El Niños in the last 40 years are more intense than in the previous millennium, study shows

A University of Michigan study has found that El Niño events have become 40% stronger over the last four decades than in the preindustrial era. 

As the tropical Pacific sees an El Niño of historic proportions, researchers have found that El Niño events over the last 40 years have been stronger than any in the millennium before about 1850, when greenhouse gases began affecting the climate, according to U-M. 

"We don't see a time in the past where El Niños have been as strong as today, and we show that the strength of El Niño changes in parallel with the warming of global temperature," said lead author Julia Cole, professor and chair of the U-M Department of Earth and Environmental Sciences. "Our findings tell us that the big El Niño events of the last 40 years are not normal in the context of the last thousand years."

The study examined modern and ancient corals in the Galápagos Islands. Cole and fellow researchers sampled cores from 13 corals, including living colonies and ancient coral boulders.

"The question is not whether the current El Niño is going to happen, but how bad is it going to be, and how bad will the impacts be?" Cole said. "This event is superimposed on global warming, and it's likely to supercharge the temperature increase that we would normally see from greenhouse gases. There are forecasts that we might get as hot as 1.7 or 1.8 degrees Celsius above pre-industrial temperatures, which is quite a bit higher than the current record."    

How corals tell the story

The researchers observed the layers of the corals, which provide a record of the seawater temperature in which the corals grew.

El Niño extremes occur every few years, so the researchers focused on core samples that spanned at least 20 years.  The researchers measured two separate aspects of the coral skeleton's chemistry that both reflect the temperature at which the coral grew.

They were left with a history of temperature variations in the Galápagos — a location, Cole says, where El Niño has its greatest impact. They saw that strong El Niños occurred over the last 40 to 50 years, whereas El Niños prior to that period showed "a pretty consistent pattern of lower intensity El Niños."

"We kept adding records, thinking well, this is going to get more complicated, but it really didn't," Cole said. "This is such a clear story."

Comparing the results to the previous 1,000 years

The researchers then examined whether natural processes could have caused similar El Niño escalations over the past 1,000 years. To do this, they used climate models that simulate the last thousand years using histories of volcanic eruptions and solar variability. 

The models found no large shifts in El Niño that suggested natural processes could create such large changes.  

Cole says their findings underscore the need to mitigate more global warming. She adds:

"El Niño is a really big source of climate extremes, and so if it's getting stronger, the impacts are getting stronger. Impacts like droughts, floods, wildfire and food insecurity. Changes in the hydrologic cycle also lead to issues like damage to infrastructure: floods that wipe out homes, highways, or railroads, or to health effects, such as diseases like cholera.  

We believe global warming is supercharging El Niño, and if that's true, then we expect stronger climate extremes that will amplify ecological, infrastructural and human losses. No country has the resources to be fully protected from these impacts. This is one more reason we need to move away from fossil fuels, the root cause of the problem."  

The findings of the study were published in Science and supported by the U.S. National Science Foundation and the United Kingdom Natural Environment Research Council.        

What are El Niños?

El Niño is a natural phenomenon that causes the tropical Pacific to warm above average every few years.

Under normal conditions, trade winds blow along the equator from east to west. This pushes warm water from South America towards Australia.

When trade winds weaken, warm water spreads in the opposite direction, back towards South America, kicking off an El Niño event.

As a result, the atmospheric circulation is disrupted and strong rainfall shifts from Indonesia into the central Pacific, leaving the western Pacific in drought. This further weakens the trade winds, locking in El Niño conditions that can persist for one to two years.

These temperature and precipitation fluctuations originate in the tropical Pacific, but they affect the weather of the whole globe.

Storm tracks over the U.S. shift southward, bringing more rain to the desert southwest and less to the northwest.

Similar shifts around the world lead to droughts and floods that bring disease, crop failure, wildfires and other crises that affect people's lives.