What La Niña Will do to Earth in 2025

Imagine a force so powerful that it  can change weather patterns around the world and even alter the  fate of ancient civilisations. Earth’s short term weather patterns and long term  climate are influenced by a complex collection of factors, from our place in the solar system and  the planet’s rotation, to atmospheric patterns and seasonal changes. To further complicate things,  every few years our planet experiences El Niño and La Niña events – two opposite ends of a cycle  that are part of the El Niño Southern Oscillation, or ENSO for short.

Evidence of the ENSO  goes back tens of thousands of years, and may have even played a role in destabilising  some of the world’s great ancient civilisations. One of the five strongest El Niño  events ever recorded has finally come to an end as of June 2024, after months  of record-high ocean surface temperatures, unprecedented heat stress on coral  reefs, drought in the Amazon rainforest, and extreme rainfall with dangerous  consequences for North America. With La Niña predicted to begin in late 2024 or  early 2025, what changes can we expect globally, and locally?

I’m Alex McColgan, and  you’re watching Astrum. Join me as we take a look at our changing planet, the  ENSO, and what La Niña will do to Earth. Our previous video about El Niño  explored one side of a global cycle that typically takes between 2 to 7 years to  swing from one extreme to the other.

These El Niño and La Niña episodes usually last 9 to  12 months, but can last for several years. In this video we will take a closer look at how  this cycle works, what neutral periods are, and what might happen as we head into the  opposite extreme of La Niña in the coming months. When our Earth experiences average conditions, we call those periods “ENSO-Neutral.

” But  every few years, fluctuations in wind and ocean surface temperatures can signal the  beginning of an El Niño or La Niña event, and a departure from Earth’s normal conditions.  These events alter worldwide atmospheric patterns and are known to wreak havoc by contributing  to extreme weather and environmental harm. Imagine we're on the International Space  Station orbiting Earth.

From here we can see our planet’s spherical shape, and as you might  expect, sunlight affects the Earth’s surface unevenly. More light and heat reaches Earth at  the equator where sunlight strikes most directly, compared to the poles where sunlight  reaches our planet at a low angle. In the same way that a hot air balloon rises,  or hot steam rises over a pot of boiling water, the same thing happens along the equator.

.  Direct sunlight warms up the air, and that hot, moist, low pressure air rises up into the  atmosphere. As the warm air gets higher, it begins to cool off and condense into clouds – this is why we see an abundance  of tropical rainforests close to the equator.

More warm air continues to rise, pushing the  cooler air away from the equator and out towards the north and south, where it will eventually sink  back down to the surface. Then, that cool air will move from higher pressure, along the surface  of the Earth, back to lower pressure near the equator to start the cycle all over again and  complete what we call Hadley Cell rotation. But how does this worldwide circulation of air, driven  by the Sun, relate to El Niño and La Niña events?

The surface winds created by these Hadley  Cells are deflected towards the equator due to the Earth’s rotation, a phenomenon we  call the Coriolis Effect. It’s this effect that creates the trade winds on either side  of the equator, and it’s changes to these trade winds that indicate when we will  experience El Niño and La Niña events. Historically, the trade winds have been  so reliable that sailors have used them to navigate the globe for centuries, hence the  name, “trade winds.

” Chemical signatures of the ENSO stretch back tens of thousands of years  in paleoclimate indicators like coral fossils, and we have written records of the ENSO as far  back as the 1500’s. . El Niño events may have aided Spain in their conquest of the Incan Empire  in the 1500’s, and in the late 1700’s, likely contributed to crop failures and unrest that  sparked the French Revolution.

Despite this long record of ENSO activity and the massive impact  it has on worldwide weather and environments, it wasn’t until the 20th century that we finally  started to understand the mechanisms behind it. The first defining breakthrough came in the 1920s,  when a British scientist named Sir Gilbert Thomas Walker set out to better understand the strength  of monsoons in India. In his search for a way to predict monsoon strength, he ended up  documenting the Southern Oscillation, a repeating shift in air pressure that  happens across the equatorial Pacific Ocean.

This oscillation was part of  another large-scale air circulation that had not been documented before, and  was later named the Walker Circulation. Remember how I said that Hadley Cells circulate  air north and south? The Walker Circulation is just like Hadley Cells, except instead of moving  air north and south, the Walker Circulation moves air to the east and west over the equatorial  Pacific.

And instead of being driven by sunlight, the Walker Circulation is guided by the  easterly trade winds and ocean temperature. It would be 60 more years before scientists  were able to connect these changes in air pressure over the Pacific with the alternating  pattern of warm and cool surface water in the Pacific. Combined, these make up what  we now know as the El Niño Southern Oscillation – ENSO.

El Niño refers to  the changes in sea surface temperature, and the Southern Oscillation refers to  the simultaneous changes in air pressure. Unlike Hadley Cells that reliably move air north  and south, the equatorial Walker Circulation is not consistent and can experience colossal  shifts as part of the Southern Oscillation. Every few years, the surface temperature and trade  winds over the Pacific experience fluctuations, signalling an oncoming shift in  the Walker Circulation.

In turn, these shifts, which we refer to as El Niño  or La Niña events, can upset the balance of weather and ecosystems over the entire Earth. So  what happens to the Earth during each of these? During neutral ENSO periods, the sea surface  temperature and trade winds are near average conditions.

Trade winds blow across the Pacific  Ocean, guiding warm surface waters to travel west from South America towards Australia and  Asia. As that warm surface water moves west, it makes way for deep, cooler waters  to rise up in its place. This ocean circulation brings nutrient-rich cool water  to the surface in a process called upwelling, where it feeds phytoplankton and in turn  supports other parts of the ecosystem like fish.

In neutral periods, weather across  the world occurs, more or less, as expected. This can include normal  hurricane development in the Atlantic, and average monsoon rainfall across  southeast Asia. Walker Circulation drives columns of warm moist air to rise  above southern Asia,northern South America, and middle Africa, so it’s no coincidence  that these three regions are where we see a concentration of vast, lush rainforests.

The  influence of this equatorial airflow is vast, so it’s easy to imagine how changes to this system  could cause a ripple effect around the world. The first signs of trouble are when  the trade winds begin to weaken and sea surface temperature rises in the Pacific, which can indicate an oncoming El Niño event  like the one we experienced in 2023 and 2024. During El Niño, the colossal columns of warm  air that rise above our world’s rainforests are shifted to the east or west.

This change disrupts  Asia’s monsoon season with prolonged droughts and water scarcity, and affects the livelihoods  of billions of people in east Asia. The last El Niño also brought nine atmospheric rivers  to the western United States that led to major transportation issues, dangerous landslides, and  flooding. You can think of an atmospheric river like a river of moisture streaming through the  air.

When these atmospheric rivers reach land, they release all of that moisture,  causing monumental precipitation. Everywhere on Earth, this shift in Walker  Circulation is felt during El Niño. However, the changes you experience in your local weather  conditions may be completely different from the changes another person sees in their local weather  elsewhere on our planet.

El Niño typically brings a reversal of the normal conditions for a  given area. This is why places like east Asia or the Amazon rainforest, which typically  get plenty of rain, will experience drought during an El Niño event, or why usually  dry climates like western North America, will experience tremendous rainfall events.  The recent El Niño event was also responsible for worldwide shipping delays in 2023, as there  wasn’t enough water to feed the Panama Canal, which relies on consistent rainfall to accommodate  all of the cargo ships hoping to pass through.

El Niño is described as the warm part of the ENSO  cycle because Pacific sea surface temperatures are higher than average during this time. In  addition to changing worldwide weather patterns, this also negatively affects  ecosystems. Take, for example, coral reefs.

They rely on particular  sea surface temperatures to survive, and support some of the most important  and biologically diverse life on Earth. Corals have a symbiotic relationship with algae,  but an increase in water temperatures can cause the coral to expel this algae, leaving it drained  of colour and vulnerable. A reef can recover from this bleaching if conditions improve in  time, but their risk of dying is high, and the last El Niño event was no exception.

An  unprecedented 99. 7 percent of Atlantic tropical reefs were impacted by bleaching-level  heat stress during the 2023 to 2024 El Niño event, as part of the fourth worldwide  mass-bleaching event in recorded history. The warmer Pacific waters and weakened trade winds  from El Niño also cause the upwelling of cooler, nutrient-rich water to temporarily slow or  stop, leading to a dire situation where less phytoplankton means large numbers of fish  must migrate or perish.

As you can imagine, this ripples across the food chain and can  impact other animals. For coastal families and communities who rely on those fish for nourishment  or income, this El Niño effect can be devastating. Now that we’ve discussed what it’s  like during a neutral ENSO period, and the destructive changes that can happen with  El Niño conditions like we saw in 2023 and 2024, what can we expect from this  upcoming La Niña phenomenon?

La Niña is the other extreme. This period is  marked by stronger than usual trade winds, and cooler than average Pacific  sea surface temperatures. While El Niño usually causes the  reversal of neutral conditions, the best way to understand La Niña is to think  of it as a more intense version of neutral conditions for most parts of the world, with  a few exceptions.

During La Niña, the neutral columns of rising warm air above south Asia and  eastern North America become more pronounced, while the typical column of warm air above  Africa reverses. Just as your experience of El Niño is highly dependent on where you are  located, the same is also true of La Niña. As of August 2024, the U.

S. National  Oceanic and Atmospheric Administration predicts a 66 percent chance that La Niña will  develop between September to November of 2024, and a 74 percent chance it will last well into  the Northern Hemisphere’s winter of 2025 to 2026. And as of this video, models are predicting  a roughly 50 percent chance that this La Niña event will peak at a moderate strength.

However,  while forecasts for a La Niña event happening are usually correct, the predicted strength for these  events will likely change from month to month. A strong El Niño ending in 2024 does not  necessarily mean the upcoming La Niña will be as extreme. Sometimes a strong El Niño leads  into a strong La Niña, but other times a strong El Niño is followed by a weak La Niña.

With only  10 times in the historical record where the ENSO has changed between El Niño and La Niña within  a one year time period, as is expected with this year’s switch, there just isn’t enough historical  data to draw many conclusions. Besides, scientists warn that the strength of an ENSO event does not  always line up with the severity of its impacts. So what do we know about the upcoming La Niña?

For the northern part of North America, La Niña  brings with it a colder, wetter winter, while the southern part of the continent might experience  a warmer and more dry winter. U. S.

Winter Source And notably, La Niña will increase the likelihood  of a more active hurricane season in the Atlantic, with the potential for more,  and stronger, hurricanes. For east Asia and Australia, this typically  means a significant increase in rainfall. While in Africa, La Niña can mean  some areas to the west are more wet, while eastern Africa tends  to experience more drought.

The connection between ENSO and  Europe isn’t quite as clear, since the continent is farther from  the source, but La Niña is expected to bring lower than average temperatures  to central and western Europe, with less precipitation across the mainland this winter,  and more precipitation to the north and south. There’s one final thing we need to talk  about when it comes to La Niña predictions: The El Niño and La Niña extremes of the  ENSO have been happening for millennia, but what’s less certain is how global warming  from climate change will impact this cycle. While we see short term, localised temperature  swings from ENSO, the all-over trend of global warming continues on an upward trajectory. 

This means we are entering uncharted territory. There’s clear evidence that as our planet  continues to warm from climate change, the occurrence of severe weather will escalate.  But the ENSO is a complicated, worldwide, and in many ways, still an unpredictable  phenomenon.

Just in recent history, El Niño and La Niña events have become stronger  and more frequent, leading to more droughts, floods, heat waves, wildfires, and severe  storms, like we saw during the last La Niña event that lasted for three years, from 2020  to 2023. Exactly how global warming may impact the ENSO cycle is unclear, but we do know that  climate change is likely to amplify that, too. Luckily, life on our planet is nothing  if not resilient and adaptable, and as our world continues to change and experience the  millennia-old ENSO swings, scientists will learn more each year and be able to make improved  predictions about the complex climate system.

The approaching La Niña will undoubtedly teach us  more about our planet's climate. Let's hope we are paying attention and use these lessons to adapt  and prepare for our future in sustainable ways. I’d love to hear in the comments what  question you have about our planet’s climate.

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