El Niño in World History

Richard Grove, George Adamson

• Publisher: Palgrave Macmillan
• Year: 2017
• ISBN:
  9781137457400
• Topic: Geschichte
• Subtopic: Weltgeschichte

This book examines the role of the El Niño Southern Oscillation (ENSO) in society. Throughout human history, large or recurrent El Niños could cause significant disruption to societies and in some cases even contribute to political change. Yet it is only now that we are coming to appreciate the significance of the phenomenon. In this volume, Richard Grove and George Adamson chart the dual history of El Niño: as a global phenomenon capable of devastating weather extremes and, since the 18 th century, as a developing idea in science and society. The chapters trace El Niño's position in world history from its role in the revolution in Australian Aboriginal Culture at 5, 000 BP to the 2015-16 'Godzilla' event. It ends with a discussion of El Niño in the current media, which is as much a product of the public imagination as it is a natural process.

© The Author(s) 2018

R. Grove, G. AdamsonEl Niño in World HistoryPalgrave Studies in World Environmental Historyhttps://doi.org/10.1057/978-1-137-45740-0_1

Begin Abstract

1. Introduction

Richard Grove¹ and George Adamson²

(1)

Centre for World Environmental History, University of Sussex, Brighton, UK

(2)

Department of Geography, King’s College London, London, UK

End Abstract

George Adamson and Richard Grove

There is a debate occurring within climate science. It is an argument between scientists: esoteric disagreements played out in discussions at conferences and on the opinion pages of scientific journals. It may look, on the surface, of little interest beyond the academy. Yet it speaks to a broader question that should interest all with a stake in climate, or natural disasters, or even global geopolitics. It is a question of relevance to researchers across disciplines, to journalists involved in the multifaceted and contradictory world of science communication, and to the political worlds of development and risk management. Most importantly it speaks to millions of people whose livelihoods are threatened by drought or flood or cyclones the world over. What exactly is El Niño?

To understand this debate we must look back at the most severe El Niño event to have been recorded. The 1997–1998 El Niño saw record-breaking sea temperatures, the so-called ‘climate event of the century’. El Niño was, at this point, considered to be a phenomenon that was well understood. Its codification at the turn of the twentieth century had precipitated decades of research—slowly at first, then from the 1980s onwards in huge quantities—on the global climate anomaly, on its mechanisms and impacts, why it was formed and how it developed, where it produces rainfall and where it leads to drought. Of the latter issue one of the most heavily studied areas was El Niño’s impact on the Indian monsoon, a relationship that had been postulated in 1932 and explained in the 1980s.¹ Long-term El Niño forecasts introduced in the late 1980s had allowed the 1997–1998 El Niño to be the first ‘severe’ event to be correctly forecast 6 months in advance, enabling policies to be implemented across the world to prepare for anticipated hazards. In India this meant the planting of drought-resistant crops. In Zimbabwe development loans usually provided to farmers against the collateral of forthcoming harvests were refused in anticipation of poor harvest.²

Meteorological anomalies in 1997 and 1998 were severe. In Peru and California, devastating floods caused destruction to property and infrastructure and multiple deaths. In Mexico and Indonesia, drought caused wildfires that could be seen in neighbouring countries, and which briefly raised Indonesia to the highest per capita global emitter of carbon dioxide.³ Rainfall in India and southern Africa, however, remained around average, and drought-resistant crops yielded poorly. Indeed, during the early part of the Indian monsoon in 1997 rainfall was slightly above average. Neither did the expected droughts materialise in Australia, with the exception of parts of the east coast.

Why did rains in India not fail when the relationship between El Niño and the monsoon was apparently so clear? Why then again did drought occur in 2002 and 2004, years technically classified as El Niño but so weak as to barely register under accepted scientific definitions?⁴ No drought was forecast in India during these years, yet drought did occur, with devastating impacts on food supplies and cascading effects across the Indian economy. Perhaps inevitably, given current climatic anxieties, the explanations first provided for this apparent ‘breakdown’ in the relationship between El Niño and the monsoon concerned anthropogenic climate change (an idea that was subsequently dropped).⁵ Dr. K. Krishna Kumar of the Indian Institute of Tropical Meteorology posited another explanation in 2006. Through statistical analysis he suggested that there were in fact two El Niños, with quite different global impacts. These were the El Niño ‘flavours’: the classic El Niño such as 1997–1998, which did not produce drought in India, and the alternative El Niño such as 2004 which did. The differences in their characteristics related to the location of Pacific warming: mostly to the east or mostly in the equatorial centre. Subsequent authors called these flavours Central and Eastern Pacific El Niño, or El Niño and El Niño Modoki, the latter a Japanese word meaning ‘similar but different’.⁶

At the time of writing this debate is still ongoing. Have we been defining El Niño wrongly for the past 100 years, when we should really be talking about two El Niños, or even more? Counter arguments continue: whether El Niño Modoki is a ‘partially-formed’ or weak El Niño; whether it is expedient to develop separate indices for El Niño and Modoki; whether Modoki is simply a statistical anomaly or the outcome of bad mathematics.⁷ The debates are characterised by the intricacies of complex statistical analyses. No doubt they will continue into the future.

The El Niño Southern Oscillation

Despite widespread media coverage, the El Niño Southern Oscillation (shortened to ENSO in this book) has actually been understood for a relatively short period of time. The oceanic component of ENSO—the El Niño current—was discovered in the 1890s. The atmospheric the Southern Oscillation was first isolated in the 1920s; yet the two were not linked until the 1960s and the global significance of the phenomenon not appreciated until much later. Only a relatively few El Niños have been observed in detail, a factor that has created the confusion over the exact dimensions of the phenomenon. The three severe events that have been observed—1982–1983, 1997–1998 and 2015–2016—demonstrated a climatic event that can exhibit unpredictable behaviour, but one which has unusual severity and global influence.

As with many scientific phenomena, the accepted definition of El Niño has emerged through scientific consensus. Although now considered to be a global system with global effects, the El Niño that was first identified and researched was the manifestation of the global phenomenon off the coast of northern Peru. This is a region of unusually cold water and a shallow thermocline, which allows cold, nutrient-rich bottom water to upwell to the surface, supporting marine plankton blooms and rich anchovy fisheries. The predominant ocean direction is from the south, caused by the southerly Humboldt Current, which brings further cold water from the southern tip of the continent. This combination of factors limits evaporation and hence rainfall making coastal Peru one of the driest regions on Earth.⁸

The term ‘El Niño’ was first used in scientific literature in the 1890s to apply to the occasional years when the direction of ocean flow reverses and unusually warm surface water flows in from the north. During these years native fish species migrate southwards and tropical crab and fish species arrive from the north. Seabirds migrate westwards to follow their anchoveta catch and can sometimes die in large numbers. Populations of seal and penguin around the coast and nearby Galapagos Islands can decline dramatically. Moisture evaporating off the unusually warm water causes heavy rain, which is fundamental to the desert ecosystem but can be destructive to crops, property and infrastructure. This phenomenon was named ‘El Niño’ in Peru as it arrived around Christmas and was associated with the Christ Child, a term taken from local fishermen (although its original meaning was somewhat different).⁹

The Peruvian scientists who first analysed the El Niño phenomenon considered it to be a local event and it was considered as such for around 50 years after its discovery. Later scientists studying the phenomenon after the Second World War—equipped with observations from ocean vessels, buoys, weather balloons, satellites and complex computer models—realised that the event is a local manifestation of a Pacific-wide phenomenon with global effects. In 1969 the climatologist Jacob Bjerknes linked the El Niño with the Southern Oscillation, a ‘see-saw’ pressure relationship between the Indian and Pacific Oceans that had been identified by the British meteorologist Gilbert Walker in the 1920s. The whole phenomenon was named the El Niño Southern Oscillation or ENSO,¹⁰ with El Niño one extreme of the system and the opposite—where the ocean is unusually warm in the western Pacific and the eastern Pacific unusually cold—called La Niña.¹¹

During the last five decades the El Niño Southern Oscillation has become one of the most heavily studied climatic phenomena in the world. It is now considered the most important source of year-on-year ‘natural’ meteorological variability, its mechanism understood to be related to the position of the thermocline, the ocean region that marks the transition between warmer surface waters and the colder deep waters. In most oceans this is located around 100 m below the surface, but in the equatorial Pacific easterly trade winds drive the surface water westwards creating a huge ‘basin’ of warm water near Indonesia known as the Pacific Warm Pool. Here the thermocline is unusually deep and the surface waters particularly warm. Off Peru the thermocline is located at the surface and the waters are unusually cold. This differential in thermocline depth and surface temperature causes distinct climatic variability. Near Indonesia and Australia, warm sea surface temperature causes evaporation, heavy rainfall and high humidity. Evaporated air moves eastward in the upper atmosphere and descends over the South American coast, where the region is a desert. Thus the whole system is stabilised and self-maintaining, comprising an enormous ‘conveyor belt’ of air across the equatorial Pacific called the Walker Circulation.¹²

El Niño events—in so far as they can be called events—are related to the breakdown of this circulation. This can be caused by minor fluctuations in the trade winds, cyclones in the western Pacific or random changes in water currents. Once occurring, such minor changes can be self-reinforcing. Reduction in the strength of the trade winds causes the Pacific Warm Pool to flow east and the thermocline to depress, the area of low pressure moving correspondingly eastward. This further reduces the west–east pressure gradient and the intensity of the trade winds, allowing the warm water to flow even further east. During a developed El Niño phase, the region of evaporation can move to the central or eastern Pacific, which brings unusual rain to these regions. Indonesia and Northern Australia experience drought and often forest fires, and Peru and Ecuador serious floods. El Niño episodes occur approximately once every 3–7 years, often followed by La Niña as the rapid return of the Walker Circulation creates ‘extreme normal’ conditions (Fig. 1.1).

Fig. 1.1

Conceptual diagram of the Walker Circulation under neutral and El Niño conditions. Image courtesy of NOAA Pacific Marine Environmental Laboratory

The El Niño Southern Oscillation is not the only global climatic mode of variability but it is considered unique in the scale of its influence. The Walker Circulation is one of many interlinking circulation patterns across the Earth and a change in its position can result in a major redistribution of tropical convective regions. El Niño has been associated with unusual rainfall in southern (and sometimes Sahelian) Africa, Ethiopia, South and Southeast Asia, parts of China, Australasia, Central America, northeast Brazil and Amazonia.¹³ It can result in low river discharge in the Nile,¹⁴ the Senegal, the Orange River, the Indus, the Narmada, the Murray-Darling and the Amazon, amongst others. In New Guinea and southeast Australia El Niño is associated with increased incidences of severe frosts. There are even some indications that El Niño is associated with forerunning cycles of cold winters in Europe and inner Asia.¹⁵ When other less frequent physical influences on global climate, such as large volcanic eruptions, add their impact to pre-existing El Niño effects, climatic variability can be even more marked.

In other parts of the world El Niño produces above-average rainfall. In Peru and central Chile rainfall can be particularly intense. Similar effects occur in northern Vietnam and southern China, in Japan and the South Island of New Zeala...

Table of contents

• Cover
• Front Matter
• 1. Introduction
• Part I. A Millennial History of El Niño
• Part II. The Science of El Niño and the Southern Oscillation
• Part III. El Niño and Epidemic Disease
• Part IV. El Niño in Contemporary Society
• Back Matter