The heat arrives the year after the peak.
The summer while an El Niño builds is ordinary in the U.S. (– strong events). The summer after the peak is not: U.S. cooling degree days were above the neutral median after – El Niño peaks (mean –; it survives the correction), after – strong ones, and after – El Niños that followed a multi-year La Niña. Globally, – calendar years after a strong El Niño peak set a record (HadCRUT5); years between two La Niña winters set –, and every one ran cooler than the neutral years' median (–). That is the sequence that produces record spikes: La Niña years hold temperature down, the El Niño that follows releases it.
For 2027 this site's planet page gives – odds of a global record across four datasets; Hausfather (The Climate Brink, 28 Sep 2026) gives –. The number depends on the method, so both are quoted. Summers are calendar years: “after” = the summer following the winter peak.
U.S. summers and cooling demand
nClimDiv 1950–2025Cooling degree days by climate region
Cooling degree days track electricity demand for air conditioning, the summer side of winter energy, where the regime shows nothing. More on the year after in the U.S.: The year after.