E1 Nino and La Nina currents formed in the Pacific Ocean are part of the natural climatic cycle. E1 Nino and La Nina are Spanish words meaning male and female child respectively. They are often referred as 'Children of Pacific'. The formation of a warm current in the Pacific Ocean, on the western side of south America, and near the Equator, is called E1 Nino. Whenever E1 Nino forms those years are referred as EI Nino years and the rest as Normal Years. Let us first understand the prevailing climatic conditions in a normal year.
In normal years, Easterly winds push the warm surface waters westward across equatorial South Pacific, causing warm surface water to accumulate near Indonesia. This warm surface water helps in the formation of clouds, which give heavy rainfall to Northern Australia and Indonesia. At the same time, the Peru Current, which is a cold current, flows northwards along the South American coast, brings the cold water to the surface. This cold current carries oxygen and nutrients that sustain fish, and hence, a fishing economy flourish along south American coast. Now let us investigate the climatic conditions in an E1 Nino year.
During E1 Nino years, Easterly winds slacken or even reverse. Warm surface water flows from west to east, increasing the depth of warm water off the South American coast. Heavy rainfall follows the warm water, leading to flooding in Peru. This warm water suppresses the nutrient-rich Peru Current. Hence, fish and seabirds move away or die. E1 Nino can cause global climatic disturbances like rain and floods in one part of the world, and drought in another part. Every year a small E1 Nino occurs in December, usually lasting a few weeks. But in some years, exceptionally intense and persistent E1 Nino events occur. In 1982-1983 and 1997-1998 the E1 Nino was particularly severe. Prior to the 1980s and 1990s, strong E1 Nino events occurred on average every 10 to 20 years. In the early 1980s, the first of a series of strong events developed. The E1 Nino of 1982-83 brought extreme warming to the equatorial Pacific. Surface sea temperatures in some regions of the Pacific Ocean rose 6' Celsius above normal. The warmer waters had a devastating effect on marine life existing off the coast of Peru and Ecuador. Fish catches off the coast of South America were 50% lower than the previous year.
E1 Nino also influences the climate in Indonesia and Australia. The surface water near Australia and Asia becomes very cold and so rain bearing clouds donot appear, which leads to drought. Monsoon winds and jet streams are also affected. Vegetation becomes so dry that the slightest spark can ignite a fire. This can result in huge bush fires and in turn affects the nitrogen and carbon cycles. Ecological disturbances occur. Let us now investigate the climatic conditions when a La Nina current event.
After an E1 Nino event weather conditions usually return back to normal. However, in some years the trade winds can become extremely strong and an abnormal accumulation of cold water can occur in the central and eastern Pacific. This event is called a La Nina. A strong La Nina occurred in 1988 and scientists believe that it may have been responsible for the summer drought over central North America.
The most recent La Nina began developing in the middle of 1998 and have been persistent into the winter of 2000. During this period, the Atlantic ocean has seen very active hurricane seasons in 1998 and 1999. In 1998, ten tropical cyclones developed of which six become full-blown hurricanes.One of the hurricances that developed, named Mitch, was the strongest October hurricane ever to develop in about 100 years of record keeping.
These cycles reveal that Earth is currently in a period in which a natural rise in global temperatures, combined with global warming effect, will push the planet through an era of rapid global warming. Strong oceanic tides are the engines behind this warming- cooling cycle. The current phase in the cycle suggests that a natural warming trend began a hundred years ago, increased in the 1970s, and should continue over the next five centuries.
In the following lesson, let us study how the atmosphere, a component of the Earth system, creats a complex and delicately balanced system that is crucial to the continuation of present lifeforms on Earth.