There are many anthropogenic forcings on the climate, in particular the volume of carbon and greenhouse gases pumped into the atmosphere as a part of our everyday lives.
Yet there are a number of natural processes that affect local weather, regional climate and global conditions. Some effects on our climate are a result of fluctuations and anomalies in the complex water conveyor belts of the ocean currents of the world. These fluctuations are known as “oscillations” and the two best-known oscillations are -
The latter is the opposite of the former and make up an oscillation known as ENSO.
Oscillations occur naturally in oceans all across the world; some have a limited impact on the regional weather and wider climate, and some have a much greater impact. The above-mentioned two oscillations are examples of those having a greater impact on our climate with effects that are perhaps surprisingly felt all over the globe.
Certain economies are dependent on certain weather conditions occurring regularly and on time (annual summer rainfall, spring ice melt etc), erratic oscillations can cause problems in these areas leading to drought. Knock on effects can lead to fish migrations and economic hardship for areas that rely on fish stocks. Marginal areas suffer or thrive depending on the effects of El Nino and La Nina leading to further knock on effects elsewhere.
What are El Nino and La Nina?
These are caused by the same phenomenon called the ENSO (El Nino Southern Oscillation) but these effects are opposite to each other. Both are an oscillation in the temperatures between the atmosphere and the ocean of the eastern equatorial Pacific region, roughly between the International Dateline and 120 degrees west. El Nino - the conditions for which build up between June and December - is caused by a change in the wind patterns. Here, the Pacific Trade Winds fail to replenish following the summer monsoons of Asia. This warmer air leads to an oscillation between the cooler and warmer waters, leading to warmer ocean temperatures than normal.
Up-swellings from the sea bed occur in normal years that bring nutrients up to the plankton to feed on and in turn abundance of plankton is beneficial to marine life up the food chain. In an El Nino year, that swelling does not occur so the plankton is reduced and in turn, so are the fish stocks, mostly through failure to reproduce.
La Nina is effectively the opposite of El Nino, indicated by prolonged periods of sea temperatures in the same region, and the effects stated above are generally reversed.
During non El Nino years, atmospheric pressure is lower than normal over the western Pacific area and higher over the colder waters of the western Pacific. With La Nina, the Trade Winds are particularly strong in carrying warmer water westwards across the Pacific leading to colder than average temperatures in the east and warmer than average temperatures in the west. The result is that plankton increases in the areas where the temperature is cooler, leading to a positive effect on the marine life that depends on plankton or depends on those creatures that depend on plankton.
It is commonly expected that La Nina will follow immediately on from an El Nino event, but this is not always the case. Typically, both occur every three to five years but they have varied anything between two and seven years. Both phenomena last anything between nine and twelve months.