The ocean is not a giant bathtub, with water of uniform temperature, salt content or circulation. These properties tend to change over time and place, often oscillating between different recurring patterns. One of the most important of these patterns is the El Niño Southern Oscillation (ENSO).
Much as a change in the winds brings about the North American Monsoon, dousing the southwest in rain or leaving it bone dry, oscillations in the ocean can have huge effects on the weather. And, according to observations by NOAA and NASA, the Pacific Ocean seems to be gearing up for a powerful El Niño, the first since 1998.
In the tropical eastern Pacific, temperature changes of the surface ocean can bring about one of two patterns of activity. When the area is much hotter than usual, we call it an El Niño. When it's much colder, we call it La Niña. (There's also the possibility of a normal, or neutral, state.) By affecting circulation patterns in both the ocean and the atmosphere, both of these phases can have important effects on global weather patterns.
The video above, by NASA, has more detail on what researchers are seeing right now to make them think an El Niño is brewing. If the system gets fully into gear it could have some important consequences.
For one, 1998 was one of the hottest years on record. Part of that was due to the warming effects of global climate change, but a big part of it was due to that year's powerful El Niño, says New Scientist. Since El Niño conditions cause winds to die down and heat to move from the ocean into the air, a strong El Niño this year would likely mean we're in for a real scorcher.
El Niño also has huge effects on rainfall patterns across the U.S., which could be both a good thing and a bad thing. On the one hand, El Niño tends to bring lots of rain to California, particularly in winter. Given that the region has been plagued by drought for the past three years, this could be a needed respite. On the other hand, heavy rains are dangerous. An El Niño in 1982 to 1983 contributed to flooding, mudslides and other strong storms that battered California and the Gulf states, says the University of Illinois.
If a strong El Niño develops—and researchers expect that it will—it could also have important political ramifications, says Nate Cohn for the New York Times. Peoples' opinions on global climate change tend to ebb and flow with the weather, and the hot temperatures associated with the ocean pattern could change the tone of the discussion.