|Frequently Asked Questions about El Niño and La Niña|
What is El Niño?
What is La Niña?
Where can I find educational material about El Niño?
Is El Niño a theory or a fact?
Why is it called El Niño?
What are the impacts of El Niño?
Would you be able to give me some feed back on how we as global citizens, can do something about El Niño and it's effects?
Why does El Niño occur?
How often does El Niño occur?
Where is a list of El Niño and La Niña years?
Are all El Niños the same?
Do El Niños occur only in the Pacific Ocean?
What is the current El Niño forecast?
What is the present climate in different countries?
How do we detect El Niño?
What indices are used to see if an El Niño or La Niña is occurring?
What is the relationship between hurricanes and El Niño?
What is the relationship between tornados and El Niño?
What is the relationship between coral bleaching and El Niño/La Niña?
What is the relationship between greenhouse warming, El Niño and La Niña?
What is the relationship between the Earth's rotation, the Coriolis force, and El Niño and La Niña?
Is it feasible to haul icebergs from Antarctica to the tropical Pacific to cool down El Niño?
What are the implications of our observations of the 1997-1998 El Niño on prediction?
Is the strong 1998-1999 La Niña related to severe winter weather in the northern hemisphere?
Why was El Niño such a big deal in 1998?
Has a reasonable, scientific body come up with any meaningful conclusions and/or predictions in the field of physical oceanography regarding forcasting of the ocean?
What are some sources of information about El Niño and Climate Change Research?
El Niño Web Sites:
NOAA sites about El Niño
Non-NOAA sites about El Nino
Answers to Less Frequently Asked Questions
FAQ on El Niño, La Niña and the Western US, Alaska, Hawaii
FAQ at National Weather Service/Climate Prediction Center
FAQ at Earth System Research Laboratory (NOAA ESRL)
Click here for:
Different aspects of El Niño
On the other hand, a difference from thunderstorms is that we have a very good idea what triggers thunderstorms, what conditions make it likely for them to occur, to the point where weather forecast models commonly pinpoint the locations and predicted severity of thunderstorms a day or so in advance. We do not have such knowledge for El Niño. Once an El Niño has started, we have reasonably good skill in predicting the subsequent evolution over the next 6-9 months, but before it has started we have very little skill in predicting the onset before the event has become obvious. There are a variety of theories for why EL Niños start, but none of them has given us real skill in making a forecast in advance, the way we can for thunderstorms.
It must be said that there is still plenty of social utility in predicting the evolution of an El Niño after it starts, since that gives 6 months or so warning before the effects come to the US. For instance, a fairly weak El Niño started earlier this year, and that enables forecasters to predict that the coming winter is likely to be warmer than normal across the northern states, and wetter than normal along the Gulf Coast. Such forecasts are certainly useful for farmers and water managers, but from a scientific point of view they are unsatisfying because they do not answer the fundamental question of why the event started in the first place.
One reason for this state of affairs is that El Niños only come along every 4-5 years or so, so there aren't very many to study (we've had decent instrumentation in the tropical Pacific for less than 20 years). Thunderstorms happen every day in summer, so there's been lots of opportunity to carefully observe their development.
Perhaps this is a deeper question, though, concerning the meaning of the word "theory". In science, we use the word theory somewhat differently from ordinary usage. Ordinarily, to say something is a theory means it is kind of a guess, not proven. Scientists, on the other hand, speak of the "theory of gravitation", or the "theory of evolution", and in that case it means the precise description of the mechanism. In no way does it indicate that the phenomenon in question is less than a fact. No one doubts that gravity is a fact, but the exact way it works is still a subject of research (Einstein spent the last 40 years of his life trying to explain gravitation without simply postulating it, that is, to explain it in connection with the other atomic forces. This is still a major question of physics, and you may have heard of the search for a "unified field theory"). Similarly, no serious scientist doubts that evolution is a fact, but there is plenty of discussion about its specific mechanisms, whether it happens fast or slowly, what size population of an organism is likely to produce new species, under what conditions a species will die out, etc). All these are part of honing the theory. In the case of El Niño, one theory is that these events are the means by which heat is drained from the equatorial oceans after a period of accumulation. Such a theory predicts that by observing the growth of heat content, it should be possible to forecast when an El Niño will occur. That seems to be at least partly true, but it was contradicted by the El Niño of 1993, which occurred immediately after one the previous year, and no accumulation had occurred. Another theory argues that El Niños are triggered by random events occurring in other parts of the climate system, and suggests that we will never be able to predict them. Some scientists argue for an opposite (cold) phase called La Niña, and see the whole thing as an oscillation swinging back and forth, while others think there is just the normal situation disturbed by occasional El Niños. However, you can see that despite the existence of competing theories for El Niño, there is no doubt that it is a real, factual occurrence.
You can see data for the tropical Pacific at:
For example, click the "Assorted plots" button, then pull down the menu and click "Monthly EQ UWND SST 20C anoms", which shows the simulataneous changes of zonal (east-west) wind, SST (sea surface temperature) and 20C isotherm depth (the depth of the interface between the warm upper water and the cold abyss). You will get a small plot; click on that to make it bigger). El Niños are marked by simultaneous westerly (from the west) winds, warm SST and deep interface, and occurred in 1986, 1991-92, 1993 (the weak one I mentioned earlier), 1994-95, 1997-98 (an extremely strong one) and you can see the present one developing. The fact that these are reasonably well-defined occurrences in these different variables, though with different amplitude in different years, shows that there really is a thing called El Niño.
There is lots of various El Niño information (including many other links) on this website:
Forecasts for the coming months are given at:
There is a description of how it works on Dr. Billy Kessler's FAQ page:
See question 1.
El Niño happens when tropical Pacific Ocean trade winds die out and ocean temperatures become unusually warm. There is a flip side to El Nino called La Nina, which occurs when the trade winds blow unusually hard and the sea temperature become colder than normal. El Nino and La Nina are the warm and cold phases of an oscillation we refer to as El Nino/Southern Oscillation, or ENSO, which has a period of roughly 3-7 years. Although ENSO originates in the tropical Pacific ocean-atmosphere system, it has effects on patterns of weather variability all over the world. It also affects Pacific marine ecosystems and commercially valuable fisheries such as tuna, sardines, salmon, and Peruvian anchovetta.
Information contained in the chemical composition of ancient tropical Pacific coral skeletons tells us that ENSO has been happening for at least 125 thousand years. This span of time covers the last ice age cycle when the earth's climate was cooler and very different from today's climate. In addition, we can reasonably assume that the ENSO cycle has been operating ever since geologic processes closed the Isthmus of Panama about 5 million years ago to form the modern boundaries of the Pacific basin.
There is nothing we can do to stop El Nino and La Nina events from occurring. The year-to-year oscillations between normal, warm, and cold conditions in the tropical Pacific associated with the ENSO cycle involve massive redistributions of upper ocean heat. For instance, the accumulation of excess heat in the eastern Pacific during a strong El Nino like that which occurred in 1997-98 is approximately equivalent to the output of one million medium-sized 1000 megawatt power plants operating continuously for a year. The magnitude of these natural variations clearly indicates that society cannot hope to consciously control or modify the ENSO cycle. Rather, we must learn to better predict it, and to adapt to its consequences.
The challenge for physical scientists therefore is to improve ENSO forecast models, to improve our understanding of underlying physical processes at work in the climate system, and to improve the observational data base needed to support these goals. Capitalizing on advances in the physical sciences for practical purposes is a challenge for social scientists, economists, politicians, business leaders, and the citizenry of those countries affected by ENSO variations. The promise of the future is that continued research on ENSO and related problems will be rewarded with new scientific breakthroughs that translate into a broad range of applications for the benefit of society.
Here is a graph showing El Niño and La Niña years since 1950 and going back to 1876, as indicated by the Southern Oscillation Index.
In a plot of Sea Surface Temperature along the Equator from 1986-present, you can see that warm water (red) penetrated further to the East in the 1986 and 1997 El Niños than it did during the 1991-1993 El Niños. Click here to see today's conditions compared with others in the twentieth century in plots and animations.
There is another way in which the width of the Pacific allows ENSO to develop there as compared to the other basins. In the narrower Atlantic and Indian Oceans, bordering land masses influence seasonal climate more significantly than in the broader Pacific. The Indian Ocean in particular is governed by monsoon variations, under the strong influence of the Asian land mass. Seasonally changing heat sources and sinks over the land are associated with the annual migration of sun. Heating of the land in the summer and cooling of the land in the winter sets up land-sea temperature contrasts that affect the atmospheric circulation over the neighboring ocean. This land influence competes with ocean and atmosphere interactions which are essential for generating ENSO.
See Indian Ocean may have El Niño of Its Own, from the American Geophysical Union EOS publication.
At higher latitudes, El Niño is only one of a number of factors that influence climate. However, the impacts of El Niño and La Niña at these latitudes are most clearly seen in wintertime. In the continental US, during El Niño years, temperatures in the winter are warmer than normal in the North Central States, and cooler than normal in the Southeast and the Southwest. During a La Niña or El Viejo year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.
See lists of El Niño and La Niña years.
Realtime Pacific Ocean data from the NOAA network of moored buoys is updated daily to show the current conditions in the Equatorial Pacific Ocean.
The Climate Prediction Center issues special climate summaries which monitor current and developing climate variations. These are current, and very interesting. Current conditions and typical global impacts are also discussed in the NCEP pages.
For a look at operations aboard NOAA's newly commissioned research ship, which is dedicated to servicing the TAO bouy network component of the ENSO observing system, please see realitme images and data from the KA'IMIMOANA.
Large computer models of the global ocean and atmosphere, such as those at the National Centers for Environmental Prediction use data from the ENSO observing system as input to predict El Niño. Other models are used for El Niño research, such as those at NOAA's Geophysical Fluid Dynamics Laboratory, at Center for Ocean-Land-Atmosphere Studies, and other research institutions.
A variety of indices are used to characterize ENSO because it effects so many elements of the atmosphere-ocean climate system. Probably the two principal indices are the Southern Oscillation Index (SOI), which is given by the difference in sea-level pressure between Tahiti and Darwin, Australia, and the Nino 3 index, which referes to the anomalous SST within the region bounded by 5N-5S and 150W-90W. The measurements needed for these indices are straightforward, and we have long historical records, especially for the the SOI.
However, other indices are effective at characterizing other aspects of ENSO. For example, the anomalous 850 mb zonal winds show how the low-level atmospheric flow is responding to low-level pressure anomalies associated with ENSO and other mechanisms. Often the 850 mb flow (about 1.5 km above sea level) exhibits a "cleaner" signal than the winds at the surface, which are subject to local effects such as terrain. An index involving the 200 mb zonal flow is used to describe the upper tropospheric winds, whose anomalies tend to be opposite to those at 850 mb and below. The 200 mb flow is particularly important because it is changes at around this level in the tropics that tend to have the biggest consequences for the atmospheric circulation outside of the tropics. The 500 mb temperature represents a proxy for the anomalous heat content of the tropical troposphere. In an overall sense, there is greater heating of the troposphere, and more deep cumulus convection, than normal during warm ENSO events (El Ninos).
Finally, there is one more widely used index for the atmosphere and that relates to the outgoing longwave radiation or OLR. The deeper the cumulus convection, the colder the cloud tops, which means the thermal or infrared radiation to space is reduced. It is straightforward to monitor OLR via satellite; its value in the tropical Pacific near the dateline is an effective way to gauge the frequency and magnitude of the thunderstorm activity that changes with ENSO.
Current values of these indices provided on-line by the Climate Prediction Center.
If you type in "coral bleaching and El Niño " on a web search engine, you will find lots of web sites that describe coral bleaching and its relation to El Niño.
We don't know the answer to this question. It is certainly a plausible hypothesis that global warming may affect El Niño, since both phenomena involve large changes in the earth's heat balance. However, computer climate models, one of the primary research tools for studies of global warming, are hampered by inadequate representation of many key physical processes (such as the effects of clouds on climate and the role of the ocean). Also, no computer model yet can reliably simulate BOTH El Niño AND greenhouse gas warming together. So, depending on which model you choose to believe, you can get different answers. For example, some scientists have speculated that a warmer atmosphere is likely to produce stronger or more frequent El Niños, based on trends observed over the past 25 years. However, some computer models indicate El Niños may actually be weaker in a warmer climate. This is a very complicated (but very important!) issue that will require further research to arrive at a convincing answer.
Both 1998 and 1997 had record-setting global mean temperatures and also El Niño. What influences what?
El Nino clearly influences globally averaged temperatures which go up a few tenths of a degree C a few months following the peak warming in the tropical Pacific. This is because the tropical Pacific loses large amounts of heat to the overlying atmosphere during El Niño. So some of the extreme warming observed in global temperatures in 1997-98 can be traced back to the occurrence of El Nino in the tropical Pacific. However, underlying the El Nino effect (which should diminish in the next year) is an long term global trend towards warmer temperatures. Two questions arise, for which we do not have answers at this point: 1) Exactly how much of the extreme rise in global temperatures during 1997-98 was due to the 1997-98 El Nino, versus the contribution from the underlying long term trend? and 2) Did the extreme El Nino occur in response to global warming trends? This second question ties into your first question above. In fact, how global warming projects onto natural modes of climate variability like El Nino, the Pacific Decadal Oscillation, and the North Atlantic Oscillation (all of which can have an affect on global air temperatures) is a very compelling research problem.
Could the problem of disentangling the many factors and dynamics at play in El Niño and global warming can be compared to writing down the scores of many different tunes whilst they are played all at the same time. Might cacophony be a good image to describe circulation patterns?
That's a nice analogy. However, it could be refined in the following way: when the scores are played together, they not only become entangled, but they may actually metamorphose into a slightly different tune, one for which no score existed at the start of the piece. That is to say, that El Nino, global warming, and other climate signals are actually physically altered by their interaction in ways you would not expect by considering them in isolation. Sorting out these complex interactions is in fact one of the major challenges of climate research today.
For more information, see Why can't I find any information about links between El Niño and global warming?
El Nino results in a decrease in the earth's rotation rate, an increase in the length of day, and therefore a decrease in the the strength of the Coriolis force. La Nina tends to have the opposite effect.
El Nino is associated with a weakening of the tropical Pacific trade winds, and also with a strengthening of the mid-latitude westerlies both at the surface and aloft. To balance these changes in atmospheric winds, the earth's rotation rate decreases in order to conserve total angular momentum of the earth/atmosphere system. Conservation of angular momentum is a basic physical principal which operates, for example, when a ballerina brings her arms closer to her body to spin faster.
The change, however, is only about 1 millisecond at the peak of a strong El Nino. There are 86400 seconds in a day, so this change represents one part in 100 million. Such a change will have little effect on normal activities on a human scale, such as flying an airplane.
The simple reason is that to cool the tropical Pacific down to its normal state once an El Nino is underway would take an amount of ice 10 m thick covering an area equal in size to the continental US. That's a lot of ice, and there's no way to extract and transport that amount of ice with existing technology. Even if it were technically feasible, it would in all likelihood cost an astronomical amount of money, many times over the combined global losses due to El Nino.
Furthermore, it would take a long time to transport. The inevitable delays that attend any grand project would probably mean you'd get all the ice to the tropical Pacific just as the El Nino was ending. It would be too late to do any good. But worse, since El Nino is often followed by La Nina (which has it's own set of adverse consequences on weather), you could end up exacerbating the effects of natural climate variability on society.
Finally, the extraction of that much ice would seriously damage the environment of Antarctica. It could also have potentially serious consequences on global climate if it lead to changes in surface reflection of sunlight, or had other effects on land surface processes.
So economically and environmentally, it's a much better strategy to invest in research on how to better predict El Nino, and to invest in developing ways to adapt to its impacts on society.
It is an interesting question to ask why El Niño suddenly became headline news in 1998. The scientific community has known about El Niño and it's impacts on global weather, Pacific marine ecosystems, and fisheries for about 35 years. The regional impacts of El Niño along the coast of South America have been known for hundreds of years by the people living in that area. There are three factors though that made reporting of the 1997-98 El Niño different from other recent El Niño events.
1. The 1997-98 El Niño was the strongest on record, and it developed more rapidly than any El Niño of the past 40 years. As a result, we started to see it impacts on weather, marine ecosystems and fisheries very quickly, and these impacts were spectacular. Early effects in August-October 1997 included record flooding in Chile, Marlin caught off the coast of Washington, the extensive smog cloud over Indonesia, and a quiet Atlantic hurricane season. The press is geared towards reporting sensational stories, and this El Niño provided high drama through natural disasters and other unusual events.
2. In the past 15 years, scientists developed new observational tools that allowed us to track the development of El Niño in greater detail than ever before. The new observations, from satellites and from sensors in the ocean itself, provided a day by day account of events as they unfolded in the tropical Pacific. These technological advances, providing high definition information on the tropical ocean and atmosphere system like never before, fueled a lot of interest in the press about El Niño, how we track it, and how it affects people's lives.
3. Another technological advance in the past 15 years was the development of long range forecasting capabilities for predicting the evolution of El Niño sea surface temperatures, and the consequences of those temperatures on global weather. The effects of El Niño on North American climate are most pronounced in the winter season. Because the El Niño developed so rapidly, with record high sea surface temperatures in the equatorial Pacific by July 1997, forecasters could predict a full 6 months in advance with some reliability that the winter over the US would be very unusual. The credibility of these forecasts was high, because of the clearly identifiable impacts of El Niño earlier in the year (see point 1 above). The anticipation of an unusual winter motivated a lot of disaster preparedness efforts by local and state governments, by the federal government, by businesses, and by individuals. This mobilization of people and resources based on a climate forecast was unprecedented, and therefore caught the attention of the press. Once winter arrived, the predicted unusual weather set in, and that was also newsworthy. It turns out that the forecasts for heavy rains over the southern part of the US for the winter of 1997-98, and for an unusually mild winter in the Midwest proved to be largely correct. Record rains occurred in particular in California and Florida, two of the most populous states in the nation.
Regarding forecasting of the ocean, you may want to check out the following web page: http://www.pmel.noaa.gov/tao/elnino/forecasts.html, which summarizes a number of current El Nino/Southern Oscillation (ENSO) forecasts. These forecasts rely on predicting tropical Pacific sea surface temperatures (SST) months to seasons in advance. Various kinds of forecast schemes have been developed. Some are based on the statistics of previous ENSO variations, whereas others are based on actually simulating future changes in ocean currents and subsurface thermal structure.
ENSO forecasts are not perfect. However, they are sufficiently skillful at this point that individuals, corporations, municipalities, states, and national governments have used them to prepare for El Nino and La Nina events. We know that unsually warm or cold tropical Pacific sea surface temperatures have major consequences for global climate and for Pacific marine ecosystems. Forecasting Pacific SSTs can therefore provide society with an opportunity to mitigate against adverse consequences or to take advantage of some of the positive aspects of ENSO-related environmental change. The recent 1997-98 El Nino was the most recent example of success in ENSO forecasting.
The advances in ENSO forecasting over the past 15 years have come about because of a major coordinated and ongoing international research effort, and there is a vast technical literature that describes this progress. If you want to learn more, a user friendly web gateway to El Nino and related information can be found at http://www.pmel.noaa.gov/tao/elnino/nino-home.html
There are other examples where ocean forecasting has been carried out successfully, but this El Nino example illustrates how one segment of the oceanographic community (in collaboration with meteorologists) has developed practical predictive applications of its research.
Text: Michael J. McPhaden, Nancy N. Soreide