Another El Niño Already? What Can We Learn from It?
- Feb 25
- 5 min read
Hansen projects 2027 temperature record of 1.7°C driven by high climate sensitivity and 2015 aerosol reduction, testing acceleration hypothesis.
A February 2026 analysis by James Hansen and colleagues projects that the world is headed into another El Niño just three years after the last one—an unusually rapid return that would normally produce only a moderate event. However, the researchers argue that even a moderately strong El Niño may yield record global temperatures already in 2026 and greater warming in 2027, not because of an exceptional El Niño per se, but due to high climate sensitivity and a recent increase in net global climate forcing.
The analysis identifies approximately 2015 as the principal turning point when global warming acceleration began, driven primarily by reduced aerosol cooling as emissions from East Asia and ships declined. This timing implies that 2°C global warming will likely be reached in the 2030s rather than midcentury, contradicting IPCC's more conservative projections.
Key Findings: Testing the Acceleration Hypothesis
La Niña Minimum Confirms Elevated Baseline Warming
The 12-month running-mean global temperature is projected to reach a minimum of approximately +1.4°C (relative to 1880-1920) in the first half of 2026 as the current La Niña persists. This minimum is critically significant: it exceeds any El Niño maximum in the prior decade, including the 2015-16 "Super El Niño," providing strong evidence that the baseline global temperature has risen substantially independent of ENSO variability.
The NOAA's newly introduced Relative Oceanic Niño Index (RONI), which subtracts the SST anomaly of the global tropics (20°N-20°S) from the traditional Niño3.4 index, reduces the apparent magnitude of the 2023-24 El Niño while strengthening recent La Niñas—demonstrating that human-made global warming now exaggerates recent El Niño strength and reduces the depth of La Niñas when measured by traditional indices.
Upper Ocean Heat Provides Nine-Month Lead Time
Analysis of equatorial upper ocean temperature anomaly (top 300 meters, longitudes 180-100°W) reveals it provides superior El Niño prediction compared to surface Niño3.4 SST, with correlation exceeding 50% with global temperature while leading by nine months (versus only four months for Niño3.4). At the end of December 2025, while Niño3.4 remained at a minimum deep in La Niña conditions, the upper ocean heat anomaly climbed to zero and reached +0.7°C by late January 2026.
This 300-meter depth metric is less polluted by human-made surface warming and correctly shows the 1997-98 El Niño as the strongest when measured by subsurface heat content. If this index continues rising, it suggests an El Niño peaking near the end of 2026, though there are many historical instances where the 300-meter anomaly reached 1°C without achieving an El Niño, reflecting the complexity of factors including initial ocean state, Madden-Julian atmospheric disturbances, fickle westerly wind bursts, and salinity anomalies.
Climate Models Project El Niño Development Despite Uncertainty
NOAA NCEP ensemble forecasts issued in late January and early February 2026 suggest an El Niño may begin by early summer, with Niño3.4 SST reaching the +0.5°C threshold indicative of El Niño conditions by June 2026 for the average of all model runs. However, individual model runs show enormous range, with several using the most recent initial conditions (blue curves) failing to produce an El Niño at all.
Historical precedent argues against a strong event: there is no example in the past 75 years of strong El Niños separated by only three years, perhaps because of the time required for the ocean to replenish heat lost during an El Niño. Equatorial wind anomalies in the past month show dominant westerlies (orange-red in low-level zonal wind analysis), which weaken the east-to-west trade winds and allow warmer Western Pacific water to slosh eastward toward Peru—a necessary condition for El Niño development that may or may not persist into Northern Hemisphere spring.
Forcing Changes Began Around 2015, Not 2020
Detrended temperature analysis (Fig. 9) shows global warming began diverging from the linear 1970-2015 trend around 2015, regardless of whether detrending uses 1979-2005 or 1979-2015 as the base period. Greenhouse gas forcing increased by approximately 20% between 2010 and 2015, with the main increase slightly closer to 2015. Global SO₂ emissions show the major turning point between 2010 and 2015, with Chinese emissions declining most rapidly between 2013 and 2014 (ship emissions declined most in 2020).
The change in absorbed solar radiation (ASR)—which must result mainly from reduced aerosol amount and feedbacks (primarily reduced cloud albedo, also reduced sea ice)—begins between 2010 and 2015, mostly around 2015. Characterizing this forcing change with a single turning point places it in the range 2010-2015, probably closer to 2015, with linear fit to accelerated warming starting in 2015 resulting in 2°C warming being reached in the 2030s.
Why This Matters: Climate Sensitivity Under Scrutiny
This research delivers three critical messages for climate physics and policy:
High Climate Sensitivity Explains Observed Acceleration: The researchers argue climate sensitivity is at least ~4°C for doubled CO₂, significantly higher than IPCC's 3°C estimate. This matches observed post-1970 warming of 0.18°C/decade if aerosol cooling increased moderately during 1970-2005 (approximately -0.5 W/m²). Standard GCMs likely underestimate cloud feedback—a widespread suspicion among modelers despite resistance from mainstream climate scientists who responded with ad hominem attacks rather than scientific engagement.
Decade-Long Acceleration Tests Sensitivity More Definitively Than Brief Events: Brief events like El Niño or volcanic eruptions provide little information on climate sensitivity because initial responses are nearly independent of sensitivity for 1-2 years—feedbacks emerge only after delayed temperature change occurs. However, after several years with sustained forcing, responses for different sensitivities separate significantly. The persistent gap between observations and models since 2015 implies increased net forcing, and by 2026-2027 this acceleration will provide definitive evidence distinguishing high from low sensitivity.
Projected 2027 Record Tests Model Physics: The +1.7°C projection for 2027 (with only moderate El Niño) represents a critical test occurring just four years after the 2023 peak, with the 2026 La Niña minimum of +1.4°C already exceeding prior decade maxima. The "horse race" between observations and models will become impossible to dismiss as simulation uncertainty. Extreme warming results from high sensitivity and increased forcing since 2015, not exceptional El Niño strength—contradicting models that underestimate cloud feedbacks and aerosol effects.
Beyond Conservative Consensus
The 2026 El Niño projection forces confrontation with fundamental climate physics that IPCC's GCM-dominated assessment process has systematically underestimated. The convergence of multiple 2026 temperature projections (Schmidt, Met Office, Berkeley Earth, Carbon Brief) around 1.41-1.46°C masks profound disagreement about 2027, where Hansen projects 1.70°C while others provide error bars so large "as to make predictions useless for any purpose other than covering one's posterior."
The resolution of this disagreement in the next 12-18 months will vindicate either the conservative IPCC consensus with low climate sensitivity and minimal aerosol effects, or the higher-sensitivity physics with substantial aerosol forcing changes driving acceleration since 2015.
Realistic understanding of the climate situation—and public recognition of it—is the essential first step toward effective climate policy, as pressure for action will grow along with climate impacts as global temperature approaches +2°C and the "current flippant attitude of people who should know better" dissolves in the face of evidence that we are approaching the point of no return.
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