The transition to a La Niña event in the tropical Pacific Ocean — which could have knock-on effects on weather patterns worldwide — isn’t going smoothly. Why it matters: The slow slide into a La Niña is revealing some of the influences of long-term, human-caused global warming , and how these key climate events may be changing as a result. Threat level: La Niña events — and those of its sibling, El Niño — are the most important sources of natural climate variability around the world on short-to-medium-range time scales. La Niña events can make the difference between a famine-causing drought in east Africa or deadly flooding, and a blockbuster snow year in California’s Sierra Nevada versus a descent into drought. The big picture: The occurrence of this La Niña, which by some measures is now in place, is causing climate scientists and meteorologists to rethink some long-standing practices for how to measure and predict these events. What’s now happening is that the signal of La Niña in the equatorial tropical Pacific Ocean is getting muted amid some of the noise from record-warm ocean temperatures outside the much-studied region. This means the framework that meteorologists use to diagnose, detect and describe a La Niña event may need updating. Yes, but: Luckily, researchers have been working on this problem and may have a solution. It all has to do with how climate change is muting the signal of La Niña and El Niño events by spiking ocean temperatures across vast stretches of ocean, and potentially altering weather patterns that La Niña would ordinarily affect. How it works: La Niña is a climate cycle in which the ocean affects the atmosphere in the equatorial tropical Pacific, and vice versa. Scientists refer to this as air and sea “coupling.” Sea surface temperatures […]