La Niña effects on jet stream and weather

This week we talk about oceanic surface temperatures, trade winds, and global climate change.

We also discuss the Polar Jet Stream, hurricanes, and climate models.

Recommended Book: Kleptopia by Tom Burgis

Transcript

Under normal circumstances, the Pacific Ocean’s average surface temperature, the distribution of heat across its vast expanse, is moderated by trade winds that blow east to west along the equator, which help move warm water from South America over toward Asia.

Those winds are called trade winds because, back during the European age of Exploration, they helped ships from Europe head west toward Asia and the Americas. And these winds form in part because of the Earth’s rotation, the Coriolis effect funneling air toward the equator, where it is then more concentrated and thus potent, which is useful if you’re trying to move a ship with sails, but also serves the purpose of moving warm water from one part of the ocean to another part of the ocean.

As those warmer surface waters are shifted from the Americas to Asia, water is pulled up to the surface from lower down in the ocean as part of a process called upwelling. This process results in cooler temperatures on the surface, because lower down, oceanic water is colder, and that lower-down water is also more rich in nutrients, which has the knock-on effect of stimulating more biological activity along these cooling surface waters.

That’s the normal state of things in the Pacific Ocean.

There are sometimes deviations in this norm, however, that result in very different outcomes; these deviations are broadly called the El Niño Southern Oscillation Cycle, and that cycle consists of opposite El Niño and La Niña climate patterns.

During La Niña patterns, trade winds are more powerful than usual and they shove a lot more of that warm surface water to Asia than is typical, and that has the net impact of moving more deep-down cold, nutrient-rich, ocean water to the surface.

This, in turn, nudges the Polar Jet Stream, which is a channel of fast-moving, westerly winds that lives about 30,000 ft or just over 9000 meters up in the sky, and which crosses both warmer, mid-latitudes and far colder Arctic latitudes, further north. The Polar Jet Stream is responsible for moderating or intensifying weather patterns around the world, and like the trade winds, it’s influenced by the spin of the planet, but it’s also adjusted by surface systems, like the temperature of the Pacific. So the arrival of a La Niña pattern pushes the jet stream further north, and as a result, weather patterns change, and in North America, we tend to see drought in the southwest, heavier rains and flooding and in the Pacific Northwest and Canada, warmer winters in the South, and cooler winters in the North.

La Niñas also tend to result in more severe hurricane seasons in the Atlantic basin, while suppressing hurricane activity in the central and eastern Pacific basins.

El Niño, in contrast, results from weaker trade winds, which, because these winds don’t pack as much of a punch, means less warm water is being shoved from South America to Asia, and thus the surface temperature of that part of the Pacific is warmer, lacking that upwelling of cold water to replace the warm water that would otherwise be displaced over to Asia.

El Niño also adjusts the location of the jet stream, but in the opposite direction, pulling it south of its usual spot. That then causes more heat and dryness across the northern US and Canada, but makes the southern US and Gulf Coast a lot wetter, leading to more flooding.

What I’d like to talk about today are predictions about an anticipated upcoming El Niño climate pattern, and why some climate scientists are warning that it could be a doozy.

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Climate scientists with the US’s National Oceanic and Atmospheric Administration, the NOAA, released new model forecasts in mid-May, and one of those models indicated that an El Niño pattern could form in the Pacific as soon as June.

The NOAA puts together and releases new models on a regular basis, as the variables influencing these massively complex patterns are always changing, and the trend over the past three months has been increasing certainty about the formation of this El Niño pattern, but also an increasing likelihood that this potential El Niño would be very strong, perhaps historically so.

There have been a total of 27 El Niños since 1950, when we started officially tracking such things, and we get one every three or four years, on average. The last one occurred from the summer of 2023 into spring of 2024.

The current models show that we could see another one of these systems as soon as next month, then, and there’s currently a nearly 60% chance that this particular El Niño would become strong—and that’s an official designation, by the way, a strong El Niño being one that sees an ocean surface temperature increase of between 1.5 and 2 degrees Celsius—and a one-in-three chance that it could become a very strong, or super El Niño, which means it tallies an oceanic surface temperature increase of 2 degrees celsius or higher.

These so-called super El Niños are a lot rarer than the typical kind. There have only been five recorded since 1950, the last one straddling 2015 and 2016.

Some of these models suggest that this system could be historically strong, though, pushing into territory where we might need a new rank on that existing scale—it could surpass 2.5 degrees celsius above the standard oceanic surface temperature, which would make it the most, or among the most intense El Niño systems on record.

I want to note real quick here, before we get into possible implications, that these models are inherently imperfect, because of how complex these systems are, and how many variables influence them. But also that, again, it’s just some models saying this, that it’s only a 60% chance of even a strong El Niño, and that it’s still a 1 in 3 chance of a very strong one—so this isn’t at all certain, and the scientists behind all this are urging preparedness, but not panic, and are trying really hard to make it clear that this isn’t some kind of prophecy or guarantee. The reporting on this NOAA announcement has been frantic and panicky in some cases, but that’s probably not the proper response to this, and the real-deal experts here are encouraging awareness and that we recognize the potential for something wild with this pattern, but it’s definitely not the declaration of the end of the world or anything.

So, that important caveat noted, let’s talk about some potential impacts of this system, if it does indeed hit that currently unlikely, but possible, very strong designation, or higher.

In general, during El Niño patterns, hurricane seasons in the Atlantic are quieter, while hurricane seasons in the Eastern and Central Pacific are more active. This isn’t 100% the case, but it’s the overwhelming trend. So there’s a good chance we would see more and more powerful hurricanes in the Pacific during this period, should we step into super El Niño territory.

Beyond hurricane impacts, though, these systems also influence water cycles around the world; during El Niño patterns, the US south tends to be wetter, as does East Central Africa, while northern South America tends to be drier, as does Australia and Northern and Central India.

Shifting or amplifying water cycles, in one direction or the other, drier or wetter, can cause all sorts of issues, ranging from flooded homes to devastated crops. Just like with hurricanes, this usually represents a break in the normal way of things, so we tend to see things like mudslides and erosion and unplanned-for droughts that cause a lot of damage.

Another significant component of these patterns are the temperature spikes they stoke. During the last recorded normal El Niño in 2023, global temperature levels were pushed up by 1.45 degrees C above pre-industrial levels, causing global mean temperatures to peak at 1.58 degrees C between July 2023 and June 2024.

In practice,…

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