Axios

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 during these episodes are cooler than average in the so-called ENSO region (ENSO is the larger cycle that La Niña and El Niño are a part of).
• Given that global sea surface temperatures hit record highs in 2023 and 2024 — and, while slightly cooler now, are still extremely high — the way that scientists calculate the presence of a La Niña is being thrown out of whack.

According to top ENSO forecaster Michele L'Heureux of NOAA's Climate Prediction Center, comparing ocean temperatures to a 30-year average may no longer be as effective, since so much rapid warming is taking place.

• Instead, a relative ENSO index may be the better diagnostic tool, she said.
• It compares ocean temperatures in the relevant part of the equatorial tropical Pacific with surrounding oceans to diagnose whether a La Niña is developing or present.

Zoom in: L'Heureux has published studies on a "Relative ENSO index," and NOAA scientists are in discussions with forecasters elsewhere, including Australia's Bureau of Meteorology, to determine when it is advantageous to use it.

• "The 1991-2020 base period normal we're using may not be up to the task" for La Niña detection and forecasting, she told Axios in an interview.
• A relative index, which doesn't use a 30-year normal to diagnose La Niña, can get around the possibility that the 30-year base period is missing some of the effects of fast-moving climate change.
• Other research published during the past two years has shown that climate change has accelerated in recent years, including through record hot ocean temperatures.
• "There's open questions as to what exactly is going on here," L'Heureux said, referring to La Niña's development and the broader pattern of ocean temperature anomalies across the Pacific Ocean.

Between the lines: Winter is typically when the effects of La Niña are most evident, but this event is predicted to be weak.

• An important question facing forecasters is whether this winter will see typical La Niña weather patterns, given the intensity forecast.
• L'Heureux says a weak event doesn't necessarily translate to minor impacts.
• In fact, the ENSO Blog on climate.gov has published a climate explainer showing how different La Niña measurements and a suite of computer models show the likelihood of a heavily influenced La Niña winter across the Lower 48 states, for example.
• And there will still be surprises, she said, as La Niña interacts with other climate influences, including global warming.

None of NOAA's computer models would need to be fundamentally altered to continue accurately making climate and weather projections, even with a relative index in use.

The bottom line: Count La Niña among the phenomena that human-caused global warming is altering, leading forecasters to consider measuring it differently.

Sunairio, an AI-driven weather and climate modeling software firm aimed at boosting energy grid reliability, raised $6.4 million in a new funding round, Axios has learned.

Why it matters: The investment demonstrates the demand for software that uses AI to provide specific and actionable information for the energy industry.

Court cases involving climate change are taking on increased importance with global efforts proceeding far slower than the climate is warming and national policy subject to whiplash.

Why it matters: Cases under deliberation at the Hague, newly decided in Montana and in process elsewhere show that courts are increasingly receptive to the duty of governments and corporations to limit emissions.