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examBoard: Cambridge
examType: IGCSE
lessonTitle: El Niño Southern Oscillation Phenomenon
The El Niño Southern Oscillation (ENSO) is one of the most important climate phenomena on Earth. It affects weather patterns, ocean temperatures and marine ecosystems worldwide, with particularly strong impacts on global fisheries.
Key Definitions:
Under normal conditions, trade winds blow from east to west across the Pacific Ocean. These winds push warm surface water westward, causing cooler, nutrient-rich water to rise from the depths near South America (upwelling). This upwelling brings nutrients to the surface, supporting rich marine ecosystems and productive fisheries along the west coast of South America.
During El Niño, the trade winds weaken or reverse direction. Warm water that normally accumulates in the western Pacific flows eastward, suppressing the upwelling of cold, nutrient-rich water near South America. This leads to higher sea surface temperatures and reduced nutrient availability, severely affecting marine life and fisheries.
ENSO is a complex interaction between the ocean and atmosphere. Scientists measure ENSO using several indicators, including sea surface temperatures, atmospheric pressure differences and wind patterns.
La Niña represents the opposite phase of El Niño. During La Niña events, the trade winds strengthen, pushing more warm water toward Asia and increasing upwelling of cold water along South America. This creates cooler than normal sea surface temperatures in the central and eastern Pacific. La Niña typically brings increased nutrients to fishing grounds, often resulting in higher fish productivity.
The complete ENSO cycle typically lasts 2-7 years. While these events follow a somewhat predictable pattern, each ENSO event has unique characteristics in terms of intensity, duration and impacts. Climate scientists can now predict El Niño and La Niña events several months in advance, giving fishing communities and governments time to prepare.
ENSO affects weather patterns globally through what scientists call "teleconnections" - changes in one region affecting climate in distant parts of the world.
Increased rainfall in Peru and Ecuador, droughts in northeast Brazil, warmer winters in northern United States and Canada, increased hurricane activity in the eastern Pacific, decreased hurricane activity in the Atlantic.
Droughts in Australia, Indonesia and the Philippines, reduced monsoon rainfall in India, increased risk of wildfires in Southeast Asia, warmer winters in Japan.
Droughts in southern Africa, increased rainfall in eastern Africa, changes to the West African monsoon.
The fishing industry is one of the sectors most directly affected by ENSO events. Changes in ocean temperatures and nutrient availability dramatically alter marine ecosystems and fish populations.
Peru and Chile experience the most dramatic fishery impacts from ENSO. These countries host some of the world's largest fisheries, particularly for anchovies, which form the basis of an important fishmeal industry.
During El Niño events, the suppression of nutrient-rich upwelling leads to:
During La Niña events, enhanced upwelling typically results in:
The 1982-83 El Niño was one of the strongest on record and devastated Peru's anchovy industry. Before the event, Peru's anchovy fishery was the largest single-species fishery in the world, producing up to 12 million tonnes annually. During this El Niño:
This event highlighted the vulnerability of fishery-dependent economies to ENSO and led to improved monitoring and management practices.
While South American fisheries experience the most direct impacts, ENSO affects fisheries worldwide:
Changes in tuna migration patterns affect fisheries across the Pacific. During El Niño, tuna often move eastward, benefiting fisheries in the eastern Pacific while reducing catches in the western Pacific. Salmon returns to Alaska and the Pacific Northwest can be reduced during strong El Niño events due to warmer ocean temperatures affecting their food supply.
Through teleconnections, ENSO can affect fisheries far from the Pacific. For example, El Niño has been linked to reduced sardine catches off South Africa, changes in North Sea fish populations and altered shrimp production in the Gulf of Mexico. These wide-ranging impacts affect global seafood markets and prices.
As our understanding of ENSO has improved, so have strategies to manage its impacts on fisheries:
Advanced satellite systems and ocean buoys now provide early warning of developing El Niño or La Niña conditions. Fishery managers use this information to adjust catch quotas and fishing seasons accordingly.
Flexible fishing quotas that can be adjusted based on ENSO conditions help prevent overfishing during vulnerable periods. Diversifying target species can reduce dependence on ENSO-sensitive fish like anchovies.
Training fishers to understand ENSO and its effects helps communities prepare for and adapt to changing conditions. Economic support programs can help fishing communities during severe El Niño events.
After several devastating El Niño events, Peru developed one of the world's most responsive fishery management systems:
This approach has helped Peru's fisheries become more resilient to ENSO events, though challenges remain during extreme El Niño years.
Scientists are concerned about how climate change might affect ENSO patterns in the future:
Research suggests climate change may lead to more frequent and intense El Niño events. Some models predict El Niño events could become twice as common in the 21st century. The combination of ENSO-related warming and background warming from climate change could create "super El Niño" events with unprecedented impacts on fisheries.
Fishing communities will need to develop enhanced adaptation strategies, including diversifying livelihoods, improving forecasting systems and creating more flexible management approaches. International cooperation will be crucial as fish stocks migrate across national boundaries in response to changing conditions.
The El Niño Southern Oscillation is a powerful natural climate cycle with far-reaching effects on world fisheries. Its alternating warm (El Niño) and cool (La Niña) phases create dramatic changes in marine ecosystems, particularly affecting the productive fisheries off South America. While ENSO events cannot be prevented, improved monitoring, forecasting and adaptive management strategies can help reduce their negative impacts on fishing communities and economies.
As climate change potentially alters ENSO patterns, understanding this phenomenon becomes even more critical for sustainable fisheries management. The lessons learned from historical ENSO events provide valuable guidance for building more resilient fishing practices and communities in the face of an uncertain climate future.
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