El Niño -- or to be precise, the El Niño Southern Oscillation, or ENSO -- is back, scientists say. So get set for some freaky stuff to happen around the world this summer and fall.

The U.S. government’s Climate Prediction Center now puts the chances of El Niño, which occurs naturally once or twice a decade, at 70 percent in the Northern Hemisphere this summer, and 80 percent during the fall and winter.

In the extreme weather phenomenon, the waters of the Pacific Ocean off the west coast of South America becomes abnormally warm, and moist rising water vapor forms thunderstorm clouds, which in turn cause the upper atmosphere to become warmer than usual too, according to this handy primer from the National Oceanic and Atmospheric Administration.

NEWS: Brace for Record Heat as El Niño Approaches

As that warm air branches out, it moves upward in altitude toward the poles and then sinks back into the tropics in loops that are called Hadley cells. All this change disrupts weather conditions across the planet, and that in turn tends to cause a cascade of weird and disturbing events, ranging from heavy rains and flooding to food shortages.

One 2011 study even found that El Niño was associated with an increased risk of civil war in tropical countries. 

According to the center's latest forecast, the first warning signs were in March, when sea surface temperatures (SSTs) began to rise abnormally. Over the past four weeks, above-average SSTs have been observed across the Pacific Ocean, near Indonesia, and in the eastern Atlantic Ocean.

VIDEO: The Ocean Is in Danger

In a 2013 Nature article, researchers reported that the frequency of El Niño events is increasing due to climate change. If you remember lava lamps, you'll enjoy this psychedelic-like animation showing the day-to-day fluctuation of  El Niño's equatorial temperature effects.

Photo: Satellite and sensor data indicate that El Niño conditions developing in the equatorial Pacific Ocean are similar in ways to those of May 1997, a year when the weather phenomenon was really potent. Credit: NOAA