El Nino is a weather phenomenon that occurs in Pacific ocean and causes a major disturbance in weather patterns around the world. El Nino appears every two to seven years. It has the tendency to bring severe droughts and extreme floods in different parts of the globe. So let’s explore What is El Nino, how does it occurs and what are causes and effects of El Nino.
What Causes El Nino?
Under Normal conditions
During Normal conditions, Trade winds blow from east to west in tropical Pacific( the region surrounding equator). These Trade winds push warm surface water from east to west.
This leads to the formation of the large pool of warm waters in the western Pacific( region near Australia). The surface water present in eastern Pacific is replaced by nutrient-rich cold water from the bottom of the ocean.
This again leads to the formation of the large pool of cool waters in the eastern Pacific( region near South America). Thus the sea surface is 40 to 50 centimetres higher and is 45° F warmer in western Pacific compared to east.
Now, the warm water present in the western Pacific( region near Australia) heats up the air above it to form clouds which rise in the atmosphere and further leads to precipitation. After precipitation, these dry air rises above and heads toward eastern Pacific creating areas of low pressure in western Pacific.
Also, the cool water present in eastern Pacific ocean( region near South America) cools up the air above it. This cool air creates the area of high pressure.
As we know air flows from high pressure to low pressure. Thus the air in high-pressure areas of eastern Pacific flows back to low-pressure areas of western Pacific. Again when the air reaches western Pacific, the above cycle repeats.
This cyclic movement of warm and cold air above the equatorial region in Pacific ocean is termed as ‘Walker Circulation’.
During El Nino Conditions.
When El Nino condition develops, the trade winds which pushes the warm surface water gets weak or sometimes even reverse their direction. These weak trade winds lose the ability to push the warm surface water from eastern to western Pacific.
As Trade winds weaken, there is less upwelling of nutrient-rich cold water from the bottom of the ocean. This results in warming up of the surface water in eastern Pacific and further leads to cancellation of the temperature and pressure difference between eastern and western Pacific. This concentrates pools of warm waters in eastern and central Pacific ocean.
Above warm surface water(+ 5° C) in eastern Pacific brings increased rainfall in the region of South America(i.e. Ecuador, Peru etc.). Also, it brings severe droughts in western Pacific region (i.e. Australia, India, Indonesia etc.)
Monitoring of El Nino
Climate scientists continuously monitor El Nino conditions by studying different parameters such as sea surface temperature, sea surface height, wind direction and wind speed. Floating weather Buoys and Weather satellites are used for measuring these parameters. Researchers from agencies such as National Oceanic and Atmospheric Administration and NASA Earth Observatory collects the data from weather satellites and weather Buoys to form Ocean Maps. These Ocean maps help climate scientists to study and predict El Nino conditions.
Weather Buoy Satellite imagery of Sea surface temperature
Effects of El Nino on Global climate
Pacific Oceans is the biggest ocean on planet earth and occupies almost 30% of earth’s surface. It also covers almost 50% of the earth’s water surface. So any climatic event occurring in Pacific ocean has direct and indirect influences around the globe. El Nino has the direct impact on countries located in equatorial Pacific region.
El Nino alters rainfall patterns over east and west of Pacific Ocean. Countries located in the west such as Australia, India, Indonesia etc. experience low rainfall and sometimes even severe drought. Below average rainfall leads to poor crop yields and sometimes extremely high temperatures breaks into forest fires. Countries located in the east such as Peru, Ecuador, Chile etc. and Southern United States experience above normal rainfall and heavy floodings. These heavy floods cause damage to property, destruction of crops, deterioration of health conditions etc.
Besides these factors, one lesser known effect of El Nino is its indirect contribution to Global Warming. The enormous El Nino of 2016 released over 3 billion tonnes of carbon dioxide pushing global carbon dioxide levels to record high. El Nino contributed to carbon dioxide releases by Extensive forest fires in southeast Asia, reduction in plant growth that absorbs carbon dioxide, warm weather and low rainfalls causing forests to exhale more carbon dioxide.
Effects of El Nino on Global Economy
El Nino even has the negative economic impact on countries dependent on Agriculture and fisheries. For instance, In countries such as India, Australia and Indonesia where farming and agriculture is one of the major components of the economy, lower precipitation due to El Nino impacts agricultural output. The decline in agricultural output stalls growth of rural economy thereby decreasing the GDP of the country.
South American countries such as Chile, Peru and Argentina where Fishing and Aquaculture is prominent also gets affected by El Nino. El Nino lessens upwelling of nutrient-rich cold water from the bottom of the ocean. The growth of seaweeds, planktons etc. which rely on these nutrients rich waters is severely affected. These create disturbance in the marine food chain which negatively affects the commercial Fishing industry.
Walker Circulation: https://commons.wikimedia.org/wiki/File:LaNina.png
EL Nino: https://commons.wikimedia.org/wiki/File:ElNino-schematisch.svg
Weather Buoy: https://commons.wikimedia.org/wiki/File:NOAA-NDBC-discus-buoy.jpg
Satellite Imagery: NASA-JPL.