Super El Nino? Super Warming is the Main Issue
- Jun 24
- 6 min read
A 2026 commentary by Hansen et al. argues accelerating ocean warming, not El Niño strength, is the key story — driven by high climate sensitivity of 4–5°C and declining aerosol cooling.
When models began converging on a prediction of an El Niño starting in 2026 and peaking in early 2027, parts of the science media — having largely missed the possibility just weeks earlier — pivoted quickly to "Super El Niño" coverage.
James Hansen and colleagues find this predictable and, more importantly, beside the point. In a commentary published on 20 March 2026, Hansen, Kharecha, Morgan, and Vest use the El Niño forecast as a springboard for what they consider the far more consequential story hiding beneath the near-term weather noise: an extraordinary, ongoing acceleration of ocean surface warming that standard climate models have been systematically underestimating — because they have been working with the wrong climate sensitivity.
The piece is a hybrid document, part scientific synthesis, part urgent briefing, and it closes with an open letter to environmental writer Bill McKibben appealing for help in communicating what the authors describe as a paradigm shift that mainstream climate commentary has been slow to absorb.
Key Arguments
El Niño 2026–27: Real, But Not the Main Event
An El Niño is anticipated to begin in mid-2026 and peak in early 2027, driven by a sequence of Kelvin waves — large thermal pulses that transport accumulated heat from the warm pool of the western Pacific eastward toward South America, suppressing the upwelling of cold deep water along the South American coast and releasing heat into the atmosphere. The ECMWF model predicts a strong event, though as of March 2026 the upper-ocean (300 m) heat anomaly had reached only around +1°C — a level the authors consider too modest for a Super El Niño on its own, while noting that El Niños are frequently constructed by a series of Kelvin waves rather than a single pulse, and a second wave may already be forming.
Comparing the current trajectory of subsurface heat content against historical El Niño events, the authors find that the present build-up resembles the Super El Niño precursor profiles of 1997–98 and 2015–16 more closely than the moderate events of intervening years — an early start and rapid rise consistent with the stronger category. Whether the event ultimately crosses that threshold depends on the behavior of equatorial trade winds over the coming months, which remain chaotic and difficult to model precisely. The authors commit to weekly updates as the situation develops.
The Bigger Story: Accelerating Ocean Warming and Its Causes
Regardless of how the El Niño unfolds, the authors argue that the more consequential scientific question concerns what is driving the exceptional acceleration of sea surface temperature warming observed over the past decade — a trend that has continued to outpace model projections and that carries land warming roughly double that of the ocean surface, along with increased extreme precipitation and poleward expansion of subtropical climate zones.
Their answer rests on two independent factors that compound each other. The first is that equilibrium climate sensitivity — the amount of warming produced by a doubling of atmospheric CO₂ once the climate system reaches equilibrium — is substantially higher than the 3°C figure that has served as the IPCC's central estimate for decades. The second is that aerosol cooling, which partially masked this high sensitivity during the period of rapid linear warming from approximately 1970 to 2005, has been declining since around 2015, removing a cooling brake that was hiding the full force of greenhouse gas forcing.
Four Lines of Evidence for a Climate Sensitivity of 4–5°C
The conventional 3°C sensitivity estimate rests heavily on observed warming over the past century, interpreted under the assumption that aerosol forcing changed little during the post-1970 period of rapid warming. The commentary assembles four independent lines of evidence pointing to a substantially higher sensitivity of 4–5°C for doubled CO₂:
The first and most direct is paleoclimate comparison with the last glacial maximum. Recent analyses by Tierney and colleagues established that the last major ice age, roughly 20,000 years ago, was about 6°C colder than the present interglacial — rather than the 4°C long assumed — after correcting for a dubious prior assumption about marine organism adaptation to temperature. Osman et al. similarly estimated peak ice age cooling at around 7°C globally. Crucially, Alan Seltzer's noble gas measurements from groundwater deposited during the ice age confirmed land cooling of around 6°C across latitudes 45°S to 35°N — a physically direct and assumption-minimal method. When adjustments are made for the ocean warming less than land and for the additional cooling from the ice sheets themselves, the two corrections nearly cancel, yielding a consistent ice age to present-day comparison that implies a climate sensitivity of 4–5°C.
The second line of evidence is the large reduction of Earth's albedo (reflectivity) observed in the satellite record since 2000. A reduction this large cannot be accounted for by declining sea ice or reduced aerosols alone; it requires a strong positive cloud feedback. Cloud-neutral climate sensitivity would be roughly 2.4°C. The magnitude of the observed albedo reduction implies that clouds are amplifying warming substantially, pushing sensitivity to at least 4°C.
The third is the history of snowball Earth episodes. The Sun's brightness has increased by roughly 6% since the last time Earth was entirely glaciated, around 600 million years ago. A 2% change in solar irradiance is climatically equivalent to a doubling of CO₂; a 6% increase is therefore equivalent to three CO₂ doublings. The fact that this change was sufficient to permanently end snowball conditions implies high climate sensitivity.
The fourth, and in the authors' assessment the least precise, is the observed warming record of the past one to two centuries — least precise because it requires accurate knowledge of aerosol forcing, which was not directly measured.
Aerosols: The Hidden Forcing That Changes the Story
The mechanism connecting these sensitivity arguments to current observed warming acceleration lies in the evolution of aerosol forcing. Aerosols cool the climate primarily by acting as condensation nuclei for cloud droplets, producing more numerous, brighter clouds — but this cooling effect saturates as aerosol concentrations rise. During the 1970 to early 2000s period, global sulfur dioxide emissions held roughly steady in total but became more globally dispersed as U.S. and European emissions fell while East Asian emissions rose and aerosols spread more widely over the ocean. This increased dispersion enhanced the aerosol cooling effect even without an increase in total emissions, producing a negative climate forcing that offset roughly one-third of greenhouse gas forcing during that period.
If this aerosol forcing evolution is correctly accounted for, the climate sensitivity required to explain observed post-1970 warming rises from approximately 3°C to approximately 4.5°C. Since around 2015, aerosol reductions from East Asian emission controls and from new international shipping fuel regulations have reversed this trend: aerosol cooling is now declining rather than increasing, adding to greenhouse gas forcing rather than subtracting from it. The net climate forcing per decade has approximately doubled, from around 0.3 W/m² to around 0.6 W/m² — which, in the authors' framing, is the direct cause of the ongoing acceleration in sea surface temperature warming that current models have been failing to reproduce.
The Argument the Authors Say Isn't Being Heard
The commentary is also a document about scientific communication and institutional resistance. The authors argue that a small group of prominent climate scientists who serve as media "go-to" commentators responded to their earlier published findings on accelerating warming not with engagement on the physics — the four lines of evidence on climate sensitivity, the aerosol forcing evolution, the energy imbalance data — but with ad hominem dismissal.
The open letter to Bill McKibben, who commands an audience orders of magnitude larger than any academic climate scientist, is an appeal to help close this communication gap. Hansen frames the stakes explicitly: high climate sensitivity and declining aerosol cooling are independent findings that together substantially change the timeline of climate risk, and that young people in particular need accurate information about the situation they are inheriting.
Whether the 2026–27 event proves to be a Super El Niño or merely a strong one, the authors argue, it is the warming beneath it — structural, accelerating, and poorly captured by mainstream model estimates — that deserves the headline.
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