycle. Increasing attention to the impacts of changes in sea surface temperatures in non-El Niño years (e.g., La Niña and normal years) has only recently surfaced.

In other parts of the world, during La Niña episodes, the Indian monsoon tends to fare well, rains favor Australia (even flooding occurs), rains also return to the Philippines, Indonesia and Papua New Guinea. Arid conditions return to the western coast of South America from Peru to Chile.

What will worldwide weather be like in the fall or winter of 1998/9?

There are composite maps that have been constructed suggesting that there are certain areas around the globe where the regional climatic conditions are linked to SSTs in the central and eastern equatorial Pacific. these maps are based on assessments of researchers at NOAA (eg, Ropelewski and Halpert; Kiladis and Diaz; Hoerling) and at Florida State University (eg, O’Brien and others). Other impacts maps provide information about La Niña impacts in a given year (e.g., 1988-89 and 1995). The use of composite impacts maps or single event impacts maps carries with it different problems. For example, composite maps provide averages of impacts of ENSO events, where as the single event impacts maps shows only one set of the many possible sets of impacts that could accompany an ENSO extreme event.

What are the likely impacts of La Niña in North America?

For example, during La Niña, there is an increase in hurricanes and tropical storms in the Atlantic Ocean and in the Gulf of Mexico. Also, the northern tier of North America becomes relatively colder and wetter in winter. The southern tier of the US becomes relatively warmer and drier. Florida State University has a composite showing impacts of La Niña in North America in various seasons.

Are the fires in Florida the result of La Niña?

First of all, should we blame the fires on El Niño or on La Niña? In fact, we could find logical reasons for placing the blame on either one or on both. For example, during El Niño, the southern tier of the US becomes wet due to the persistence in the location of the jet stream across North America. This creates favorable conditions for vegetative growth. when El Niño fades away and the region dries out, there is considerable underbrush that serves as kindling during thunderstorms with lightening strikes.

We are presently in a transitional state with El Niño in its decay phase and La Niña in its apparent growth phase. It is difficult, if not impossible, to attribute with certainty any single weather-related episode to El Niño or La Niña such as the specific Florida fires to extremes of the ENSO cycle. However, there could be a recognized shift in the probability of the occurrence of such fires during extreme ENSO events.

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