The weather pattern known as El Niño, which can bring heavy rains to Southern California, has doubled in intensity and warmth and shifted westward over several decades, according to scientists from the Jet Propulsion Laboratory and the National Oceanic and Atmospheric Administration.

The findings, published in Geophysical Research Letters, a journal of the American Geophysical Union, measured ocean temperature and analyzed satellite data over the last three decades.

JPL oceanographer Tong Lee, an author of the paper, said in an interview that more research is needed to determine whether the changes in El Niño are due to the documented rise in global air and ocean temperatures worldwide since the Industrial Revolution or to natural variability.

But he noted: “El Niño is the largest fluctuation of the climate system. It has worldwide impact on climate patterns, so any change in El Niño’s behavior might cause a change in its impact.”

Lee suggested that the findings reveal “two competing effects. Shifting El Niño’s location could mean less rainfall” in Southern California, he said. “But since it is getting stronger, we may get more rainfall. How these two effects play out is something that needs to be investigated.”

The study, he said, “documents the change of a major climate system, but I cannot tell you the impact.”

El Niño is a climate event in the Pacific Ocean in which trade winds weaken and warm, and nutrient-poor ocean water builds up in the western Pacific, disrupting fish populations and leading to severe weather events worldwide.

Bill Patzert, a JPL climatologist who was not involved in the paper, said three decades is too short a period from which to draw conclusions on the data. But, he added: “This is another piece of evidence that the climate is shifting. It is clear that in the last century the planet has warmed by almost two degrees Fahrenheit. More than 80% of that is taken up by oceans. Oceans are the canary in the coal mine.”

Patzert said the paper was observational rather than conclusive. “What will happen if this new type of El Niño becomes permanent? Will it give us wetter or drier El Niños?” he asked. “It is too early to tell. The one thing we know is that the future ain’t what it used to be. The planet is definitely warming, and El Niño has morphed into something different.”

The paper was co-written by Michael McPhaden of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle.

margot.roosevelt@latimes.com