Rebecca Beadling, assistant professor in the College of Science and Technology, explains the climate pattern known as El Niño and its global weather impacts.
Photo by Betsy Manning
The term “El Niño” is used to describe the periodic shift in how heat moves around within the Pacific Ocean, forming a massive pool of warm ocean water that is powerful enough to shift weather patterns, resulting in heavy rainfall, flooding, drought, wildfires and rising global temperatures. While it occurs along the equator between Asia and the Americas, its impacts are felt all over the planet.
Rebecca Beadling, assistant professor of earth and environmental science in Temple’s College of Science and Technology, studies the ocean and its role in the climate system. Her research helps explain why changes beneath the surface of the ocean can have consequences for weather and climate on land and how it is compounded by additional heat from climate change.
Temple Now spoke with Beadling to break down the phenomenon of El Niño, why experts expect the impacts of El Niño to be more severe this year and how it relates to climate change.
Temple Now: What exactly is El Niño?
Rebecca Beadling: El Niño is part of a larger natural oscillation within the climate system called the El Niño-Southern Oscillation, or ENSO. There are two sides to it: El Niño and La Niña. Basically, it’s an oscillation, or a seesaw, between where we find warm sea surface temperatures in the equatorial Pacific and the opposite La Niña state. Normally, trade winds blow water from east to west across the Pacific and that piles up warm water in the western Pacific, near Indonesia. We consider that region of the climate system to be kind of a heat engine because you have a lot of warm water and that’s a lot of energy that can then exist in the climate system.
What happens is that something triggers those easterlies to weaken, and that big pile of warm water starts to move toward the central Pacific and eventually over to the eastern Pacific, near Peru and Ecuador. All of a sudden, we went from having all of our heat piled up in the western Pacific to having really warm water in the eastern Pacific. When that happens, that’s El Niño.
TN: How does El Niño affect weather?
RB: Wherever you have those high sea surface temperatures, that’s where you get the most evaporation, and that causes what we call deep convection—really big clouds that extend up through the top of the troposphere, the layer of the atmosphere where we live and where all of our weather occurs. Even though this is happening in the equatorial Pacific, it has huge impacts on our weather here in Philadelphia and across the United States because the heat released in the troposphere from increased tropical convection actually pushes around our jet stream.
TN: How does a strong El Niño lead to more extreme weather?
RB: El Niño changes where heat is distributed on the planet. You have this deep pool of water with a ton of heat stored in it piled up in the western Pacific. When the trade winds start weakening, that heat basically starts coming toward the surface and spreading out. You’re taking this heat that’s piled up there and just spreading it, so now our atmosphere has access to a ton of energy that usually sits deeper beneath the ocean surface.
Since the atmosphere has so much more energy in it and we have more heat that we’re tapping into, that's why it’s associated with more extreme events. How it manifests is very regionally dependent. For example, normally Indonesia would have a monsoon, but during an El Niño that shifts, so Indonesia is more likely to have a drought. Peru and Ecuador, on the other side of the ocean, are more likely to experience heavy rainfall and flooding events.
To me, as an oceanographer, understanding how much ocean heat really drives the intensity of these events, I would say the fact that we are building up so much heat in a warming climate is important. We’ve had, over the past several years, record-breaking temperatures. With climate change, the ocean is continuing to take up more heat, so we’re going to have more heat in the engine each time an El Niño sets up, basically.
TN: What does the typical El Niño life cycle look like?
RB: A typical life cycle of the transition from a neutral or La Niña state into an El Niño, or vice versa, happens over roughly a 12- to 18-month cycle. You basically have this onset in the spring, when for whatever reason the trade winds start weakening and you start to see the migration of sea surface temperatures from the western Pacific toward the central Pacific. As you get through the spring into summer, we’re able to say with more confidence whether we’re definitely setting up for an El Niño and what the potential strength of that might be. Then, as you go into the fall (November through January) is really when we expect to hit the peak of El Niño. And then it starts to decay again through the spring and transition into another phase of the oscillation.
TN: What kind of data do scientists use to predict the severity of El Niño?
RB: The things that scientists monitor for ENSO include sea surface temperature, as well as subsurface temperature so we can get an idea of just how big the ocean heat reservoir is and where it’s moving.
We can get this information ocean buoys, drifting floats and from satellite measurements taken from space. Satellite altimetry measures the height of the ocean surface. Warm water expands, so you can actually use the height of the ocean surface to get an idea of how much heat is within a layer beneath the surface
We also monitor the atmosphere. There are weather stations and specific arrays in the equatorial Pacific that monitor things like the strength of the easterlies and look for signs that indicate they’re weakening or shifting.
TN: What’s the biggest thing you want people to understand about El Niño and the climate system?
RB: I think it’s important to emphasize the importance of the ocean in the broader climate system. To me, global warming is really all about ocean warming. When I think about the future and this intersection between weather and climate, that’s going to be driven by whatever happens to the ocean. The ocean is really at the center of this whole story.