How a triple La Niña year could impact the US

If La Niña conditions develop in the Pacific for the third year in a row, as the National Oceanic and Atmospheric Administration (NOAA) predicts, cool ocean temperatures along the equator will once again crank up Earth’s air conditioner. And once again, climate change will overpower it and deliver yet another hot year.

Years ago, that forecast might have been more of a toss-up. It’s still possible — but less likely — that global temperatures dip a little before La Niña conditions switch back to normal. The cycle between La Niña, neutral (or normal), and El Niño conditions — where warm water dominates the equatorial Pacific — has historically alternated warming and cooling influences on global weather. But as greenhouse gas emissions trap more heat in our atmosphere, La Niña’s cooling effects are increasingly muted. Global warming is winning.

While the equatorial Pacific may seem far away, the change in ocean temperatures associated with La Niña affects weather conditions across the globe. In the US, higher temperatures from the Southwest to the Mid-Atlantic are expected when La Niña is at play, along with lower temperatures in the Upper Midwest and Northern Plains. As the entire planet trends warmer, though, that could translate to extreme departures from the norm in hot spots, and not much difference in cold ones.

Of course, even as warming climate trends continue, weather is erratic. Cold winter days and snow aren’t going away. In fact, snowfall could increase, partly because of winter weather patterns that La Niña influences, partly because a warming atmosphere holds more moisture, which in winter falls back down as snow — especially in the Midwest and Great Lakes. So, La Niña and climate change can team up to increase the odds of snow days across the Northern United States.

That alignment can do the same for rain. In moist climates — the Pacific Northwest, along with the Missouri, Mississippi and Tennessee Valleys, and the Great Lakes — our warmer, wetter atmosphere already generates higher hourly rainfall rates, amplifying the risk of flash flooding. The influence of La Niña can mean more rain in all of those regions, so the danger is even greater.

In other places, the effects of climate change and La Niña align in the opposite way: Both tend to produce drier conditions in the Southwest. The severe drought currently depleting water supplies and escalating wildfire risks will likely continue; and even when La Niña gives way to a warming Pacific, the growing influence of climate change will probably keep trending toward a hotter, drier American West.

There are no guarantees, though. Conditions in the Pacific can increase the chances of regional weather patterns developing, but they don’t always materialize. This year’s unusually quiet Atlantic hurricane season is a great example. La Niña generally causes weaker winds over the Atlantic Basin, making it easier for hurricanes to form, but 2022 hasn’t produced many, so far.

At this point, it is hard to say whether a warming climate makes tropical cyclones more common, but the ones that form are more likely to grow stronger and faster, fueled by warm ocean temperatures in the Western Atlantic and Caribbean. Their capacity to push higher storm surges on top of rising seas makes hurricanes increasingly dangerous and costly, so even in a quiet year the threat of a disaster still looms.

The current cycle will eventually flip. La Niña will fade back to a neutral state, warmer El Niño conditions will emerge, and some of the impacts of climate change exaggerated by recent patterns might instead be tempered — but overall, it’s not making the difference it used to.

Last year, La Niña pushed global average temperatures down by about 0.02 degrees Celsius (0.04 degrees Fahrenheit) and will likely prevent 2022 from setting a heat record. Even so, these have been the warmest La Niña years ever, with global temperature comparable to what we saw from the warming influence of the 2009-2010 El Niño.

This is not a surprise. As long as the blanket of greenhouse gases wrapped around our planet keeps getting thicker and the temperature beneath it keeps rising, climate change will only exert a more and more dominant influence over our weather.

Lauren Casey is a meteorologist for the Climate Matters program at Climate Central. Casey specializes in communicating the connections between climate change and extreme weather. Prior to joining Climate Central, Casey worked as a broadcast meteorologist for more than 15 years.

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