Prioritize...
When you're finished with this page, you should be able to:
- define the term "teleconnection" and give an example of one in the climate system
- give at least two examples of how ENSO impacts weather statistics in various places around the world
Read...
The SST and atmospheric pressure patterns associated with ENSO are primarily located over the tropical Pacific. However, the climate impacts of ENSO are communicated to the extratropics through “atmospheric bridges” (or atmospheric teleconnections). Thus, the ENSO can influence weather patterns, the hydrological cycle, ecosystems, and human activities all around the globe, as illustrated in the schematic map below.
With the resultant changes in pressure distribution of the tropical Pacific, the sinking and rising of air across the tropics and extratropics changes as well. Thus, the ENSO events can significantly modulate the distribution of precipitation at various locations, contributing to the occurrence of drought and floods across the globe. For example, El Niño is often associated with heavy rainfall and flooding in the southern United States and Peru, while La Niña can lead to severe droughts in these regions. Conversely, La Niña brings heavy rain and floods to Australia and Indonesia, while El Nino causes drought and wildfire in the region. These observed changes in precipitation and the hydrological cycle consequently impact terrestrial ecosystems, wildlife, vegetation growth, and crop yield. Countries dependent on agriculture are particularly vulnerable to these changes due to ENSO.
In addition to the impacts on the terrestrial area, the changes in SST during the ENSO can disrupt marine ecosystems. During El Niño, reduced upwelling off the coast of Peru, along with the warmer water, deprives the nutrient supplies for fish, forcing them to migrate, which substantially reduces fishery productivity and causes economic loss. Coral reefs, which are sensitive to temperature changes, can also experience bleaching events during strong El Niño periods.
Let's focus a little closer to home -- while they are born in the equatorial Pacific, El Niño and La Niña can have significant impacts on weather patterns across the United States. During El Niño years, the southern states, including Texas, Florida, and Southern California, typically experience above-average rainfall, which can increase the risk of flooding and landslides. Conversely, regions such as the Pacific Northwest often face drier conditions, potentially affecting water resources and increasing the likelihood of drought. The warmer ocean temperatures associated with El Niño can also lead to milder winter conditions across the northern United States, reducing snowpack and impacting activities like skiing as well as spring water supplies.
In contrast, La Niña events tend to bring cooler, wetter conditions to the Pacific Northwest and northern Rockies, which can result in increased snowfall and more robust winter sports seasons. However, this phase is often accompanied by drier and warmer conditions across the southern tier of the country, raising the risk of drought and wildfires, particularly in states like California and the Southwest. The Midwest and Southeast may also experience heightened severe weather activity during La Niña, including more frequent tornadoes and intense thunderstorms in the spring.
Another thing affected by ENSO is hurricane activity in the North Atlantic. During El Niño years, the increased vertical wind shear and more stable atmospheric conditions tend to suppress hurricane formation, leading to fewer and weaker storms. This can be a relief for coastal communities that are vulnerable to hurricane impacts. However, during La Niña years, the opposite is true: reduced wind shear and favorable atmospheric conditions create an environment that supports more frequent and intense hurricanes. This can elevate the risk of major storms making landfall, potentially damaging infrastructure and communities along the Gulf Coast and the Eastern Seaboard. In fact, you may have heard in the media about "seasonal hurricane outlooks" in late spring or early summer -- these outlooks almost always involve scientists combining factors like ocean temperatures and ENSO state to try and predict how much to worry about the upcoming summer and fall with respect to tropical cyclones. The variability in hurricane activity linked to ENSO highlights the broader influence these ocean-atmosphere interactions have on weather-related hazards in the United States.
ENSO events in historical records
The 1997-1998 El Niño was one of the strongest on record and had a profound impact worldwide. It caused massive flooding in Peru and Ecuador, devastating droughts and wildfires in Indonesia and Australia, and a milder winter in the northern United States. The economic toll was estimated at around $35 billion globally, highlighting the immense influence of these natural phenomena.
In contrast, the 2010-2011 La Niña event led to some of the worst flooding in Australia's history. Queensland experienced unprecedented rainfall, resulting in widespread floods that affected thousands of homes, disrupted industries, and caused billions of dollars in damage.
El Niño and La Niña are powerful reminders of the dynamic and interconnected nature of our climate system. These natural phenomena have shaped human history, influenced cultures, and continue to impact our world in profound ways! By studying and understanding ENSO, scientists can improve climate predictions and help societies better prepare for the challenges posed by these natural climate variations. As we move forward, the knowledge gained from studying El Niño and La Niña will be crucial in helping us adapt to a changing climate and mitigate the impacts of extreme weather events.