What is the reason for the formation of El Niño. Climatic phenomena of La Niña and El Niño and their impact on health and society

La Nina

Southern Oscillation and El Niño(Spanish) El Nino- Kid, Boy) is a global ocean-atmospheric phenomenon. As a feature of the Pacific Ocean, El Niño and La Niña(Spanish) La Nina- Baby, Girl) are temperature fluctuations in surface water in the tropics of the eastern Pacific Ocean. The names of these phenomena, borrowed from Spanish local residents and first introduced into scientific circulation in 1923 by Gilbert Thomas Walker, mean "baby" and "baby", respectively. Their influence on the climate of the southern hemisphere is difficult to overestimate. The Southern Oscillation (atmospheric component of the phenomenon) reflects monthly or seasonal fluctuations in the difference in air pressure between the island of Tahiti and the city of Darwin in Australia.

Named after Walker, the circulation is an essential aspect of the Pacific ENSO (El Niño Southern Oscillation) phenomenon. ENSO is a set of interacting parts of one global system of ocean-atmospheric climate fluctuations that occur as a sequence of oceanic and atmospheric circulations. ENSO is the world's best-known source of interannual weather and climate variability (3 to 8 years). ENSO has signatures in the Pacific, Atlantic and Indian Oceans.

In the Pacific, during significant El Niño warm events, as it warms up, it expands over much of the Pacific tropics and becomes directly related to the intensity of the SOI (Southern Oscillation Index). While ENSO events are mostly between the Pacific and Indian Oceans, ENSO events in the Atlantic Ocean lag behind the first by 12-18 months. Most of the countries that are subject to ENSO events are developing countries, with economies heavily dependent on the agricultural and fishing sectors. New opportunities to predict the onset of ENSO events in three oceans could have global socio-economic implications. Since ENSO is a global and natural part of the Earth's climate, it is important to know whether changes in intensity and frequency can be the result of global warming. Low frequency changes have already been detected. Inter-decadal ENSO modulations may also exist.

El Niño and La Niña

El Niño and La Niña are officially defined as long-term marine surface temperature anomalies greater than 0.5 °C across the Pacific Ocean in its central tropical region. When a +0.5 °C (-0.5 °C) condition is observed for up to five months, it is classified as an El Niño (La Niña) condition. If the anomaly persists for five months or longer, then it is classified as an El Niño (La Niña) episode. The latter occurs at irregular intervals of 2-7 years and usually lasts one or two years.

The first signs of El Niño are as follows:

1. Rising air pressure over the Indian Ocean, Indonesia and Australia.
2. Drop in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean.
3. The trade winds in the South Pacific are weakening or heading east.
4. Warm air appears next to Peru, causing rain in the deserts.
5. Warm water spreads from the western part of the Pacific Ocean to the east. She brings rain with her, causing it in areas where it is usually dry.

The warm El Niño Current, made up of plankton-poor tropical water and heated by its eastern branch in the Equatorial Current, replaces the cold, plankton-rich waters of the Humboldt Current, also known as the Peruvian Current, which contains large populations of game fish. Most years, warming lasts only a few weeks or months, after which weather patterns return to normal and fish catches increase. However, when El Niño conditions last several months, more extensive ocean warming occurs and its economic impact on local fisheries for the export market can be severe.

The Volcker circulation is visible on the surface as easterly trade winds, which move westward water and air heated by the sun. It also creates oceanic upwelling off the coast of Peru and Ecuador and cold waters rich in plankton flow to the surface, increasing fish stocks. The western equatorial Pacific Ocean is characterized by warm, humid weather and low atmospheric pressure. The accumulated moisture falls out in the form of typhoons and storms. As a result, in this place the ocean is 60 cm higher than in its eastern part.

On the Pacific Ocean La Niña is characterized by unusually cold temperatures in the eastern equatorial region compared to El Niño, which in turn is characterized by unusually high temperature in the same region. Atlantic tropical cyclone activity generally increases during La Niña. The La Niña condition often occurs after El Niño, especially when the latter is very strong.

Southern Oscillation Index (SOI)

The Southern Oscillation Index is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

Long-term negative SOI values ​​often signal El Niño episodes. These negative values ​​are usually associated with prolonged warming in the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific trade winds and a decrease in precipitation in the east and north of Australia.

Positive SOI values ​​are associated with strong Pacific trade winds and warming water temperatures in northern Australia, well known as the La Niña episode. The waters of the central and eastern tropical Pacific become colder during this time. Together, all of this increases the likelihood of more rainfall in eastern and northern Australia than usual.

Extensive influence of El Niño conditions

As El Niño's warm waters fuel storms, this creates an increase in rainfall in east-central and eastern parts Pacific Ocean.

In South America, the El Niño effect is more pronounced than in North America. El Niño is associated with warm and very wet summers (December-February) along the coasts of northern Peru and Ecuador, causing severe flooding whenever the event is strong. Effects during February, March, April can become critical. Southern Brazil and northern Argentina also experience wetter than normal conditions, but mostly during the spring and early summer. The central region of Chile gets a mild winter with plenty of rain, and the Peruvian-Bolivian Plateau experiences occasional winter snowfalls that are unusual for this region. more dry and warm weather observed in the Amazon Basin, Colombia and Central America.

The direct effects of El Niño lead to a decrease in humidity in Indonesia, increasing the likelihood of forest fires, in the Philippines and northern Australia. Also in June-August, dry weather is observed in the regions of Australia: Queensland, Victoria, New South Wales and eastern Tasmania.

The west of the Antarctic Peninsula, Ross Land, the Bellingshausen and Amundsen seas are covered with large amounts of snow and ice during El Niño. The latter two and the Wedell Sea are getting warmer and under higher atmospheric pressure.

In North America, winters tend to be warmer than usual in the Midwest and Canada, while it is getting wetter in central and southern California, northwestern Mexico, and the southeastern United States. The Pacific Northwest states, in other words, are drained during El Niño. Conversely, during La Niña, the US Midwest dries up. El Niño is also associated with a decrease in Atlantic hurricane activity.

Eastern Africa, including Kenya, Tanzania and the White Nile Basin, experience prolonged rains from March to May. Droughts haunt the southern and central regions of Africa from December to February, mainly Zambia, Zimbabwe, Mozambique and Botswana.

Warm Basin of the Western Hemisphere

A study of climate data has shown that there is an unusual warming of the Western Hemisphere Warm Basin in about half of the post-El Niño summers. This affects the weather in the region and seems to be related to the North Atlantic Oscillation.

Atlantic effect

An El Niño-like effect is sometimes observed in the Atlantic Ocean, where the water along the equatorial African coast is getting warmer, while off the coast of Brazil it is getting colder. This can be attributed to the Volcker circulations over South America.

Non-climatic effects

Along the east coast South America El Niño reduces the upwelling of cold, plankton-rich water that supports large fish populations, which in turn support an abundance of seabirds whose droppings support the fertilizer industry.

The local fishing industry along the coastline may be short of fish during long El Niño events. The largest global fish collapse due to overfishing, which occurred in 1972 during El Niño, led to a decrease in the population of Peruvian anchovies. During the events of 1982-83, populations of southern horse mackerel and anchovies decreased. Although the number of shells in warm water increased, but the hake went deeper into the cold water, and the shrimps and sardines went south. But the catch of some other fish species has been increased, for example, the common horse mackerel increased its population during warm events.

Changes in location and types of fish due to changing conditions have provided challenges for the fishing industry. The Peruvian sardine left due to El Nino to the Chilean coast. Other conditions have only led to further complications, such as the government of Chile in 1991 created restrictions on fishing.

It is postulated that El Niño led to the disappearance of the Mochico Indian tribe and other tribes of the pre-Columbian Peruvian culture.

Causes of El Niño

The mechanisms that can trigger El Niño events are still under investigation. It is difficult to find patterns that can show causes or allow predictions to be made.

History of the theory

The first mention of the term "El Niño" refers to the city, when Captain Camilo Carrilo reported at the congress of the Geographical Society in Lima that Peruvian sailors called the warm north current "El Niño", since it is most noticeable in the Christmas area. However, even then, the phenomenon was only interesting because of its biological impact on the efficiency of the fertilizer industry.

Normal conditions along the western Peruvian coast are a cold south current (Peruvian current) with upwelling water; upwelling of plankton leads to active ocean productivity; cold currents lead to a very dry climate on earth. Similar conditions exist everywhere (California Current, Bengal Current). So replacing it with a warm northern current leads to a decrease in biological activity in the ocean and to heavy rains, leading to flooding, on earth. A connection to flooding has been reported in Peset and Eguiguren.

Towards the end of the nineteenth century, interest arose in predicting climate anomalies (for food production) in India and Australia. Charles Todd suggested that droughts in India and Australia occur at the same time. Norman Lockyer pointed out the same in d. In d. Gilbert Walker was the first to coin the term "Southern Oscillation".

For most of the twentieth century, El Niño was considered a large local phenomenon.

The history of the phenomenon

ENSO conditions have happened every 2-7 years for at least the last 300 years, but most have been mild.

Big ENSO events occurred in - , , - , , - , - and -1998.

The last El Niño events occurred in -, -,,,, 1997-1998 and -2003.

The 1997-1998 El Niño in particular was strong and brought international attention to the phenomenon, while it was unusual for the 1997-1998 period that El Niño was very frequent (but mostly weak).

El Niño in the history of civilization

Scientists tried to establish why at the turn of the 10th century AD, at opposite ends of the earth, the two largest civilizations of that time almost simultaneously ceased to exist. It's about about the Maya Indians and the fall of the Chinese Tang Dynasty, followed by a period of internecine strife.

Both civilizations were located in monsoonal regions, the moistening of which depends on the seasonal precipitation. However, at the indicated time, apparently, the rainy season was not able to provide the amount of moisture sufficient for the development of agriculture.

The ensuing drought and subsequent famine led to the decline of these civilizations, the researchers believe. They bind climate change with the natural phenomenon "El Niño", which refers to temperature fluctuations in the surface waters of the eastern Pacific Ocean in tropical latitudes. This leads to large-scale disturbances in atmospheric circulation, which causes droughts in traditionally wet regions and floods in dry ones.

Scientists arrived at these conclusions by examining the nature of sedimentary deposits in China and Mesoamerica dating back to the specified period. The last emperor of the Tang Dynasty died in 907 AD, and the last known Mayan calendar dates from 903.

Links

• The El Nino Theme Page Explains El Nino and La Nina, provides real time data, forecasts, animations, FAQ, impacts and more.
• The International Meteorological Organization announced the discovery of the beginning of the event La Niña in the Pacific Ocean. (Reuters/YahooNews)

Literature

• Cesar N. Caviedes, 2001. El Nino in History: Storming Through the Ages(University Press of Florida)
• Brian Fagan, 1999. Floods, Famines, and Emperors: El Niño and the Fate of Civilizations(Basic Books)
• Michael H. Glantz, 2001. Currents of change, ISBN 0-521-78672-X
• Mike Davis, Late Victorian Holocausts: El Niño Famines and the Making of the Third World(2001), ISBN 1-85984-739-0

The natural phenomenon of El Niño, which broke out in 1997-1998, had no equal in scale in the entire history of observations. What is this mysterious phenomenon that has made so much noise and attracted close attention of the media?

In scientific terms, El Niño is a complex of interdependent changes in the thermobaric and chemical parameters of the ocean and atmosphere, which take on the character of natural disasters. According to reference literature, it is a warm current that sometimes occurs for unknown reasons off the coast of Ecuador, Peru and Chile. In Spanish, "El Niño" means "baby". This name was given to it by Peruvian fishermen, because the warming of the water and the mass fish kills associated with it usually occur at the end of December and coincide with Christmas. Our journal already wrote about this phenomenon in N 1 for 1993, but since that time researchers have accumulated a lot of new information.

NORMAL SITUATION

To understand the anomalous nature of the phenomenon, let us first consider the usual (standard) climatic situation near the South American Pacific coast. It is rather peculiar and is determined by the Peruvian current, which carries cold waters from Antarctica along the western coast of South America to the Galapagos Islands lying on the equator. Usually the trade winds blowing here from the Atlantic, crossing the high barrier of the Andes, leave moisture on their eastern slopes. And because the western coast of South America is a dry rocky desert, where rain is extremely rare - sometimes it does not fall for years. When the trade winds pick up so much moisture that they carry it to the western shores of the Pacific Ocean, they form the prevailing westerly direction of surface currents here, causing a surge of water off the coast. It is unloaded by the counter-trade current of Cromwell in the equatorial zone of the Pacific Ocean, which captures here a 400-kilometer strip and, at depths of 50-300 m, carries huge masses of water back to the east.

The attention of specialists is attracted by the colossal biological productivity of the Peruan-Chilean coastal waters. Here, in a small space, constituting some fractions of a percent of the entire water area of ​​the World Ocean, the annual fish production (mainly anchovy) exceeds 20% of the world's. Its abundance attracts here huge flocks of fish-eating birds - cormorants, boobies, pelicans. And in the areas of their accumulation, colossal masses of guano (bird droppings) are concentrated - a valuable nitrogen-phosphorus fertilizer; its deposits with a thickness of 50 to 100 m became the object of industrial development and export.

CATASTROPHE

During the El Niño years, the situation changes dramatically. First, the water temperature rises by several degrees and the mass death or departure of fish from this area begins, and as a result, birds disappear. Then atmospheric pressure drops in the eastern Pacific Ocean, clouds appear above it, the trade winds subside, and air currents over the entire equatorial zone of the ocean change direction. Now they go from west to east, carrying moisture from the Pacific region and bringing it down on the Peruvian-Chilean coast.

Events are developing especially catastrophically at the foot of the Andes, which now block the path of the western winds and take all their moisture onto their slopes. As a result, in a narrow strip of rocky coastal deserts west coast floods, mudflows, floods are raging (at the same time, the territories of the Western Pacific region are suffering from a terrible drought: tropical forests in Indonesia and New Guinea are burning out, crop yields in Australia are falling sharply). To top it off, so-called "red tides" are developing from the Chilean coast to California, caused by the rapid growth of microscopic algae.

So, the chain of catastrophic events begins with a noticeable warming of surface waters in the eastern part of the Pacific Ocean, which in recent times successfully used to predict El Niño. A network of buoy stations has been installed in this water area; with their help, the temperature of ocean water is constantly measured, and the data obtained through satellites are promptly transmitted to research centers. As a result, it was possible to warn in advance about the onset of the most powerful El Niño known so far - in 1997-98.

At the same time, the reason for the heating of ocean water, and therefore the emergence of El Niño itself, is still not completely clear. The appearance of warm water south of the equator is explained by oceanographers as a change in the direction of the prevailing winds, while meteorologists consider the change in winds to be a consequence of the heating of the water. Thus, a kind of vicious circle is created.

To get closer to understanding the genesis of El Niño, let's pay attention to a number of circumstances that are usually overlooked by climate scientists.

EL NIÑO DEGASSING SCENARIO

For geologists, the following fact is quite obvious: El Niño develops over one of the most geologically active parts of the world rift system - the East Pacific Rise, where maximum speed spreading (the expansion of the ocean floor) reaches 12-15 cm/year. In the axial zone of this underwater ridge, a very high heat flow from the earth's interior was noted, manifestations of modern basalt volcanism are known here, thermal water outcrops and traces of an intensive process of modern ore formation in the form of numerous black and white "smokers" were found.

In the water area between 20 and 35 s. sh. nine hydrogen jets were recorded at the bottom - the outlets of this gas from the earth's interior. In 1994, an international expedition discovered here the most powerful hydrothermal system in the world. In its gaseous emanations, the isotope ratios 3He/4He turned out to be anomalously high, which means that the source of degassing is located at a great depth.

A similar situation is typical for other "hot spots" of the planet - Iceland, Hawaiian Islands, Red Sea. There, at the bottom, there are powerful centers of hydrogen-methane degassing and above them, most often in the Northern Hemisphere, the ozone layer is destroyed.
, which gives grounds to apply my model of the destruction of the ozone layer by hydrogen and methane flows to El Niño.

Here is how this process begins and develops. Hydrogen, released from the ocean floor from the rift valley of the East Pacific Rise (its sources were found there instrumentally) and reaching the surface, reacts with oxygen. As a result, heat is generated, which begins to heat the water. For oxidative reactions the conditions here are very favorable: the surface layer of water is enriched with oxygen during wave interaction with the atmosphere.

However, the question arises: can hydrogen coming from the bottom reach the ocean surface in appreciable quantities? A positive answer was given by the results of American researchers who found in the air over the Gulf of California twice the content of this gas compared to the background. But here at the bottom there are hydrogen-methane sources with a total debit of 1.6 x 10 8 m 3 / year.

Hydrogen, rising from the water depths into the stratosphere, forms an ozone hole into which ultraviolet and infrared solar radiation "falls". Falling on the surface of the ocean, it intensifies the heating of its upper layer that has begun (due to the oxidation of hydrogen). Most likely, it is the additional energy of the Sun that is the main and determining factor in this process. The role of oxidative reactions in heating is more problematic. One could not talk about this if it were not for the significant (from 36 to 32.7%o) desalination of ocean water going synchronously with it. The latter is probably carried out by the very addition of water that is formed during the oxidation of hydrogen.

Due to the heating of the surface layer of the ocean, the solubility of CO 2 in it decreases, and it is released into the atmosphere. For example, during the El Niño of 1982-83. an additional 6 billion tons of carbon dioxide got into the air. Evaporation of water also intensifies, and clouds appear over the eastern Pacific Ocean. Both water vapor and CO 2 are greenhouse gases; they absorb thermal radiation and become an excellent accumulator of additional energy that came through the ozone hole.

Gradually, the process is gaining momentum. The anomalous heating of the air leads to a decrease in pressure, and a cyclonic region is formed over the eastern part of the Pacific Ocean. It is she who breaks the standard trade wind scheme of atmospheric dynamics in the area and "sucks in" air from the western part of the Pacific Ocean. Following the subsiding of the trade winds, the water surge near the Peruvian-Chilean coast decreases and the Cromwell equatorial countercurrent ceases to operate. A strong heating of the water leads to the emergence of typhoons, which is very rare in normal years (due to the cooling effect of the Peruvian current). From 1980 to 1989, ten typhoons appeared here, seven of them in 1982-83, when El Niño raged.

BIOLOGICAL PRODUCTIVITY

Why is there a very high biological productivity off the western coast of South America? According to experts, it is the same as in the abundantly "fertilized" fish ponds of Asia, and 50 thousand times higher (!) than in other parts of the Pacific Ocean, if we count on the number of fish caught. Traditionally, this phenomenon is explained by upwelling - a wind driven warm water from the coast, forcing cold water enriched with nutrients, mainly nitrogen and phosphorus, to rise from the depths. During El Niño years, when the wind changes direction, the upwelling is interrupted and, consequently, the feed water stops flowing. As a result, fish and birds die or migrate due to starvation.

All this resembles a perpetual motion machine: the abundance of life in surface waters is explained by the flow from below nutrients, and their excess below - an abundance of life above, because the dying organic matter settles to the bottom. However, what is primary here, what gives impetus to such a cycle? Why does it not dry out, although, judging by the thickness of the guano deposits, it has been operating for millennia?

The mechanism of wind upwelling itself is not very clear either. The rise of deep water associated with it is usually determined by measuring its temperature on profiles of different levels oriented perpendicular to the coastline. Then they build isotherms that show the same low temperatures near the coast and at great depths away from it. And in the end, they conclude that the rise of cold waters. But it is known that near the coast the low temperature is due to the Peruvian current, so the described method for determining the rise of deep waters is hardly correct. And finally, one more ambiguity: the mentioned profiles are built across the coastline, and the prevailing winds here blow along it.

I am by no means going to overthrow the concept of wind upwelling - it is based on an understandable physical phenomenon and has the right to life. However, with a closer acquaintance with it in a given region of the ocean, all of the above problems inevitably arise. Therefore, I propose a different explanation for the anomalous biological productivity off the western coast of South America: it is again determined by the degassing of the earth's interior.

In fact, not the entire strip of the Peruvian-Chilean coast is equally productive, as it should be under the action of climatic upwelling. Two "spots" are isolated here - northern and southern, and their position is controlled by tectonic factors. The first is located above a powerful fault leaving the ocean to the continent to the south of the Mendana fault (6-8 o S) and parallel to it. The second spot, somewhat smaller, is located just north of the Nazca Ridge (13-14 S). All of these oblique (diagonal) geological structures running from the East Pacific Rise towards South America are, in essence, zones of degassing; through them, a huge amount of various chemical compounds comes from the bowels of the earth to the bottom and into the water column. Among them there are, of course, vital elements - nitrogen, phosphorus, manganese, and enough trace elements. In the thickness of the coastal Peruvian-Ecuadorian waters, the oxygen content is the lowest in the entire World Ocean, since the main volume here is made up of reduced gases - methane, hydrogen sulfide, hydrogen, ammonia. But a thin surface layer (20-30 m) is abnormally rich in oxygen due to the low temperature of the water brought here from Antarctica by the Peruvian Current. In this layer above the fault zones - sources of nutrients of endogenous nature - unique conditions are created for the development of life.

However, there is an area in the World Ocean that is not inferior in bioproductivity to Peruvian, and possibly even surpasses it - off the western coast of South Africa. It is also considered a wind upwelling zone. But the position of the most productive area here (Walvis Bay) is again controlled by tectonic factors: it is located above a powerful fault zone running from the Atlantic Ocean to the African continent somewhat north of the Southern Tropic. And along the coast from the Antarctic runs the cold, oxygen-rich Benguela Current.

The region of the Southern Kuril Islands, where the cold current passes over the submeridional marginal-ocean fault of Iona. In the midst of saury fishing season, literally the entire Far Eastern fishing fleet of Russia gathers in the small water area of ​​the South Kuril Strait. It is appropriate here to recall Kuril Lake in South Kamchatka, where one of the largest spawning grounds for sockeye salmon (a type of Far Eastern salmon) is located in our country. The reason for the very high biological productivity of the lake, according to experts, is the natural "fertilization" of its water with volcanic emanations (it is located between two volcanoes - Ilyinsky and Kambalny).

But back to El Niño. During the period when degassing intensifies off the coast of South America, a thin surface layer of water saturated with oxygen and teeming with life is blown through with methane and hydrogen, oxygen disappears, and mass death of all living things begins: a huge number of bones of large fish are lifted from the bottom of the sea by trawls, on Seals are dying in the Galapagos Islands. However, it is unlikely that the fauna is dying due to a decrease in the bioproductivity of the ocean, as the traditional version says. She is most likely poisoned by poisonous gases rising from the bottom. After all, death comes suddenly and overtakes the entire marine community - from phytoplankton to vertebrates. Only birds die of starvation, and even then mostly chicks - adults simply leave the danger zone.

"RED TIDES"

However, after the mass disappearance of biota, the amazing riot of life off the western coast of South America does not stop. In oxygen-deprived waters purged with poisonous gases, unicellular algae, dinoflagellates, begin to flourish. This phenomenon is known as the "red tide" and is so named because only intensely colored algae thrive in such conditions. Their coloration is a kind of protection from solar ultraviolet, acquired back in the Proterozoic (over 2 billion years ago), when there was no ozone layer and the surface of water bodies was subjected to intense ultraviolet radiation. So during the "red tides" the ocean, as it were, returns to its "pre-oxygen" past. Due to the abundance of microscopic algae, some marine organisms, usually acting as water filterers, such as oysters, at this time become poisonous and their consumption threatens with severe poisoning.

Within the framework of the gas-geochemical model developed by me of the anomalous bioproductivity of local areas of the ocean and the periodically rapid death of biota in it, other phenomena are also explained: the mass accumulation of fossil fauna in the ancient shales of Germany or phosphorites of the Moscow region, overflowing with remains of fish bones and cephalopod shells.

MODEL CONFIRMED

I will give some facts testifying to the reality of the El Niño degassing scenario.

During the years of its manifestation, the seismic activity of the East Pacific Rise sharply increases - such a conclusion was made by the American researcher D. Walker, after analyzing the relevant observations from 1964 to 1992 in the section of this underwater ridge between 20 and 40s. sh. But, as it has long been established, seismic events are often accompanied by increased degassing of the earth's interior. In favor of the model I have developed is also the fact that the waters off the western coast of South America during El Niño years are literally seething from the release of gases. The hulls of the ships are covered with black spots (the phenomenon was called "El Pintor", translated from Spanish - "painter"), and the fetid smell of hydrogen sulfide spreads over large areas.

In the African Gulf of Walvis Bay (mentioned above as an area of ​​anomalous bioproductivity), ecological crises also occur periodically, proceeding according to the same scenario as off the coast of South America. In this bay, emissions of gases begin, which leads to the mass death of fish, then "red tides" develop here, and the smell of hydrogen sulfide on land is felt even 40 miles from the coast. All this is traditionally associated with copious excretion hydrogen sulfide, but its formation is explained by the decomposition of organic residues into seabed. Although it is much more logical to consider hydrogen sulfide as an ordinary component of deep emanations - after all, it comes out here only above the fault zone. The penetration of gas far on land is also easier to explain by its flow from the same fault, tracing from the ocean into the depths of the mainland.

It is important to note the following: when deep gases enter the ocean water, they are separated due to a sharply different (by several orders of magnitude) solubility. For hydrogen and helium, it is 0.0181 and 0.0138 cm 3 in 1 cm 3 of water (at temperatures up to 20 C and a pressure of 0.1 MPa), and for hydrogen sulfide and ammonia it is incomparably more: 2.6 and 700 cm, respectively 3 in 1 cm3. That is why the water above the degassing zones is greatly enriched with these gases.

A strong argument in favor of the El Niño degassing scenario is a map of the average monthly ozone deficit over the planet's equatorial region, compiled at the Central Aerological Observatory of the Hydrometeorological Center of Russia using satellite data. It clearly shows a powerful ozone anomaly over the axial part of the East Pacific Rise a little south of the equator. I note that by the time the map was published, I had published a qualitative model explaining the possibility of the destruction of the ozone layer just above this zone. By the way, this is not the first time that my predictions of the place where ozone anomalies might appear are confirmed by field observations.

LA NINA

This is the name of the final phase of El Niño - a sharp cooling of the water in the eastern part of the Pacific Ocean, when its temperature drops several degrees below normal for a long period. The natural explanation for this is the simultaneous destruction of the ozone layer both over the equator and over Antarctica. But if in the first case it causes the water to warm up (El Niño), then in the second case it causes a strong melting of ice in Antarctica. The latter increases the inflow of cold water into the Antarctic area. As a result, the temperature gradient between the equatorial and southern parts of the Pacific Ocean increases sharply, and this leads to an increase in the cold Peruvian Current, which cools the equatorial waters after degassing weakens and the ozone layer recovers.

THE ROOT CAUSE IS IN SPACE

First, I would like to say a few "justifying" words about El Niño. The media is, to put it mildly, not quite right when they accuse him of causing such disasters as floods in South Korea or unprecedented frosts in Europe. After all, deep degassing can simultaneously intensify in many regions of the planet, which leads there to the destruction of the ozonosphere and the appearance of anomalous natural phenomena, which have already been mentioned. For example, the heating of water preceding the occurrence of El Niño occurs under ozone anomalies not only in the Pacific, but also in other oceans.

As for the intensification of deep degassing, it is determined, in my opinion, by cosmic factors, mainly by the gravitational effect on the liquid core of the Earth, which contains the main planetary reserves of hydrogen. An important role in this is probably played by the relative position of the planets and, first of all, interactions in the Earth-Moon-Sun system. G.I. Voitov and his colleagues from the Joint Institute of Physics of the Earth named after V.I. O. Yu. Schmidt of the Russian Academy of Sciences established a long time ago: the degassing of the bowels noticeably increases in periods close to the full moon and new moon. It is also influenced by the position of the Earth in the near-solar orbit, and the change in the speed of its rotation. A complex combination of all these external factors with the processes in the depths of the planet (for example, the crystallization of its inner core) determines the impulses of increasing planetary degassing, and hence the El Niño phenomenon. Its 2-7-year quasi-periodicity was revealed by the domestic researcher N. S. Sidorenko (Hydrometeorological Center of Russia), who analyzed a continuous series of atmospheric pressure drops between the stations of Tahiti (on the island of the same name in the Pacific Ocean) and Darwin (the northern coast of Australia) over a long period - from 1866 to the present.

Candidate of Geological and Mineralogical Sciences V. L. SYVOROTKIN, Moskovsky State University them. M. V. Lomonosov

El Niño- a natural phenomenon associated with global changes climatic conditions occurring on earth.

El Niño brings with it natural disasters, destruction and misfortune. Scientists have found that this natural phenomenon ruined more than one civilization of the past.

The scientific community has determined that the interaction of the ocean current and air masses is quite stable, but periodically failures occur in this system, the causes of which have not been established.

As a result, the direction of air flows and water masses changes, which in turn leads to an increase in temperature in the surface layer of the ocean near the coast by up to 10 degrees. Failure necessarily brings catastrophic changes in the climate: prolonged droughts, endless rains, floods.

• The frequency of El Niño is approximately 10 years.

La Niña is the exact opposite of El Niño. Feature– decrease in water temperature in the east of the Pacific basin. This gives rise to tornadoes, drought, rains with floods.

Scientists have proven the destructive role of El Niño. American archaeologists have found that the disappearance of molluscs of a particular species and the appearance of others is an indicator of climate fluctuations.

Scientists, observing the movement of mollusks, confirmed that when El Niño occurs, respectively, with an increase in the temperature of the water surface, some types of mollusks quickly die, while others move south. Having studied the shells of mollusks, scientists have found that in ancient times, this phenomenon of nature arose extremely rarely compared to the present.

For the scientific world, the mystery of the disappearance of the Olmec civilization that existed in the 14th-13th centuries remains relevant. in. BC, the region of residence of which roughly corresponded to the borders of modern Mexico.

The Olmecs built monumental structures. But around the 5th century BC, the Olmecs suddenly stopped their construction, buried huge stone heads and disappeared into the swamps around their cities.

Scientists suggest that the death of the Olmec civilization is associated with another El Niño.

Also, according to scientists, the Moche culture, which appeared around the beginning of the 2nd century BC in the region of the north coast of Peru, fell victim to the El Niño natural phenomenon.

The Moche Indians are known for building huge buildings out of brick, the raw material of which was dried under the sun. This civilization is well known to scientists for its characteristic products made of gold and ceramics. Archaeologists have explored a pyramid near Trujillo, built during the Moche culture. About a hundred skeletons were found buried under a thick layer of silt.

• This indicates a severe flood that occurred at that time.

However, scientists do not exclude the fact that the found human remains could be the result of a sacrificial rite. The Moche Indians believed that this act would turn away from them the impending flood caused by another El Niño.

A natural phenomenon El Niño / La Niña, scientists refer to the category of global catastrophes of the planet, radically changing the climate: in some parts of the planet it rains incessantly, leading to real floods, in other parts of the Earth there are severe droughts that plunge people into hunger.

So several hundred years ago there was a severe drought, which caused the complete death of the Anasazi Indian culture that existed in southwestern Colorado. The Anasazi Indians built stone dwellings. But somewhere in 1150 AD. the stone dwelling was abandoned for unknown reasons. Modern scientists conducted a study of the found remains of the Indians and came to the conclusion that most of the Indians were simply eaten.

In the course of research, scientists were able to establish that cannibalism flourished within the territory of the Anasazi Indians.

Scientists believe that the cannibalism of that time was the result of a rampant drought that drove other tribes from their homes. In search of food, other tribes came to the territory of the Anasazi Indians, but they did not find anything edible here either. The source of their livelihood was the local residents - the Anasazi Indians.

• By about 1200, the drought had receded, and with it, so did cannibalism.

German scientists of the National Center for Geosciences made a discovery - world civilizations Central America Maya and China's Tang Dynasty were victims of a global El Niño. Despite the fact that these civilizations were located in different parts of our planet, they died almost simultaneously.

The reason that caused the death of civilizations was the most severe drought that prevailed in the 9th-10th centuries. in. AD

The mystery of the El Niño phenomenon has not yet been completely solved. However, it is clear that it is almost impossible to defeat such a formidable opponent. A person can only rely on modern technologies and on a system of mutual assistance between countries.

FEDERAL AGENCY FOR EDUCATION

State educational institution higher professional education

"NATIONAL RESEARCH TOMSK POLYTECHNICAL UNIVERSITY"

Institute of Non-Destructive Testing

Department - Ecology and life safety

"The El Niño Phenomenon"

Individual task

in the discipline "Hazardous natural processes"

Student (signature)

Lecturer __________ Krepsha N.V.

(signature)

Tomsk, 2011

El Niño phenomenon

In recent years, there have been many alarming reports in the press and the media about weather anomalies that have covered almost all the continents of the Earth. At the same time, the unpredictable phenomenon of El Niño (baby-boy in Spanish, as Peruvian fishermen called him) was called the main culprit for all climatic and social turmoil, which is a warm current that causes warming of the surface of the eastern Pacific Ocean.

Moreover, some scientists viewed this phenomenon as a harbinger of even more radical climate change. What data does science have today about the mysterious El Niño current?

The El Niño phenomenon consists in a sharp increase in temperature (by 5-9o C) of the surface water layer in the eastern Pacific Ocean (in the tropical and central parts) over an area of ​​about 107 km2.

According to the scheme, the processes of formation of the strongest warm current in the ocean in our century are presented as follows. In ordinary weather conditions, when the El Niño phase has not yet begun, the warm surface waters of the ocean are transported and held by easterly winds - trade winds in the western zone of the tropical Pacific Ocean, where the so-called tropical warm basin (TTB) is formed. It should be noted that the depth of this warm water layer reaches 100-200 meters. The formation of such a huge reservoir of heat is the main necessary condition for the transition to the regime of the El Niño phenomenon. At the same time, as a result of the surge of water, the sea level off the coast of Indonesia is two feet higher than off the coast of South America. At the same time, the temperature of the water surface in the west in the tropical zone averages 29-30 ° C, and in the east 22-24 ° C. A slight cooling of the surface in the east is the result of upwelling - the rise of deep cold waters to the surface of the ocean when water is sucked trade winds. At the same time, the largest area of ​​heat and stationary unstable equilibrium in the ocean-atmosphere system (when all forces are balanced and the TTB is immobile) is formed above the TTB in the atmosphere.

For unknown reasons, the trade winds weaken at intervals of 3-7 years, the balance is disturbed, and the warm waters of the western basin rush to the east, creating one of the strongest warm currents in the oceans. Over a huge area in the eastern Pacific Ocean, in the tropical and central equatorial parts, there is a sharp increase in the temperature of the surface layer of the ocean. This is the onset of the El Niño phase. Its beginning is marked by a long onslaught of squall westerly winds, which serve as a trigger for a new phase. They replace the usual weak trade winds over the warm western Pacific and prevent the rise of cold deep waters to the surface. As a result, upwelling is blocked.

Although the processes that develop during the El Niño phase are regional, nevertheless, their consequences are global in nature. El Niño is usually accompanied by environmental disasters: droughts, fires, heavy rains, causing flooding of vast areas of densely populated areas, which leads to the death of people and the destruction of livestock and crops in different parts of the Earth. El Niño has a significant impact on the state of the world economy. According to American specialists in 1982-83 economic damage from the consequences of El Niño amounted to 13 billion dollars, and according to the world's leading insurance company Munich Re, the damage from natural disasters in the first half of 1998 is estimated at 24 billion dollars.

The warm western basin usually enters the opposite phase, the so-called La Niña, when the eastern Pacific cools a year after El Niño. The phases of warming and cooling alternate with the normal state, when heat is accumulated in the western basin (TTB) and the state of stationary unstable equilibrium is restored. The question arises - what is the secret of the global impact on the Earth's climate El Niño? Climatologist P.-J. Webster believes that "first of all - in the nonlinearity and non-equilibrium of the climate system. El Niño cannot cause instantaneous changes in the atmosphere itself, but the phenomenon affects the stochastic choice of the most probable state of the disturbed atmosphere."

Meteorological data on the temperature of the surface layer of the atmosphere, collected over the past hundred years, show that the climate on Earth has warmed by 0.5 ° C. The steady increase in temperature was interrupted by a short-term cooling in 1940-1970, after which the warming resumed.

Although the increase in temperature is consistent with the "greenhouse effect" hypothesis, there are other factors that influence warming (volcanic eruptions, ocean currents, etc.). It will be possible to establish the uniqueness of the cause of warming after the receipt of new data in the next 10-15 years. All models predict that warming will increase significantly in the coming decades. From this we can conclude that the frequency of the occurrence of the El Niño phenomenon and its intensity will increase.

Climate variations over a period of 3-7 years are determined by changes in the vertical circulation in the ocean and atmosphere and ocean surface temperature (SST). In other words, they change the intensity of heat and mass transfer between the ocean and the atmosphere. The ocean and atmosphere are open, non-equilibrium, non-linear systems, between which there is a constant exchange of heat and moisture.

These processes are irreversible, and the movement in the water and air environments is turbulent. Such systems are characterized by self-organization of dissipative structures, for example, the formation of such formidable structures as tropical cyclones (TCs), which transport the energy and moisture received from the ocean over long distances.

It seems to us that insufficient knowledge of the physics of the processes of formation of dissipative structures, taking into account nonlinearity and feedback, limits the possibility of constructing perfect predictive models. All this indicates, firstly, the need for a qualitative analysis to describe the phenomena as a whole and, secondly, the need to search for the key energy parameters that determine the energy exchange in climate systems.

Such key parameters, of course, are the fluxes of heat and matter. However, as far as we know, at present there are still no quantitative estimates of the values ​​of heat and moisture fluxes between the ocean and the atmosphere, obtained from the results of field observations or theoretical calculations of the El Niño phenomenon. Earlier in 1980-90s. a group of employees of the Department of Atmospheric Physics on ocean expeditions carried out instrumental measurements from the vessel, which made it possible to obtain estimates of heat and moisture fluxes in extreme conditions during a thunderstorm squall and storm wind, that is, under conditions close to the TC parameters. It was found that in energy-active zones with strong winds(Northern Atlantic, thunderstorms of the Northern Caspian, Crimean forest on the Black Sea), the density of the total heat flux from the sea to the atmosphere, taking into account the fluxes of water vapor, infrared radiation of the ocean surface and contact transport, reach high values. Therefore, the determining parameter of the degree of transfer intensity is the wind speed.

According to the generalized materials of all these expeditions, the density of the total heat flux at a wind of about 10 m/s was about 3 kW/m2, and at 15 m/s it was about 5 kW/m2, which was an order of magnitude higher than the flows in calm weather. Moreover, with artificial blowing of the sea surface by a helicopter hovering at a height of 20 m, when the wind speed reached 40 m/s (this is the beginning of the TC), the flows reached values ​​of 9 kW/m2.

Based on the above, the preliminary estimate of the energy emitted by the ocean into the atmosphere in the El Niño area per day is the following value: W=P(W/m2)*S (m2)*T(day) = 5*103 W/ m2 * 1013 m2 * 8.6 * 104 s = 4.3 * 1021 J, which is commensurate with the energy of the entire atmosphere ~ 1022 J.

The estimates obtained for the energy of the interaction between the ocean and the atmosphere allow us to conclude that the energy of El Niño is able to disturb the entire atmosphere of the Earth, which leads to environmental disasters taking place in recent years.

In the book "Knowledge of the Complex" G. Nicolis and I. Prigogine drew attention to the fact that new data on the state of the climate, obtained in the 60s of our century, showed a very pronounced internal variability of the earth's climate. "This fact surprises and worries specialists, politicians and the public. For the first time, man has realized the global, planetary nature of the climate system, as well as the fact that his own activities could also affect the operation of the impressive climate machine."

In the long term, as noted Canadian climate change scientist Henry Hincheveld has shown, “...society needs to abandon the notion that the climate is something permanent. It is changeable, changes will continue, and humanity needs to develop an infrastructure that would allow ready to face the unexpected."

El Niño

Southern Oscillation and El Niño(Spanish) El Nino- Kid, Boy) is a global ocean-atmospheric phenomenon. As a feature of the Pacific Ocean, El Niño and La Niña(Spanish) La Nina- Baby, Girl) are temperature fluctuations in surface water in the tropics of the eastern Pacific Ocean. The names of these phenomena, borrowed from the Spanish language of the locals and first introduced into scientific circulation in 1923 by Gilbert Thomas Walker, mean "baby" and "baby", respectively. Their influence on the climate of the southern hemisphere is difficult to overestimate. The Southern Oscillation (atmospheric component of the phenomenon) reflects monthly or seasonal fluctuations in the difference in air pressure between the island of Tahiti and the city of Darwin in Australia.

Named after Walker, the circulation is an essential aspect of the Pacific ENSO (El Niño Southern Oscillation) phenomenon. ENSO is a set of interacting parts of one global system of ocean-atmospheric climate fluctuations that occur as a sequence of oceanic and atmospheric circulations. ENSO is the world's best-known source of interannual weather and climate variability (3 to 8 years). ENSO has signatures in the Pacific, Atlantic and Indian Oceans.

In the Pacific, during significant El Niño warm events, as it warms up, it expands over much of the Pacific tropics and becomes directly related to the intensity of the SOI (Southern Oscillation Index). While ENSO events are mostly between the Pacific and Indian Oceans, ENSO events in the Atlantic Ocean lag behind the first by 12-18 months. Most of the countries that are subject to ENSO events are developing countries, with economies heavily dependent on the agricultural and fishing sectors. New opportunities to predict the onset of ENSO events in three oceans could have global socio-economic implications. Since ENSO is a global and natural part of the Earth's climate, it is important to know if the change in intensity and frequency could be the result of global warming. Low frequency changes have already been detected. Inter-decadal ENSO modulations may also exist.

El Niño and La Niña

El Niño and La Niña are officially defined as long-term marine surface temperature anomalies greater than 0.5 °C across the Pacific Ocean in its central tropical region. When a +0.5 °C (-0.5 °C) condition is observed for up to five months, it is classified as an El Niño (La Niña) condition. If the anomaly persists for five months or longer, then it is classified as an El Niño (La Niña) episode. The latter occurs at irregular intervals of 2-7 years and usually lasts one or two years.

The first signs of El Niño are as follows:

1. Rising air pressure over the Indian Ocean, Indonesia and Australia.
2. Drop in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean.
3. The trade winds in the South Pacific are weakening or heading east.
4. Warm air appears next to Peru, causing rain in the deserts.
5. Warm water spreads from the western part of the Pacific Ocean to the east. She brings rain with her, causing it in areas where it is usually dry.

The warm El Niño Current, made up of plankton-poor tropical water and heated by its eastern branch in the Equatorial Current, replaces the cold, plankton-rich waters of the Humboldt Current, also known as the Peruvian Current, which contains large populations of game fish. Most years, warming lasts only a few weeks or months, after which weather patterns return to normal and fish catches increase. However, when El Niño conditions last several months, more extensive ocean warming occurs and its economic impact on local fisheries for the export market can be severe.

The Volcker circulation is visible on the surface as easterly trade winds, which move westward water and air heated by the sun. It also creates oceanic upwelling off the coast of Peru and Ecuador and cold waters rich in plankton flow to the surface, increasing fish stocks. The western equatorial part of the Pacific Ocean is characterized by warm, humid weather and low atmospheric pressure. The accumulated moisture falls out in the form of typhoons and storms. As a result, in this place the ocean is 60 cm higher than in its eastern part.

In the Pacific, La Niña is characterized by unusually cold temperatures in the eastern equatorial region compared to El Niño, which in turn is characterized by unusually high temperatures in the same region. Atlantic tropical cyclone activity generally increases during La Niña. The La Niña condition often occurs after El Niño, especially when the latter is very strong.

Southern Oscillation Index (SOI)

The Southern Oscillation Index is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.

Long-term negative SOI values ​​often signal El Niño episodes. These negative values ​​are usually associated with prolonged warming in the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific trade winds and a decrease in precipitation in the east and north of Australia.

Positive SOI values ​​are associated with strong Pacific trade winds and warming water temperatures in northern Australia, well known as the La Niña episode. The waters of the central and eastern tropical Pacific become colder during this time. Together, all of this increases the likelihood of more rainfall in eastern and northern Australia than usual.

Extensive influence of El Niño conditions

As El Niño's warm waters feed the storms, it creates an increase in rainfall in the east-central and eastern Pacific Oceans.

In South America, the El Niño effect is more pronounced than in North America. El Niño is associated with warm and very wet summers (December-February) along the coasts of northern Peru and Ecuador, causing severe flooding whenever the event is strong. Effects during February, March, April can become critical. Southern Brazil and northern Argentina also experience wetter than normal conditions, but mostly during the spring and early summer. The central region of Chile gets a mild winter with plenty of rain, and the Peruvian-Bolivian Plateau experiences occasional winter snowfalls that are unusual for this region. Dryer and warmer weather is observed in the Amazon Basin, Colombia and Central America.

The direct effects of El Niño lead to a decrease in humidity in Indonesia, increasing the likelihood of wildfires in the Philippines and northern Australia. Also in June-August, dry weather is observed in the regions of Australia: Queensland, Victoria, New South Wales and eastern Tasmania.

The west of the Antarctic Peninsula, Ross Land, the Bellingshausen and Amundsen seas are covered with large amounts of snow and ice during El Niño. The latter two and the Wedell Sea are getting warmer and under higher atmospheric pressure.

In North America, winters tend to be warmer than usual in the Midwest and Canada, while it is getting wetter in central and southern California, northwestern Mexico, and the southeastern United States. The Pacific Northwest states, in other words, are drained during El Niño. Conversely, during La Niña, the US Midwest dries up. El Niño is also associated with a decrease in Atlantic hurricane activity.

Eastern Africa, including Kenya, Tanzania and the White Nile Basin, experience prolonged rains from March to May. Droughts haunt the southern and central regions of Africa from December to February, mainly Zambia, Zimbabwe, Mozambique and Botswana.

Warm Basin of the Western Hemisphere

A study of climate data has shown that there is an unusual warming of the Western Hemisphere Warm Basin in about half of the post-El Niño summers. This affects the weather in the region and seems to be related to the North Atlantic Oscillation.

Atlantic effect

An El Niño-like effect is sometimes observed in the Atlantic Ocean, where the water along the equatorial African coast is getting warmer, while off the coast of Brazil it is getting colder. This can be attributed to the Volcker circulations over South America.

Non-climatic effects

Along the east coast of South America, El Niño reduces the upwelling of cold, plankton-rich water that supports large populations of fish, which in turn support an abundance of seabirds whose droppings support the fertilizer industry.

The local fishing industry along the coastline may be short of fish during long El Niño events. The largest global fish collapse due to overfishing, which occurred in 1972 during El Niño, led to a decrease in the population of Peruvian anchovies. During the events of 1982-83, populations of southern horse mackerel and anchovies decreased. Although the number of shells in warm water increased, but the hake went deeper into the cold water, and the shrimps and sardines went south. But the catch of some other fish species has been increased, for example, the common horse mackerel increased its population during warm events.

Changes in location and types of fish due to changing conditions have provided challenges for the fishing industry. The Peruvian sardine left due to El Nino to the Chilean coast. Other conditions have only led to further complications, such as the government of Chile in 1991 created restrictions on fishing.

It is postulated that El Niño led to the disappearance of the Mochico Indian tribe and other tribes of the pre-Columbian Peruvian culture.

Causes of El Niño

The mechanisms that can trigger El Niño events are still under investigation. It is difficult to find patterns that can show causes or allow predictions to be made.

History of the theory

The first mention of the term "El Niño" refers to the city, when Captain Camilo Carrilo reported at the congress of the Geographical Society in Lima that Peruvian sailors called the warm north current "El Niño", since it is most noticeable in the Christmas area. However, even then, the phenomenon was only interesting because of its biological impact on the efficiency of the fertilizer industry.

Normal conditions along the western Peruvian coast are a cold south current (Peruvian current) with upwelling water; upwelling of plankton leads to active ocean productivity; cold currents lead to a very dry climate on earth. Similar conditions exist everywhere (California Current, Bengal Current). So replacing it with a warm northern current leads to a decrease in biological activity in the ocean and to heavy rains, leading to flooding, on earth. A connection to flooding has been reported in Peset and Eguiguren.

Towards the end of the nineteenth century, interest arose in predicting climate anomalies (for food production) in India and Australia. Charles Todd suggested that droughts in India and Australia occur at the same time. Norman Lockyer pointed out the same in d. In d. Gilbert Walker was the first to coin the term "Southern Oscillation".

For most of the twentieth century, El Niño was considered a large local phenomenon.

The history of the phenomenon

ENSO conditions have happened every 2-7 years for at least the last 300 years, but most have been mild.

Big ENSO events occurred in - , , - , , - , - and -1998.

The last El Niño events occurred in -, -,,,, 1997-1998 and -2003.

The 1997-1998 El Niño in particular was strong and brought international attention to the phenomenon, while it was unusual for the 1997-1998 period that El Niño was very frequent (but mostly weak).

El Niño in the history of civilization

Scientists tried to establish why at the turn of the 10th century AD, at opposite ends of the earth, the two largest civilizations of that time almost simultaneously ceased to exist. We are talking about the Maya Indians and the fall of the Chinese Tang dynasty, followed by a period of internecine strife.

Both civilizations were located in monsoonal regions, the moistening of which depends on the seasonal precipitation. However, at the indicated time, apparently, the rainy season was not able to provide the amount of moisture sufficient for the development of agriculture.

The ensuing drought and subsequent famine led to the decline of these civilizations, the researchers believe. They attribute climate change to the natural phenomenon El Niño, which refers to temperature fluctuations in the surface waters of the eastern Pacific Ocean in tropical latitudes. This leads to large-scale disturbances in atmospheric circulation, which causes droughts in traditionally wet regions and floods in dry ones.

Scientists arrived at these conclusions by examining the nature of sedimentary deposits in China and Mesoamerica dating back to the specified period. The last emperor of the Tang Dynasty died in 907 AD, and the last known Mayan calendar dates from 903.

Links

• The El Nino Theme Page Explains El Nino and La Nina, provides real time data, forecasts, animations, FAQ, impacts and more.
• The International Meteorological Organization announced the discovery of the beginning of the event La Niña in the Pacific Ocean. (Reuters/YahooNews)

Literature

• Cesar N. Caviedes, 2001. El Nino in History: Storming Through the Ages(University Press of Florida)
• Brian Fagan, 1999. Floods, Famines, and Emperors: El Niño and the Fate of Civilizations(Basic Books)
• Michael H. Glantz, 2001. Currents of change, ISBN 0-521-78672-X
• Mike Davis, Late Victorian Holocausts: El Niño Famines and the Making of the Third World(2001), ISBN 1-85984-739-0