Rapidly developing El Niño set to boost global warming

• El Niño teams up with human-caused climate change and pushes global average surface temperatures higher.
• Even a relatively weak event could lead to new records for the warmest year in 2023 and 2024.

What's happening: Three straight years of La Niña, which features cooler-than-usual sea surface temperatures in the tropical Pacific, have given way to a rapid transition to an El Niño state.

• The National Oceanic and Atmospheric Administration (NOAA) declared an El Niño watch last week, putting 62% odds of an event setting up during the May to July period.
• The odds jump to about 85% later in the year, according to Michelle L'Heureux, a meteorologist who leads the El Niño-Southern Oscillation team at NOAA's Climate Prediction Center.

Threat level: The last global record occurred in 2016, which was also an El Niño year.

• The planet has continued to warm since: The past eight years were the warmest such period on record. And in just the last few weeks, ocean temperatures reached unprecedented levels.
• The ocean and atmosphere climate pattern also shifts weather across the globe, shutting down much-needed rains for tens of millions, while bringing deluges to other areas.
• El Niño can lead to drier-than-average conditions in parts of eastern Australia, wet conditions in East Africa — plus a host of shifts across North America during the fall and winter.

Between the lines: Typically, computer models are less accurate in forecasting El Niño events during the spring, which is known as the "spring prediction barrier."

• But L’Heureux told Axios via email that the "key precursors to El Niño development" are already evident in observations, which makes forecasters more confident.
• "Specifically, we currently are seeing a large amount of subsurface oceanic heat building in the tropical Pacific," which will eventually bubble up to the surface, she explained.
• In addition, east-to-west trade winds along parts of the equatorial tropical Pacific have slackened somewhat, which is a key ingredient for setting an El Niño into motion and maintaining it, L'Heureaux added.

By the numbers: Model projections have been leaning toward a moderate-to-strong El Niño by the fall and winter, notes Zeke Hausfather, climate research lead at web payments company Stripe.

• He said these events can boost global temperatures by about 0.2°C (0.36°F), on top of the larger long-term, human-caused warming trend.

• "While it's too early to know for sure, it is likely that 2024 will be the warmest year on record. Exactly how warm will depend on how long El Niño conditions persist," Hausfather said.
• Hausfather echoed Adam Scaife, head of long range prediction for the U.K. Met Office. Both say the developing El Niño may cause global average surface temperatures to temporarily come very close to, or even briefly reach, the Paris Agreement's temperature guard rail of 1.5°C (2.7°F) above pre-industrial levels.

Yes, but: This would be a symbolic milestone, since the Paris Agreement targets refer to long-term averages, not one or two years.

• "Perhaps the important thing is not whether it actually reaches 1.5 degrees next year," Scaife told Axios via email, "But that this will be the first time in history we are within reach of this level for [the] annual global [average] temperature."

The intrigue: One potentially positive aspect of an El Niño is that they tend to reduce, but not eliminate, Atlantic Ocean hurricane activity by increasing upper atmospheric winds, which can tear nascent storms apart.

What we're watching: If a spate of weather extremes and a new record warm year reverberate politically. The so-called super El Niño of 2015-2016 coincided with the negotiating and adoption of the Paris Agreement.

• The upcoming U.N. climate summit in Dubai starting in November will test whether nations can commit to more aggressive near-term emissions reduction targets.