A new study reports compelling evidence that El Niño has gotten more intense during the industrial age than in the previous thousands of years. El Niño is a complex weather phenomenon that develops in the equatorial Pacific Ocean and has worldwide effects.

As reported in Geophysical Research Letters, researchers collected physical evidence related to El Niño over 7,000 years and found that during the last 120 years, the variation that happens during its irregular (but periodical) appearance has become 25 percent more pronounced compared to pre-industrial times. Since El Niño plays a role in storms, droughts, and coral bleaching, this is concerning.

"What we're seeing in the last 50 years is outside any natural variability. It leaps off the baseline. Actually, we even see this for the entire period of the industrial age," principal investigator Dr Kim Cobb, a professor at the Georgia Institute of Technology, said in a statement. "There were three extremely strong El Nino-La Nina events in the 50-year period, but it wasn't just these events. The entire pattern stuck out."

During El Niño, or technically the El Niño Southern Oscillation (ENSO), a long streak of warm ocean water hits the western coast of South America. When the cycle reverses, a period nicknamed La Niña, airstreams push the hot water westward and colder waters move into the tropical region of the ocean. These changes affect corals in particular ways, so the team decided to take fossil coral oxygen isotope records from the Line Islands to mark temperatures spanning millennia. 

The team remarked on just how good the coral data measured up. Comparison of the coral data with satellite measurements between 1981 and 2015 matched so well that when plotted on the same graphs, the two measurement sets looked like a single one.

"When I present it to people, I always get asked, 'Where's the temperature measurement?' I tell them it's there, but you can't see it because the corals' records of sea surface temperatures are that good," said lead author Dr Pam Grothe, an associate professor at the University of Mary Washington.

The study suggests climate change is a contributing factor in the intensification of El Niño, but it is unclear at the moment just how much of a contribution it plays. Data from the study showed that the ENSO can become extremely mild without external cause.

"The recent spate of large El Niño events raises the prospect that climate change may already be contributing to an intensification of ENSO extremes. However, the small number of ENSO extremes captured in the decades-long instrumental climate record precludes the direction of robust trends in ENSO properties," the researchers write in the paper.

Whatever the cause, the changes in El Niño can be damaging and have long-lived consequences if they persist.