Unusually warm winter weather has been forecast for parts of the U.S. as El Niño conditions strengthen across the Pacific. But what does this mean and how do these conditions form?
Here are five maps that illustrate what is going on.
1. What Is El Niño?
El Niño is a term used to describe warming weather patterns in the Pacific. However, its effect is so large that it can affect weather conditions around the world.
Under normal conditions, trade winds in the Pacific blow west along the equator, shuttling warm water from South America toward Asia. When this happens, the warm water is replaced by cooler water rising up to the surface along the coast of South America.
But in some years the trade winds weaken and the warm water is pushed back to the east, toward the west coast of the Americas. As this warm water piles up around the equator, it gets pushed sideways, toward California and Chile.
This process usually begins in September and October and typically peaks around December.
2. How Does El Niño Affect Sea Surface Temperatures?
During El Niño years, the sea surface becomes unusually warm around the equatorial parts of Central and South America. Already, the National Oceanic and Atmospheric Association's Physical Sciences Laboratory has detected abnormally warm temperatures in this region, which are expected to increase in the coming months.
The map below highlights these anomalous sea surface temperatures, with particularly high measurements around Peru. The more red the map, the more unusually hot the sea surface is in that area, compared with other years (over the past three decades).
3. How Will El Niño Affect the U.S.?
The warmer waters of El Niño cause the Pacific jet stream to move south of its natural position, bringing warmer, drier weather to the northern U.S. and Canada. However, as the ocean warms around the equator, more water evaporates into the atmosphere, creating rain clouds that move inland and dump water over the Southern and Gulf Coast states.
"The widespread warming across the tropical eastern Pacific associated with the natural El Niño cycle is large enough to disrupt weather patterns across the globe," Richard Allan, a professor in climate science at the U.K.'s University of Reading, previously told Newsweek.
"Southwestern Europe can be warmer and wetter in October and November, while the southern U.S. is often wetter and cooler in the winter, and where unusually moist air clashes with colder air to the north, heavy snow can be produced," he said.
4. How Does El Niño Affect Food Production?
The weather changes brought by El Niño can affect food production worldwide. Warmer, wetter weather improves crop yields in certain areas, while too much or too little rain can negatively affect food production in others.
According to the Famine Early Warning Systems Network, this year's El Niño event is expected to leave 110 million people in need of food assistance.
The map below highlights which areas will see positive and negative effects on crop yields, with particularly negative impacts seen in southern African countries.
5. How Will El Niño Affect Marine Life?
As the waters warm off the coast of South America, many local fish move away to cooler climates or die. The warming waters can also have devastating effects on already vulnerable coral reefs.
Corals get their food from symbiotic algae that live inside them and are also responsible for the corals' color. However, when water temperatures increase, the algae start producing molecules that can damage their coral host, forcing the corals to kick out their resident food source. If high temperatures persist, the corals will eventually starve.
Coral reefs are among the most biodiverse places on the planet, supporting around 500 million people globally. Just like trees in a rainforest, corals give the reefs their structure. So when corals die, the ecosystems that rely on them can collapse.
The map below shows that coral reefs along the eastern Pacific and western Atlantic coastlines are already under a high bleaching alert, as of October 31. This pattern is expected to continue as El Niño conditions progress.
About the writer
Pandora Dewan is a Senior Science Reporter at Newsweek based in London, UK. Her focus is reporting on science, health ... Read more
To read how Newsweek uses AI as a newsroom tool, Click here.
