La Niña typically casts a bit of a chill over the globe, and that certainly has been the case during its reign over the past three years. Yet despite the climate phenomenon's continuing influence, last month turned out to be one of the warmest Januarys ever recorded globally.
Moreover, even though La Niña exerted its maximum cooling effect in 2022, that year still entered the record books as being warmer than 2021. The reason, of course, was human-caused climate change.
Now, La Niña is fading away, and El Niño — which usually warms the climate — stands a 60 percent chance of emerging in the fall. So the globe could be on the verge of some very significant warming.
The Heat Goes On
In their latest monthly climate analyses, NASA and NOAA have found that last month was the seventh warmest January in records dating back to the 1800s. "January 2023 marked the 47th consecutive January and the 527th consecutive month with global temperatures, at least nominally, above the 20th-century average," NOAA noted in its report.
Looking ahead, if El Niño does emerge in the fall, it would likely add its warming influence on top of human-caused warming. If it's strong enough, 2024 could supplant 2016 — a strong El Niño year — as the warmest year on record.
According to a recently published study, a moderate-to-strong El Niño is, in fact, likely in 2023. "A new record in global average temperature can then be expected for 2024," says study co-author Josef Ludescher, a scientist with the Potsdam Institute for Climate Impact Research. "For a short time, it could even be 1.5°C degrees above the pre-industrial mean." This is a key threshold that nearly all nations of the world have pledged to avoid as part of the Paris Agreement.
Exceeding 1.5 degrees C of warming sometimes is portrayed in media accounts as being the equivalent of plunging over a climatic cliff. In reality, there's nothing particularly special about that very specific number. It's not as if the world is doomed at 1.6 degrees C of warming but saved at just 1.5.
That said, if we do push beyond 1.5 degrees C, and stay there, risks for extreme heatwaves, droughts, and precipitation events would be significantly higher than at present, according to a 2018 report from the Intergovernmental Panel on Climate Change. And above 2 degrees C of warming, the risks of very dangerous impacts accelerate.
How close are we to exceeding 1.5 degrees C due to El Niño, even just temporarily, and what are the odds of this happening?
The global average surface temperature in 2022 (again, when La Niña was exerting it's maximum cooling effect) was 1.15 degrees C warmer than the preindustrial average. In their study, Josef Ludescher and his colleagues assumed 2023 will bring an additional amount of human-caused warming. To this, they added estimated warming from a relatively strong El Niño starting this fall. The result: a 1 in 5 chance of pushing above 1.5 degrees C of warming by the end of 2024.
How Do La Niña and El Niño Affect Global Temperatures?
La Niña and El Niño are two sides of a climatic coin known as the El Niño-Southern Oscillation, or ENSO. And their opposite impacts are linked to the effects they have on the formation of clouds.
Let's look at El Niño first. The natural climate phenomenon is characterized by warmer than normal sea surface temperatures in the central and eastern tropical Pacific Ocean, leading to greater evaporation of water into the atmosphere. As the water vapor rises, it condenses to form masses of billowing clouds, releasing huge amounts of heat in the process — enough, in fact, to ultimately affect the entire globe.
With La Niña, on the other hand, sea surface temperatures in the tropical Pacific cool. That means less water evaporates from the sea surface, suppressing formation of clouds and resulting in less heat pouring into atmosphere.
Through a process that scientists call teleconnections, these impacts of El Niño and La Niña are carried for thousands of miles throughout the tropics.
"So, the atmosphere warms more during El Niño and less during La Niña, and that affects global average temperature," says Mike McPhaden, an oceanographer and ENSO expert at NOAA's Pacific Marine Environmental Laboratory, quoted recently in the agency's ENSO Blog.
For every degree Celsius that La Niña chills the surface waters of the central equatorial Pacific, the global average surface temperature of the globe cools by about 0.07 degrees C (0.13 F), according to McPhaden. Similarly, for every degree of sea surface warming caused by El Niño, global average surface temperatures rise by about 0.07 degrees C.
"It may not sound like much, but it involves huge transfers of heat between the ocean and atmosphere that affect the entire globe," he says.
We still do not know for sure whether El Niño is coming in the fall, let alone how strong it might be. In fact, predictions made at this time of year for what will happen in the fall are quite uncertain.
Even without El Niño, though, a study published on Jan. 30 of this year found that we're already on the verge of crossing the 1.5 degree C threshold. And even if the nations of the world were to somehow act in concert to very quickly and aggressively reduce emissions of greenhouse gases, we're very likely to cross the threshold in the early 2030s.
But the researchers found that with aggressive action, we can still avoid the even worse 2 degrees C threshold.
Will we take that action?