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Global climate patterns are mainly due to the circulation of air in the atmosphere, but ocean currents can have a major influence on weather patterns and climate.

El Niño

Around every seven years the Humboldt current is interrupted by the El Niño which causes warm waters which are normally sent west, towards the shores of South America and the Galapagos Islands. El Niño typically begins in December and lasts for a few months. El Niño (meaning the Christ Child) is a warm, southward current that occurs in the Pacific off the coast of Peru in December. The intensity and persistence of this current vary. A large El Niño will cause global scale weather disruption. With a periodicity of 3-7 years El Niño is not uncommon, but the extent to which it causes havoc with the worlds normal weather systems is more unpredictable.

In 1997 when there was a significant El Niño event it caused increases in rainfall as well as increased temperatures throughout 1990. While this suitable for some be vegetation of the Galapagos islands, some animals, particularly those than live in the sea or used it as a source for food had problems. This was because the introduction of warm waters altered the food chain, and this particularly affected the marine iguana due to a lack of green algae their population experienced a significant decline. It meant that many seabirds, seals and fish had disappeared form areas where they would have normally been searching for food themselves. In addition birds such as albatrosses, penguins and cormorants were unable to breed successfully.

In normal (non-El Niño) years, winds in the Pacific Ocean taking warm surface water with them. The cold Humboldt current which flows northwards along the west coast of South America is then drawn into the circulation and flows further westwards. As the current flows west it is heated by the tropical sun which means that warm, moist air rises over Indonesia, creating a low pressure area, tropical cumulonimbus clouds and heavy rain. The air then circulates east in the upper atmosphere and sinks into the cooler high pressure area over the west coast of south America, giving the dry conditions that created the Atacama Desert in Peru.

During El Niño years, pressure systems and weather patterns reverse. Warmer waters develop in the eastern Pacific, with temperatures rising by up to 8°C. Low pressure systems forms over the area, drawing in westerly winds from across the Pacific. Warm, moist air rises, creating heavy rainfall over the Eastern Pacific. The air circulates west in the upper atmosphere. Around northern Australia and Indonesia the descending air gives drier conditions than usual and can cause drought. During El Niño years air currents move eastwards across the Pacific, bringing moist air to South America and the eastern Pacific. The Californian coast is also affected by this current, which brings torrential rains which often causes flooding and landslides.

La Niña

At certain times, the ‘normal’ situation intensifies and is known as La Niña. During a La Niña event the low pressure over the western Pacific becomes even lower and high pressure over the eastern Pacific even higher. As a result of this, rainfall increases over South East Asia, and South America experiences drought. Trade winds become stronger due to the increased presence between the two areas. La Niña can occur just or before, or just after El Niño. During La Niña years the current reverses to move across the Pacific towards Australia, bringing moist air to Australia and the western Pacific. During this time, warm dry air blows over California from the American desserts, bring drought and the threat of forest fires to California.

An El Niño event can have consequences across the Globe – including the Galapagos Islands.