ITCZ and La Niña Linked to 2025 Panama Upwelling Collapse

The Aaron O'Dea et al. PNAS paper identifies a specific mechanical signature behind the 2025 collapse. Three properties of the Panama wind jets were measured: frequency (how often jet events occurred), duration (how long each event lasted), and strength (peak wind speed during events). Frequency and duration both dropped sharply. Strength, however, was unchanged — when the northerly winds did blow, they were as strong as in any other year. The cycle failed not because the winds got weaker but because they did not blow long enough or often enough to drive the full upwelling response. The paper's leading candidate for the proximate cause is the position of the Intertropical Convergence Zone (ITCZ) during the weak 2024–2025 La Niña. The ITCZ is the equatorial belt where the northeast and southeast trade winds converge; its latitudinal position controls the trade wind regime that produces the Panama jets. Prior research suggests climate change may be narrowing and weakening the ITCZ over time, which would lower the threshold for disruption — making La Niña a trigger rather than a sole cause. The authors are explicitly hedged on attribution. The paper notes that "despite occurring during only a weak La Niña, the 2025 collapse defied expectations, suggesting that small regional-scale shifts — such as in wind-jet frequency or ITCZ placement — can now interrupt systems once thought resilient." A single anomalous year does not establish a trend, but it does demonstrate that a previously stable system can now fail under modest forcing.